Download METABOLISM OF POLYSACCHARIDES

MINISTRY OF HEALTH OF UKRAINE
ZAPORIZHZHIA STATE MEDICAL UNIVERSITY
Biological Chemistry Department
Biological chemistry
A manual for independent work at home and in class
preparation for licensing examination “KROK 1”
on semantic modules 8, 9, 10 of module 2
for students of International Faculty
(the second year of study)
Zaporizhzhia, 2016
UDC 577.1(075)
BBC 28.902я73
B 60
Reviewers:
Prihodko O. B., Head of Department of Medical Biology, Parasitology and
Genetics. Dr. Hab, assoc. professor
Voskoboynik O. Yu., assoc. professor of Organic and Bioorganic Chemistry
Department, Ph. D.
Authors:
Aleksandrova K.V.
Krisanova N.V.
Ivanchenko D.G.
Rudko N.P.
Levich S.V.
Tikhonovska M.A.
Biological chemistry : a manual for independent work at home and in class
preparation for licensing examination "KROK 1" on semantic modules 8, 9, 10 of
module 2 for students of International Faculty (the second year of study) / K. V.
Aleksandrova, N. V. Krisanova, D. G. Ivanchenko, N. P. Rudko, S. V. Levich, M.
A. Tikhonovska. – Zaporizhzhia : ZSMU, 2016. – 187 p.
This manual is recommended for II year students of International Faculty of specialty
"General medicine" studying biological chemistry, as additional material to prepare for practical
training semantic modules 8, 9, 10 of module 2 and licensing exam "KROK 1: General medical
training".
Біологічна хімія : навч.-метод. посіб. для самостійної роботи при
підготовці до ліцензійного іспиту "КРОК 1" змістових модулів 8, 9, 10
модулю 2 для студентів 2 курсу міжнар. ф-ту / К. В. Александрова, Н. В.
Крісанова, Д. Г. Іванченко, Н. П. Рудько, С. В. Левіч, М. А. Тихоновська. Запоріжжя : ЗДМУ, 2016. – 187 с.
UDC 577.1(075)
BBC 28.902я73
©Aleksandrova K.V., Krisanova N.V., Ivanchenko D.G.,
Rudko N.P., Levich S.V., Tikhonovska M.A.2016
©Zaporizhzhia State Medical University, 2016
2
INTRODUCTION
The handbook "Biological chemistry. A manual for independent work at
home and in class preparation for licensing examination “KROK 1” on semantic
modules 8 “Biochemistry of Vitamins”, and 9 “Functional biochemistry of organs
and tissues”, and 10 “Biochemical indexes of blood and urine in diagnostics of
metabolic disorders” of module 2 “Molecular Biology. Biochemistry of cell-to-cell
interactions. Of tissues and physiological functions” for students of International
Faculty (the second year of study) speciality «General Medicine» contains a
summary of the theory, which facilitates finding the right answer test tasks.
Tests of this manual are similar in content and form to the test tasks,
provided Testing Center of Ministry of Health of Ukraine. Each test task has only
one either correct or more correct answer that must be chosen among the available
ones by a student. As a self-study students are invited to give rationale for the
choice of the correct answer, identify key words for case described in a test task.
The authors hope that this special form of student work with test tasks, with
detailed explanation described in these tasks mostly clinical situations allow
foreign English-speaking students to prepare properly and pass licensing exam
"KROK 1: General medical training".
3
THE ROLE OF WATER-SOLUBLE AND FAT-SOLUBLE VITAMINS IN
THE METABOLISM OF HUMANS.
VITAMIN SIMILAR SUBSTANCES. ANTIVITAMINS
(Rudko N. P.)
INFORMATIONAL MATERIAL
Vitamins are a group of organic nutrients of various nature required in small
quantities for multiple biochemical reactions for the growth, survival and
reproduction of the organism, and which, generally, cannot be synthesized by the
body and must therefore be supplied by the diet. The most prominent function of
the vitamins is to serve as coenzymes (or prosthetic group) for enzymatic reactions.
Vitamins are grouped together according to the following general biological
characteristics:
1. Vitamins are not synthesized by the body and must come from food. An
exception are vitamin B3 (PP), which active form NADH (NADPH) can be
synthesized from tryptophan and vitamin D3 (cholecalciferol), synthesized from 7dehydrocholesterol in the skin. Amount of those ones and vitamins partially
synthesized by intestinal microflora (В1, В2, В3, B5, В6, К, and others) is normally
not sufficient to cover the body's need them.
2. Vitamins are not plastic material. Exception is vitamin F.
3. Vitamins are not an energy source. Exception is vitamin F.
4. Vitamins are essential for all vital processes and biologically active
already in small quantities.
5. They influence biochemical processes in all tissues and organs, i.e. they
are not specific to organs.
6. They can be used for medicinal purposes as a non-specific tools in high
doses for: diabetes mellitus - B1, B2, B6; colds and infectious diseases - vitamin C;
bronchial asthma - vitamin PP; gastrointestinal ulcers - vitamin-like substance U
and nicotinic acid; in hypercholesterolemia - nicotinic acid.
4
Since only a few vitamins can be stored (A, D, E, B12), a lack of vitamins
quickly leads to deficiency diseases (hypovitaminosis or avitaminosis). These
often affect the skin, blood cells, and nervous system. The causes of vitamin
deficiencies can be treated by improving nutrition and by administration vitamins
in tablet form. An overdose of vitamins leads to hypervitaminosis state only, with
toxic symptoms, in the case of vitamins A and D. Normally, excess vitamins are
rapidly excreted with the urine.
Lack of vitamins leads to the development of pathological processes in the
form of specific hypo- and avitaminosis. Widespread hidden forms of vitamin
deficiency have not severe external manifestations and symptoms, but have a
negative impact on performance, the overall tone of the body and its resistance to
various adverse factors.
Avitaminosis is a disease that develops in the absence of a particular vitamin.
Currently avitaminosis are not commonly found, but hypovitaminoses are observed
with vitamin deficiency in the body. Numerous examples you can see in the table 1.
Table 1. Vitamin functions and manifestations of hypo- and avitaminoses
B1
Vitamin
Thiamin
B2
Riboflavin
B3
Niacin,
nicotinic
acid,
nicotinamide
Pantothenic
acid
(PP)
B5
Functions
Functional
part
of
coenzyme TPP in pyruvate
and
α-ketoglutarate
dehydrogenases,
transketolase;
poorly
defined function in nerve
conduction
Functional
part
of
coenzymes FAD, FMN in
oxidation-reduction
reactions
Functional
part
of
coenzymes NAD+, NADP+
in
oxidation-reduction
reactions
Functional
part
of
coenzyme CoA (universal
acyl carrier in Krebs cycle,
fatty and other carboxylic
acid
metabolism)
and
phosphopantetheine (acyl
carrier protein in fatty acid
5
Hypovitaminosis symptomes
Peripheral nerve damage (polyneuritis
beriberi) or central nervous system lesions
(Wernicke-Korsakoff syndrome)
Concentration of pyruvate is increased in the
patient's blood, the most of which is excreted
with urine
Epithelial, mucosa, cutaneous, corneal
lesions: lesions of corner of mouth, lips, and
tongue; seborrheic dermatitis
Pellagra: photosensitive dermatitis, glossitis
(tongue inflammation), alopecia (hair loss),
edema (swelling), diarrhea, depressive
psychosis, aggression, ataxia (lack of
coordination), dementia, weakness
Numbness in the toes, burning sensation in
the feet, the defeat of mucous membranes of
internal organs, early graying, hair loss,
various disorders of the skin: the
development of small cracks in the corners of
the mouth, the appearance of white patches
on various parts of the body. There may also
synthesis)
Functional
part
of
coenzyme
PLP
in
transamination
and
decarboxylation of amino
acids
and
glycogen
phosphorylase
Coenzyme in carboxylation
reactions
in
gluconeogenesis and fatty
acid synthesis
B6
Pyridoxine,
pyridoxal,
pyridoxamine
B7
(H)
Biotin
B9
Folic acid
Functional
part
of
coenzyme THFA in transfer
of one-carbon fragments
B12
Cobalamin
Functional
part
of
coenzymes
adenosylcobalamin
(Methylmalonyl Co A
mutase)
and
methylcobalamin
(Methionine synthase) in
transfer of one-carbon
fragments and metabolism
of folic acid
C
Ascorbic
acid
A
Retinol
be depressed mood, fatigue.
Dermatitis of the eyes, nose, and mouth.
There is mental confusion, glossitis and
peripheral neuropathy, convulsions (due to
lack of inhibitory neurotransmitter GABA)
Seborrheic dermatitis, anemia, depression,
hair loss, high blood sugar levels,
inflammation or pallor of the skin and
mucous membranes, insomnia, loss of
appetite, muscle aches, nausea, sore tongue,
dry skin, high blood cholesterol
Megaloblastic anemia: red tongue, anemia,
lethargy, fatigue, insomnia, anxiety, digestive
disorders, growth retardation, breathing
difficulties, memory problems.
Deficiency during pregnancy is associated
with neural tube defects
Vitamin B12-deficiency anemia (in other
words pernicious anemia or Addison–
Biermer anemia) is one of many types of
megaloblastic anemias with degeneration of
the spinal cord, anemia, fatigue, depression,
low-grade fevers, diarrhea, weight loss,
neuropathic pain, glossitis (swollen, red and
smooth appearance of the tongue), angular
cheilitis (sores at the corner of the mouth)
Possible manifestations are also hypochromic
anemia, splitting hair and loss of hair,
increased nail bottling and taste alteration
Scurvy: general weakness, subcutaneous
hemmorhages (frequent hemorrhages from
internals and mucous membranes), gingival
hemmorhages, loss of teeth, formation of
spots on the skin, spongy gums, yellow skin,
fever, neuropathy
Multiple hemorrages in the places of clothes
friction are possible if a person often
experiences acute respiratory infections
It serves as a donor of
protons in hydroxylation
reaction for:
- collagen synthesis (prolyland lysyl residues are
hydroxylated by prolyl
3(4)-hydroxylase and lysyl
5-hydroxylase respectively;
catecholamines
and
steroid hormone synthesis;
It
has
properties
of
antioxidant;
enhances
absorption of iron
Functional part of visual Vision impairment hemeralopia (night
pigments (rhodopsins and blindness), xerophthalmia; keratinization of
iodopsins) in the retina; skin
regulation
of
gene
expression
and
cell
differentiation; β-carotene
(provitamin A) is an
antioxidant
6
D
E
K
Stimulation
of
Ca2+
absorption
through
intestinal wall, maintenance
of calcium balance and
mobilization
of
bone
mineral
Tocopherols Antioxidant, especially in
cell membranes
PhylloCoenzyme in formation of
quinone, γ-carboxyglutamate
menaresidues in structure of:
quinones - factors II (prothrombin),
VII, IX, X, XIV, protein S
(blood coagulation system);
- bone matrix proteins
Calciferol
Rickets = poor mineralization of bone;
osteomalacia = bone demineralization
Osteoectasia of the lower extremities and
delayed mineralization of cranial bones are
onserved in infants
Extremely rare is a serious neurologic
dysfunction
Impaired blood clotting, hemorrhagic
disease, osteoporosis and coronary heart
disease
Intestinal dysbacteriosis occurs hemorrhagic
syndrome
External causes for hypovitaminosis
1. Lack of the vitamin in the diet or presence of food factors hindering the
absorption of vitamin. For example, use of large amounts of raw eggs (they contain
protein avidin binds vitamin H (biotin)) as a result may develop a state of
hypovitaminosis H.
2. Do not take into account the need for a particular vitamin. For example, in
protein-free diet is increasing demand for vitamin PP (with normal diet it may be
partially synthesized from tryptophan). If a person consumes much protein, it can
increase the need for vitamin B6 and reduce the need for vitamin PP.
3. Social reasons: urbanization, power and extremely high purity of canned
food; antivitamin presence in food. People are not enough exposed to sunlight in
large cities - so it can be hypovitaminosis D. In such cases, the medicine uses
ultraviolet radiation in the form of different physical treatments, which activate the
synthesis of vitamin D3 from 7-dehydrocholesterol in the skin cells.
Internal causes of hypovitaminosis
1. Physiological increased need for vitamins, for example, during pregnancy,
with heavy physical labor.
2. Long-term severe infectious diseases, as well as during the recovery
period.
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3. Disturbance of vitamin absorption in some diseases of the digestive tract,
for example impaired absorption of fat-soluble vitamins is observed at
cholelithiasis; vitamin B12 is done with atrophy of the gastric mucosa and a
deficiency of Castle intrinsic factor. Another case if a person who hadn’t been
consuming fats but had been getting enough carbohydrates and proteins for long
time revealed dermatitis, poor wound healing, vision impairment. Lack of vitamins
A, D, E, K, F (linoleic, linolenic, arachidonic acids) is probable cause of the
metabolic disorder.
4. Intestinal dysbacteriosis. It has the meaning as some vitamins are
synthesized by the intestinal microflora (these vitamins are B3, B6, B7 (H), B9, B12,
and K).
5. Cirrhosis. The liver is the major depot of many vitamins, particularly fatsoluble (especially high hepatic reserves of fat soluble vitamins A, D), but also
certain water-soluble, such as B9, B12, etc. In case of vitamin consumption increase
and reducing their dietary intake, which is usually the case, for example, in
alcoholism, megaloblastic anemia is developed in a short time as a characteristic
sign of hypovitaminosis B9. Patients with cirrhosis may experience blurred vision
in the twilight due to malabsorption of vitamin A in the intestine and its reduced
deposit in the liver.
6. Genetic defects of some enzymatic systems. For example, vitamin Dresistant rickets occurs in children lack the enzymes involved in the formation of
the active form of vitamin D - calcitriol (1, 25-dihydroxycholecalciferol).
Classification of vitamins
1. Fat-soluble vitamins: A (retinol), D (calciferol), E (tocopherol), K
(naphthoquinone), F (polyunsaturated fatty acid: linoleic, linolenic, arachidonic).
2. Water-soluble vitamins:
- Group B: B1 (thiamine), B2 (riboflavin), B3 or PP (nicotinamide, niacin), B5
(pantothenic acid), B6 (pyridoxine), B7 or H (biotin), B9 or Bc (folic acid), B12
(cyanocobalamin) ;
- Vitamin C (ascorbic acid);
8
- Vitamin P (rutin and other bioflavonoids).
3. Also vitamin-like substances are separated:
- fat-soluble: Coenzyme Q (ubiquinone),
- water-soluble vitamins: B4 (choline), B8 (inositol), BT or B11 (carnitine), , B13
(orotic acid), B15 (pangamic acid), U (S-methylmethionine), N (lipoic acid).
Water-soluble vitamins are usually functioning as precursors of coenzymes
and prosthetic groups of enzymes. For example, coenzyme form of
- Vitamin B1 is TPP (thiamine pyrophosphate) (trade name - cocarboxylase);
- Vitamin B2 is FMN (flavin mononucleotide) and FAD (flavin adenine
dinucleotide);
- Vitamin B3 is NAD+ (nicotinamide adenine dinucleotide) or NADP+
(nicotinamide adenine dinucleotide phosphate);
- Vitamin B5 is Coenzyme A (coenzyme of acylation);
- Vitamin B6 is PLP (pyridoxal phosphate);
- Vitamin B9 is THFA (tetrahydrofolic acid);
- Vitamin B12 is adenosylcobalamin and methylcobalamin.
Holoenzymes containing coenzymes (as its non-protein part) which are often
vitamin derivatives perform multiple functions. For example, the first enzyme in
gluconeogenesis pyruvate carboxylase uses biotin for carboxylation of pyruvate;
but the transformation of the pyruvate to acetyl-CoA by pyruvate dehydrogenase
complex requires five coenzymes: TPP, lipoic acid, CoA, FAD, NAD+. Since TPP
is involved in this conversion first, pyruvate accumulation in cells of the nervous
system (primarily) and then increase in pyruvate content in the blood and urine of
patients in the case of vitamin B1 deficiencies becomes obvious.
Most water-soluble vitamins must be supplied regularly with food, as they
are quickly removed or destroyed in the body. Fat-soluble vitamins can be
deposited in the body. Furthermore, they are poorly excreted, therefore,
hypervitaminosis as diseases associated with high doses of fat-soluble vitamin
intoxication of organism are observed. Such diseases are described for vitamins A
and D.
9
Currently, vitamins and antivitamins widely used to prevent and treat a
variety of disorders of metabolism. For example:
- vitamin K or menadione, or vicasol (both are synthetic water-soluble analogue of
vitamin K) are prescribed to stimulate the synthesis (specifically post-translational
γ-carboxylation of glutamic acid residues) such enzymes of coagulation system as
factors II (prothrombin), VII, IX and X in the liver. They are usually used after
long-term antibiotic treatment (if there is increased bleeding with small injuries,
increase in blood clotting time) and in the preoperative period;
- vitamin K antagonist (antivitamin K) dicumarol reduces the efficiency of
the blood coagulation promoting blood thinning thereby it use for the treatment of
blood clotting diseases, in particular, thrombosis, thrombophlebitis;
- Vitamin A and its derivatives like retinol acetate are used for treating of
vitamin A deficiency. For example, they can be administered a patient in order to
restore his vision if the patient suffers from vision impairment hemeralopia (night
blindness, twilight vision impairment), age-related glaucoma, cataracts etc.
Vitamin A drug is also used for skin conditions including acne, eczema, psoriasis,
cold sores, wounds, burns, sunburn. It is also used for gastrointestinal ulcers, gum
disease, urinary tract infections, diseases of the nervous system;
- drug isoniazid which is antivitamin nicotinic acid and pyridoxine is used In
the treatment of patients with pulmonary tuberculosis;
- the structural analogue of vitamin B2 acriсhine is formerly widely used as
an antimalarial drug but superseded by chloroquine in recent years. It has also been
used as an anthelmintic (in enterobiasis) and in the treatment of giardiasis and
malignant effusions. The mechanism action of the drug is based on preventing of
microorganism FAD(FMN)-dependent dehydrogenases;
- Ascorutinum is recommended to use as a more effective drug in
comparison with ascorbic acid for patients with reduced immunity and frequent
colds. Vitamin C (Ascorbic acid) is involved in the hydroxylation of prolyl- and
lysyl residues by prolyl 3(4)-hydroxylase and lysyl 5-hydroxylase during collagen
synthesis. Effect of the vitamin C is enhanced by vitamin P, which stabilizes the
10
ground substance of fibrous connective tissue in way of hyaluronidase inhibition.
Ascorutinum can be recommended in case of bleeding gums, petechial
hemorrhages;
- Sulfonamide drugs are folic acid antivitamin. They are structurally
resemble paraaminobenzoic acid and due to this similarity it is displaced from its
complex with the enzyme synthesizing folic acid. This leads to the inhibition of
bacterial growth. This mechanism of action of sulfonamides allows their use as
antibacterial agents;
- Pregnant women with a history of several miscarriages is assigned the
therapy including α-tocopherol (vitamin E) vitamin supplements using, It
contributes to the childbearing. Furthermore, tocopherol acetate, vitamin
preparation is usually given in the course of radiation therapy, since this substance
has a distinct radioprotective membrane stabilizing action due to its antioxidant
activity;
- Derivatives of pyridoxine (vitamin B6) are used as neurotrophic agents for
the correction of mental retardation in childre; in cases of mental disorders in
adults; as neuroprotective agents in rehabilitation of patients with stroke and other
pathological conditions. The positive effects of pyridoxine is explained by its use
as a precursor of PLP that is prosthetic group of the enzyme glutamate
decarboxylase in neurons. The enzyme carries out inhibitory neurotransmitter
GABA formation.
- Cabbage and potato juices rich in vitamin U are recommended to drink for
patient with duodenal ulcer after the therapy course. Whether taken as a
supplement or from foods, vitamin U has been shown to be able to treat a variety
of gastrointestinal conditions, including ulcerative colitis, acid reflux, and peptic
ulcers. It may also be able to treat skin lesions, improve the symptoms of diabetes,
and strengthen the immune system. Some studies show that it can also help prevent
liver damage by protecting the organ from the effects of high doses of
acetaminophen. Additionally, it may be able to reduce allergies and sensitivities to
cigarette smoke and improve cholesterol levels.
11
The aforecited examples are only a small part of the use of vitamins and
their derivatives in medicine.
Therefore, knowledge of the biochemical basis of vitaminology is of great
importance for future doctors.
EXERCISES FOR INDEPENDENT WORK. In the table with test tasks
emphasize keywords, choose the correct answer and justify it:
№
1.
Test tasks:
Examination
of
a
Explanations:
patient
with
frequent hemorrhages from internals
and mucous membranes revealed
proline and lysine being a part of
collagen
fibers.
What
vitamin
absence caused disturbance of their
hydroxylation?
A. Vitamin A
B. Thiamine
C. Vitamin K
D. Vitamin E
E. Vitamin C
2.
Examination of a man who hadn’t
been consuming fats but had been
getting enough carbohydrates and
proteins for long time revealed
dermatitis, poor wound healing,
vision impairment. What is the
probable
cause
of
metabolic
disorder?
A. Lack of vitamins PP, H
12
№
Test tasks:
Explanations:
B. Lack of oleic acid
C. Lack of linoleic acid, vitamins A,
D, E, K.
D. Lack of palmitic acid
E. Low caloric value of diet
3.
A woman who has been keeping to a
clean-rice diet for a long time was
diagnosed
(beriberi).
results
with
What
in
polyneuritis
vitamin
development
deficit
of
this
disease?
A. Folic acid
B. Thiamine
C. Ascorbic acid
D. Riboflavin
E. Pyridoxine
4.
A
patient
suffers
impairment
from
vision
hemeralopia (night
blindness). What vitamin preparation
should be administered the patient in
order to restore his vision?
A. Pyridoxine
B. Retinol acetate
C. Vicasol
D. Thiamine chloride
E. Tocopherol acetate
13
№
Test tasks:
5.
There is disturbed process of Ca2+
Explanations:
absorption through intestinal wall
after the removal of gall bladder in
patient. What vitamin will stimulate
this process?
A. K
B. C
C. D3
D. PP
E. B12
6.
A 6 y.o child was administered
vicasol to prevent postoperative
bleeding. Vicasol is a synthetic
analogue of vitamin K. Name posttranslation
changes
of
blood
coagulation factors that will be
activated by vicasol:
A. Carboxylation of glutamic acid
residues
B. Polymerization
C. Partial proteolysis
D. Glycosylation
E. Phosphorylation of serine radicals
7.
Most
participants
of
Magellan
expedition to America died from
avitaminosis. This disease declared
itself
by
general
weakness,
subcutaneous hemmorhages, falling
14
№
Test tasks:
Explanations:
of teeth, gingival hemmorhages.
What
is
the
name
of
this
avitaminosis?
A. Biermer's anemia
B. Polyneuritis
(beriberi)
C. Pellagra
D. Rachitis
E. Scurvy
8.
A patient with hypochromic anemia
has splitting hair and loss of hair,
increased nail bottling and taste
alteration. What is the mechanism of
the development of these symptoms?
A. Deficiency of vitamin B12
B. Decreased production of thyroid
hormones
C. Deficiency of vitamin K
D. Decreased
production
of
parathyrin
E. Deficiency
of
iron-containing
enzymes
9.
The structural analogue of vitamin
B2 is administered (acriсhine) in a
case of enterobiasis. The disorder of
which enzyme synthesis is caused by
this medicine in microorganisms?
A. NAD-dependent dehydrogenases
15
№
Test tasks:
Explanations:
B. Cytochrome oxidases
C. FAD-dependent dehydrogenases
D. Peptidases
E. Aminotransferases
10. A patient who was previously ill
with mastectomy as a result of breast
cancer
was
prescribed
radiation
therapy. What vitamin preparation
has marked radioprotective action
caused by antioxidant activity?
A. Tocopherol acetate
B. Riboflavin
C. Folic acid
D. Ergocalciferol
E. Thiamine chloride
11. There is an inhibited coagulation in
the
patients
with
bile
ducts
obstruction, bleeding due to the low
level of absorption of vitamin. What
vitamin is in deficiency?
A. K
B. E
C. D
D. A
E. Carotene
12. Concentration
of
pyruvate
is
increased in the patient's blood, the
16
№
Test tasks:
Explanations:
most of which is excreted with urine.
What avitaminosis has the patient?
A. Avitaminosis B1
B. Avitaminosis B2
C. Avitaminosis E
D. Avitaminosis B9
E. Avitaminosis B3
13. Hydroxylation
of
endogenous
substrates and xenobiotics requires a
donor of protons. Which of the
following vitamins can play this
role?
A. Vitamin C
B. Vitamin E
C. Vitamin P
D. Vitamin A
E. Vitamin B6
14. A 2-year-old child has got intestinal
dysbacteriosis,
which
results
in
hemorrhagic syndrome. What is the
most likely cause of hemorrhage of
the child?
A. Activation
of
tissue
thromboplastin
B. PP hypovitaminosis
C. Fibrinogen deficiency
17
№
Test tasks:
Explanations:
D. Vitamin K insufficiency
E. Hypocalcemia
15. A 10-year-old girl often experiences
acute respiratory infections with
multiple hemorrages in the places of
clothes friction. Hypovitaminosis of
what vitamin is in this girl organism?
A. A
B. B2
C. B1
D. B6
E. С
16. A doctor recommends a patient with
duodenal ulcer to drink cabbage and
potato
juices
after
the
therapy
course. Which substances contained
in these vegetables help to heal and
prevent the ulcers?
A. Vitamin U
B. Vitamin B5
C. Vitamin K
D. Vitamin B1
E. Vitamin C
17. Ultraviolet radiation can be used in
the form of physical treatments.
What vitamin formation is activated
under UV light in the skin:
A. Vitamin B6
18
№
Test tasks:
Explanations:
B. Vitamin A
C. Vitamin E
D. Vitamin C
E. Vitamin D3
18. A 9-month-old infant is fed with
artifical formulas with unbalanced
vitamin B6 concentration. The infant
presents with pellagral dermatitis,
convulsions, anaemia. Convulsions
development might be caused by the
disturbed formation of:
A. Dopamine
B. Histamine
C. Serotonin
D. DOPA
E. GABA
19. During examination of an 11-monthold infant a pediatrician revealed
osteoectasia of the lower extremities
and delayed mineralization of cranial
bones. Such pathology is usually
provoked by the deficit of the
following vitamin:
A. Thiamin
B. Riboflavin
C. Bioflavonoids
19
№
Test tasks:
Explanations:
D. Pantothenic acid
E. Cholecalciferol
20. A patient presents with twilight
vision impairment. Which of the
following
vitamins
should
be
administered?
A. Cyanocobalamin
B. Ascorbic acid
C. Nicotinic acid
D. Retinol acetate
E. Pyridoxine hydrochloride
21. After the disease a 16-year-old boy
is presenting with decreased function
of protein synthesis in the liver as a
result of vitamin K deficiency. This
may cause disorder of:
A. Erythropoietin production
B. Erythrocyte sedimentation rate
C. Blood coagulation
D. Osmotic blood pressure
E. Anticoagulant production
22. In clinical practice tuberculosis is
treated with izoniazid preparation –
that is an antivitamin able to
penetrate
into
the
tuberculosis
20
№
Test tasks:
Explanations:
bacillus. Tuberculostatic effect is
induced by the interference with
replication processes and oxidationreduction
reactions
due
to
the
buildup of pseudo-coenzyme:
A. FMN
B. NAD
C. CoQ
D. FAD
E. TPP
23. Some infections diseases caused by
bacteria
are
treated
with
sulfanilamides, which block the
synthesis of bacteria growth factor.
What is the mechanism of their
action?
A. They inhibit the absorption of
folic acid
B. They
are
allosteric
enzyme
inhibitors
C. They are allosteric enzymes
D. They
are
antivitamins
of
paraaminobenzoic acid
E. They are involved in red-ox
processes
24. A
20-year
old
male
patient
complains of general weakness,
rapid
fatigability,
irritability,
21
№
Test tasks:
decreased
Explanations:
performance,
bleeding
gums, petechiae on the skin. What
vitamin deficiency may be caused of
these changes?
A. Riboflavin
B. Ascorbic acid
C. Retinol
D. Thiamine
E. Folic acid
25. A number of disorders can be
diagnosed by evaluation activity of
blood transaminases. What vitamin
is
one
of
cofactors
for
these
enzymes?
A. B6
B. B1
C. B5
D. B2
E. B8
26. Symptoms of pellagra (vitamin PP
deficiency)
is
particularly
pronounced in patients with low
protein diet, because nicotine amide
precursor in humans is one of the
essential amino acids, namely:
A. Lysine
22
№
Test tasks:
Explanations:
B. Threonine
C. Tryptophan
D. Arginine
E. Histidine
27. A
patient
complains
of
photoreception disorder and frequent
acute viral diseases. He has been
prescribed a vitamin that affects
photoreception
producing
processes
by
rhodopsin,
the
pigment.
What
photosensitive
vitamin is it?
A. Cyanocobalamin
B. Tocopherol acetate
C. Pyridoxine hydrochloride
D. Thiamine
E. Retinol acetate
28. A 36-year-old female patient has a
history of B2-hypovitaminosis. The
most
likely
symptoms
cause
of
(epithelial,
specific
mucosa,
cutaneous, corneal lesions) is the
deficiency of:
A. Cytochrome oxidase
B. Cytochrome B
C. Cytochrome A1
D. Cytochrome C
E. FAD or FMN
23
№
Test tasks:
Explanations:
29. A patient, who has been suffering for
a
long
time
disbacteriosis,
from
has
intestine
increased
hemorrhaging caused by disruption
of posttranslational modification of
blood coagulation factors II, VII, IX
and X in the liver. What vitamin
deficiency is the cause of this
condition?
A. K
B. B12
C. B9
D. C
E. P
30. A 6-year-old child suffers from
delayed
growth,
disrupted
ossification
processes,
decalcification of teeth. What can be
the cause?
A. Vitamin D deficiency
B. Hyperthyroidism
C. Vitamin C deficiency
D. Decreased glucagon production
E. Insulin deficiency
31
A patient is diagnosed with chronic
atrophic
gastritis
attended
by
deficiency of Castle`s (intrinsic)
24
№
Test tasks:
Explanations:
factor. What type of anemia does the
patient have?
A. B12-deficiency anemia
B. Iron-deficiency anemia
C. Hemolytic anemia
D. Protein-deficiency anemia
E. Iron refractory anemia
32
During regular check-up a child is
detected
with
mineralization
of
interrupted
bones.
What
vitamin deficiency can be the cause?
A. Calciferol
B. Riboflavin
C. Tocopherol
D. Folic acid
E. Cobalamin
33
Point
out
the
vitamin,
whose
deficiency leads to pellagra:
A. Vitamin P
B. Vitamin A
C. Vitamin C
D. Vitamin B3
E. Vitamin B2
34
The avitaminosis of ascorbic acid is
named as:
A. Cushing`s syndrome
25
№
Test tasks:
Explanations:
B. Addison`s disease
C. Kwashiorkor
D. Hemolytic anemia
E. Scurvy
35
Find
out
the
deficiency
is
vitamin
associated
whose
with
disturbed transamination of amino
acids:
A. Pyridoxine
B. Rutin
C. Thiamine
D. Folic acid
E. Ascorbic acid
36
Choose
the
vitamin,
whose
antivitamin is named as dicoumarol:
A. Vitamin A
B. Vitamin B6
C. Vitamin C
D. Vitamin D
E. Vitamin K
37
Choose the vitamin, which is a
powerful natural antioxidant:
A. Retinal
B. Tocopherol
C. Ergocalciferol
D. Riboflavin
26
№
Test tasks:
Explanations:
E. Pyridoxine
38
Name the blood plasma index
whose low value will prove the
deficiency of vitamin K in patient:
A. Urea
B. Albumins
C. Immunoglobulin G
D. Prothrombin
E. C-reactive protein
39
Name the active form of vitamin
whose level in the blood is depended
on the secretion rate of parathyroid
hormone:
A. Ascorbic acid
B. Calcitriol
C. Thiamine
D. Tocopherol
E. Naphtoquinone
40
Choose the vitamin, whose precursor
is named as β-carotene:
A. Vitamin C
B. Vitamin D
C. Vitamin A
D. Vitamin B12
E. Vitamin P
27
BIOCHEMISTRY OF MUSCULAR AND CONNECTIVE TISSUES
(Ivanchenko D. H., Tikhonovska M. A.)
INFORMATIONAL MATERIAL
Muscular tissue
Muscle tissue account for 40-42 % of body mass.
Muscular tissues consist of elongated cells called muscle fibers or myocytes that
can use ATP to generate force. As a result, muscular tissues produce body
movements, maintain posture, and generate heat. They also provides protection.
Based on their location and certain structural and functional features, muscular
tissues are classified into three types: skeletal, cardiac, and smooth (Table 1).
Table 1. Characteristic of different types of muscular tissues
Description
Location
Function
Skeletal muscle tissue
Long, cylindrical, striated fibers (striations Usually attached
Motion,
are alternating light and dark bands within to bones by
posture, heat
fibers that are visible under a light tendons.
production,
microscope). Skeletal muscle fibers vary
protection.
greatly in length, from a few centimeters in
short muscles to 30-40 cm in longest
muscles. A muscle fiber is a roughly
cylindrical, multinucleated cell with nuclei
at periphery. Skeletal muscle is considered
voluntary because it can be made to
contract or relax by conscious control.
Cardiac muscle tissue
Branched, striated fibers with usually only Heart wall.
Pumps blood to
one centrally located nucleus (occasionally
all parts of
two). Attach end to end by transverse
body.
28
thickenings of plasma membrane called
intercalated discs (intercalate – to insert
between), which contain desmosomes and
gap junctions. Desmosomes strengthen
tissue and hold fibers together during
vigorous
contractions.
Gap
junctions
provide route for quick conduction of
electrical signals (muscle action potentials)
throughout
heart.
Involuntary
(not
conscious) control.
Smooth muscle tissue
Fibers usually involuntary, nonstriated Iris of eyes; walls
Motion
(lack striations, hence the term smooth). of hollow internal (constriction of
Smooth muscle fiber is a small spindle- structures such as
blood vessels
shaped cell thickest in middle, tapering at blood vessels,
and airways,
each end, and containing a single, centrally airways to lungs,
propulsion of
located nucleus. Gap junctions connect stomach,
foods through
many individual fibers in some smooth intestines,
gastrointestinal
muscle tissues (for example, in wall of gallbladder,
tract,
intestines).
Can
contraction of
contractions
as
produce
many
powerful urinary bladder,
muscle
fibers and uterus.
urinary bladder
contract in unison. Where gap junctions are
and
absent, such as iris of eye, smooth muscle
gallbladder).
fibers contract individually, like skeletal
muscle fibers.
Skeletal muscle tissue is so named because most skeletal muscles move bones of
the skeleton. A few skeletal muscles attach to and move the skin or other skeletal
muscles. Skeletal muscle tissue is striated: Alternating light and dark protein bands
(striations) are seen when the tissue is examined with a microscope. Skeletal
29
muscle tissue works mainly in a voluntary manner. Its activity can be consciously
controlled by neurons (nerve cells) that are part of the somatic (voluntary) division
of the nervous system. Most skeletal muscles also are controlled subconsciously to
some extent. For example, your diaphragm continues to alternately contract and
relax without conscious control so that you don’t stop breathing. Also, you do not
need to consciously think about contracting the skeletal muscles that maintain your
posture or stabilize body positions.
Only the heart contains cardiac muscle tissue, which forms most of the heart wall.
Cardiac muscle is also striated, but its action is involuntary. The alternating
contraction and relaxation of the heart is not consciously controlled. Rather, the
heart beats because it has a pacemaker that initiates each contraction. This built-in
rhythm is termed autorhythmicity. Several hormones and neurotransmitters can
adjust heart rate by speeding or slowing the pacemaker.
Smooth muscle tissue is located in the walls of hollow internal structures, such as
blood vessels, airways, and most organs in the abdominopelvic cavity. It is also
found in the skin, attached to hair follicles. Under a microscope, this tissue lacks
the striations of skeletal and cardiac muscle tissue. For this reason, it looks nonstriated, which is why it is referred to as smooth. The action of smooth muscle is
usually involuntary, and some smooth muscle tissue, such as the muscles that
propel food through your gastrointestinal tract, has autorhythmicity. Both cardiac
muscle and smooth muscle are regulated by neurons that are part of the autonomic
(involuntary) division of the nervous system and by hormones released by
endocrine glands.
Functions of Muscular Tissue. Through sustained contraction or alternating
contraction and relaxation, muscular tissue has four key functions: producing body
movements, stabilizing body positions, storing and moving substances within the
body, and generating heat.
1. Producing body movements. Movements of the whole body such as walking
and running, and localized movements such as grasping a pencil, keyboarding, or
30
nodding the head as a result of muscular contractions, rely on the integrated
functioning of skeletal muscles, bones, and joints.
2. Stabilizing body positions. Skeletal muscle contractions stabilize joints and
help maintain body positions, such as standing or sitting. Postural muscles contract
continuously when you are awake; for example, sustained contractions of your
neck muscles hold your head upright when you are listening intently to your
anatomy and physiology lecture.
3. Storing and moving substances within the body. Storage is accomplished by
sustained contractions of ringlike bands of smooth muscle called sphincters, which
prevent outflow of the contents of a hollow organ. Temporary storage of food in
the stomach or urine in the urinary bladder is possible because smooth muscle
sphincters close off the outlets of these organs. Cardiac muscle contractions of the
heart pump blood through the blood vessels of the body. Contraction and
relaxation of smooth muscle in the walls of blood vessels help adjust blood vessel
diameter and thus regulate the rate of blood flow. Smooth muscle contractions also
move food and substances such as bile and enzymes through the gastrointestinal
tract, push gametes (sperm and oocytes) through the passageways of the
reproductive systems, and propel urine through the urinary system. Skeletal muscle
contractions promote the flow of lymph and aid the return of blood in veins to the
heart.
4. Generating heat. As muscular tissue contracts, it produces heat, a process
known as thermogenesis. Much of the heat generated by muscle is used to
maintain normal body temperature. Involuntary contractions of skeletal muscles,
known as shivering, can increase the rate of heat production.
Microscopic Anatomy of a Skeletal Muscle Fiber. The most important
components of a skeletal muscle are the muscle fibers themselves. The diameter of
a mature skeletal muscle fiber ranges from 10 to 100 μm. The typical length of a
mature skeletal muscle fiber is about 10 cm, although some are as long as 30 cm.
Because each skeletal muscle fiber arises during embryonic development from the
fusion of a hundred or more small mesodermal cells called myoblasts (Fig. 1 a),
31
each mature skeletal muscle fiber has a hundred or more nuclei. Once fusion has
occurred, the muscle fiber loses its ability to undergo cell division. Thus, the
number of skeletal muscle fibers is set before you are born, and most of these cells
last a lifetime.
Figure 1. Microscopic organization of skeletal muscle.
Sarcolemma, Transverse Tubules, and Sarcoplasm. The multiple nuclei of a
skeletal muscle fiber are located just beneath the sarcolemma, the plasma
32
membrane of a muscle cell (Fig. 1 b, c). Thousands of tiny invaginations of the
sarcolemma, called transverse (T) tubules, tunnel in from the surface toward the
center of each muscle fiber. Because T tubules are open to the outside of the fiber,
they are filled with interstitial fluid. Muscle action potentials travel along the
sarcolemma and through the T tubules, quickly spreading throughout the muscle
fiber. This arrangement ensures that an action potential excites all parts of the
muscle fiber at essentially the same instant.
Within the sarcolemma is the sarcoplasm, the cytoplasm of a muscle fiber.
Sarcoplasm includes a substantial amount of glycogen, which is a large molecule
composed of many glucose molecules. Glycogen can be used for synthesis of ATP.
In addition, the sarcoplasm contains a red-colored protein called myoglobin. This
protein, found only in muscle, binds oxygen molecules that diffuse into muscle
fibers from interstitial fluid. Myoglobin releases oxygen when it is needed by the
mitochondria for ATP production. The mitochondria lie in rows throughout the
muscle fiber, strategically close to the contractile muscle proteins that use ATP
during contraction so that ATP can be produced quickly as needed (Fig. 1 c).
Myofibrils and Sarcoplasmic Reticulum. At high magnification, the sarcoplasm
appears stuffed with little threads. These small structures are the myofibrils, the
contractile organelles of skeletal muscle (Fig. 1 c). Myofibrils are about 2 μm in
diameter and extend the entire length of a muscle fiber. Their prominent striations
make the entire skeletal muscle fiber appear striped (striated).
A fluid-filled system of membranous sacs called the sarcoplasmic reticulum or
SR encircles each myofibril (Fig. 1 c). This elaborate system is similar to smooth
endoplasmic reticulum in nonmuscular cells. Dilated end sacs of the sarcoplasmic
reticulum called terminal cisterns butt against the T tubule from both sides. A
transverse tubule and the two terminal cisterns on either side of it form a triad. In a
relaxed muscle fiber, the sarcoplasmic reticulum stores calcium ions (Ca2+).
Release of Ca2+ from the terminal cisterns of the sarcoplasmic reticulum triggers
muscle contraction.
33
Filaments and the Sarcomere. Within myofibrils are smaller protein structures
called filaments or myofilaments (Fig. 1 c). Thin filaments are 8 nm in diameter
and 1-2 μm long and composed mostly of the protein actin, while thick filaments
are 16 nm in diameter and 1-2 μm long and composed mostly of the protein
myosin. Both thin and thick filaments are directly involved in the contractile
process. Overall, there are two thin filaments for every thick filament in the regions
of filament overlap. The filaments inside a myofibril do not extend the entire length
of a muscle fiber. Instead, they are arranged in compartments called sarcomeres,
which are the basic functional units of a myofibril (Fig. 2 a).
Figure 2. The arrangement of filaments within a sarcomere.
Narrow, plate-shaped regions of dense protein material called Z discs separate one
sarcomere from the next. Thus, a sarcomere extends from one Z disc to the next Z
disc.
The extent of overlap of the thick and thin filaments depends on whether the
muscle is contracted, relaxed, or stretched. The pattern of their overlap, consisting
34
of a variety of zones and bands (Fig. 2 b), creates the striations that can be seen
both in single myofibrils and in whole muscle fibers. The darker middle part of the
sarcomere is the A band, which extends the entire length of the thick filaments
(Fig. 2 b). Toward each end of the A band is a zone of overlap, where the thick and
thin filaments lie side by side. The I band is a lighter, less dense area that contains
the rest of the thin filaments but no thick filaments (Fig. 2 b), and a Z disc passes
through the center of each I band. A narrow H zone in the center of each A band
contains thick but not thin filaments. A mnemonic that will help you to remember
the composition of the I and H bands is as follows: the letter I is thin (contains thin
filaments), while the letter H is thick (contains thick filaments). Supporting
proteins that hold the thick filaments together at the center of the H zone form the
M line, so named because it is at the middle of the sarcomere. Table 2 summarizes
the components of the sarcomere.
Table 2. Components of a Sarcomere
Component Description
Z discs
Narrow, plate-shaped regions of dense material that separate one
sarcomere from the next.
A band
Dark, middle part of sarcomere that extends entire length of thick
filaments and includes those parts of thin filaments that overlap
thick filaments.
I band
Lighter, less dense area of sarcomere that contains remainder of
thin filaments but no thick filaments. A Z disc passes through
center of each I band.
H zone
Narrow region in center of each A band that contains thick
filaments but no thin filaments.
M line
Region in center of H zone that contains proteins that hold thick
filaments together at center of sarcomere.
Muscle Proteins. Myofibrils are built from three kinds of proteins: (1)
contractile proteins, which generate force during contraction; (2) regulatory
35
proteins, which help switch the contraction process on and off; and (3) structural
proteins, which keep the thick and thin filaments in the proper alignment, give the
myofibril elasticity and extensibility, and link the myofibrils to the sarcolemma and
extracellular matrix.
The two contractile proteins in muscle are myosin and actin, components of
thick and thin filaments, respectively. Myosin is the main component of thick
filaments and functions as a motor protein in all three types of muscle tissue. Motor
proteins pull various cellular structures to achieve movement by converting the
chemical energy in ATP to the mechanical energy of motion, that is, the production
of force. In skeletal muscle, about 300 molecules of myosin form a single thick
filament. Each myosin molecule is shaped like two golf clubs twisted together (Fig.
3 a). The myosin tail (twisted golf club handles) points toward the M line in the
center of the sarcomere. Tails of neighboring myosin molecules lie parallel to one
another, forming the shaft of the thick filament. The two projections of each
myosin molecule (golf club heads) are called myosin heads. The heads project
outward from the shaft in a spiraling fashion, each extending toward one of the six
thin filaments that surround each thick filament.
Figure 3. Structure of thick and thin filaments.
Limited proteolysis can be a powerful tool in probing the activity of large
proteins. The treatment of myosin with trypsin and papain results in the formation
of four fragments: two S1 fragments; an S2 fragment, also called heavy
meromyosin (HMM); and a fragment called light meromyosin (LMM; Fig. 4). Each
S1 fragment corresponds to one of the heads from the intact structure and includes
850 amino-terminal amino acids from one of the two heavy chains as well as one
36
copy of each of the light chains. Examination of the structure of an S1 fragment at
high resolution reveals the presence of a P-loop NTPase-domain core that is the
site of ATP binding and hydrolysis.
Thin filaments are anchored to Z discs (Fig. 2 b). Their main component is the
protein actin. Filamentous actin, or F-actin, is a twisted strand composed of two
rows of 300–400 individual globular molecules of G-actin (Fig. 3 b). On each
actin molecule is a myosin-binding site, where a myosin head can attach.
Figure 4. Myosin dissection.
Smaller amounts of two regulatory proteins – tropomyosin and troponin –
are also part of the thin filament. In relaxed muscle, myosin is blocked from
binding to actin because strands of tropomyosin cover the myosin-binding sites on
actin. The tropomyosin strands in turn are held in place by troponin molecules.
You will soon learn that when calcium ions bind to troponin, it undergoes a change
in shape; this change moves tropomyosin away from myosin-binding sites on actin
and muscle contraction subsequently begins as myosin binds to actin.
Besides contractile and regulatory proteins, muscle contains about a dozen
structural proteins, which contribute to the alignment, stability, elasticity, and
extensibility of myofibrils. Several key structural proteins are titin, α-actinin,
myomesin, nebulin, and dystrophin. Titin is the third most plentiful protein in
skeletal muscle (after actin and myosin). This molecule’s name reflects its huge
size. With a molecular mass of about 3 million daltons, titin is 50 times larger than
an average-sized protein. Each titin molecule spans half a sarcomere, from a Z disc
to an M line (Fig. 2 b), a distance of 1 to 1.2 μm in relaxed muscle. Each titin
37
molecule connects a Z disc to the M line of the sarcomere, thereby helping
stabilize the position of the thick filament. The part of the titin molecule that
extends from the Z disc is very elastic. Because it can stretch to at least four times
its resting length and then spring back unharmed, titin accounts for much of the
elasticity and extensibility of myofibrils. Titin probably helps the sarcomere return
to its resting length after a muscle has contracted or been stretched, may help
prevent overextension of sarcomeres, and maintains the central location of the A
bands.
The dense material of the Z discs contains molecules of α-actinin, which bind to
actin molecules of the thin filament and to titin. Molecules of the protein
myomesin form the M line. The M line proteins bind to titin and connect adjacent
thick filaments to one another. Myosin holds the thick filaments in alignment at the
M line. Nebulin is a long, nonelastic protein wrapped around the entire length of
each thin filament. It helps anchor the thin filaments to the Z discs and regulates
the length of thin filaments during development. Dystrophin links thin filaments of
the sarcomere to integral membrane proteins of the sarcolemma, which are
attached in turn to proteins in the connective tissue extracellular matrix that
surrounds muscle fibers. Dystrophin and its associated proteins are thought to
reinforce the sarcolemma and help transmit the tension generated by the
sarcomeres to the tendons.
Sliding Filaments and Muscle Contraction. Muscle contraction occurs because
myosin heads attach to and “walk” along the thin filaments at both ends of a
sarcomere, progressively pulling the thin filaments toward the M line (Fig. 5). As a
result, the thin filaments slide inward and meet at the center of a sarcomere. They
may even move so far inward that their ends overlap (Fig. 5 c). As the thin
filaments slide inward, the Z discs come closer together, and the sarcomere
shortens. However, the lengths of the individual thick and thin filaments do not
change. Shortening of the sarcomeres causes shortening of the whole muscle fiber,
which in turn leads to shortening of the entire muscle.
38
Figure 5. Sliding filament mechanism of muscle contraction, as it occurs in two
adjacent sarcomeres.
The Contraction Cycle. At the onset of contraction, the sarcoplasmic reticulum
releases Ca2+ into the sarcoplasm. There, they bind to troponin. Troponin then
moves tropomyosin away from the myosin-binding sites on actin. Once the binding
sites are “free,” the contraction cycle – the repeating sequence of events that causes
the filaments to slide – begins. The contraction cycle consists of four steps (Fig. 6):
1. ATP hydrolysis. The myosin head includes an ATP-binding site and an ATPase,
an enzyme that hydrolyzes ATP into ADP (adenosine diphosphate) and a
phosphate group. This hydrolysis reaction reorients and energizes the myosin head.
39
Notice that the products of ATP hydrolysis – ADP and a phosphate group – are
still attached to the myosin head.
2. Attachment of myosin to actin to form cross-bridges. The energized myosin
head attaches to the myosin-binding site on actin and releases the previously
hydrolyzed phosphate group. When the myosin heads attach to actin during
contraction, they are referred to as cross-bridges.
3. Power stroke. After the cross-bridges form, the power stroke occurs. During the
power stroke, the site on the cross-bridge where ADP is still bound opens. As a
result, the cross-bridge rotates and releases the ADP. The cross-bridge generates
force as it rotates toward the center of the sarcomere, sliding the thin filament past
the thick filament toward the M line.
4. Detachment of myosin from actin. At the end of the power stroke, the crossbridge remains firmly attached to actin until it binds another molecule of ATP. As
ATP binds to the ATP-binding site on the myosin head, the myosin head detaches
from actin.
Figure 6. The contraction cycle.
The contraction cycle repeats as the myosin ATPase hydrolyzes the newly bound
molecule of ATP, and continues as long as ATP is available and the Ca2+ level near
40
the thin filament is sufficiently high. The cross-bridges keep rotating back and forth
with each power stroke, pulling the thin filaments toward the M line. Each of the
600 cross-bridges in one thick filament attaches and detaches about five times per
second. At any one instant, some of the myosin heads are attached to actin,
forming cross-bridges and generating force, and other myosin heads are detached
from actin, getting ready to bind again.
As the contraction cycle continues, movement of cross-bridges applies the force
that draws the Z discs toward each other, and the sarcomere shortens. During a
maximal muscle contraction, the distance between two Z discs can decrease to half
the resting length. The Z discs in turn pull on neighboring sarcomeres, and the
whole muscle fiber shortens. Some of the components of a muscle are elastic: They
stretch slightly before they transfer the tension generated by the sliding filaments.
The elastic components include titin molecules, connective tissue around the
muscle fibers (endomysium, perimysium, and epimysium), and tendons that attach
muscle to bone. As the cells of a skeletal muscle start to shorten, they first pull on
their connective tissue coverings and tendons. The coverings and tendons stretch
and then become taut, and the tension passed through the tendons pulls on the
bones to which they are attached. The result is movement of a part of the body.
Muscles energy supply. Muscle’s major fuels are glucose from glycogen, fatty
acids, and ketone bodies. Rested, well-fed muscle, in contrast to brain, synthesizes
a glycogen store comprising 1 to 2% of its mass. The glycogen serves muscle as a
readily available fuel depot since it can be rapidly converted to glucose-6phosphate for entry into glycolysis.
Muscle cannot
export
glucose because it
lacks
glucose-6-phosphatase.
Nevertheless, muscle serves the body as an energy reservoir because, during the
fasting state, its proteins are degraded to amino acids, many of which are converted
to pyruvate, which in turn, is transaminated to alanine. The alanine is then exported
via the bloodstream to the liver, which transaminates it back to pyruvate, a glucose
precursor. This process is known as the glucose-alanine cycle.
41
Since muscle does not participate in gluconeogenesis, it lacks the machinery that
regulates this process in such gluconeogenic organs as liver and kidney. Muscle
does not have receptors for glucagon, which stimulates an increase in blood
glucose levels. However, muscle possesses epinephrine receptors (β-adrenergic
receptors),
which
through
the
intermediacy
of
cAMP
control
the
phosphorylation/dephosphorylation cascade system that regulates glycogen
breakdown and synthesis. This is the same cascade system that controls the
competition between glycolysis and gluconeogenesis in liver in response to
glucagon.
Heart muscle and skeletal muscle contain different isozymes of PFK-2/FBPase-2.
The heart muscle isozyme is controlled by phosphorylation oppositely to that in
liver,
whereas
skeletal
muscle
PFK-2/FBPase-2
is
not
controlled
by
phosphorylation at all. Thus the concentration of F2,6P rises in heart muscle but
falls in liver in response to an increase in [cAMP]. Moreover the muscle isozyme
of pyruvate kinase, which, it will be recalled, catalyzes the final step of glycolysis,
is not subject to phosphorylation/dephosphorylation as is the liver isozyme. Thus,
whereas an increase in liver cAMP stimulates glycogen breakdown and
gluconeogenesis, resulting in glucose export, an increase in heart muscle cAMP
activates glycogen breakdown and glycolysis, resulting in glucose consumption.
Consequently, epinephrine, which prepares the organism for action (fight or flight),
acts independently of glucagon which, acting reciprocally with insulin, regulates
the general level of blood glucose.
Muscle contraction is driven by ATP hydrolysis and is therefore ultimately
dependent on respiration. Skeletal muscle at rest utilizes ~30% of the O 2 consumed
by the human body. A muscle’s respiration rate may increase in response to a
heavy workload by as much as 25-fold. Yet, its rate of ATP hydrolysis can
increase by a much greater amount. The ATP is initially regenerated by the
reaction of ADP with phosphocreatine as catalyzed by creatine kinase:
Phosphocreatine + ADP ↔ creatine + ATP
42
(phosphocreatine is resynthesized in resting muscle by the reversal of this
reaction). Under conditions of maximum exertion, however, such as occurs in a
sprint, a muscle has only an ~5-s supply of phosphocreatine. It must then shift to
ATP production via glycolysis of glucose-6-phosphate resulting from glycogen
breakdown, a process whose maximum flux greatly exceeds those of the citric acid
cycle and oxidative phosphorylation. Much of this glucose-6-phosphate is
therefore degraded anaerobically to lactate which, in the Cori cycle, is exported via
the bloodstream to the liver, where it is reconverted to glucose through
gluconeogenesis. Gluconeogenesis requires
ATP generated by oxidative
phosphorylation. Muscles thereby shift much of their respiratory burden to the
liver and consequently also delay the O2-consumption process, a phenomenon
known as oxygen debt. The source of ATP during exercise of varying duration is
summarized in Fig. 7.
Figure 7. Source of ATP during exercise in humans.
Biosynthesis of creatine. Creatine is present in the tissues (muscle, brain,
blood etc.) as the high energy compound, phosphocreatine and as free creatine.
Three amino acids – glycine, arginine and methionine – are required for creatine
formation (Fig. 8). The first reaction occurs in the kidney. lt involves the transfer
of guanidino group of arginine to glycine, catalyzed by arginine-glycine
43
transamidinase to produce guanidoacetate (glycocyamine). S-Adenosylmethionine
(active methionine) donates methyl group to glycocyamine to produce creatine.
This reaction occurs in liver. Creatine is reversible phosphorylated to
phosphocreatine (creatine phosphate) by creatine kinase. It is stored in muscle as
high energy phosphate.
Creatinine is an anhydride of creatine. It is formed by spontaneous
cyclization of creatine or creatine phosphate. Creatinine is excreted in urine.
Figure 8. Creatine metabolism.
Clinical significance of creatine and creatinine determination. The normal
concentrations of creatine and creatinine in human serum and urine are:
44
Serum: creatine – 0.2-0.6 mg/dL, creatinine – 0.6-1 mg/dL;
Urine: creatine – 0-50 mg/day, creatinine – 1-2 g/day.
Estimation of serum creatinine (along with blood urea) is used as a
diagnostic test to assess kidney function. Seru m creati n i ne concentration is not
influenced by endogenous and exogenous factors, as is the case with urea. Hence,
some workers consider serum creatinine as a more reliable indicator of renal
function.
The amount of creatinine excreted is proportional to total creatine phosphate
content of the body and, in turn, the muscle mass. The daily excretion of creatinine
is usually constant. Creatinine coefficient is defined as the mg of creatinine and
creatine (put together) excreted per kg body weight per day. For a normal adult
man, the value is 24-26 mg, while for a woman, it is 20-22 mg.
Increased output of creatine in urine is referred to as creatinuria. Creatinuria is
observed in muscular dystrophy, diabetes mellitus, hyperthyroidism, starvation etc.
Connective tissue
Cells are the basis units of life. Most mammalian cells are located in tissues, where
they are surrounded by a complex of extra-cellular matrix, often referred to as
“connective tissue”. Extra-cellular matrix contains three major classes of
biomolecules:
1.
Structural proteins: collagen, elastin and fibrillin.
2.
Certain specialized proteins, such as fibrillin, fibronectin, and lamilin.
3.
Proteoglycans, which consist of long chains of repeating disaccharides
fragments (glucosoaminoglycans or mucopolysaccharides) attached to specific
core proteins.
Collagen. Collagen, which is present in all multicellular organisms, is not
one protein but diversity a family of structurally related proteins. It is the most
abundant protein in mammals and is present in most organs of the body, where it
serves to hold cells together in discrete units. It is also the major fibrous element of
skin, bones, tendons, cartilage, blood vessels and teeth. The different collagen
proteins have very diverse functions. The extremely hard structures of bones and
45
teeth contain collagen and a calcium phosphate polymer. In tendons, collagen
forms rope-like fibers of high tensile strength, while in the skin collagen forms
loosely woven fibers that can expand in all directions. The different types of
collagen are characterized by different polypeptide compositions (Table 3). Each
collagen is composed of three polypeptide chains, which may be all identical (as in
types II and III) or may be of two different chains (types I, IV and V). A single
molecule of type I collagen has a molecular mass of 285 kDa, a width of 1.5 nm
and a length of 300 nm.
Table 3. Types of collagen.
Type
Polypeptide composition
Distribution
I
[α1(I)]2α2(I)
Skin, bone, tendon, cornea, blood vessels
II
[α1(II)]3
Cartilage, intervertebral disk
III
[α1(III)]3
Fetal skin, blood vessels
IV
[α1(IV)]2α2(IV)
Basement membrane
V
[α1(V)]2α2(V)
Placenta, skin
VII
[α1(VII)]3
Beneath stratified squamous epithelia
IX
α1(IX)α2(IX)α3(IX)
Cartilage
XII
[α1(XII)]3
Tendon, ligaments, some other tissues
Collagen has a distinctive amino acid composition: nearly one-third of its residues
are Gly; another 15 to 30% of them are Pro and 4-hydroxyprolyl (Hyp) residues:
3-Hydroxyprolyl and 5-hydroxylysyl (Hyl) residues also occur in collagen but in
smaller amounts. Radioactive labeling experiments have established that these
nonstandard hydroxylated amino acids are not incorporated into collagen during
46
polypeptide synthesis: If 14C-labeled 4-hydroxyproline is administered to a rat, the
collagen synthesized is not radioactive, whereas radioactive collagen is produced if
the rat is fed
14
C-labeled proline. The hydroxylated residues appear after the
collagen polypeptides are synthesized, when certain Pro residues are converted to
Hyp in a reaction catalyzed by the enzyme prolyl hydroxylase.
The amino acid sequence of bovine collagen α1(I), which is similar to that of
other collagens, consists of monotonously repeating triplets of sequence Gly-X-Y
over a continuous 1011-residue stretch of its 1042-residue polypeptide chain (Fig.
9). Here X is often Pro (~28%) and Y is often Hyp (~38%). The restriction of Hyp
to the Y position stems from the specificity of prolyl hydroxylase. Hyl is similarly
restricted to the Y position.
Figure 9. The amino acid sequence at the C-terminal end of the triple helical region
of the bovine α1(I) collagen chain.
Each of the three polypeptide chains in collagen is some 1000 residues long
and they each fold up into a helix that has only 3.3 residues per turn, rather than the
3.6 residues per turn of an α-helix. This secondary structure is unique to collagen
and is often called the collagen helix. The three polypeptide chains lie parallel and
wind round one another with a slight right-handed, rope-like twist to form a triplehelical cable (Fig. 10). Every third residue of each polypeptide passes through the
center of the triple helix, which is so crowded that only the small side chain of Gly
can fit in. This explains the absolute requirement for Gly at every third residue.
The residues in the X and Y positions are located on the outside of the triple47
helical cable, where there is room for the bulky side-chains of Pro and other
residues. The three polypeptide chains are also staggered so that the Gly residue in
one chain is aligned with the X residue in the second and the Y residue in the third.
The triple helix is held together by an extensive network of hydrogen bonds, in
particular between the primary amino group of Gly in one helix and the primary
carboxyl group of Pro in position X of one of the other helices. In addition, the
hydroxyl groups of Hyp residues participate in stabilizing the structure. The
relatively inflexible Pro and Hyp also confer rigidity on the collagen structure.
Figure 10. Arrangement of the three polypeptide chains in collagen.
Collagen synthesis. Collagen biosynthesis and secretion follow the normal
pathway for a secreted protein. The collagen α-chains are synthesized as longer
precursors, called pro-α-chains, by ribosomes attached to the endoplasmic
reticulum (ER). The pro-α-chains undergo a series of covalent modifications and
fold into triple-helical procollagen molecules before their release from cells (Fig.
11).
48
Figure 11. Major events in biosynthesis of fibrillar collagens.
After the secretion of procollagen from the cell, extracellular peptidases (e.g., bone
morphogenetic protein-1) remove the N-terminal and C-terminal propeptides. In
regard to fibrillar collagens, the resulting molecules, which consist almost entirely
of a triple-stranded helix, associate laterally to generate fibrils with a diameter of
50-200 nm. In fibrils, adjacent collagen molecules are displaced from one another
by 67 nm, about one-quarter of their length. This staggered array produces a
striated effect that can be seen in electron micrographs of collagen fibrils. The
unique properties of the fibrous collagens (e.g., types I, II, III) are mainly due to
the formation of fibrils.
Short non-triple-helical segments at either end of the collagen chains are of
particular importance in the formation of collagen fibrils. Lysine and
hydroxylysine side chains in these segments are covalently modified by
extracellular lysyl oxidases to form aldehydes in place of the amine group at the
49
end of the side chain. These reactive aldehyde groups form covalent crosslinks
with lysine, hydroxylysine, and histidine residues in adjacent molecules. These
cross-links stabilize the side-by-side packing of collagen molecules and generate a
strong fibril. The removal of the propeptides and covalent cross-linking take place
in the extracellular space to prevent the potentially catastrophic assembly of fibrils
within the cell.
The post-translational modifications of pro-α-chains are crucial for the formation
of mature collagen molecules and their assembly into fibrils. Defects in these
modifications have serious consequences, as ancient mariners frequently
experienced. For example, ascorbic acid (vitamin C) is an essential cofactor for the
hydroxylases responsible for adding hydroxyl groups to proline and lysine residues
in pro-α-chains. In cells deprived of ascorbate, as in the disease scurvy, the pro-αchains are not hydroxylated sufficiently to form stable triple-helical procollagen at
normal body temperature, and the procollagen that forms cannot assemble into
normal fibrils. Without the structural support of collagen, blood vessels, tendons,
and skin become fragile. Because fresh fruit in the diet can supply sufficient
vitamin C to support the formation of normal collagen, early British sailors were
provided with limes to prevent scurvy, leading to their being called “limeys”.
When the collagen polypeptides are synthesized they have additional amino
aggregation acid residues (100-300) on both their N and C termini that are absent
in the mature collagen fiber (Fig. 12). These extension peptides often contain Cys
residues, which are usually absent from the remainder of the polypeptide chain.
The extension peptides help to correctly align the three polypeptides as they come
together in the triple helix, a process that may be aided by the formation of
disulfide bonds between extension peptides on neighboring polypeptide chains.
The extension peptides also prevent the premature aggregation of the procollagen
triple helices within the cell. On secretion out of the fibroblast the extension
peptides are removed by the action of extracellular peptidases. The resulting
tropocollagen molecules then aggregate together in a staggered head-to-tail
arrangement in the collagen fiber (Fig. 12).
50
Figure 12. Role of the extension peptides in the folding and secretion of
procollagen.
Elastin. In contrast to collagen, which forms fibers that are tough and have
high tensile strength, elastin is a connective tissue protein with rubber-like
properties. Elastic fibers composed of elastin and glycoprotein microfibrils are
found in the lungs, the walls of large arteries, and elastic ligaments. They can be
stretched to several times their normal length, but recoil to their original shape
when the stretching force is relaxed.
Elastin is an insoluble protein polymer synthesized from a precursor, tropoelastin,
which is a linear polypeptide composed of about 700 amino acids that are primarily
small and nonpolar (for example, glycine, alanine, and valine). Elastin is also rich
in proline and lysine, but contains only a little hydroxyproline and hydroxy lysine.
Tropoelastin is secreted by the cell into the extracellular space. There it interacts
with specific glycoprotein microfibrils, such as fibrillin, which function as a
scaffold onto which tropoelastin is deposited. Some of the lysyl side chains of the
51
tropoelastin poly peptides are oxidatively deaminated by lysyl oxidase, forming
allysine residues. Three of the allysyl side chains plus one unaltered lysyl side
chain from the same or neighboring polypeptides form a desmosine cross-link (Fig.
13). This produces elastin – an extensively interconnected, rubbery network that
can stretch and bend in any direction when stressed, giving connective tissue
elasticity (Fig. 14). Mutations in the fibrillin-1 protein are responsible for Marfan
syndrome – a connective tissue disorder characterized by impaired structural
integrity in the skeleton, the eye, and the cardiovascular system. With this disease,
abnormal fibrillin protein is incorporated into microfibrils along with normal
fibrillin, inhibiting the formation of functional microfibrils.
Figure 13. Desmosine structure.
Figure 14. Elastin fibers in relaxed and
stretched conformations.
52
EXERCISES FOR INDEPENDENT WORK. In the table with test tasks
emphasize keywords, choose the correct answer and justify it:
№
Test:
1.
A 30 y.o. woman had been ill for a
Explanation:
year when she felt pain in the area of
joints for the first time, they got
swollen,
and
became
skin
reddened.
above
them
Provisional
diagnosis is rheumatoid arthritis.
One of the most probable causes of
this disease is a structure alteration
of a connective tissue protein:
A. Ovoalbumin
B. Collagen
C. Myosin
D. Troponin
E. Mucin
2
Increased fragility of vessels, enamel
and dentine destruction resulting
from scurvy are caused by disorder
of collagen maturation. What stage
of
procollagen
modification
is
disturbed under this avitaminosis?
A. Hydroxylation of proline
B. Detaching of N-ended peptide
C. Formation of polypeptide chains
D. Glycosylation of hydroxylysine
residues
53
№
Test:
Explanation:
E. Removal of C-ended peptide from
procollagen
3
The high levels of creatine kinase
(MB-isozyme)
and
lactate
dehydrogenase LDH1 activity were
revealed. Point out the most probable
pathology in the patient:
A. Hepatitis
В. Myocardium infarction
С. Osteoartritis
D. Pancreatitis
Е. Cholecystitis
4
Name
the
polysaccharide
represented in connective tissue:
A. Collagen
B. Elastin
C. Laminin
D. Hyaluronic acid
Е. Fibrillin
5
It is established that there is specific
system of energy supply in muscular
54
№
Test:
Explanation:
cell. Point out this system:
A. Renin-angiotensinogen system
B. Creatine phosphate kinase system
C. Adenylate cyclase system
D. Translation system of a cell
Е. Palmitate synthetase complex
6
A patient with serious damage of
muscular tissue was admitted to the
trauma
department.
What
biochemical urine index will be
increased in this case?
A. Glucose
B. Common lipids
C. Uric acid
D. Creatinine
E. Mineral salts
7
A 46-year-old female patient has a
continuous history of progressive
muscular (Duchenne`s) dystrophy.
Which blood enzyme activity
changes will be of diagnostic value
in this case?
A.
Lactate dehydrogenase
55
№
8
Test:
Explanation:
B.
Glutamate dehydrogenase
C.
Adenylate cyclase
D.
Pyruvate dehydrogenase
E.
Creatine phosphokinase
A
53-year-old
male
patient
is
diagnosed with Paget’s disease. The
concentration of oxyproline in daily
urine is sharply increased, which
primarily
means
intensified
disintegration of:
A. Albumin
B. Hemoglobin
C. Collagen
D. Fibrinogen
E. Keratin
9
It is established, that muscular
contraction
depends
on
Са2+
concentration. Point out the protein
that is able to conjugate Са2+ ion
during muscular contraction:
A. Ceruloplasmin
B. С-reactive protein
C. Myosin
D. Ferritin
Е. Troponin
56
№
Test:
Explanation:
10 The collagen triple helix structure is
not found in
A. Cytoplasm
B. Golgi apparatus
C. Lumen of endoplasmic reticulum
D. Intracellular vesicles
E. All positions are right
11 Choose
the
guanidoacetate
product
of
transmethylation
from following list:
A. Chlorine
B. Hydroxyproline
C. Creatinine
D. Creatine
E. Glutathione
12 Point out compounds required for
creatine synthesis:
A. Glycine, arginine and methionine
B. Glycine and methionine
C. Ornithine and glycine
D. Thymine and ornithine
E. Glycine, cysteine and glutamine
57
№
Test:
Explanation:
13 Triple helix is seen in one compound
listed bellow. Choose it:
A. Collagen
B. Fibrinogen
C. Histones
D. Serum amylase
E. F-actin
14 Name the immediate source of
energy for muscular contraction.
A. Glycogen
B. ATP
C. Creatine phosphate
D. Glucose
E. Pyruvate
15 What does cardiac muscle prefer as
source of energy?
A. Fatty acids
B. Glucose
C. Ketone bodies
D. Glycogen
E. Fructose
16 Hydroxylation
of
proline
to
58
№
Test:
Explanation:
hydroxyproline in collagen synthesis
requires all except one. Point out it.
A. Pyridoxal phosphate
B. Ascorbic acid
C. O2
D. Specific hydroxylase
E. Iron ion
17 What is the product of guanidoacetic
acid transmethylation?
A. Acetylcholine
B. Choline
C. Creatinine
D. N-methyl nicotinamide
E. Creatine
18 Creatine is formed metabolically
using one compound listed below.
Choose it:
A. Tryptophan
B. Phenylalanine
C. Lysine
D. Valine
E. Leucine
59
№
Test:
19 Three
residues
Explanation:
(Gly-X-Y-)
are
repeated many times, and it is the
absolute requirement for formation
of the triple helix of collagen
molecule type 1. What amino acid
and
its
derivative
mainly
is
represented as letters X and Y?
A. Proline
B. Tryptophan
C. Lysine
D. Valine
E. Leucine
20 Name biochemical tests used for
diagnostics of muscular dystrophy
development:
A. Creatine content in the blood
plasma and urine
B. Creatinine content in the blood
plasma
C. Ctreatine
phosphate
kinase
activity in the blood plasma
D. Myofibril
proteins
content
in
tissue homogenate obtained due to
biopsy method
E. All that is placed above
60
BIOCHEMISTRY OF NERVOUS TISSUE
(Krisanova N. V.)
INFORMATIONAL MATERIAL
INTRODUCTION
The nervous system, a network of neurons in active communication, reaches
its ultimate development in the 1.5 kg human brain. The human brain contains
~1011 neurons. Each of these neurons interconnects through synapses with
hundreds or thousands of other neurons. The number of connections is estimated to
be as many as 60,000 with each Purkinje cell of the human cerebellum. There may
be many more than 1014 synapses in the human brain.
Figure 1. Schematic picture of neurons
In addition to neurons, the brain contains 5–10 times as many glial cells of
several types. The neuroglia occupy 40% of the volume of brain and spinal cord in
61
the human. Some glial cells seem to bridge the ace between neurons and blood
carrying capillaries. Others synthesize myelin. Some are very irregular in shape.
Figure 1 shows all the compartments of neurons (two) which are involved in
transmission of nerve impulse:
The brain, which must function in a chemically stable environment, is protected by
a tough outer covering, the arachnoid membrane, and by the blood–brain
barrier and the blood–cerebrospinal barrier. Both of these barriers consist of
tight junctions. They are formed between the endothelial cells of the cerebral
capillaries and between the epithelial cells that surround the capillaries of the
choroid plexus. The choroid plexus consists of capillary beds around portions of
the fluid-filled ventricles deep in the interior of the brain. They serve as a kind of
“kidney” for the brain assisting in bringing nutrients in from the blood and helping
to keep dangerous compounds out.
NERVOUS TISSUE REGULATES AND CONTROLS BODY FUNCTIONS.
ITS MAIN FUNCTIONS ARE:
• Metabolic (promoted in neurons and neuroglia)
• Generation of nerve impulses
• Transmission of nerve impulse
• Remembering and keeping of information
• Creation of emotions and models of behavior
• Thinking
IT IS COMPOSED OF: NEURONS, THE NEUROGLIAL CELLS,
THE MICROGLIAL CELLS
Any type of a cell is important for all the functions described before, but
differences we have to underline, first of all for astrocytes:
 they are involved in the physical structuring of the brain. Astrocytes get their
name because they are "star-shaped". They are the most abundant glial cells in the
brain that are closely associated with neuronal synapses. They regulate the
transmission of electrical impulses within the brain.
62
 astrocytes contain glycogen and are capable of glycogenesis. Astrocytes can fuel
neurons with glucose during periods of high rate of glucose consumption and
glucose shortage.
 they provide neurons with nutrients such as lactate.
 astrocytes in tight junctions with basal lamina of the cerebral endothelial cells
play substantial role in maintaining the blood-brain barrier
 astrocytes express plasma membrane transporters such as glutamate transporters
for several neurotransmitters, including Glutamate, ATP, and GABA
 they are involved in regulation of ion concentration in the extracellular space
(potassium ions, mostly).
Microglia
Neuron
Astrocyte
Capillary
Oligodendro
cyte
Ependymocyte
Myelinated
axon
Figure 2. Structural organization of nervous tissue
Oligodendrocytes are very important in the promotion of myelination of axons to
create myelin sheaths which reduce ion leakage and decrease the capacitance of the
cell membrane. Myelin also increases impulse speed, as saltatory propagation of
action potentials occurs at the nodes of Ranvier in between Schwann cells (in
peripheral nervous system) and oligodendrocytes (in CNS). Metabolic activity of
them is associated with creation of myelin components.
63
Ependymocytes. Lining the cerebrospinal fluid (CSF)-filled ventricles, the
ependymal cells play an important role in the production of substances for CSF and
regulation of CSF composition.
Microglial cells. In the case where infectious agents are directly introduced to the
brain or cross the blood–brain barrier, microglial cells must react quickly to
decrease inflammation and destroy the infectious agents before they damage the
sensitive neural tissue. Due to the unavailability of antibodies from the rest of the
body (few antibodies are small enough to cross the blood–brain barrier), microglia
must be able to recognize foreign bodies, swallow them, and act as antigenpresenting cells activating T-cells.
CHEMICAL COMPOSITION OF BRAIN TISSUE
PROTEINS
 Account for about 40% of the dry weight of the brain
 Over 100 soluble fractions have been isolated from the brain tissue
 The grey matter is more rich in water-soluble proteins than the white
matter
 There are both simple and conjugated proteins
SIMPLE PROTEINS:
 Neuroalbumins (90% of soluble proteins)
 Neuroglobulins (5%)
 Histones
 Neuroscleroproteins: collagens, elastins, stromatins (5%)
CONJUGATED PROTEINS
 Lipoproteins
 Proteo-lipid complexes (in myelin substance, mainly)
 Phosphoproteins (2%)
 Nucleoproteins
 Glycoproteins
 Chromoproteins
64
SPECIFIC PROTEINS
 S-100 protein (Moore protein): Ca2+-binding protein, contains a large number
of Glu and Asp , occurs chiefly in the neuroglia – 90%, in the neurons – 10% . Its
concentration rises in the brain of animal subjected to training.
 14-3-2 protein: Is acidic too, occurs chiefly in the neurons, functions of it are
unclear.
 Glial Fibrous Acidic Protein (GFAP): placed mainly in astrocytes, specific for
CNS, the biggest content is observed in differentiation of astrocytes.
 N-CAM (neural cells adhesion molecule; NG-CAM (neuralglial cells adhesion
molecule); MAG (myelin-associated glycoprotein) : neurospecific glycoproteins
participated in formation of myelin substance, in processes of cells adhesion, etc.
ENZYMES
 Lactate dehydrogease
 C- izoform of Aldolase
 BB- izoform of Creatine phospho kinase (CPK)
 Hexokinase
 Cholinesterase
 Monoaminoxidase
 Acidic phosphatase
 Gamma-izoform of enolase
MAIN LIPIDS
 Phosphoglycerides
 Cholesterol
 Sphingomyelins
 Cerebrosides
 Gangliosides
65
CHEMICAL COMPOSITION OF MYELIN SUBSTANCE
Myelin is a dielectric material that forms a layer, the myelin sheath, usually around
only the axon of a neuron. Myelin is an outgrowth of a type of glial cell. Its
composition is:
 ~ 40 % water
 the dry mass of myelin is ~ 70-85 % of lipids (sphingomyelins,
cholesterol,cerebrosides); the primary lipid of myelin is galactocerebroside
 the dry mass of myelin is 15-30 % proteins
 Some of the proteins make up myelin are:
 Myelyn basic protein (MBP)
 Myelin oligodendrocyte glycoprotein (MOG)
 Proteolipid protein (PLP) - Folch complex
ENERGY REQUIREMENTS OF BRAIN TISSUE ARE PROMOTED BY:

Aerobic oxidation of glucose (90%) up to СО2 and Н2О
 Non-oxidative phase of HMP shunt using other monosaccharides, and
Glycolysis
 Keto acids and products of neurotransmitters utilization across catabolic
pathways for them
 Lactate utilized by mitochondrial Lactate dehydrogenase to form pyruvate (in
glial cells and neurons)
 Ketone bodies destruction
 Fatty acids oxidation in glial cells
 Branched chain amino acids destruction
It should be noted that Glucose is transported across the cell membrane by
specific saturable transport system, which includes two types of glucose
transporters: 1) sodium dependent glucose transporters (SGLTs) which transport
glucose against its concentration gradient and 2) sodium independent glucose
transporters (GLUTs), which transport glucose by facilitative diffusion in its
concentration gradient. In the brain, both types of transporters are present with
66
different function, affinity, capacity, and tissue distribution. GLUT1 occurs in
brain in two isoforms. The more glycosylated GLUT1 is produced in brain
microvasculature and ensures glucose transport across the blood brain barrier. The
less glycosylated form is localized in astrocytic end-feet and cell bodies and is not
present in axons, neuronal synapses or microglia. Glucose transported to astrocytes
by GLUT1 is metabolized to lactate serving to neurons as energy source. GLUT2
is present in hypothalamic neurons and serves as a glucose sensor in regulation of
food intake. In neurons of the hippocampus, GLUT2 is supposed to regulate
synaptic activity and neurotransmitter release. GLUT3 is the most abundant
glucose transporter in the brain having five times higher transport capacity than
GLUT1. It is present mostly in axons and dendrites. Its density and distribution
correlate well with the local cerebral glucose demands. GLUT5 is predominantly
fructose transporter. In brain, GLUT5 is the only hexose transporter in microglia,
whose regulation is not yet clear. It is not present in neurons. GLUT4 and GLUT8
are insulin-regulated glucose transporters in neuronal cell bodies in the cortex and
cerebellum, but mainly in the hippocampus, where they maintain hippocampusdependent cognitive functions. Insulin translocates GLUT4 from cytosol to plasma
membrane to transport glucose into cells, and GLUT8 from cytosol to rough
endoplasmic reticulum to recover redundant glucose to cytosol after protein
glycosylation.
SYNTHESIS OF ATP IN BRAIN TISSUE IS DUE TO:
• Oxidative phosphorylation (95%)
• Substrate
phosphorylation
(ВВ-isoform
of
CPK,
pyruvate
kinase,
phosphoglycerate kinase) (5%)
It should be noted that content of glycogen is too small in brain tissue, and its
utilization to give energy as the result usually is discussed under special states
beginning for neurons (like hypoxia) according the way shown in figure 3. But in
glial cells its utilization is up to lactate.
67
Production of ATP
Small
amount
Constantly
required
Glycogen
Energy suppliers
during prolonged
starvation
Glucose
Ketone bodies
Glycogenolysis
Glycolysis
Lactate
(glial)
No O2
Lactate
Pyruvate
Krebs
cycle
Acetyl-CoA
oxidative
phosphorylation
Branched Chain AA
Ile, Leu, Val
Figure 3. Main metabolic pathways to promote energy requirements of brain tissue.
MAIN NEUROTRANSMITTERS
 Acetylcholine. It is produced due to the action of acetyl-CoA Choline
transferase from acetyl-CoA and specific alcohol choline. Its destruction is
made by acetylcholine esterase to form free acetic acid and choline.
 Amino acids: Glutamate, Aspartate, Glycine, D-Serine, dihydroxy phenyl
alanine (DOPA)
 Biogenic amines: dopamine, norepinephrine, epinephrine, histamine,
serotonin, gamma-amiobutyric acid (GABA) . They are produced mostly
due to alpha-decarboxylation from amino acids.
 Purine derivatives: ATP, ADP, AMP, adenosine
68
Structures and functions of some of them is placed in figure 4.
Figure 4. Structure and function of neurotransmitters
Main function
Feature of
action
excitation
suppression
GABA
Glutamate
neuromediator
Acetylcholine
Glycine
Nor-epinephrine
Adenosine
neuromodulator
Dopamine
Serotonin
Amino acids may be precursors for formation of neurotransmitters. αDecarboxylation of histidine gives histamine:
CH 2
HN
N
NH 2
CO2
CH
Decarboxylase
CH 2
HN
N
COOH
Histamine
Histidine
Biological role of histamine
69
CH 2
NH 2
 Histamine is vasodilator. This fact markedly differentiates its action from
other biogenic amines on blood vessels.
 Histamine facilitates the afflux of leukocytes during the inflammation of
tissue and activates thereby the defence function of the organism.
 Histamine stimulates the gastric juice secretion.
 Histamine is directly involved in the effects of sensitization and
desensitization.
In the figure 5 it is shown how other neurotransmitters are produced from
corresponded amino acids.
Figure 5. Synthesis of some neurotransmitters: PLP – pyridoxal phosphate;
deCO2ase - decarboxylase.
GABA. Formation of this substance in CNS (reaction is shown below) is very
important for braking of super-excitation. Synthetic derivatives of this substance
are used in therapy of epilepsy.
HOOC
CH 2
CH 2
CO2
COOH
CH
vit B6
Glutamate  -Decarboxylase
Glutamate
CH 2
HOOC
CH 2
NH 2
CH 2
GABA
NH 2
GABA -
 -aminobutyric acid
In figure 6 amino acids phenyl alanine and tyrosine may be discussed as
precursors for dihydroxy phenyl alanine (DOPA), dopamine, norepinephrine and
70
epinephrine. All enzymes for hydroxylation (*, figure 5) have special prosthetic
group: Tetrahydrobiopterin (THBP). This cofactor is oxidized to dihydrobiopterin
during the hydroxylation of corresponding substrate and must be regenerated by
another enzyme, dihydrobiopterin reductase, which uses NADPH as donor of
protons and electrons.
O
O
O
H2N
H2N
CH
C
CH
C
OH
H2N
CH 2
CH 2
CH
C
OH
OH
CH 2
1 / 2 O2
1 / 2 O2
Phenylalanine
4-monooxygenase*
Tyrosine
3-monooxygenase*
OH
Phenylalanine
OH
OH
Dihydroxyphenylalanine
Tyrosine
Decarboxylase
HO
HO
HO
CH
CO2
1 / 2 O2
OH
CH 2
Hydroxylase
H2
C
HO
NH 2
Norepinephrine
NH 2
Methyltransferase
S-Adenosyl methionine
CH 2
Dopamine
HO
OH
S-Adenosyl homocysteine
HO
CH
H3C
CH 2
Epinephrine
NH
Figure 6. A production ways for DOPA, dopamine, norepinephrine and
epinephrine.
Decarboxylation of amino acids is catalyzed by amino acid alphadecarboxylases (Pyridoxal phosphate – the non-protein part). This enzyme subclass
is abundant in the adrenal glands and CNS.
Directed alpha-decarboxylation of tryptophan gives tryptamine, and 5-hydroxy
tryptophan decarboxylation is finished by formation of serotonin (figure 6).
Serotonin takes part in:
1) exhibition of vasoconstrictive action;
2) regulation of arterial pressure, body temperature, respiration, renal filtration;
71
3) serotonin may be (some scientists proposed) a causative factor in the
development of allergy, dumping syndrome, carcinoid syndrome, hemorrhagic
diatheses,
4) stimulation of smooth muscle contraction.
Serotonin and Tryptamine are considered as neuromedulators of CNS.
H2N
O
O
Tryptophan
CH
CH2
C
H2N
OH
CH
1/2 O2
C
OH
CH2
Hydroxylase
HN
HN
Decarboxylase
Decarboxylase
H2N
OH
5-Hydroxytryptophan
CH2
CO2
CO2
CH2
H2N
CH2
CH2
HN
OH
Serotonin
HN
Tryptamine
Figure 7. Reactions to form neuromodulators Tryptamine and Serotonin.
MAIN WAYS TO UTILIZE NEUROTRANSMITTERS
1. Diffusion: the neurotransmitter drifts away, out of the synaptic cleft
2. Enzymatic degradation (deactivation): a specific enzyme changes the
structure of the neurotransmitter so it is not recognized by the receptor
3. Glial cells: astrocytes remove neurotransmitters from the synaptic cleft
4. Reuptake: the whole neurotransmitter molecule is taken back into the axon
terminal that released it.
72
For acetylcholine p.p.2, 4 may be considered, its destruction is due to acetylcholine
esterase to form free acidic acid and free choline.
As example in the figure 8 formation of gamma-amino butyric acid (GABA)
in GABA-neuron, its utilization in GABA-shunt across succinic acid and alphaketoglutarate to form Glutamate, Glutamine in glial cell, and the use of Glutamine
to form Glutamate as neurotransmitter in Glutamate neuron are shown.
Figure 8. Metabolism of Glutamine, Glutamate and GABA in nervous tissue cells.
THE UTILIZATION OF NEUROTRANSMITTERS BY
MONOAMINOOXIDASE (MAO)
 MAO is in most cell types in the body
 There are two types of MAO: A and B
73
 Both are found in neurons and astroglia and bound to the outer membrane of
mitochondria
 Serotonin, nor-epinephrine, epinephrine are mainly broken down by MAO-A
 Both forms break down dopamine equally.
The reaction for MAO is oxidative deamination type, it is shown below:
H2O
NH3
R
CH2
O
O
NH2
R
FAD+
FADÍ
Í 2Î
C
OH
H
2
Î
R
C
2
1/2 Î
2
2
+ Í 2Î
Amino cid metabolism and neurotransmitters utilization is in close relation with
toxic ammonia formation, its utilization pathways in nervous tissue are shown in
figure 9.
Ammonia utilization ways
in the nervous tissue
NH3+α-ketoglutarate+NADPH GDH
Glu + NADP+
Gln synthase
NH3 + Glu + ATP
Gln + ADP + Pi
Asn synthase
Asp + Gln + ATP
Asn + Glu + AMP + PiPi
Figure 9. Reductive amination of alpha-ketoglutarate, synthesis of glutamine (Gln)
and asparagine (Asn).
First two reactions (fig.9) are the most important for nervous tissue to utilize
ammonia: reductive amination of alpha-ketoglutarate catalyzed by glutamate
dehydrogenese (GDH) and synthesis of glutamine (Gln) from glutamic acid (Glu)
74
with the use of ATP due to glutamine synthase. Toxicity of ammonia partially may
be explained due to decrease of alpha-ketoglutarate use in Citric acid cycle as
energy source for neurons because of its increased content to utilize ammonia in
GDH reaction.
EXERCISES FOR INDEPENDENT WORK. In the table with test tasks
emphasize keywords, choose the correct answer and justify it:
№
Test tasks:
1.
Monoamine oxidase inhibitors are
widely
Explanations:
used
as
psychopharmacological drugs. They
change the level of nearly all
neurotransmitters in synapses, with
the following neurotransmitter being
the exception:
A. Acetylcholine
B. Serotonin
C. Dopamine
D. Noradrenalin
E. Adrenalin
2.
Decarboxylation
induces
of
production
aminobutyric
glutamate
of
acid
gamma(GABA)
neurotransmitter. After breakdown,
GABA
is
converted
into
a
metabolite of the Citric acid cycle,
that is:
A. Fumarate
B. Succinate
C. Oxaloacetate
75
№
Test tasks:
Explanations:
D. Malate
E. Citric acid
3.
An unconscious patient was taken by
ambulance to the hospital. On
objective examination the patient
was found to have no reflexes,
periodical convulsions, irregular
breathing. After laboratory
examination the patient was
diagnosed with hepatic coma.
Disorders of the central nervous
system develop due to the
accumulation of the following
metabolite:
A. Urea
B. Histamine
C. Glutamine
D. Ammonia
E. Bilirubin
4.
Disruption of nerve fiber
myelinogenesis causes neurological
disorders and mental retardation.
These symptoms are typical for
hereditary and acquired alterations in
the metabolism of:
A. Phosphatidic acid
B. Cholesterol
C. Sphingolipids
76
№
Test tasks:
Explanations:
D. Neutral fats
E. Higher fatty acids
5.
Depressions and emotional insanities
result
from
the
deficit
of
noradrenalin, serotonin and other
biogenic amines in the brain. Their
concentration in the synapses can be
increased
by
antidepressants
means
that
of
the
inhibit
the
following enzyme:
A. Phenylalanine-4-monooxygenase
B. Monoamino oxidase
C. D-amino-acid oxidase
D. L-amino-acid oxidase
E. Diamine oxidase
6.
It is known that the monoamino
oxidase (MAO) enzyme plays an
important part in the metabolism of
catecholamine neurotransmitters. In
what way this enzyme inactivates
these neurotransmitters
(norepinephrine, epinephrine,
dopamine)?
A. Oxidative deamination
B. Carboxylation
C. Addition of an amino group
D. Removal of methyl group
E. Hydrolysis
77
№
Test tasks:
7.
An inhibitory mediator is formed by
Explanations:
the decarboxylation of glutamate in
the CNS. Name it:
A. Asparagine
B. Serotonine
C. Histamine
D. GABA
E. Glutathione
8.
A dizziness, memory impairment
and periodical convulsions are
observed in patient. It was revealed
that these changes were caused by a
deficiency of a product of glutamic
acid decarboxylation. Name this
product:
A. TDP
B. GABA
C. THFA
D. Pyridoxal phosphate
E. ATP
9.
During hypersensitivity test a patient
got subcutaneous injection of an
antigen which caused reddening of
skin, edema, pain as a result of
histamine action .This biogenic
78
№
Test tasks:
Explanations:
amine generated as a from histidine
amino acid across:
A. Methylation
B. Isomerization
C. Phosphorylation
D. Decarboxylation
E. Deamination
10. A patient diagnosed with carcinoid
of bowels was admitted to the
hospital. Analysis revealed high
production of serotonin. It is known
that this substance is formed of
tryptophan
amino
acid.
What
biochemical mechanism underlies
this process?
A. Decarboxylation
B. Microsomal oxidation
C. Transamination
D. Desamination
E. Formation of paired compounds
11. Cerebral trauma caused the increase
of ammonia formation. What amino
acid takes part in removal of
ammonia from cerebral tissue?
A. Tryptophan
B. Lysine
C. Glutamic acid
D. Valine
79
№
Test tasks:
Explanations:
E. Туrosine
12. Glutamate decarboxylation results in
the
formation
of
inhibitory
transmitter in CNS. Name it:
A. Glutathione
B. Gamma amino butyric acid
C. Serotonin
D. Histamine
E. Asparagine
13. Ammonia is a very toxic substance,
especially for the nervous system.
What substance takes the most
active
part
in
ammonia
detoxification in the brain tissue?
A. Lysine
B. Glutamic acid
C. Histidine
D. Proline
E. Alanine
14. Neurotransmitter
derived
from one
serotonin
amino
is
acid.
Choose it:
A. Phenylalanine
B. Serine
C. Tryptophan
D. Cysteine
E. Proline
15. In the brain ammonia is converted to
80
№
Test tasks:
Explanations:
product from following list. Point
out it:
A. Aspartate
B. Glutamine
C. Alanine
D. Histidine
E. Urea
16. The brain contains relatively high
amounts of all compounds from the
following list except one. Point out
it:
A. Glutamine
B. N-Acetylaspartate
C. Gamma-aminobutyric acid
(GABA)
D. Glycogen
E. Proteolipid
17. Point out the main pathways of
catabolism in brain:
A. Glycolysis and Citric Acid Cycle
B. Glycogenolysis and Glycogenesis
C. Glycogenolysis and Citric Acid
Cycle
D. Embden-Meyerhof pathway and
HMP shunt
E. Oxidation of fatty acids and
ketogenesis
18. This enzyme may be promoter of
81
№
Test tasks:
Glutamate
utilization
Explanations:
in
direct
reaction, and in opposite reaction it
can utilize toxic ammonia in nervous
tissue. Name it:
A. Glutaminase
B. Glutamine oxidase
C. Glutamate dehydrogenase
D. Glutamate decarboxylase
E. Glutamate reductase
19. Tetrahydrobiopterin (THBP) is in
need for hydroxylation reactions of
some
amino
acids
to
produce
neurotransmitters in nervous tissue.
Name these neurotransmitters:
A. Dopamine, Serotonin
B. Glycine, Glutamate
C. GABA, Glycine
D. Histamine, Tryptamine
GABA, Histamine
20. Insulin-regulated
glucose
trans-
porters are found in neuronal cell
bodies in the brain cortex of humans.
Name them:
A. GLUT4, GLUT8
B. GLUT1
C. GLUT2
D. GLUT1, GLUT2
E. GLUT5
82
BIOCHEMICAL FUNCTIONS OF THE LIVER
AT HEALTHY AND DISEASED PEOPLE
(Rudko N.P., Ivanchenko D. G.)
INFORMATIONAL MATERIAL
The liver is the largest parenchymal organs. It is a vital organ that supports
nearly every other organ in the body in some facet. Without a healthy liver, a
person cannot survive. Liver performs multiple critical functions:
1. Maintenance of blood glucose level.
2. Regulation of blood lipid levels:
- fatty acid synthesis, lipoprotein formation (VLDL, HDL) and transformation
(ChM).
3. Synthesis of ketone bodies (for using by other tissues).
4. Synthesis of plasma proteins:
- albumins (100%), α-globulins (85%), β-globulins (50%) (there are
components of blood clotting system and other plasma enzymes among
them).
5. Exocrine secretion:
- bile acid synthesis and bile secretion (help in emulsification of fats in the
intestine).
6. Excretion (blood filtering):
- RBCs phagocytosed by Kupffer cells, waste product bilirubin is conjugated
by hepatocytes and secreted in bile.
7. Biotransformation (Detoxification):
- ammonia to urea;
- xenobiotics to more soluble and easily excretable compounds;
- hormones and biogenic amines to inactive forms.
83
The role of the liver in the metabolism of carbohydrates
Carbohydrates are very important nutrients for humans. 200g/day is total intake
as a requirement. Main metabolic form of carbohydrate is glucose. Only 10g of
glucose present in blood plasma and 300g in liver.
Blood glucose must be replenished constantly (most of glucose (80%)
consumed daily is utilized by RBCs and brain). Hypoglycemia and coma may
result if concentration of glucose in the blood is less 45mg/dL.
The liver plays a key role in maintaining the physiological concentration of
glucose in the blood.
The total amount of glucose entering the liver after absorption from intestine
is distributed in the following way: 60% - for oxidative process (NADH, NADPH
generation), 30% - for fatty acid synthesis, 10-15% of that is used for the synthesis
of glycogen.
Hyperglycemia state
Excessive dietary intake of glucose increases in the intensity of all metabolic
pathways of its transformation in hepatocytes. So, most glucose is involved into
aerobic glycolysis: glucose →…→ 2 pyruvates. Further splitting of pyruvates
requires a large amount of CoA, which is also used for the oxidation of fatty acids.
As a result mobilization of lipids from fat depots and oxidation of higher fatty
acids (HFA) in the liver is decreased.
Glycogenesis - conversion of glucose to glycogen for storage (the major
pathway in hepatocytes at hyperglycemia). High activity of glycogenesis in the
liver from blood glucose is due to:
- glucose transporter type GLUT-2. The transporter provides glucose permeability
of liver cells if high concentrations is in portal blood. Liver cell do not require
insulin for amino acid or glucose uptake;
- glucokinase. It is glucose specific enzyme in liver (but in pancreas, gut, brain
too). It catalyzes glucose conversion to glucose 6-phosphate. It acts as a glucose
sensor, triggering shifts in metabolism or cell function in response to rising or
84
falling levels of glucose. Glucokinase has a low affinity for glucose (high Km);
it is not inhibited by glucose 6-phosphate; and it is inducible by insulin.
Hypoglycemia state
Glycogenolysis - degradation of liver glycogen stores to glucose. At physiological
hypoglycemia glycogen breakdown by the action of glycogen phosphorylase is
activated in the liver. The resulting glucose-6-phosphate can be spent in three
areas:
1) cleaved by glucose-6-phosphatase to form glucose and phosphoric acid;
2) the pentose phosphate pathway;
3). by way of glycolysis to form pyruvic acid and lactate.
A product formed from glucose-6-phosphate mainly is glucose. This leads to
the exit of free glucose from liver to bloodstream.
Hepatic glycogen not sufficient during 12 hr fast. During sleep there is shift
from glycogenolysis to de novo synthesis of glucose in liver - gluconeogenesis. It
is essential during fasting or starvation.
Substrates for gluconeogenesis are:
-
glucogenic amino acids mainly coming from muscle proteins (starvation);
-
lactate (from RBC & muscle after intensive physical activity) and pyruvate;
-
glycerol from backbone of the fats and glycerophospholipids. Aside from
propionyl-CoA produced by oxidation of rare, odd-chain fatty acids, glycerol is
the only portion of the fat molecule that can be made directly into glucose by
animal fat. Acetyl CoA (formed from even-chain fatty acids) cannot be termed
glucogenic, since the conversion back to pyruvate is not possible due to
irreversible nature of the reaction. In plants the glyoxylate cycle produces fourcarbon dicarboxylic acids that can enter gluconeogenesis. The existence of
glyoxylate cycles in humans has not been established, and it is widely held that
fatty acids cannot be converted to glucose in humans directly. (These substrates
are usual for fasting).
85
In humans the main gluconeogenic precursors are lactate, glycerol (which is
a part of the triacylglycerol molecule), alanine and glutamine. Altogether, they
account for over 90% of the overall gluconeogenesis.
Even-chain fatty acids can’t be converted into glucose in animals. Only oddchain fatty acids can be oxidized to yield propionyl-CoA, a precursor for succinylCoA, which can be converted to pyruvate and enter into gluconeogenesis.
The role of the liver in the metabolism of lipids
Most of the nutrients entering the liver follow metabolic pathways to lipids
rather than glycogen, ex: glucose----> acetyl CoA---> triacylglycerols, cholesterol.
Triacylglycerols can be stored in the liver or released into the blood plasma to
travel to adipose tissue. Lipids travel in the bloodstream in the form of lipoproteins
(complexes of triacylglycerols, phospholipids, cholesterol and proteins);
LIPOPROTEINS:
-
Very Low Density Lipoproteins (VLDL): liver forms and releases lipids in the
form of VLDL. They exist average about 3 hours in the circulatory system;
they deliver their main elements triacylglycerols to cells (first of all they are
adipocytes, skeletal and cardiac muscles). They lost triacylglycerols then
become Low Density Lipoproteins.
-
Low Density Lipoproteins (LDL): cholesterol that they contain may be taken
up by a variety of cells including those of arterial walls; ultimately they return
to the liver.
-
Chylomicrones (ChM): blood rich with ChM following a meal; they are
formed and released from intestine and have a relatively short life span in the
blood stream - about 8 minutes. Their remnant forms are trapped by
hepatocytes for subsequent utilization.
-
High Density Lipoproteins (HDL): They are synthesized primarily in the liver;
they facilitate the uptake of lipids and activation of lipoprotein lipase; HDL
particles collect liberated cholesterol in the blood and carry it back to the liver
for excretion as bile acids or recycled as bile.
86
Liver taking part in the transformation of the lipoproteins carries cholesterol
metabolism regulation.
The liver plays a key role in the regulation of cholesterol metabolism. The
initial substrate for cholesterol synthesis is acetyl-CoA. As acetyl-CoA is formed
by the decomposition of glucose and fatty acids excess meal containing
carbohydrates and fats stimulates the synthesis of cholesterol (due to increased
availability of the substrate for the synthesis of cholesterol - acetyl-CoA).
FORMATION OF BILE
Bile consists of watery mixture of organic and inorganic compounds.
Lecithin and bile salts are quantitatively the most important organic components of
bile. Bile can either pass directly from the liver where it is formed into the
duodenum through the common bile duct, or the stored in the gallbladder.
Daily bile secretion is 0.6 L, pH 6.9–7.7
Bile composition:
1) bile acids
- are synthesized from cholesterol (0.5 gram/day);
- are combined with amino acids like glycine or taurine before secretion;
- form a water soluble form called bile salts
2) cholesterol and lecithin (phospholipid)
- normally the cholesterol secreted in bile is kept in solution by the detergent
action of lecithin;
- excessive secretion of cholesterol by the liver or over concentration of bile
in the gall bladder can cause precipitation of cholesterol from solution and
formation of aggregates called gallstones
3) bilirubindiglucuronides (bile pigment)
4) detoxified chemicals
5) NaHCO3
87
Components
Function or substrate
Water
Solvent
HCO3-
Neutralizes gastric juice
Bile salts
Facilitate lipid digestion
Phospholipids
Facilitate lipid digestion
Bile pigments
Waste product
Cholesterol
Waste product
SYNTHESIS OF KETONE BODIES
The ketone bodies are produced from acetyl CoA which comes from three
sources: glucose, fatty acids and amino acids. These ketone bodies cannot be
utilized by the liver because hepatocytes lack β-ketoacyl-CoA transferase
(thiophorase) which converts acetoacetate to acetoacetyl-CoA and hence these
ketone bodies are supplied to the peripheral tissues for oxidation. Brain can use
ketone bodies if glucose supplies fall: prolonged starvation (>1 week of fasting),
glycogen and glucogenic substrates are exhausted. Ketogenesis can provide energy
to body in prolonged energy needs. The ketone bodies are synthesized in the liver
even under normal conditions.
In normal metabolism, some ketone bodies are continuously produced and
broken down in energy production. The normal blood level of ketone bodies
seldom exceeds 3 mg/100 mL of blood. In diabetes, however, the liver produces
large quantities of ketone bodies, releasing them into the blood-stream for delivery
to other tissues. This causes a substantial increase in the level of ketone bodies in
the blood of untreated diabetics.
The role of the liver in the metabolism of proteins
The most critical aspects of protein metabolism that occur in the liver are:
1)
The liver is central to the metabolism of amino acids, as it actively proceed
their chemical modification processes:
-
deamination and transamination of amino acids, followed by
conversion of the non-nitrogenous part of those molecules to glucose or
88
lipids. Several of the enzymes used in these pathways (for example, alanine
and aspartate aminotransferases) are commonly assayed in serum to assess
liver damage;
-
removal of ammonia from the body by synthesis of urea. Ammonia is
very toxic and if not rapidly and efficiently removed from the circulation,
will result in central nervous system disease.
-
synthesis of non-essential amino acids.
2) Hepatocytes use the amino acids coming from the digestive tract for
synthesis of own proteins, but most of them used for synthesis of plasma
proteins. In the liver are synthesized protein-transporters for: lipids
(apolipoproteins, albumin), steroid, thyroid hormones, iones (Cu 2+, Fe2+,
Ca2+); components for blood clotting system: prothrombin, fibrinogen,
proconvertin, proaccelerin, Stuart-Prower factor etc.
Specific enzymes for the liver are: arginase, ornithine carbamoyltransferase,
histidase, sorbitol dehydrogenase, urocaninase, α-antitrypsin.
The role of the liver in pigment metabolism
Bilirubin must be conjugated to a water-soluble substance. This increase its
water solubility, decreases its lipid solubility and makes easier its excretion.
Conjugation is accomplished by attaching two molecules of glucuronic acid to it in
two step process.
The enzyme is UDP-glucuronyl transferase. The substrates are: bilirubin (or
bilirubin monoglucuronide), UDP-glucuronic acid. Glucuronide synthesis is the
rate-determining
step in hepatic bilirubin metabolism.
Drugs such
as
phenobarbital, for example, can induce both conjugate formation and the transport
process.
The bilirubin glucuronides are then excreted by active transport into the bile,
where they form what are known as the bile pigments.
CAUSES OF INCREASED BILIRUBIN
1. Abnormal metabolism of bilirubin:
89
- overproduction of bilirubin due to hemolysis. Ex: incompatible blood
transfusion
2. Hepatic cell (liver) disease:
- impaired uptake of bilirubin by the liver cells. Ex: hepatitis and cirrhosis
3. Obstruction to outflow of bilirubin:
- liver damage (scarred bile ducts)
- gallstones, inflammation of bile ducts
Levels of bilirubin in blood are normally below 1.0 mg% (17 µmol/L) and
levels over 2.5-3mg% (34-51µmol/L) typically results in JAUNDICE.
HEPATITIS: - inflammation of the liver, may be caused by viral or toxic
factors. Viral hepatitis produced by 3 known viral agents known as hepatitis A, B
and C
CIRRHOSIS: condition in which necrosis of the liver leads to a proliferation
of fibrous connective tissue (fibrosis). It can be caused by alcoholism, hepatitis
infection, obstructed bile flow and back pressure from elevated hepatic vein
pressure. Blood ammonia levels are frequently elevated since normally ammonia is
converted to urea by the liver.
The role of the liver in the harmful substance detoxication
Alcohol is metabolized usually by liver the rate of about 50 ml of spirits (a
typical drink-size serving of beer, wine, or spirits) every 90 minutes. It takes
approximately 90 minutes for a healthy liver to metabolize a 30 ml of pure ethanol.
But diseased liver with conditions such as hepatitis, cirrhosis, cancer, and
gallbladder disease are likely to result in a slower rate of metabolism.
Ethanol's acute effects are due largely to its nature as a central nervous
system depressant, and are dependent on blood alcohol concentrations. As drinking
increases, people become sleepy, or fall into a stupor. After a very high level of
consumption, the respiratory system becomes depressed and the person will stop
breathing. Comatose patients may aspirate their vomit (resulting in vomitus in the
lungs, which may cause "drowning" and later pneumonia if survived). In addition
to respiratory failure and accidents caused by effects on the central nervous system,
90
alcohol causes significant metabolic derangements. Hypoglycemia occurs due to
ethanol's inhibition of gluconeogenesis, especially in children, and may cause
lactic acidosis, ketoacidosis, and acute renal failure. Metabolic acidosis is
compounded by respiratory failure. Patients may also present with hypothermia.
What is the biochemical basis of these health problems? Ethanol cannot be
excreted and must be metabolized, primarily by the liver. This metabolism occurs
by two pathways. The first pathway comprises two steps. The first step, catalyzed
by the enzyme alcohol dehydrogenase (Alcohol DH), takes place in the cytoplasm:
Alcohol DH
CH3-CH2-OH + NAD+ −−−−→
Ethanol
CH3CHO + NADH + H+
Acetaldehyde
The second step, catalyzed by aldehyde dehydrogenase (Aldehyde DH), takes
place in mitochondria:
Aldehyde DH
CH3CHO + NAD+ + H2O −−−−→ CH3-COO- + NADH + H+
Acetaldehyde
Acetate
Desulfiram is widely used in medical practice to prevent alcoholism, it
inhibits aldehyde dehydrogenase. Increased level of acetaldehyde causes aversion
to alcohol.
1.
High level of ethanol consumption leads to an accumulation of NADH.
- This high concentration of NADH inhibits gluconeogenesis by preventing
the oxidation of lactate to pyruvate. In fact, the high concentration of NADH
will cause the reverse reaction to predominate, and lactate will accumulate.
The consequences may be hypoglycemia and lactic acidosis.
- NADH glut also inhibits fatty acid oxidation. The metabolic purpose of
fatty acid oxidation is to generate NADH for energy (ATP) generation by
oxidative phosphorylation, but an alcohol consumer's NADH needs are met
by ethanol metabolism. In fact, the excess NADH signals that conditions are
right for fatty acid synthesis. Hence, triacylglycerols are accumulated in the
liver, leading to a condition known as “fatty liver.”
91
2.
The second pathway for ethanol metabolism is called the ethanol inducible
microsomal ethanol-oxidizing system (MEOS). This is cytochrome P450dependent pathway.
- It generates acetaldehyde and subsequently acetate herewith oxidizing
biosynthetic reducing power NADPH to NADP+. Moreover, because the
system consumes NADPH, the antioxidant glutathione cannot be
regenerated, exacerbating the oxidative stress.
-MEOS uses oxygen, this pathway generates free radicals that damage
tissues.
Under these conditions demands in NADPH as fuel for functioning of
antioxidant system like glutathione dependent increases. But NADPH
consumed by MEOS and it causes its deficiency.
What are the effects of the other metabolites of ethanol? Liver mitochondria
can convert acetate into acetyl CoA in a reaction requiring ATP. The enzyme is the
thiokinase that normally activates short-chain fatty acids.
Thiokinase
CH3-COO- + CoA + ATP −−−−→ CH3-CO˜CoA + ADP + Pi
Acetate
Acetyl CoA
However, further processing of the acetyl CoA by Krebs cycle is blocked,
because accumulated NADH inhibits two important regulatory enzymes: isocitrate
dehydrogenase and α-ketoglutarate dehydrogenase. This cause accumulation of
acetyl CoA and has several consequences. First, ketone bodies will form and be
released into the blood, exacerbating the acidic condition already resulting from
the high lactate concentration. The processing of the acetate in the liver becomes
inefficient, leading to a buildup of acetaldehyde. This very reactive compound
forms covalent bonds with many important functional groups in proteins,
impairing protein function. If ethanol is consistently consumed at high levels, the
acetaldehyde can significantly damage the liver, eventually leading to cell death.
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Thus liver damage from excessive ethanol consumption occurs in three
stages. The first stage is the aforementioned development of fatty liver. In the
second stage—alcoholic hepatitis—groups of cells die and inflammation results.
This stage can itself be fatal. In stage three – cirrhosis - fibrous structure and scar
tissue are produced around the dead cells. Cirrhosis impairs many of the liver's
biochemical functions. The cirrhotic liver is unable to convert ammonia into urea,
and blood levels of ammonia rise. Ammonia is toxic to the nervous system and can
cause coma and death. Cirrhosis of the liver arises in about 25% of alcoholics, and
about 75% of all cases of liver cirrhosis are the result of alcoholism. Viral hepatitis
is a nonalcoholic cause of liver cirrhosis.
Liver inactivates many flowing substances. This process can be done in
different ways: by oxidation, destruction and connection with other substances.
One of the main mechanisms of detoxification - the so-called protective synthesis,
i.e. the transformation of toxic metabolic products in more complex non-toxic
complexes, which are excreted from the body. By type of such synthesis is the
forms hippuric acid by combining benzoic acid with glycine. In normal conditions
are formed and excreted in the urine insignificant amount of hippuric acid (0,1-1,0
g / day), its quantity increases by eating fruit with peel containing benthological
sodium.
The synthesis of hippuric acid is a physiological basis of the sample with the
load benzalkonium sodium proposed by the Quick and modified A. Ya. by Pytel in
1945. Clinical-anatomical mapping by L. A. Vinnik (1956) showed the existence
of parallelism between the degree of anatomical lesion of the liver cells and
reduced synthesis of hippuric acid in the formulation of samples of Quick - Pytel.
A test for assessing the detoxification function of liver is Quick`s test:
measurement of hippuric acid in the urine.
Hippuric acid is produced in the liver in two reactions:
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1. This reaction is catalyzed by Xenobiotic medium-chain fatty acid:CoA ligase:
Benzoic acid
Benzoyl-CoA
2. The reaction is catalyzed by Glycine transferase:
CoASH
Load by sodium benzoate is given in the amount of 6 grams dissolved in 250
ml of water per os. The amount of hippuric acid excreted in the urine during the
first 4 hours after the loading is estimated. 6 g of sodium benzoate should yield 7,5
g of hippuric acid. In the healthy persons, more than 60 % sodium benzoate
equivalent to 4,5 g of hippuric acid is excreted in urine. A reduction in hippuric
acid excretion indicates hepatic damage. The definition is not only a total for 4
hours removing the hippuric acid, but defining it in each time portion allows you to
more accurately assess the degree of disturbance antitoxic function of the liver.
Normal curve excretion the hippuric acid has a rapid rise in the 1-St and 2-nd hour
followed a sharp decline to the 4th hour. Slow increase excretion by the end of the
4-hour research indicates severe violation of antitoxic function of the liver. In
addition, this type of curve total number derived the hippuric acid, as a rule,
considerably reduced. The total number of the hippuric acid in cases of the most
94
severe liver injury can be reduced to 35-20%. Defeat moderate give the decrease
excretion to 60%.
Laboratory tests for to estimate liver function
Liver function tests are a battery of tests that give your doctor an idea of how
well your liver is working. From these studies, your doctor can identify possible
liver disease, medication stress on liver function, or infections of the liver such as
hepatitis. There are several different tests that comprise LFT's.
What do you understand as Liver Function Tests (LFT)? They:
- are crude indices of hepatic structure, cellular integrity, and function;
- are based on measurements of substances released from damaged hepatic cells
into the blood;
- are measurements of blood components that gives an idea of the existence, extent
and type of liver damage;
- provide useful information regarding the presence and severity of hepatobiliary
injury or impairment of liver function.
Biochemical parameters in LFT are:
3) bilirubin (conjugated and unconjugated);
4) aminotransferases (ALT, AST);
5) alkaline phosphatase (ALP);
6) serum albumin and total protein.
The biochemical parameters assist in differentiating:
OBSTRUCTION TO THE BILIARY TRACT
7) indices of cholestasis, blockage of bile flow are indicated by 1) serum total
bilirubin concentration and 2) serum alkaline phosphatase activity;
ACUTE HEPATOCELLULAR DAMAGE
8) serum aminotransferase (ALT & AST) activities are measure of the integrity
of hepatocytes,
9) ALT & AST levels in plasma/serum are sensitive index of hepatocellular
damage,
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10) ALT & AST are located mainly in the peri-portal hepatocytes, thus do not
give reliable indication of centri-lobular liver damage;
CHRONIC LIVER DISEASE
11) serum albumin concentration is a crude measure of the synthetic capacity of
the liver, although it is affected by many other factors.
Liver is highly compartmentalized, therefore no single biochemical test can
be used to fully access functional state of liver. What are the criteria used to select
parameters in LFT?
1. Tests based on substances produced or synthesized by liver. Example: albumin,
cholinesterase, coagulation factors.
2. Tests based on substances released from damaged hepatocytes. Tests separated
into two groups:
12) endogenous compounds released by damaged hepatocytes. Examples:
enzymes such as AST and ALT;
13) endogenous compounds synthesized at increased rate or released by
canalicular membrane, bile duct epithelium and endothelium of central and
periportal veins. Examples: ALP, gamma glutamyl transpeptidase (GGTP or
γGT), 5’nucleotidase.
3. Test based on substances cleared from plasma by liver. They can be separated
into two groups:
14) endogenous metabolites. Examples: bilirubin, bile acids, ammonia;
15) exogenous compounds. Examples: benzoic acid, indole, aminopyrine,
lidocaine, indocyanine green, caffeine
What is the diagnostic significance of Aspartate Aminotransferase?
AST was formerly called Serum Glutamate Oxaloacetate Transaminase
(SGOT). Its activity is high in heart muscle, liver, skeletal muscle, but found in
lesser degree in kidneys, pancreas, RBC
serum/plasma level rises.
damage or injury.
Damage tissues releases AST in blood:
AST elevation is directly related to extent of cellular
Elevation of AST in plasma depends on length of time that the
96
blood is drawn after damage or injury because AST is cleared from the blood in a
few days.
AST level in plasma is elevated 8 hours after cellular injury, peak at 24
to 36 hours, and return to normal in 3 to 7 days.
AST level is persistently elevated in chronic hepatocellular disease.
In acute hepatitis, AST can be elevated as much as 20 times the normal
value.
In Acute Extra-hepatic Obstruction (e.g., Gallstone), AST levels quickly
rise to 10 times the normal and swiftly fall.
In Cirrhotic patients level of AST depends on the amount of active
inflammation.
Factors that interfere with serum AST include: pregnancy – can cause
decreased levels of AST; exercise – can cause increased levels of AST; drugs such
as anti-hypertensives, cholinergic agents, coumarin-type anticoagulants, oral
contraceptives, opiates, salicylates, hepatotoxic medications.
What is the diagnostic significance of Alanine Aminotransferase ?
ALT was formerly called Serum Glutamate-Pyruvate Transaminase
(SGPT). It is mainly in liver, lesser quantities are in kidneys, heart and skeletal
muscle.
Liver dysfunction or injury causes elevation of ALT level in blood.
ALT is a sensitive and specific indicator of hepatocellular disease.
ALT level is more liver-specific than AST.
extent of cellular damage or injury.
Plasma
ALT elevation is directly related to
Elevation of ALT in plasma depends on
length of time that the blood is drawn after damage or injury because ALT is
cleared from the blood in a few days.
ALT level in plasma is elevated 8 hours
after cellular injury, peak at 24 to 36 hours, and return to normal in 3 to 7 days.
AST is released more than ALT in chronic hepatocellular disease (cirrhosis).
Large number of drugs can increase serum level of ALT.
What is the diagnostic significance of Alkaline Phosphatase (ALP)?
97
ALP activity is increased in an alkaline (pH of 9 to 10) medium. It is highest
in liver, biliary tract epithelium, bone, placenta. ALP is in Kupffer’s cells lining
Biliary collecting system. Plasma/Serum ALP level use to detect disorders in liver
and bond. In Liver disease, increase plasma ALP is due to increased synthesis by
cells lining the bile canaliculi, usually in response to cholestasis, which may be
either intra-hepatic or extra-hepatic. Levels of ALP in plasma/serum are greatly
increased in both extra-hepatic and intra-hepatic obstructive biliary disease and
cirrhosis. Hepatic tumors, hepatotoxic drugs and hepatitis, cause smaller elevations
in serum ALP levels.
What are some of the extra-hepatic sources of ALP? Bone is the most
frequent extra-hepatic source of ALP. New bone growth is associated with
elevated levels of ALP, but and healing fractures, rheumatoid arthritis,
hyperparathyroidism also.
How are the isoenzymes of ALP used in diagnosis? They are used to
distinguish between liver and bone diseases. Isoenzymes are most easily
differentiated by heat Stability test and by electrophoresis. ALP isoenzyme
produced in Liver (ALP 1) is heat stable but ALP isoenzyme produced in bone
(ALP 2) is inactivated by heat. Detection of isoenzymes helps differentiate the
source of the pathologic condition associated with elevated total ALP. ALP 1 is
expected to be higher in liver disease.
Sources of elevated ALP can be determined by analyzing 5` nucleotidase in
the same serum sample. 5`nucleotidase is produced predominantly in the liver. If
both total ALP and 5`nucleotidase are elevated, then it is liver disease. If
5`nucleotidase is normal and ALP is elevated then bone is the most probable
source of the elevated ALP.
What is the diagnostic significance of Gamma Glutamyl Transpeptidase
(GGTP or γGT)?
GGTP participates in the transfer of amino acids and peptides across cellular
membrane and possibly participates in glutathione metabolism. Its level is very
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high in liver and biliary tract. Lesser concentrations are in kidney, spleen, heart,
intestine, brain, and prostate gland. Men may have higher GGTP levels than
women because of the additional levels in the prostate.
Test for GGTP is used to detect liver cell dysfunction. GGTP test is highly
accurate in indicting cholestasis. GGTP is the most sensitive liver enzyme for
detecting biliary obstruction, cholangitis, or cholecystitis. Elevation of GGTP
parallels that of ALP in liver disease. GGTP is not increased in bone disease.
What is the diagnostic significance of albumin in blood?
Albumin is the major protein synthesized within the liver, thus can be use to
assess hepatic function. Estimation of Pre-albumin is a better assessment of liver
function. When disease affects the liver, the hepatocytes lose ability to synthesize
albumin, and the serum albumin level is diminished because the half-life of
albumin is 12 to 18 days, severe impairment of hepatic albumin synthesis may not
be recognized for several weeks or even months. Hypoalbuminaemia is a feature of
advanced chronic liver disease and severe acute liver damage. Albumin level is
low in some cases of chronic liver disease, but globulin level is high given a
normal total protein level. Reason for this might be that the liver cannot produce
albumin, thus accounting for the low albumin level, whereas the globulins are
mostly made in the reticuloendothelial system and therefore their levels tend to
increase. These changes can however be detected by measuring the
albumin/globulin (A/G) ratio or performs protein electrophoresis.
What is the significant of prothrombin time in LFT?
Prothrombin time is a measure of the activities of certain coagulation factors
synthesized by the liver. It is used as an indicator of hepatic synthetic function.
Prothrombin has a very short half-life, and an increased prothrombin time may be
the earliest indicator of hepatocellular damage.
99
EXERCISES FOR INDEPENDENT WORK. In the table with test tasks
emphasize keywords, choose the correct answer and justify it:
№
Test tasks:
1.
A patient with symptoms of acute
Explanations:
alcohol poisoning was brought to
the hospital. What carbohydrates
metabolism changes are typical for
this condition?
A. The
anaerobic
glucose
metabolism predominates in muscles
B. The gluconeogenesis is increased
in the liver
C. The breakage of glycogen is
increased in the liver
D. The gluconeogenesis velocity in
the liver is decreased
E. The
anaerobic
breakage
of
glucose is increased in muscles
2.
A patient suffers from hepatic
cirrhosis. Examination of which of
the following substances excreted
by urine can characterize the state of
antitoxic function of liver?
A. Uric acid
B. Сreatinine
C. Ammonium salts
D. Hippuric acid
E. Amino acids
100
№
Test tasks:
3.
A patient has been admitted to the
Explanations:
contagious isolation ward with signs
of jaundice caused by hepatitis virus.
Which of the symptoms given below
is strictly specific for hepatocellular
jaundice?
A. Bilirubinuria
B. Increase of ALT, AST level
C. Heperbilirubinemia
D. Cholemia
E. Urobilinuria
4.
A patient suffering from chronic
hepatitis. Antitoxic liver function
evaluation is as follows: sodium
benzoate dissolved in water is orally
given to the patient and the amount
of certain substance excreted with
urine is estimated. What chemical
compound measurement is an test
for
assessing
the
detoxification
function of liver:
A. Phenylacetic acid
B. Citric acid
C. Oxalic acid
D. Valerian acid
E. Hippuric acid
101
№
Test tasks:
5.
There is impairment of the liver
function
in
a
Explanations:
patient.
What
biochemical parameters necessary to
determine for evaluation of the liver
in the blood:
A. Aldolase
B. Lipase
C. AlAT (ALT)
D. LDH1
E. Creatine kinase
6.
Select the function that is not
inherent for the liver:
A. The distribution of substances
entering
the
body
from
the
gastrointestinal tract
B. Bile formation
C. Synthesis of substances used by
other tissues (creatine, ketones, etc.)
D.
Synthesis
of
cortisol
and
aldosterone
E. Inactivation of toxic substances
7.
What enzyme is activated in liver at
physiological hypoglycemia:
A. Glycogen phosphorylase
B. Glutaminase
C. Glutamate decarboxylase
D. Creatine kinase
102
№
Test tasks:
Explanations:
E. Glycogen synthase
8.
Gluconeogenesis is active in the
liver of human. What substance
cannot be used as a substrate for the
metabolic pathway:
A. Alanine
B. Lactate
C. Acetyl-CoA
D. Pyruvate
E. Glycerol
9.
Glycogen breakdown in the liver
leads to the formation of glucose-6phosphate. Further conversion of
this metabolite is multivariate. Select
a product formed from glucose-6phosphate mainly:
A. Pyruvate
B. Lactate
C. Alanine
D. Ribose-5-phosphate
E. Glucose
10. Mobilization of lipids from fat
depots and oxidation of higher fatty
acids (HFA) in the liver is decreased
at the use of excessive amounts of
carbohydrates. What is the basis of
103
№
Test tasks:
Explanations:
such changes:
A. Reduced absorption of HFA in
the intestine
B. Reduced HFA delivery to the
liver
C. Deficiency of CoA
D. NADPH deficit
E. Biotin deficiency
11. Liver plays a key role in the
regulation of lipid metabolism in the
body.
Only
one
of
following
functions is not characteristic of
liver. Point out it:
A. Synthesis of bile acids
B. Synthesis of cholecalciferol
C. Formation of lipoproteins
D. The regulation of cholesterol
metabolism
E. Synthesis of ketone bodies
12. Most amino acids originating from
food are used by the liver for:
A. Synthesis of blood proteins
B. Synthesis of creatine
C. Synthesis of urea
D. Synthesis of uric acid
E. Synthesis of bile acids
104
№
Test tasks:
Explanations:
13. Point out the conjugation agent used
for conjugated bilirubin formation in
hepatocytes:
A. Glycine
B. Cysteine
C. UDP-glucuronic acid
D. PAPS
E. Acetyl-CoA
14. Find the protein name that is
synthesized in the liver, only:
A. Albumin of blood plasma
B. Actin
C. Myosin
D. Tropomyosin
E. All the names above are right
answers
15. Point out the amino acid that is
conjugative agent at Quick`s test:
A. Lactic acid
B. Glycine
C. Valine
D. Leucine
E. Histidine
105
№
Test tasks:
Explanations:
16. Find out the enzyme name which is
specific for liver tissue, only:
A. Succinate dehydrogenase
B. Arginase
C. Alanine amino transferase
D. Aspartate amino transferase
E. Isocitrate dehydrogenase
17. This lipoprotein class is synthesized
in the liver, and is in need for the
transport of triacylglycerols and
cholesterol from the liver to tissues.
Name it:
A. IDL
B. HDL
C. LDL
D. VLDL
E. Chylomicrons
18. Point out the enzyme whose activity
is decreased in the blood plasma at
liver cirrhosis in patient:
A. Glutamine synthetase
B. Glutamate dehydrogenase
C. Alanine amino transferase
D. Choline esterase
106
№
Test tasks:
Explanations:
E. UDP - glucoronyl transferase
19. Disulfiram is widely used in medical
practice to prevent alcoholism, it
inhibits aldehyde dehydrogenase.
Increased level of what metabolite
causes aversion to alcohol?
A. Acetaldehyde
B. Ethanol
C. Malonyl aldehyde
D. Propionic aldehyde
E. Methanol
20. One of liver functions is
maintenance of glucose
concentration in the blood. Point out
the carbohydrate metabolic pathway
in the liver that provides realization
of this function at exception of diet
carbohydrates:
A. Aerobic oxidation of glucose
B. Anaerobic oxidation of glucose
C. Gluconeogenesis
D. Pentose phosphate cycle
E. Glycogenesis
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XENOBIOTIC TRANSFORMATION IN HUMANS.
MICROSOMAL OXIDATION
(Rudko N.P., Aleksandrova K. V.)
INFORMATIONAL MATERIAL
Biological basis for xenobiotic metabolism:
-
to convert lipid-soluble, non-polar, non-excretable forms of chemicals to
water-soluble, polar forms that are excretable in bile and urine;
-
the transformation process may take place as a result of the interaction of the
toxic substance with enzymes found primarily in the cell endoplasmic
reticulum, cytoplasm, and mitochondria;
-
the liver is the primary organ where biotransformation occurs.
Xenobiotics: the definition. The term xenobiotic is derived from the Greek
words ξένος (xenos) = foreigner, and βίος (bios) = life, plus the Greek suffix for
adjectives -τικός, -ή, -ό (tic). A xenobiotic is a chemical which is found in an
organism but which is not normally produced or expected to be present in it. It can
also cover substances which are present in much higher concentrations than are
108
usual Specifically, drugs such as antibiotics are xenobiotics in humans because the
human body does not produce them itself, nor are they part of a normal diet.
However, the term xenobiotics is very often used in the context of pollutants
such as dioxins and polychlorinated biphenyls and their effect on the alive
organism, because xenobiotics are understood as substances foreign to an entire
biological system, i.e. artificial substances, which did not exist in nature before
their synthesis by humans. So a xenobiotic is a chemical compound foreign to a
given biologic system. With respect to animals and humans, xenobiotics include
drugs, drug metabolites, and environmental compounds, such as pollutants that are
not produced by the body. In the environment, xenobiotics include synthetic
pesticides, herbicides, and industrial pollutants that would not be found in nature.
The most common classification in the modern science of xenobiotics is
reduced to the following groups:
1) chemicals (mercury, lead, cadmium, etc.);
2) the radionuclides;
3) drugs;
4) the substances used in plant cultivation and animal husbandry (pesticides,
insecticides, herbicides, nitrates, etc.);
5) polycyclic aromatic and chlorinated hydrocarbons;
6), dioxins and dioxin-like substances;
7) the metabolites of microorganisms
Current conceptions about the mechanism of xenobiotic toxic action.
The rate at which metabolism of toxic substances occurs is dependent on a
variety of factors that can be categorized into two groups:
- factors that affect the metabolic processes directly, and
- factors that affect the transport of toxic substance to tissues where
metabolism occurs.
Biotransformation is affected by the species of the test animal, age, sex,
nutritional status, disease, enzyme induction or inhibition, and genetics. Newborn
babies and young infants are more susceptible to a variety of chemicals such as
109
pesticides because the cytochrome P450 enzymes important in pesticide
detoxification reaction are not well developed.
A balanced diet will provide the necessary protein as well as essential metals
and minerals such as copper, zinc, and calcium to assist normal cellular enzymatic
activities associated with biotransformation. Protein deficient diets can result in a
decrease in protein synthesis, thus affecting the synthesis of enzymes involved in
the metabolic reactions used in detoxification.
Cirrhosis of the liver is often caused by excessive drinking of alcohol.
During the disease process the liver cells are damaged and replaced by connective
tissue. If enough cells are killed, the ability of the liver to metabolize toxic
substances is dramatically reduced. Cirrhosis can also be caused by repeated
exposure to arsenic or to high levels of vitamin A. Exposure to chemicals such as
carbon tetrachloride and vinyl chloride may result in liver cell damage and
decrease metabolism of toxic substances. These two substances are also associated
with the development of liver cancer.
Kidneys are damaged by absorption and concentration of heavy metals (e.g.,
Hg, Cd, etc.) in the cells of the proximal convoluted tubules of the nephron.
Absorption rate, perfusion rate, plasma protein binding, and storage will
affect the rate at which a toxic substance is delivered to the tissue where
metabolism occurs. The perfusion rate of a given tissue is important in determining
how quickly a toxic substance will be transformed. Organs such as the liver and
kidneys have a high perfusion rate relative to other tissue types. These organs have
the potential to extract and detoxify larger quantities of toxicants from the blood.
Toxic substances bound to proteins in the blood do not easily move across
cell membranes. In many cases this slows the rate at which the toxicant is
metabolized because the substance may not be readily absorbed by the tissue
where detoxification occurs. The faster a substance is eliminated from the body,
the more unlikely a biological effect will be.
The primary organs involved in xenobiotic excretion are the kidneys, liver,
and lung.
110
Excretion by the liver
Many toxic substances are stored and detoxified in the liver. The toxic
substances are then excreted into the bile. Bile is produced in the liver by the
hepatic cells. This mechanism is important in removing large protein-bound
toxicants such as heavy metals. Excretion of the toxicant from the liver to the
intestinal tract will usually result in the substance being removed in the feces.
However, the intestinal bacteria are also capable of producing enzymes that cause
the detoxified substance to become less water soluble. As a result, the toxic
substance may be reabsorbed from the digestive tract. The process of excreting
toxic substances from the liver and their subsequent reabsorption from the
digestive tract is referred to as enterohepatic circulation. Gluconated polycyclic
aromatic hydrocarbons and glutathione conjugates of trichloroethylene are
reabsorbed by this mechanism and therefore retained. Detoxification of toxic
substances before they reach the other portions of the systemic circulation is
referred to as the “first pass effect.” This effect can decrease the systemic toxicity
of those substances absorbed from the digestive tract.
Excretion by the kidneys
The kidneys receive 25 percent of the cardiac output. The high perfusion rate
not only results in significant exposure to circulating toxic substances, but also
facilitate the excretion of the toxicants. Toxic substances enter the kidneys as a
result of active and passive transport mechanisms present in the glomerulus and the
nephron tubules. Several heavy metals such as cadmium, lead and mercury are
excreted by the kidneys. These metals are bound to plasma protein. The protein
metal complex has a low molecular weight and is able to pass through the
glomerulus to the nephron. However, this complex may be reabsorbed by active
transport mechanisms in the proximal convoluted tubules.
Excretion by the lungs
Excretion of volatile toxic gases, such as those associated with organic
compounds, occurs in the lungs. The transfer of gases from the blood to the lungs
is influenced by concentration gradients and by their solubility in water. Ethylene
111
which is only slightly soluble in water will readily diffuse from the blood into the
lungs and will therefore be easily removed. Chloroform however, is more water
soluble and will not diffuse as easily from the blood into the lungs.
Interaction with these enzymes may change the toxicant to either a less or a
more toxic form . Generally, biotransformation occurs in two phases.
PHASE I BIOTRANSFORMATION
- Phase I involves catabolic reactions that break down the toxicant into
various components. Catabolic reactions include oxidation, reduction, and
hydrolysis . Oxidation occurs when a molecule combines with oxygen, loses
hydrogen, or loses one or more electrons. Reduction occurs when a molecule
combines with hydrogen, loses oxygen, or gains one or more electrons. Hydrolysis
is the process in which a chemical compound is split into smaller molecules by
reacting with water. In most cases these reactions make the chemical less toxic,
more water soluble, and easier to excrete.
Phase I is mainly microsomal oxidation. The cytochrome P450 mixed
function oxidase system plays a major role in the metabolism of xenobiotics. The
biological effectiveness and the potential toxicity of many drugs are strongly
influenced by their metabolism, much of which is accomplished by P450dependent monoxygenase systems.
112
Although several enzyme systems participate in phase I metabolism of
xenobiotics, perhaps the most notable pathway is the monooxygenation function
catalyzed by the cytochrome P450s (CYPs). The CYPs detoxify and/or bioactivate
a vast number of xenobiotic chemicals and conduct functionalization reactions that
include N- and O-dealkylation, aliphatic and aromatic hydroxylation, N- and Soxidation, and deamination. Examples of toxicants metabolized by this system
include nicotine and acetaminophen, as well as the procarcinogenic substances,
benzene and polyaromatic hydrocarbons. The discovery of the CYPs dates back to
1958 when Martin Klingenberg initially reported his observation of a carbon
monoxide (CO)–binding pigment present in rat liver microsomes that was
characterized by absorbance spectra at 450 nm. The spectra remained an anomaly
until the work of Ryo Sato and Tsuneo Omura, published in 1962, provided the
critical evidence that the CO chromaphore was a hemoprotein. They further
described the properties of the protein, ascribing the term, CYP. Prior to these
events, research conducted by Alan Conney and the Millers in the United States
and H. Remmer in Germany demonstrated that rates of hepatic drug metabolism
could be induced or enhanced by pretreatment of animals with several types of
compounds, including phenobarbital (PB) and 3-methylcholanthrene (3-MC);
113
however, the identities of the enzymes responsible for these biotransformation
events were not known at the time. Also in the 1950’s, the work of R. T. Williams
from the United Kingdom greatly expanded our scope of xenobiotic metabolism,
elucidating the chemistries and reactions of a great many compounds. His
achievements are summarized in a book that he authored in 1959, entitled,
“Detoxication mechanisms: the metabolism and detoxication of drugs, toxic
substances and other organic compounds”. In his book, he established the terms
phase I and phase II biotransformation, which are still used today, to denote the
biphasic nature of metabolism and together account for a large extent of chemical
detoxication that occurs in mammalian organisms. Certainly, many other scientists
have also contributed importantly in the area of phase I xenobiotic metabolism
over the past 50 years, so, with apologies, space limitations have precluded their
mention here. Suffice it to say that today, 57 functional P450 genes have been
identified in the human, and as of 2009, over 11,000 individual P450s have been
identified at the primary sequence level across all known species of organism!
The P450 catalytic cycle
1. The substrate binds to the active site of the enzyme, in close proximity to the
haem group, on the side opposite to the peptide chain. The bound substrate
induces a change in the conformation of the active site, often displacing a
water molecule from the distal axial coordination position of the haem iron,
and sometimes changing the state of the haem iron from low-spin to highspin. If no reducing equivalents are available, this complex may remain
stable.
2. The change in the electronic state of the active site favors the transfer of an
electron from NADPH via cytochrome P450 reductase or another associated
reductase. This takes place by way of the electron transfer chain, as
described above, reducing the ferric haem iron to the ferrous state.
3. Molecular oxygen binds covalently to the distal axial coordination position
of the haem iron. The cysteine ligand is a better electron donor than
histidine, which is normally found in haem-containing proteins. As a
114
consequence, the oxygen is activated to a greater extent than in other haem
proteins. However, this sometimes allows the iron-oxygen bond to
dissociate, causing the so-called "decoupling reaction", which releases a
reactive superoxide radical and interrupts the catalytic cycle.
4. A second electron is transferred via the electron-transport system, from
either cytochrome P450 reductase, ferredoxins, or cytochrome b5, reducing
the dioxygen adduct to a negatively charged peroxo group. This is a shortlived intermediate state.
5. The peroxo group formed in step 4 is rapidly protonated twice by local
transfer from water or from surrounding amino-acid side-chains, releasing
one water molecule, and forming a highly reactive iron (V)-oxo species.
6. Depending on the substrate and enzyme involved, P450 enzymes can
catalyse any of a wide variety of reactions. A hypothetical hydroxylation is
shown in this illustration. After the product has been released from the
active site, the enzyme returns to its original state, with a water molecule
returning to occupy the distal coordination position of the iron nucleus.
115
Because most CYPs require a protein partner to deliver one or more
electrons to reduce the iron (and eventually molecular oxygen), CYPs are part of
P450-containing systems of proteins. Five general schemes are known:

CPR/cyb5/P450 systems employed by most eukaryotic microsomal (i.e.,
not mitochondrial) CYPs involve the reduction of cytochrome P450
reductase (variously CPR, POR, or CYPOR) by NADPH, and the transfer of
reducing power as electrons to the CYP. Cytochrome b5 (cyb5) can also
contribute reducing power to this system after being reduced by cytochrome
b5 reductase (CYB5R).

FR/Fd/P450 systems, which are employed by mitochondrial and some
bacterial CYPs.

CYB5R/cyb5/P450 systems in which both electrons required by the CYP
come from cytochrome b5.

FMN/Fd/P450 systems originally found in Rhodococcus sp. in which a
FMN-domain-containing reductase is fused to the CYP.

P450 only systems, which do not require external reducing power. Notable
ones include CYP5 (thromboxane synthase), CYP8, prostacyclin synthase,
and CYP74A (allene oxide synthase).
CYPs are the major enzymes involved in drug metabolism, accounting for
~75% of the total metabolism. Most drugs undergo deactivation by CYPs, either
directly or by facilitated excretion from the body. Also, many substances are
bioactivated by CYPs to form their active compounds.
Human CYPs are primarily membrane-associated proteins, located either in
the inner membrane of mitochondria or in the endoplasmic reticulum of cells.
CYPs metabolize thousands of endogenous and exogenous chemicals. Some CYPs
metabolize only one (or a very few) substrates, such as CYP19 (aromatase), while
others may metabolize multiple substrates. Both of these characteristics account for
their central importance in medicine. Cytochrome P450 enzymes are present in
most tissues of the body, and play important roles in hormone synthesis and
breakdown (including estrogen and testosterone synthesis and metabolism),
116
cholesterol synthesis, and vitamin D metabolism. Cytochrome P450 enzymes also
function to metabolize potentially toxic compounds, including drugs and products
of endogenous metabolism such as bilirubin, principally in the liver.
Many drugs may increase or decrease the activity of various CYP isozymes
either by inducing the biosynthesis of an isozyme (enzyme induction) or by
directly inhibiting the activity of the CYP (enzyme inhibition). This is a major
source of adverse drug interactions, since changes in CYP enzyme activity may
affect the metabolism and clearance of various drugs. For example, if one drug
inhibits the CYP-mediated metabolism of another drug, the second drug may
accumulate within the body to toxic levels. Hence, these drug interactions may
necessitate dosage adjustments or choosing drugs that do not interact with the CYP
system. Such drug interactions are especially important to take into account when
using drugs of vital importance to the patient, drugs with important side-effects and
drugs with small therapeutic windows, but any drug may be subject to an altered
plasma concentration due to altered drug metabolism.
A classic example includes anti-epileptic drugs. Phenytoin, for example,
induces CYP1A2, CYP2C9, CYP2C19, and CYP3A4. Substrates for the latter may
be drugs with critical dosage, like amiodarone or carbamazepine, whose blood
plasma concentration may either increase because of enzyme inhibition in the
former, or decrease because of enzyme induction in the latter.
Naturally occurring compounds may also induce or inhibit CYP activity. For
example, bioactive compounds found in grapefruit juice and some other fruit
juices, including bergamottin, dihydroxybergamottin, and paradisin-A, have been
found to inhibit CYP3A4-mediated metabolism of certain medications, leading to
increased bioavailability and, thus, the strong possibility of overdosing. Because of
this risk, avoiding grapefruit juice and fresh grapefruits entirely while on drugs is
usually advised.
Other examples:

Saint-John's wort, a common herbal remedy induces CYP3A4, but also
inhibits CYP1A1, CYP1B1, CYP2D6, and CYP3A4.
117

Tobacco smoking induces CYP1A2 (example CYP1A2 substrates are
clozapine, olanzapine, and fluvoxamine)

At relatively high concentrations, starfruit juice has also been shown to
inhibit CYP2A6 and other CYPs.[18] Watercress is also a known inhibitor of
the Cytochrome P450 CYP2E1, which may result in altered drug
metabolism for individuals on certain medications (ex., chlorzoxazone).
A subset of cytochrome P450 enzymes play important roles in the synthesis
of steroid hormones (steroidogenesis) by the adrenals, gonads, and peripheral
tissue:

CYP11A1 (also known as P450scc or P450c11a1) in adrenal mitochondria
effects “the activity formerly known as 20,22-desmolase” (steroid 20αhydroxylase, steroid 22-hydroxylase, cholesterol side-chain scission).

CYP11B1 (encoding the protein P450c11β) found in the inner mitochondrial
membrane of adrenal cortex has steroid 11β-hydroxylase, steroid 18hydroxylase, and steroid 18-methyloxidase activities.

CYP11B2 (encoding the protein P450c11AS), found only in the
mitochondria of the adrenal zona glomerulosa, has steroid 11β-hydroxylase,
steroid 18-hydroxylase, and steroid 18-methyloxidase activities.

CYP17A1, in endoplasmic reticulum of adrenal cortex has steroid 17αhydroxylase and 17, 20-lyase activities.

CYP21A1 (P450c21) in adrenal cortex conducts 21-hydroxylase activity.

CYP19A (P450arom, aromatase) in endoplasmic reticulum of gonads, brain,
adipose tissue, and elsewhere catalyzes aromatization of androgens to
estrogens.
PHASE II BIOTRANSFORMATION
Phase II biotransformation is catalyzed often by the “transferase” enzymes
that perform conjugating reactions. Included in the phase II reaction schemes are
glucuronidation, sulfation, methylation, acetylation, glutathione conjugation, and
amino acid conjugation. The products of phase II conjugations are typically more
hydrophilic than the parent compounds and therefore usually more readily
118
excretable. Specific families of phase II xenobiotic-metabolizing enzymes include
the
UDP-glucuronosyltransferases
(UGTs),
sulfotransferases
(STs),
N-
acetyltransferases (arylamine N-acetytransferase; NATs), and glutathione Stransferases (GSTs) and various methyltransferases, such as thiopurine S-methyl
transferase and catechol O-methyl transferase. Perhaps of particular note, the
UGTs conduct glucuoronidation reactions, principally with electron-rich
nucleophilic heteroatoms, such as O, N, or S, present in aliphatic alcohols and
phenols. This microsomal system is a principal player in phase II metabolism and
is known for its high metabolic capacity but relatively low affinity for xenobiotic
substrates.
There are > 10 UGTs in humans. STs also constitute a large multigene
family of cytosolic enzymes that catalyze the sulfation of primarily aliphatic
alcohols and phenols and represent another important phase II pathway noted for
its high affinity for xenobiotic substrates but low capacity. The GSTs function as
cytosolic dimeric isoenzymes of 45–55 kDa size that have been assigned to at least
four classes: alpha, mu, pi, theta, and zeta; humans possess > 20 distinct GST
family members. There are two NATs, NAT1 and NAT2, that possess different but
overlapping substrate specificities and can function to both activate and deactivate
arylamine and hydrazine drugs and carcinogens. In concert with the phase I
enzymatic machinery, the phase II enzymes coordinately metabolize, detoxify, and
at times bioactivate xenobiotic substrates.
Example of indole biotransformation in two phases:
119
Indole and its derivatives are highly toxic to microorganisms and animals
and are considered mutagens and carcinogens. Experimental evidences showed
that indole caused glomerular sclerosis, hemolysis, improper oviduct functioning,
and chronic arthritis. Indol and its derivative like indole-3-acetic acid induced
neuroepithelial cell apoptosis in embryos; 6-hydroxyskatol, a metabolite of 3methylindole generated in the human intestine, has possible psychotropic effects.
Human beings can be exposed to indole via ambient air, tobacco smoke,
food, and skin contact with vapors and other products, such as perfumes that
contain indole. There is revealed a correlation between increasing of
encephalopathy and substances absorbed by the bloodstream from the intestines.
Indol and its derivatives are the substances that are formed in the intestines can
cause endotoxemia.
OTHER CASES OF HARMFUL COMPOUND BIOTRANSFORMATION
During the P450 catalytic cycle small amounts of reactive oxygen species
(ROS) such as superoxide radical anion and H2O2 are produced and cytochrome
P450 enzymes are a significant source of ROS in biological systems, especially
tissues like the liver where P450 is present in high amounts. Several factors
determine the generation of ROS by P450s including the specific form of P450,
entry of the second electron into the P450 cycle, the presence of substrate and
nature of the substrate. The toxicity of many reagents is due, in part, to increased
production of ROS when they are metabolized by cytochrome P450s e.g. CCL 4,
120
halogenated hydrocarbons, benzene, acetaminophen, anesthetics, nitrosamines etc.
CYP2E1 appears to be significant generator of ROS and this may play a role in
alcohol-induced liver toxicity.
There are several enzyme systems that catalyze reactions to neutralize free
radicals and reactive oxygen species. These enzymes include:

superoxide dismutase

glutathione peroxidise

glutathione reductase

catalases
These form the body’s endogenous defence mechanisms to help protect
against free radical-induced cell damage. The antioxidant enzymes – glutathione
peroxidase, catalase, and superoxide dismutase (SOD) – metabolize oxidative toxic
intermediates. These enzymes also require co-factors such as selenium, iron,
copper, zinc, and manganese for optimum catalytic activity. It has been suggested
that an inadequate dietary intake of these trace minerals may compromise the
effectiveness of these antioxidant defense mechanisms. The consumption and
absorption of these important trace minerals may decrease with aging.
Glutathione: enzymes and system
Glutathione, an important water-soluble antioxidant, is synthesized from the
amino acids glycine, glutamate, and cysteine. Glutathione can directly neutralize
ROS such as lipid peroxides, and also plays a major role in xenobiotic metabolism.
When an individual is exposed to high levels of xenobiotics, more glutathione is
utilized for conjugation. Conjugation with glutathione renders the toxin neutral and
makes it less available to serve as an antioxidant. Research suggests that
glutathione and vitamin C work interactively to neutralize free radicals. These two
also have a sparing effect upon each other.
The glutathione system includes glutathione, glutathione reductase,
glutathione peroxidases and glutathione ''S''-transferases. Of these glutathione
peroxidase is an enzyme containing four selenium-cofactors that catalyzes the
breakdown of hydrogen peroxide and organic hydroperoxides. Glutathione ''S''121
transferases show high activity with lipid peroxides. These enzymes are at
particularly high levels in the liver.
Lipoic acid
This is another important endogenous antioxidant. It is categorized as “thiol”
or “biothiol”. These are sulfur-containing molecules that catalyze the oxidative
decarboxylation of alpha-keto acids, such as pyruvate and alphaketoglutarate, in
the Krebs cycle. Lipoic acid and its reduced form, dihydrolipoic acid (DHLA),
neutralize the free radicals in both lipid and aqueous domains and as such has been
called a “universal antioxidant.”
Superoxide dismutase
Superoxide dismutases (SODs) are a class of enzymes that catalyse the
breakdown of the superoxide anion into oxygen and hydrogen peroxide. These
enzymes are present in almost all aerobic cells and in extracellular fluids. SODs
contain metal ion cofactors that, depending on the isozyme, can be copper, zinc,
manganese or iron. For example, in humans copper/zinc SOD is present in the
cytosol, while manganese SOD is present in the mitochondrion. The mitochondrial
SOD is most biologically important of these three.
Catalases
Catalases are enzymes that catalyse the conversion of hydrogen peroxide to
water and oxygen, using either an iron or manganese cofactor. This is found in
peroxisomes in most eukaryotic cells. Its only substrate is hydrogen peroxide. It
follows a ping-pong mechanism. Here, its cofactor is oxidised by one molecule of
hydrogen peroxide and then regenerated by transferring the bound oxygen to a
second molecule of substrate.
Peroxiredoxins
There are peroxidases that catalyze the reduction of hydrogen peroxide, organic
hydroperoxides, as well as peroxynitrite. These may be of three basic types typical 2-cysteine peroxiredoxins; atypical 2-cysteine peroxiredoxins; and 1cysteine
peroxiredoxins.
Peroxiredoxins
antioxidant metabolism.
122
seem
to
be
important
in
Rhodanase
Sodium thiosulfate (Na2S2O3) is used as an antidote to cyanide poisoning.
Thiosulfate acts as a sulfur donor for the conversion of cyanide to thiocyanate
(which can then be safely excreted in the urine), catalyzed by the enzyme
rhodanase.
EXERCISES FOR INDEPENDENT WORK. In the table with test tasks
emphasize keywords, choose the correct answer and justify it:
№
Test tasks:
1.
Study of conversion of a food
colouring
agent
Explanations:
revealed
that
utilization of this xenobiotic takes
place
only
in
one
phase
–
microsomal oxidation (modification
phase). Name an enzyme of this
phase:
A. Cytochrome aa3
B. Cytochrome C oxidase
C. Cytochrome P-450
D. Cytochrome C1
E. Cytochrome b
2.
In course of metabolic process active
forms
of
oxygen
including
superoxide anion radical are formed
in the human body. By means of
what
enzyme
is
this
anion
inactivated?
A. Catalase
B. Glutathione reductase
123
№
Test tasks:
Explanations:
C. Peroxidase
D. Superoxide dismutase
E. Glutathione peroxidase
3.
A patient with encephalopathy was
admitted to the neurological in
patient
department.
revealed
a
There
correlation
was
between
increasing of encephalopathy and
substances
absorbed
by
the
bloodstream from the intestines.
What substances that are formed in
the
intestines
can
cause
endotoxemia?
A. Indole
B. Ornithine
C. Acetacetate
D. Butyrate
E. Biotin
4.
Point out the main place for the
location of microsomal oxidation in
a cell:
A. Nucleus
B. Cytoplasm
C. EPR, smooth part
D. EPR, rough part
E. Lysosomes
124
№
5.
Test tasks:
Point
out
the
Explanations:
enzyme
of
monooxygenase chain as a final
electron acceptor from NADPН:
A. Cytochrome b5
B. Cytochrome b
C. Cytochrome P450
D. Cytochrome c1
E. Cytochrome aa3
6.
Find the enzyme participating in the
function
of
the
microsomal
monooxygenase chain:
A. НАДН - dehydrogenase
B. Cytochrome b
C. Cytochrome c1
D. Cytochrome c
E. Cytochrome P450
7.
Point
out
the
liver
enzyme
participating in the neutralization of
xenobiotics, their metabolites and
harmful endogenous products:
A. Glutamine synthetase
B. Glutamate dehydrogenase
C. Alanine amino transferase
125
№
Test tasks:
Explanations:
D. Carbomoyl phosphate synthetase
E. UDP - glucoronyl transferase
8.
Find the correct definition of the
term "xenobiotic":
A. A substance that is an obligatory
component of food products
B. A substance that is unnatural for
humans
C. A substance that is synthesized in
small quantities in humans
D.
A
substance
that
regulates
metabolism in organism
E. A substance that is a terminal
product of metabolism
9.
Point out the tripeptide participating
in the conjugation of some harmful
products in the liver:
A. Glutathione
B. Methionine
C. Trialanine
D. Oxytocin
E. Prolylproline
126
№
Test tasks:
Explanations:
10. In course of metabolic process active
forms of oxygen including hydrogen
peroxide are formed in the human
body. By means of what enzyme is
this compound inactivated?
A. Catalase
B. Glutathione reductase
C. Peroxidase
D. Superoxide dismutase
E. Glutathione peroxidase
11. Point out the donor of sulfate group
in
the
conjugation
phase
of
xenobiotics transformation:
A. Glutathione
B. UDP-glucuronic acid
C. Adenosine
3́-phosphate-5́-
phosphosulfate (PAPS)
D. Acetyl-CoA
E. S-adenosylmethionine
12. All of the following may have a
physiological antioxidant role except
A. Lipoic acid
B. Vitamin C
C. Selenium
127
№
Test tasks:
Explanations:
D. Iron
E. Vitamin E
13. Point out the chemical nature of
prosthetic
group
of
cytochrome
P450:
A. Nucleotide
B. Fe3+
C. Fe2+
D. Phosphate
E. Haem
14. Choose the exogenous factor (the
drug) that can induce the UDPglucuronosyltransferase
gene
expression in the liver:
A. Calcitriol
B. Thyroxine
C. Riboxin
D. Phenobarbital
E. Thiamine diphosphate
15. Choose one wrong continuation of a
phrase: Phase I of xenobiotics
transformation:
A. Is carried out by enzymes of
endoplasmic reticulum
128
№
Test tasks:
Explanations:
B. Demands presence of NADPH
C. Results in increase of polarity of a
substance
D. Occurs in anaerobic conditions
E. Proceeds
at
participation
of
cytochrome Р450
16. Point out the main enzyme in
monooxygenase system of EPR
responsible
for
modification
of
xenobiotics:
A. Glucuronyl transferase
B. Cytochrome P450
C. NADH reductase
D. Glutathione S-transferase
E. Cytochrome C oxidase
17. Choose the correct statement about
hepatic monooxygenases linked with
cytochrome P450 enzyme.
A. Located mainly in smooth EPR
B. Catalyzes oxidation, reduction
and hydrolysis reactions at the
same time
C. They are inducible
D. Their action always causes the
detoxification of xenobiotics
E. Positions A, C are correct
129
№
Test tasks:
Explanations:
18. Which of following cytochrome
participates in drug metabolism?
A. Cytochrome aa3
B. Cytochrome c1
C. Cytochrome P450
D. Cytochrome c
E. Cytochrome b
19. Point out the conjugation agent that
is in need to detoxify heterocyclic
alcohols in the liver:
A. Glucose
B. Methionine
C. Valine
D. PAPS
E. Histidine
20. Benzoic acid causes the toxic effect
at its accumulation in the liver.
Choose the main conjugative agent
to detoxify it:
A. Glycine
B. PAPS
C. S-adenosyl methionine
D. Glutathione
E. Acetyl-CoA
130
BIOCHEMISTRY OF BLOOD TISSUE. PROTEINS OF BLOOD PLASMA.
NON-PROTEIN COMPONENTS OF BLOOD PLASMA AT HEALTHY
AND DISEASED PEOPLE
(Levich S. V.)
INFORMATIONAL MATERIAL
Blood is a body fluid in humans and other animals that delivers necessary
substances such as nutrients and oxygen to the cells and transports metabolic waste
products away from those same cells
Functions
Blood has three main functions: transport, protection and regulation.
Transport
Blood transports the following substances:

Gases, namely oxygen (O2) and carbon dioxide (CO2), between the lungs and
rest of the body

Nutrients from the digestive tract and storage sites to the rest of the body

Waste products to be detoxified or removed by the liver and kidneys

Hormones from the glands in which they are produced to their target cells

Heat to the skin so as to help regulate body temperature
Protection
Blood has several roles in inflammation:

Leukocytes, or white blood cells, destroy invading microorganisms and cancer
cells

Antibodies and other proteins destroy pathogenic substances

Platelet factors initiate blood clotting and help minimise blood loss
Regulation
Blood helps regulate:

pH by interacting with acids and bases

Water balance by transferring water to and from tissues
131
Composition of blood
Blood is classified as a connective tissue and consists of two main
components:
1. Plasma, which is a clear extracellular fluid
2. Formed elements, which are made up of the blood cells and platelets
The formed elements are so named because they are enclosed in a plasma
membrane and have a definite structure and shape. All formed elements are cells
except for the platelets, which are tiny fragments of bone marrow cells.
Formed elements are:

Erythrocytes, also known as red blood cells (RBCs)

Leukocytes, also known as white blood cells (WBCs)

Platelets
Human RBCs do not contain mitochondria, so the main pathway for ATP
production in these cells is anaerobic glycolysis.
Platelets play important role in blood clotting. Deficiency of VIII factor lead
to hereditary coagulopathy caused by blockage of thromboplastin formation
Leukocytes are further classified into two subcategories called granulocytes which
consist of neutrophils, eosinophils and basophils; and agranulocytes which consist
of lymphocytes and monocytes. Lymphocytes synthesize interferon – universal
antiviral agents as a response to viral invasion.
The formed elements can be separated from plasma by centrifuge, where a
blood sample is spun for a few minutes in a tube to separate its components
according to their densities. RBCs are denser than plasma, and so become packed
into the bottom of the tube to make up 45% of total volume. This volume is known
as the haematocrit. WBCs and platelets form a narrow cream-coloured coat known
as the buffy coat immediately above the RBCs. Finally, the plasma makes up the
top of the tube, which is a pale yellow colour and contains just under 55% of the
total volume.
132
Anemia
Anemia, also spelled anaemia, is usually defined as a decrease in the
amount of red blood cells (RBCs) or hemoglobin in the blood. It can also be
defined as a lowered ability of the blood to carry oxygen. When anemia comes on
slowly, the symptoms are often vague and may include: feeling tired, weakness,
shortness of breath or a poor ability to exercise. Anemia that comes on quickly
often has greater symptoms, which may include: confusion, feeling like one is
going to pass out, loss of consciousness, or increased thirst. Anemia must be
significant before a person becomes noticeably pale. Additional symptoms may
occur depending on the underlying cause.
There are three main types of anemia: that due to blood loss, that due to
decreased red blood cell production, and that due to increased red blood cell
breakdown. Causes of blood loss include trauma and gastrointestinal bleeding,
among others. Causes of decreased production include iron deficiency, a lack of
vitamin B12, thalassemia, and a number of neoplasms of the bone marrow. Causes
of increased breakdown include a number of genetic conditions such as sickle cell
anemia, infections like malaria, and certain autoimmune diseases. It can also be
classified based on the size of red blood cells and amount of hemoglobin in each
cell. If the cells are small, it is microcytic anemia. If they are large, it is macrocytic
anemia while if they are normal sized, it is normocytic anemia. Diagnosis in men is
based on a hemoglobin of less than 130 to 140 g/L (13 to 14 g/dL), while in
women, it must be less than 120 to 130 g/L (12 to 13 g/dL). Further testing is then
required to determine the cause.
Signs and symptoms
Anemia goes undetected in many people and symptoms can be minor. The
symptoms can be related to an underlying cause or the anemia itself. Most
commonly, people with anemia report feelings of weakness, or fatigue, general
malaise, and sometimes poor concentration. They may also report dyspnea
(shortness of breath) on exertion. In very severe anemia, the body may compensate
for the lack of oxygen-carrying capability of the blood by increasing cardiac
133
output. The patient may have symptoms related to this, such as palpitations, angina
(if pre-existing heart disease is present). There may be signs of specific causes of
anemia, e.g., koilonychia (in iron deficiency), jaundice (when anemia results from
abnormal break down of red blood cells — in hemolytic anemia), bone deformities
(found in thalassemia major) or leg ulcers (seen in sickle-cell disease). In severe
anemia, there may be signs of a hyperdynamic circulation: tachycardia (a fast heart
rate), bounding pulse, flow murmurs, and cardiac ventricular hypertrophy
(enlargement). There may be signs of heart failure. Pica, the consumption of nonfood items such as ice, but also paper, wax, or grass, and even hair or dirt, may be
a symptom of iron deficiency, although it occurs often in those who have normal
levels of hemoglobin.
Causes
Figure shows normal red blood cells flowing freely in a blood vessel. The
inset image shows a cross-section of a normal red blood cell with normal
hemoglobin.
The causes of anemia may be classified as impaired red blood cell (RBC)
production, increased RBC destruction (hemolytic anemias), blood loss and fluid
overload (hypervolemia). Several of these may interplay to cause anemia
eventually. Indeed, the most common cause of anemia is blood loss, but this
usually does not cause any lasting symptoms unless a relatively impaired RBC
production develops, in turn most commonly by iron deficiency.
Impaired production

Disturbance of proliferation and differentiation of stem cells
o
Pure red cell aplasia
o
Aplastic anemia affects all kinds of blood cells. Fanconi anemia is a hereditary
disorder or defect featuring aplastic anemia and various other abnormalities.
o
Anemia of renal failure by insufficient erythropoietin production
o
Anemia of endocrine disorders

Disturbance of proliferation and maturation of erythroblasts
o
Pernicious anemia is a form of megaloblastic anemia due to vitamin B12
134
deficiency dependent on impaired absorption of vitamin B 12. Lack of dietary B12
causes non-pernicious megaloblastic anemia
o
Anemia of folic acid deficiency, as with vitamin B12, causes megaloblastic
anemia
o
Anemia of prematurity, by diminished erythropoietin response to declining
hematocrit levels, combined with blood loss from laboratory testing, generally
occurs in premature infants at two to six weeks of age.
o
Iron deficiency anemia, resulting in deficient heme synthesis
o
Thalassemias, causing deficient globin synthesis
o
Congenital dyserythropoietic anemias, causing ineffective erythropoiesis
o
Anemia of renal failure (also causing stem cell dysfunction)

Other mechanisms of impaired RBC production
o
Myelophthisic anemia or myelophthisis is a severe type of anemia resulting
from the replacement of bone marrow by other materials, such as malignant tumors
or granulomas.
o
Myelodysplastic syndrome
o
anemia of chronic inflammation
Increased destruction
Anemias of increased red blood cell destruction are generally classified as
hemolytic anemias. These are generally featuring jaundice and elevated lactate
dehydrogenase levels. Glutathione peroxidase deficiency and low concentration of
reduced glutathione also lead to the RBCs restruction.
Blood loss
 Anemia
of prematurity from frequent blood sampling for laboratory testing,
combined with insufficient RBC production
 Trauma
or surgery, causing acute blood loss
Fluid overload
Fluid overload (hypervolemia) causes decreased hemoglobin concentration and
apparent anemia:
 General
causes of hypervolemia include excessive sodium or fluid intake, sodium
135
or water retention and fluid shift into the intravascular space.
 Anemia
of pregnancy is induced by blood volume expansion experienced in
pregnancy.
Blood plasma
Blood plasma is a mixture of proteins, enzymes, nutrients, wastes, hormones
and gases. The specific composition and function of its components are as follows:
Proteins
These are the most abundant substance in plasma by weight and play a part
in a variety of roles including clotting, defence and transport. Collectively, they
serve several functions:

They are an important reserve supply of amino acids for cell nutrition. Cells
called macrophages in the liver, gut, spleen, lungs and lymphatic tissue can break
down plasma proteins so as to release their amino acids. These amino acids are
used by other cells to synthesise new products.

Plasma proteins also serve as carriers for other molecules. Many types of small
molecules bind to specific plasma proteins and are transported from the organs that
absorb these proteins to other tissues for utilisation. The proteins also help to keep
the blood slightly basic at a stable pH. They do this by functioning as weak bases
themselves to bind excess H+ ions. By doing so, they remove excess H+ from the
blood which keeps it slightly basic.

The plasma proteins interact in specific ways to cause the blood to coagulate,
which is part of the body’s response to injury to the blood vessels (also known as
vascular injury), and helps protect against the loss of blood and invasion by foreign
microorganisms and viruses.

Plasma proteins govern the distribution of water between the blood and tissue
fluid by producing what is known as a colloid osmotic pressure.
There are three major categories of plasma proteins, and each individual type of
proteins has its own specific properties and functions in addition to their overall
collective role:
Albumin: This is the most abundant class of plasma proteins (2.8 to 4.5
136
gm/100ml) with highest electrophoretic mobility. It is soluble in water ad is
precipitated by fully saturated ammonium sulphate. Albumin is synthesized in liver
and consists of a single polypeptide chain of 610 amino acids having a molecular
weight of 69,000. It is rich in some essential amino acids such as lysine, leucine,
valine, phenylalanine, threonine, arginine and histidine. The acidic amino acids
like aspartic acid and glutamic acid are also concentrated in albumin. The presence
of these residues makes the molecule highly charged with positive and negative
charge. Besides having a nutritive role, albumin acts as a transport carrier for
various biomolecules such s fatty acids, trace elements and drugs. Another
important role of albumin is in the maintenance of osmotic pressure and fluid
distribution between blood and tissues.
Globulins, which can be subdivided into three classes from smallest to
largest in molecular weight into alpha, beta and gamma globulins. The globulins
include high density lipoproteins (HDL), an alpha-1 globulin, and low density
lipoproteins (LDL), a beta-1 globulin. HDL functions in lipid transport carrying
fats to cells for use in energy metabolism, membrane reconstruction and hormone
function. HDLs also appear to prevent cholesterol from invading and settling in the
walls of arteries. LDL carries cholesterol and fats to tissues for use in
manufacturing steroid hormones and building cell membranes, but it also favours
the deposition of cholesterol in arterial walls and thus appears to play a role in
disease of the blood vessels and heart. HDL and LDL therefore play important
parts in the regulation of cholesterol and hence have a large impact on
cardiovascular disease.
By electrophoresis plasma globulins are separated into α1, α2,β and ¥globulins are synthesized in liver, whereas ¥-globulins are formed in the cells of
reticulo-endothelial system. The average normal serum globulin (total)
concentration is 2.5 gm / 100 ml (Howe method) or 3.53 gm/100 ml by
electrophoresis.
137
α1-Globulin: This fraction includes several complex proteins containing
carbohydrates and lipids. These are, orosomucoid, α1-glycoprotein and αlipoproteins. The normal serum level of α1-globulin is 0.42 gm/100 ml.
Orosomucoid is rich in carbohydrates. It is water-soluble, heat stable and has
a molecular weight of 44,000. It serves to transport hexosamine complexes to
tissues.
Lipoproteins are soluble complexes which contain non-covalently bound
lipid. These proteins act mainly as transport carrier to different types of lipids in
the body. Increasing of low-density lipoprotein fraction (LDL) could cause
hyperlipoproteinemia type IIa.
1-antitrypsin (1-proteinase inhibitor) – glycoprotein with a molecular
weight 55 kDa. Its concentration in blood plasma is 2-3 г/л. The main biological
property of this inhibitor is its capacity to form complexes with proteinases
oppressing proteolitic activity of such enzymes as trypsin, chemotrypsin, plasmin,
trombin. The content of 1-antitrypsin is markedly increased in inflammatory
processes. The inhibitory activity of 1-antitrypsin is very important in pancreas
necrosis and acute pancreatitis because in these conditions the proteinase level in
blood and tissues is sharply increased. The congenital deficiency of 1-antitrypsin
results in the lung emphysema.
α2-Globulins: This fraction also contains complex proteins such as α2glycoproteins, plasminogen, prothrombin, haptoglobulin, ceruloplasmin (transports
Cu) and α2-macroglobulin. The normal serum value of this fraction is 0.67
gm/100ml.
Plasminogen and prothrombin are in the inactive precursors of plasmin and
thrombin respectively. Both these proteins play an important role in blood clotting.
Haptoglobulins are also glycoproteins having a molecular weight of 85,000.
These are synthesized in liver and can bind with any free hemoglobin that may
arise in plasma due to lysis of erythrocytes and thus prevent excretion of Hb and
iron associated with it.
Ceruloplasmin - glycoprotein of the 2-globulin fraction. It can bind the
138
copper ions in blood plasma. Up to 3 % of all copper contents in an organism and
more than 90 % copper contents in plasma is included in ceruloplasmin.
Ceruloplasmin has properties of ferroxidase oxidizing the iron ions. The decrease
of ceruloplasmin in organism (Wilson disease) results in exit of copper ions from
vessels and its accumulation in the connective tissue that shows by pathological
changes in a liver, main brain, cornea.
2-Macroglobulin - protein of 2-globulin fraction, universal serum
proteinase inhibitor. Its contents (2,5 g/l) in blood plasma is highest comparing to
another proteinase inhibitors.
The biological role of 2-macroglobulin consists in regulation of the tissue
proteolysis systems which are very important in such physiological and
pathological processes as blood clotting, fibrinolysis, processes of immunodefence,
functionality of a complement system, inflammation, regulation of vascular tone
(kinine and renin-angiothensine system).
β-Globulins: This fraction of plasma proteins contain these different βlipoproteins which are very rich in lipid content. It also contains transferrin
(siderophilin) which transports non-heme iron in plasma. The normal serum value
of β-globulins is 0.91 gm/100ml.
Transferrin is an iron transport protein. In plasma it can be saturated even up
to 33% with iron. It has a low content of carbohydrate.
γ-Globulins:
Immunoglobulins (Ig A, Ig G, Ig E, Ig M) - proteins of -globulin fraction of
blood plasma executing the functions of antibodies which are the main effectors of
humoral immunity. They appear in the blood serum and certain cells of a
vertebrate in response to the introduction of a protein or some other
macromolecule foreign to that species.
Immunoglobulin molecules have bindind sites that are specific for and
complementary to the structural features of the antigen that induced their
formation. Antibodies are highly specific for the foreign proteins that evoke their
formation.
139
Molecules of immunoglobulins
are glycoproteins. The protein part of
immunoglobulins contain four polipeptide chains: two heavy H-chains and two
light L-chains.
Fibrinogen: It is a fibrous protein with a molecular weight of 340,000. It has
6 polypeptide chains which are held together by disulphide linkages. Fibrinogen
plays an important role in clothing of blood where it is converted to fibrin by
thrombin.
In addition to the above mentioned proteins, the plasma contains a number
of enzymes such as acid phosphatase and alkaline phosphatase which have great
diagnostic value.
Functions of Plasma Proteins:
1.
Protein Nutrition: Plasma proteins act as a source of protein for the tissues,
whenever the need arises.
2.
Osmotic Pressure and water balance: Plasma proteins exert an osmotic
pressure of about 25 mm of Hg and therefore play an important role in maintaining
a proper water balance between the tissues and blood. Plasma albumin is mainly
responsible for this function due to its low molecular weight and quantitative
dominance over other proteins. During the condition of protein loss from the body
as occurs in kidney diseases, excessive amount of water moves to the tissues
producing edema.
3.
Buffering action: Plasma proteins help in maintaining the pH of the body by
acting asampholytes. At normal blood pH they act as acids and accept captions.
4.
Transport of Lipids: One of the most important functions of plasma proteins us
to transport lipids and lipid soluble substances in the body. Fatty acids and
bilirubin are transported mainly by albumin, whereas cholesterol and
phospholipids are carried by the lipoproteins present in β-globulins also transport
fat soluble vitamins (A, D, K and E)
5.
Transport of other substances: In addition to lipids, plasma proteins also
transport several metals and other substances α2-Globulins transport copper
(Ceruloplasmin), bound hemoglobin (haptoglobin) and thyroxine (glycoprotein)
140
and non-heme iron is transported by transferrin present in β-globulin fraction.
Calcium, Magnesium, some drugs and dyes and several cations and anions are
transported by plasma albumin.
6.
Blood Coagulation: Prothrombin present in α2-globulin fraction and fibrinogen,
participate in the blood clotting process as follows.
Causes and consequences of protein content changes in blood plasma.
Hypoproteinemia
- decrease of the total contents of proteins in blood
plasma. This state occurs in old people as well as in pathological states
accompanying with the oppressing of protein synthesis (liver diseases) and
activation of decomposition of tissue proteins (starvation, hard infectious diseases,
state
after
hard
trauma
and
operations,
cancer).
Hypoproteinemia
(hypoalbuminemia) also occurs in kidney diseases, when the increased excretion of
proteins via the urine takes place.
Hyperproteinemia
- increase of the total contents of proteins in blood
plasma. There are two types of hyperproteinemia - absolute and relative.
Absolute hyperproteinemia – accumulation of the proteins in blood. It occurs
in infection and inflammatory diseases (hyperproduction of immunoglobulins),
rheumatic diseases (hyperproduction of C-reactive protein), some malignant
tumors (myeloma) and others.
Relative hyperproteinemia – the increase of the protein concentration but not
the absolute amount of proteins. It occurs when organism loses water (diarrhea,
vomiting, fever, intensive physical activity etc.).
Paraproteinemia, also known as monoclonal gammopathy, is the presence
of excessive amounts of paraprotein or single monoclonal gammaglobulin in the
blood. It is usually due to an underlying immunoproliferative disorder or
hematologic neoplasms, especially multiple myeloma (presence of Bence Jones
protein).
Enzymes
Blood plasma contains many enzymes, which are classified into functional
and non-functional plasma enzymes.
141
Differences between functional and non-functional plasma enzymes
represents in table 1
Table 1
Functional plasma enzymes
Non-functional
enzymes
plasma
Concentration in plasma
Present in plasma in higher Normally, present in plasma in
concentrations in comparison to very low concentrations in
tissues
comparison to tissues.
Function
Have known functions
The substrates
Their substrates are always present Their substrates are absent from
in the blood
the blood
Site of synthesis
Liver
Different organs e.g. liver, heart,
brain and skeletal muscles
Effect of diseases
Decrease in liver diseases
Different enzymes increase in
different organ diseases
Examples
Clotting factors e.g. prothrombin, ALT, AST, CK, LDH, alkaline
Lipoprotein lipase and pseudo- phosphatase, acid phosphatase
choline esterase
and amylase,
No known functions
Sources of non-functional plasma enzymes :
1. Increase in the rate of enzyme synthesis) e.g. bilirubin increases the rate of
synthesis of alkaline phosphatase in obstructive liver diseases.
2. Obstruction of normal pathway e.g. obstruction of bile ducts increases alkaline
phosphatase.
3. Increased permeability of cell membrane as in tissue hypoxia.
4. Cell damage with the release of its content of enzymes into the blood e.g.
myocardial infarction and viral hepatitis.
Medical importance of non-functional plasma enzymes :
Measurement of non-functional plasma enzymes is important for:
1. Diagnosis of diseases as diseases of different organs cause elevation of different
plasma enzymes.
2. Prognosis of the disease; we can follow up the effect of treatment by measuring
plasma enzymes before and after treatment.
Examples of medically important non-functional plasma enzymes :
1. Amylase and lipase enzymes increase in diseases of the pancreas as acute
142
pancreatitis.
2. Creatine kinase (CK) enzyme increases in heart, brain and skeletal muscle
diseases.
3. Lactate dehydrogenase (LDH) enzyme increases in heart, liver and blood
diseases.
4. Alanine transaminase (ALT) enzyme, it is also called serum glutamic pyruvic
transaminase (SGPT). It increases in liver and heart diseases.
5. Aspartate transaminase (AST) enzyme, it is also called serum glutamic
oxalacetic transaminase (SGOT). It increases in liver and heart diseases.
6. Acid phosphatase enzyme increases in cancer prostate.
7. Alkaline phosphatase enzyme increases in obstructive liver diseases, bone
diseases and hyperparathyroidism.
For example, high activity of LDH1,2, aspartate aminotransferase, creatine
phosphokinase (MB isoform) in the blood are caused by myocardial infarction.
Amino acids
These are formed from the break down of tissue proteins or from the
digestion of digested proteins. Significant proteolisys of proteins could lead to the
development of aminoacidemia (increasing of aminoacid content in blood).
Nitrogenous waste
Being toxic end products of the break down of substances in the body, these
are usually cleared from the bloodstream and are excreted by the kidneys at a rate
that balances their production.
Nutrients
Those absorbed by the digestive tract are transported in the blood plasma.
These include glucose, amino acids, fats, cholesterol, phospholipids, vitamins and
minerals.
Gases
Some oxygen and carbon dioxide are transported by plasma. Plasma also
contains a substantial amount of dissolved nitrogen.
Electrolytes
143
The most abundant of these are sodium ions, which account for more of the
blood’s osmolarity than any other solute.
Acid-base balance
The body's acid–base balance is normally tightly regulated by buffering
agents, the respiratory system, and the renal system, keeping the arterial blood pH
between 7.36 and 7.42. Several buffering agents that reversibly bind hydrogen ions
and impede any change in pH exist.
Acid-base imbalance
Acid–base imbalance is an abnormality of the human body's normal
balance of acids and bases that causes the plasma pH to deviate out of the normal
range (7.35 to 7.45). In the fetus, the normal range differs based on which
umbilical vessel is sampled (umbilical vein pH is normally 7.25 to 7.45; umbilical
artery pH is normally 7.18 to 7.38). It can exist in varying levels of severity, some
life-threatening.
An excess of acid is called acidosis or acidaemia and an excess in bases is
called alkalosis or alkalemia. The process that causes the imbalance is classified
based on the etiology of the disturbance (respiratory or metabolic) and the
direction of change in pH (acidosis or alkalosis).
Metabolic acidosis is a condition that occurs when the body produces
excessive quantities of acid or when the kidneys are not removing enough acid
from the body. If unchecked, metabolic acidosis leads to acidemia, i.e., blood pH is
low (less than 7.35) due to increased production of hydrogen ions by the body or
the inability of the body to form bicarbonate (HCO3−) in the kidney. Its causes are
diverse, and its consequences can be serious, including coma and death. Together
with respiratory acidosis, it is one of the two general causes of acidemia.
Metabolic acidosis occurs when the body produces too much acid (for
example, during intensive musle work too much lactate is produced), or when the
kidneys are not removing enough acid from the body. There are several types of
metabolic acidosis. The main causes are best grouped by their influence on the
anion gap.
144
It bears noting that the anion gap can be spuriously normal in sampling
errors of the sodium level, e.g. in extreme hypertriglyceridemia. The anion gap can
be increased due to relatively low levels of cations other than sodium and
potassium (e.g. calcium or magnesium).
Respiratory acidosis is a medical emergency in which decreased ventilation
(hypoventilation) increases the concentration of carbon dioxide in the blood and
decreases the blood's pH (a condition generally called acidosis).
Carbon dioxide is produced continuously as the body's cells respire, and this
CO2 will accumulate rapidly if the lungs do not adequately expel it through
alveolar ventilation. Alveolar hypoventilation thus leads to an increased PaCO2 (a
condition called hypercapnia). The increase in PaCO2 in turn decreases the
HCO3−/PaCO2 ratio and decreases pH.
Acute respiratory acidosis occurs when an abrupt failure of ventilation
occurs. This failure in ventilation may be caused by depression of the central
respiratory center by cerebral disease or drugs, inability to ventilate adequately due
to neuromuscular disease (e.g., myasthenia gravis, amyotrophic lateral sclerosis,
Guillain-Barré syndrome, muscular dystrophy), or airway obstruction related to
asthma or chronic obstructive pulmonary disease (COPD) exacerbation.
Chronic respiratory acidosis may be secondary to many disorders, including
COPD. Hypoventilation in COPD involves multiple mechanisms, including
decreased responsiveness to hypoxia and hypercapnia, increased ventilationperfusion mismatch leading to increased dead space ventilation, and decreased
diaphragm function secondary to fatigue and hyperinflation.
Metabolic alkalosis is a metabolic condition in which the pH of tissue is
elevated beyond the normal range (7.35-7.45). This is the result of decreased
hydrogen ion concentration, leading to increased bicarbonate, or alternatively a
direct result of increased bicarbonate concentrations.
The causes of metabolic alkalosis can be divided into two categories, depending
upon urine chloride levels.
145
Chloride-responsive (Urine chloride < 20 mEq/L)
o
Loss of hydrogen ions - Most often occurs via two mechanisms, either vomiting
or via the kidney. Vomiting results in the loss of hydrochloric acid (hydrogen and
chloride ions) with the stomach contents. In the hospital setting this can commonly
occur from nasogastric suction tubes. Severe vomiting also causes loss of
potassium (hypokalaemia) and sodium (hyponatremia). The kidneys compensate
for these losses by retaining sodium in the collecting ducts at the expense of
hydrogen ions (sparing sodium/potassium pumps to prevent further loss of
potassium), leading to metabolic alkalosis.

Congenital chloride diarrhea - rare for being a diarrhea that causes alkalosis
instead of acidosis.

Contraction alkalosis - This results from a loss of water in the extracellular
space, such as from dehydration.

Diuretic therapy - loop diuretics and thiazides can both initially cause increase
in chloride, but once stores are depleted, urine excretion will be below < 25
mEq/L.

Posthypercapnia - Hypoventilation (decreased respiratory rate) causes
hypercapnia (increased levels of CO2), which results in respiratory acidosis.
Chloride-resistant (Urine chloride > 20 mEq/L)

Retention of bicarbonate - retention of bicarbonate would lead to alkalosis

Shift of hydrogen ions into intracellular space - Seen in hypokalemia. Due to a
low extracellular potassium concentration, potassium shifts out of the cells. In
order to maintain electrical neutrality, hydrogen shifts into the cells, raising blood
pH.

Alkalotic agents - Alkalotic agents, such as bicarbonate (administrated in cases
of peptic ulcer or hyperacidity) or antacids, administered in excess can lead to an
alkalosis.

Hyperaldosteronism - Renal loss of hydrogen ions occurs when excess
aldosterone (Conn's syndrome) increases the activity of a sodium-hydrogen
exchange protein in the kidney.
146
Respiratory alkalosis is a medical condition in which increased respiration
elevates the blood pH beyond the normal range (7.35-7.45) with a concurrent
reduction in arterial levels of carbon dioxide. This condition is one of the four
basic categories of disruption of acid-base homeostasis
Respiratory alkalosis may be produced as a result of the following causes:
stress, pulmonary disorder, thermal insult, fever, hyperventilation, liver disease.
The presence of only one of the above derangements is called a simple acid–
base disorder. In a mixed disorder more than one is occurring at the same time.
Mixed disorders may feature an acidosis and alkosis at the same time that partially
counteract each other, or there can be two different conditions affecting the pH in
the same direction.
The body's acid–base balance is tightly regulated. Several buffering agents
exist which reversibly bind hydrogen ions and impede any change in pH.
Extracellular buffers include bicarbonate and ammonia, while proteins and
phosphate act as intracellular buffers. The bicarbonate buffering system is
especially key, as carbon dioxide (CO2) can be shifted through carbonic acid
(H2CO3) to hydrogen ions and bicarbonate (HCO3−).
Acid–base imbalances that overcome the buffer system can be compensated
in the short term by changing the rate of ventilation. This alters the concentration
of carbon dioxide in the blood, shifting the above reaction according to Le
Chatelier's principle, which in turn alters the pH. For instance, if the blood pH
drops too low (acidemia), the body will compensate by increasing breathing,
expelling CO2, and shifting the reaction above to the right such that fewer
hydrogen ions are free – thus the pH will rise back to normal. For alkalemia, the
opposite occurs.
Acute-phase proteins
Acute-phase proteins are a class of proteins whose plasma concentrations
increase (positive acute-phase proteins) or decrease (negative acute-phase proteins)
in response to inflammation. This response is called the acute-phase reaction (also
called acute-phase response).
147
In response to injury, local inflammatory cells (neutrophil granulocytes and
macrophages) secrete a number of cytokines into the bloodstream, most notable of
which are the interleukins IL1, IL6 and IL8, and TNFα. The liver responds by
producing a large number of acute-phase reactants. At the same time, the
production of a number of other proteins is reduced; these are, therefore, referred
to as "negative" acute-phase reactants. Increased acute phase proteins from the
liver may also contribute to the promotion of sepsis
Positive acute-phase proteins serve (part of the innate immune system)
different physiological functions for the immune system. Some act to destroy or
inhibit growth of microbes, e.g., C-reactive protein, mannose-binding protein,[2]
complement factors, ferritin, ceruloplasmin, serum amyloid A and haptoglobin.
Others give negative feedback on the inflammatory response, e.g. serpins. Alpha 2macroglobulin and coagulation factors affect coagulation, mainly stimulating it.
This pro-coagulant effect may limit infection by trapping pathogens in local blood
clots. Also, some products of the coagulation system can contribute to the innate
immune system by their ability to increase vascular permeability and act as
chemotactic agents for phagocytic cells.
Measurement of acute-phase proteins, especially C-reactive protein, is a
useful marker of inflammation in both medical and veterinary clinical pathology.
It correlates with the erythrocyte sedimentation rate (ESR), however not always
directly. This is due to the ESR being largely dependent on elevation of
fibrinogen, an acute phase reactant with a half-life of approximately one week.
This protein will therefore remain higher for longer despite removal of the
inflammatory stimuli. In contrast, C-reactive protein (with a half-life of 6-8 hours)
rises rapidly and can quickly return to within the normal range if treatment is
employed. For example, in active systemic lupus erythematosus, one may find a
raised ESR but normal C-reactive protein. They may also indicate liver failure.
During rheumatoid arthritis in the blood appear additive glycosaminoglycans as
acute-phase proteins
148
EXERCISES FOR INDEPENDENT WORK. In the table with test tasks
emphasize keywords, choose the correct answer and justify it:
№
Test:
1
12 hours after an acute attack of
Explanation:
retrosternal pain a patient presented
a jump of aspartate aminotransferase
activity in blood serum. What
pathology is this deviation typical
for?
A. Viral hepatitis
B. Diabetes insipidus
C. Collagenosis
D. Diabetes mellitus
E. Myocardial infarction
2
A patient who had been working
hard under condition of elevated
temperature of the environment has
now a changed quantity of blood
plasma proteins. What phenomenon
is the case?
A. Absolute hyperproteinemia
B. Relative hyperproteinemia
C. Absolute hypoproteinemia
D. Disproteinemia
E. Paraproteinemia
149
№
3
Test:
62
y.o.
woman
Explanation:
complains
of
frequent pains in the area of her
chest and backbone, rib fractures. A
doctor
assumed
myelomatosis
(plasmocytoma).What
of
the
following laboratory characteristics
will be of the greatest diagnostic
importance?
A. Proteinuria
B. Hypoproteinemia
C. Hypoglobunemia
D. Hyperalbuminemia
E. Paraproteinemia
4
Diabetes mellitus causes ketosis as a
result of activated oxidation of fatty
acids. What disorders of acid-base
equilibrium may be caused by
excessive accumulation of ketone
bodies in blood?
A. Metabolic alkalosis
B. Metabolic acidosis
C. Respiratory alkalosis
D. Respiratory acidosis
E. Any changes won't happen
150
№
Test:
5
A 63-year-old woman developed
Explanation:
symptoms of rheumatoid arthritis.
Their increase of which blood values
indicators could be most significant
in proving the diagnosis?
A. R-glycosidase
B. Acid phosphatase
C. Lipoproteins
D. General cholesterol
E. Additive glycosaminoglycans
6
Marked increase of activity of MBforms
of
CPK
(creatinephosphokinase) and LDH-1
was revealed by examination of the
patient's blood. What is the most
probable pathology?
A. Myocardial infarction
B. Hepatitis
C. Pancreatitis
D. Rheumatism
E. Cholecystitis
151
№
Test:
7
There is high activity of LDH1,2,
Explanation:
aspartate aminotransferase, creatine
phosphokinase in the blood of
patient. In what organs (tissues) the
development of pathological process
is the most probable?
A. In the heart muscle {initial stage
of myocardium infraction}
B. In skeletal muscle {dystrophy,
atrophy}
C. In kidneys and adrenals
D. In liver and kidneys
E. In connective tissue
8
The
high
level
Dehydrogenase
of
(LDH)
Lactate
isozymes
concentration showed the increase
of LDH-1 and LDH-2 in a patient’s
blood plasma. Point out the most
probable diagnosis.
A. Diabetes mellitus
B. Skeletal muscle dystrophy
C. Myocardial infarction
D. Acute pancreatitis
E. Viral hepatitis
152
№
Test:
9
Analysis of blood serum of a patient
Explanation:
revealed the increase of alanine
aminotransferase
and
aminotransferase
levels.
aspartate
What
cytological changes can cause such a
situation?
A. Disturbance of genetic apparatus
of cells
B. Cellular breakdown
C. Disorder of enzyme systems of
cells
D. Disturbance
of
cellular
interrelations
E. Disturbed energy supply of cells
10
A worker has decreased buffer
capacity of blood due to exhausting
muscular work. What acidic
substance that came to blood caused
this phenomenon?
3-phosphoglycerate
1,3-bisphosphoglycerate
Lactate
α-ketoglutarate
Pyruvate
153
№
Test:
11
Blood sampling for bulk analysis is
Explanation:
recommended to be performed on an
empty stomach and in the morning.
What changes in blood composition
can occur if to perform blood
sampling after food intake?
A. Reduced contents of erythrocytes
B. Increased contents of erythrocytes
C. Increased contents of leukocytes
D. Increased plasma proteins
E. Reduced
contents
of
thrombocytes
12
Examination of a 43 y.o. anephric
patient revealed anemia symptoms.
What
is
the
cause
of
these
symptoms?
A.
Folic acid deficit
B.
Vitamin B12 deficit
C.
Reduced
synthesis
of
destruction
of
erythropoietins
D.
Enhanced
erythrocytes
E.
Iron deficit
154
№
Test:
13
A 55 y.o. women consulted a doctor
about
having
Explanation:
continuous
cyclic
uterine hemorrhages for a year,
weakness, dizziness. Examination
revealed skin pallor. Hemogram: Hb
– 70 g/L, erythrocytes-3.2 x 1012/L,
color index – 0.6; leukocytes – 6.0 x
109/L,
–
1%,
hypochromia.
What
reticulocytes
erythrocyte
anemia is it?
A. Iron-deficiency anemia
B. B12-folate-deficiency anemia
C. Hemolytic anemia
D. Aplastic anemia
E. Chronic posthemorrhagic anemia
14 Blood
plasma
of
healthy
man
contains several dozens of proteins.
During an illness new proteins can
originate named as the “proteins of
acute phase». Select such protein
from the listed below:
A. Albumin
B. Immunoglobulin G
C. Immunoglobulin E
D. C-reactive protein
E. Prothrombin
155
№
Test:
Explanation:
15 A patient complains about dyspnea
provoked by the physical activity.
Clinical
examination
revealed
anaemia and presence of the paraprotein in the zone of gammaglobulins. To confirm the myeloma
diagnosis it is necessary to determine
the following index in the patient’s
urine:
A. Ceruplasmin
B. Bilirubin
C. Antitrypsin
D. Bence Jones protein
E. Haemoglobin
16 Examination of 27-year-old patient
revealed pathological changes in
liver
and
brain.
Blood
plasma
analysis revealed an abrupt decrease
in the copper concentration, urine
analysis
revealed
an
increased
copper, concentration. The patient
was
diagnosed
degeneration.
with
To
Wilson’s
confirm
the
diagnosis it is necessary to study the
activity of the following enzyme in
blood serum:
A. Leucine aminopeptidase
B. Xanthine oxidase
156
№
Test:
Explanation:
C. Alcohol dehydrogenase
D. Ceruloplasmin
E. Carbonic anhydrase
17 After a surgery a 36-year-old woman
was given an intravenous injection
of concentrated albumin solution.
This has induced intensified water
movement in the following direction:
A. From the intercellular fluid to the
capillaries
B. No changes of water movement
will be observed
C. From the intercellular to the cells
D. From the cells to the intercellular
fluid
E.
From the capillaries to the
intercellular fluid
18 Electrophoretic study of a blood
serum sample, taken from the patient
with
pneumonia,
revealed
an
increase in one of the protein
fractions. Specify this fraction:
A. γ-globulins
B. Albumins
C. α1-globulins
D. β-globulins
E. α2-globulins
157
№
Test:
Explanation:
19 Examination of a 56-year-old female
patient with a history of type 1
diabetes revealed a disorder of
protein
metabolism
that
is
manifested by aminoacidemia in the
laboratory blood test values, and
clinically by the delayed wound
healing and decreased synthesis of
antibodies. Which of the following
mechanisms causes the development
of aminoacidemia?
A. Increased proteolysis
B. Decrease in the concentration
of amino acids in blood
C. Albuminosis
D. Increase in the oncotic
pressure in the blood plasma
E. Increase in low-density
lipoprotein level
20 A 49-year-old male patient with
acute pancreatitis was likely to
develop pancreatic necrosis, while
active pancreatic proteases were
absorbed into the blood stream and
tissue proteins broke up. What
protective factors of the body can
inhibit these processes?
A. Immunoglobulin
158
№
Test:
Explanation:
B. Ceruloplasmin, transferrin
C. a2-macroglobulin, a1-antitrypsin
D. Cryoglobulin, interferon
E. Hemopexin, haptoglobin
21 A
patient
hereditary
is
diagnosed
coagulopathy
characterized
by
with
that
factor
is
VIII
deficiency. Specify the phase of
blood
clotting
during
which
coagulation will be disrupted in the
given case:
A. Clot retraction
B. Thromboplastin formation
C. Fibrin formation
D. Thrombin formation
22 A
67-year-old
male
patient
consumes eggs, pork fat, butter, milk
and
meat.
Blood
test
results:
cholesterol – 12.3 mmol/l, total
lipids – 8.2 g/l, increased lowdensity lipoprotein fraction (LDL).
What type of hyperlipoproteinemia
is observed in the patient?
A. Hyporlipoproteinemia type I.
B. Hyperlipoproteinemia type IV
C. Cholesterol, hyperlipoproteinemia
D. Hyperlipoproteinemia type IIa
E. Hyperlipoproteinemia type IIb
159
№
Test:
Explanation:
23 Human red blood cells do not
contain mitochondria. What is the
main pathway for ATP production in
these cells?
A. Creatine kinase reaction
B. Anaerobic glycolysis
C. Cyclase reaction
D. Aerobic glycolysis
E. Oxidative phosphorylation
24 A 28-year-old patient undergoing
treatment
in
a
pulmonological
department has been diagnosed with
pulmonary emphysema caused by
splitting of alveolar septum by
tripsin. The disease is caused by the
congenital
deficiency
of
the
following protein:
A. Alpha-1-proteinase inhibitor
B. Haptoglobin
C. Cryoglobulin
D. Alpha-2-macroglobulin
E. Transferrin
25 Biochemical analysis of an infant`s
erythrocytes
revealed
evident
glutathione peroxidase deficiency
and low concentration of reduced
glutathione.
What
pathological
condition can develop in this infant?
160
№
Test:
Explanation:
A. Hemolytic anemia
B. Megaloblastic anemia
C. Siclemia
D. Iron-deficiency anemia
E. Pernicous anemia
26 Lymphocytes and other cells of our
body synthesize universal antiviral
agents as a response to viral
invasion. Name this protein factors
A. Interferon
B. Tumor necrosis factor
C. Cytokines
D. Interleukin-2
E. Interleukin-4
161
THE ROLE OF KIDNEYS IN THE REGULATION
OF WATER AND SALTS METABOLISM.
THE NORMAL AND PATHOLOGICAL COMPONENTS OF URINE
(Krisanova N. V.)
INFORMATIONAL MATERIAL
STRUCTURAL ORGANIZATION OF KIDNEY TISSUE
AND ITS FUNCTIONS
Renal tissue is divided in two types:
1) outer or cortical coloured brown-red;
2) inner or medullary coloured lilac-red.
Nephron is the functional unit of renal parenchyma, the two kidneys of human
number about 2 million nephrons. Cortical nephrons are about 85% of the total
number; about 15% of total number is juxtamedullary nephrons whose glomeruli
are located at the boundary between the cortex and medulla of the kidney
Figure 1. A structural unit of kidney tissue - a nephron.
162
The kidney is involved in:
1)
the regulation of water and salt balance;
2)
the maintenance of acid-base balance and of osmotic pressure of fluid
media of the organism;
3)
the removal of terminal products of metabolic processes;
4)
the blood pressure control;
5)
the stimulation of erythropoiesis, etc;
6)
in hormonal control of a lot metabolic pathways..
Filtration at the glomerulus, tubular reabsorption and tubular secretion are
observed in the nephron
Primary urine is formed due to filtration process. The composition of primary
urine is very similar to blood plasm, but there is no any protein in the primary
urine. The pores in the glomerular basal membrane, which are made up by collagen
type IV, have an effective mean diameter of 2.9 nm. This allows all plasma
components with a molecular mass about 15 kDa to pass through the membrane,
that is because proteins are completely unable to enter to primary urine.
Reabsorption. The most of all low-molecular weight plasma components are
transported back into the blood by reabsorption, to prevent losses of valuable
metabolites and electrolytes. In the proximal tubule, organic metabolites (glucose,
amino acids, lactate, ketone bodies) are recovered by secondary active transport.
There are several group-specific transport systems for resorbing amino acids, with
which hereditary disorders can be associated (cystinuria, glycinuria, cystinosis,
Hartnup`s disease). Bicarbonate, sodium ion, phosphate and sulfate are also
resorbed by ATP dependent active mechanisms in the proximal tubule. The later
sections of nephron may only serve for additional water recovery and for regulated
resorption of Na+ and Cl-. These processes are controlled by hormones.
Secretion helps also to form final urine. Some excreted substances are released
into the urine by active transport in the renal tubules: protons, potassium ions, urea,
creatinine, some drugs (penicillin).
163
These two processes help to keep useful substances and to maintain acid-base
balance for organism. The molecular mechanism for resorption and secretion of
materials by renal tubular cells are quite well understood.
Processes associated with nephron function:
Ultrafiltration of blood at the glomerulus
Primary urine (~170L/day)
Tubular reabsorption
Tubular secretion
Final urine (~2L/day)
Figure 2. Main processes promoted by the function of nephron.
THE FUNCTION OF KIDNEY IN MAINTENANCE OF ACID-BASE
BALANCE IN ORGANISM
The renal tubule cells are capable of secreting protons (H+) from the blood into the
urine against a concentration gradient. Despite the fact that the H+ concentration in
the urine is up to a thousand times higher than in the blood.
To achieve this, carbon dioxide (CO2) is taken up from the blood and together
with water (H2O) and with a help of carbonate dehydratase is converted into
hydrogen carbonate (bicarbonate, HCO3-) and one proton H+. Formally, this yields
carbonic acid, but it is not released during the reaction. The hydrogen carbonate
returns to the plasma where it contributes to the blood base reserve. The proton is
exported into the urine by secondary active transport in anti-port for Na+. The
driving force for proton excretion is Na+ gradient established by the Na+, K+ATPase. This integral membrane protein on the basal side (towards the blood) of
tubule cells keeps the Na+ concentration in the tubule cell low, thereby maintaining
Na+ inflow. In addition to this secondary active H+ transport mechanism, there is
a V-type H+-transporting ATPase in the distal tubule and collecting duct.
164
An important function of the secreted H+ ions is to promote HCO3- reabsorption.
Hydrogen carbonate, the most important buffering base in the blood, passes into
primary urine quantitatively, like all ions. In the primary urine HCO 3- reacts with
proton ion to form water and carbon dioxide, which returns by free diffusion to the
tubule cells and from there into the blood. In this way kidneys also influence the
CO2/HCO3- buffering balance in the plasma.
1
2
Figure 3. Sodium, bicarbonate ions reabsorption (1, 2) and phosphates buffering
(2) is in close relation to protons secretion.
Approximately 60 mmol of protons are excreted with urine every day. Buffering
systems in the urine catch a large proportion of H+ ions, so that the urine becomes
weakly acidic (down to about pH=4.8). An important buffer in the urine is the
hydrogen phosphate/dihydrogen phosphate system. The conversion of disubstituted
phosphates to mono substituted phosphates is in need to keep sodium ions and
calcium ions for human organism and to remove the accumulated protons from the
blood at acidosis state.
In addition, ammonia also makes a vital contribution to buffering the secreted
protons. Since plasma concentration of ammonia are low, the kidneys release
ammonia from glutamine due to glutaminase action and during oxidative
deamination of glutamate:
165
H 2O
Glutamine
Glytamic acid + NH3
Glutaminase
+
NAD
NADH+H
+
Alpha-ketoglutarate + NH3
Glutamate
Glutamate
dehydrogenase
+
H
+ NH3
NH4
+
Ammonia can diffuse freely into the urine through the tubule membrane while the
ammonium ions that are formed as charged particles and can no longer return to
the cell. Acidic urine therefore promotes ammonia excretion which is normally 3050 mmol per day.
At metabolic acidosis glutaminase activity usually is induced and ammonium ions
excretion is increased. At metabolic alkalosis renal excretion of ammonia is
reduced. But the production of the urea
The excess levels of hydrogen ions are considered at humans during starvation and
metabolic acidosis caused by the accumulation of some substances such as lactate,
pyruvate, some ketone bodies, amino acids and others. This condition causes the
stimulation of gluconeogenesis in kidney, and this way is considered as the way for
maintenance of acid-base balance, too. The synthesized glucose is very important
source of ATP (due to oxidative phosphorylation after glucose aerobic oxidation
way) that is used for the active transport mechanism.
METABOLIC PATHWAYS AND ENERGY FORMATION IN KIDNEY
The main energy sources are glucose, fatty acids, ketone bodies, some amino acids.
To a lesser extent lactate, glycerol, and citric acid are used. The endothelial cells in
the proximal tubule are capable of gluconeogenesis from amino acids mainly.
Amino groups of amino acids are used as ammonia for buffering of urine.
Enzymes for protein degradation and the amino acid metabolism occur in the
166
kidney at high levels of activity (amino acid oxidases, amino oxidases,
glutaminase). The most important metabolic pathways for kidney tissue are:
• Aerobic oxidation of monosacharides
• Gluconeogenesis
• Hexose Monophosphate Shunt
• Fatty acids oxidation
• Ketone bodies utilization
• Replication;Transcription;Translation
• Transport systems function in cellular membrane
• Antioxidant enzyme systems function
KIDNEYS AND HORMONES
Kidneys have also endocrine function (fig.4). They produce erythropoietin and
calcitriol and play a decisive part in producing the hormone angioteinsin II by
releasing the enzyme rennin.
The activity of calcidiol-1-monooxygenase (hydroxylase) is enhanced by the
hormone PTH. Calcitriol stimulates the resorption of both calcium and phosphates
ions in renal tubules. The proportion of Ca2+ resorbed is over 99%, while for
phosphate the figure is 80-90%. PTH stimulates resorption of Ca2+ but inhibits the
resorption of phosphate.
The erythropoietin is a peptide hormone that is formed predominantly by the
kidneys, but also by the liver. Together with colony-stimulating factors it regulates
the differentiation of stem cells in the bone marrow. Erythropoietin release is
stimulated by hypoxia. The hormone ensures that erythrocyte precursor cells in the
bone marrow are converted to erythrocytes, so that their numbers in the blood
increase. Renal damage leads to reduced erythropoietin release which in turn
results in anemia. Forms of anemia with renal causes can now be successfully
treated using erythropoietin produced by genetic engineering techniques. The
hormone is also administered to dialysis patients.
167
The angiotensin II (A-II) is not secreted by any hormonal gland, it is produced in
the blood from precursor angiotensin I secreted by kidney tissue. Angiotensin I is
produced from angiotensinogen (a plasma glycoprotein in the alpha-2-fraction
synthesized in the liver) due to enzyme rennin in kidney tissue. Angiotensin I is
cleaved by peptidyl dipeptidase A (a membrane enzyme located on the vascular
endothelium in the lungs and other tissues) to form octapeptide A- II. The plasma
level of A II is mainly determined by the rate at which rennin is released by
kidneys. The production of rennin by juxtaglomerular cells is when sodium ion
levels decline in blood plasma or there is a fall in blood pressure.
Erythropoietin
Bone marrow
Calcitriol
Vasopressin
Rennin
Hypophysis
GIT
Bone tissue
Renal tubules
PTH
I
Parathyroidal
gland
Aldosterone
Adrenal cortex
Blood
Angiotensin II
Angiotensin I
Angiotensinogen
Kidney
Figure 4.The role of kidney in hormonal regulation
A-II has effects on the kidneys, brain stem, pituitary gland, adrenal cortex, blood
vessel walls and heart via membrane-located receptors.
In the brain stem and at nerve endings in sympathetic nervous system the effects of
A-II lead to increased tonicity (neurotransmitter effect). In pituitary gland A-II
stimulates vasopressin and ACTH secretion. In adrenal cortex stimulation of
aldosterone synthesis and secretion.
All of the effects of angiotensin II lead directly or indirectly to increased blood
pressure as well as increased sodium ions and water retention. This important
168
hormonal system for blood pressure regulation may be pharmacologically
influenced by inhibitors at various points:
 using angiotensinogen analogs that inhibit rennin;
 using angiotensin I analogs that competitively inhibit peptidyl
dipeptidase A;
 using hormone antagonists that block the binding of A-II to its
receptors.
The regulation of sodium, potassium ions, chloride ions content and water volume
in the blood depends on the secretion of some hormones: Aldosterone, Atrial
natriuretic peptide, Vasopressin. Kidney is the main target for them. Controlled
resorption of sodium ions from primary urine is one of the most important
functions of the kidney. Sodium ion resorption is highly effective with more than
97% being resorbed. Several mechanisms are involved: some portion of Na+ ions
is taken up passively in the proximal tubule through the junctions between cells.
There is secondary active transport together with glucose and amino acids, too.
These two pathways are responsible for 60-70% of total Na+ resorption. In
ascending part of Henle`s loop there is another transporter which takes up one Na+
ion and one K+ ion together with two Cl- ions. This symport is also dependent on
the activity of Na+/K+-ATPase, which pumps the Na+ resorbed from primary
urine into the plasma in exchange for K+. This transport system is controlled by
aldosterone an atrial natriuretic peptide.
Water resorption in the proximal tubule is a passive process in which water follows
the osmotically active particles, particularly the Na+. Final regulation of water
excretion takes place in cells of distal tubules and the collecting ducts where the
peptide hormone vasopressin operates.
CLEARANCE OF KIDNEYS
Renal clearance is used as quantitative measure of renal function. It is defined as
plasma volume cleared of a given substance per unit of time. Inulin (fructose
polysaccharide with M=6 kDa) or creatinine is used for the determination of this
169
index. These organic compounds are not reabsorbed in kidneys, and ratio of their
content in the urine to the content in the blood plasma estimates the rate of
glomerular filtration in patient. The index is named as the clearance © of kidney.
You can see the formula of its determination:
C=
UCr * V
ml/min
PCr
UCr - concentration of Creatinine in the urine;
PCr - concentration of Creatinine in the blood plasm;
V -minute diuresis.
Normal clearance index in adults equals 120 ml/min. It is usually determined at
patients which may be potential donors of kidney; in a case of to choose the initial
dose of some toxic drug to treat patients.
INDEXES OF THE BLOOD PLASMA AND URINE TO ESTIMATE KIDNEY
FUNCTION
Creatinine and urea contents in the blood plasma are very important indexes for
glomeruli function estimation. There is the increase of both indexes in the blood
plasma at renal insufficiency in patients.
Urea, as you remember, is a relatively nontoxic substance made by the liver as a
means of disposing of ammonia from protein metabolism.
Urea has MW 60, of which 28 comes from the two nitrogen atoms. Normal blood
urea nitrogen is 8-25 mg/dL (2.9-8.9 mmol/L).
Blood urea levels are quite sensitive indicators of renal disease, becoming
elevated when renal function drops to around 25-50% of normal (remember the
kidney has great functional reserve).
Increased BUN is, by definition, azotemia. It is due either to increased protein
catabolism or impaired kidney function. Increased protein catabolism results from:

a really big protein meal

severe stress (myocardial infarction, high fever, etc.)

upper GI bleeding (blood being digested and absorbed)
170
Impaired kidney function may be "prerenal", "renal", or "postrenal". Prerenal
azotemia results from under-perfusion of the kidney: dehydration, hemorrhage,
shock, congestive heart failure; glomerulonephritis is likely also to be "prerenal" if
mild, since it comprises renal blood flow more than tubular function
Renal azotemia has several familiar causes: acute tubular necrosis, chronic
interstitial nephritis, some glomerulonephritis, etc.
Postrenal azotemia results from obstruction of urinary flow:

prostate trouble, stones, surgical mishaps, tumors .
In acute renal failure, BUN increases around 20 mg/dL each day .
ENZYMES OF BLOOD PLASMA AND URINE TO PROVE SOME
PATHOLOGIC STATES OF KIDNEY
The most active enzymes of kidney are involved in aerobic type of metabolic
processes to produce energy in a form of ATP, and the enzymes used for all type of
transport across the membranes of glomeruli, renal tubules cells.
Glycine amidinotransferase - (first enzyme from creatine synthesis). It is used in
diagnostic of kidney parenchyma damage (its activity is increased in the blood
serum).
N-acetyl-beta-D-glucosaminidase ("glucosaminidase", NAG) is a lysosomal
enzyme (MW 140,000) found in serum and urine. Urinary NAG is a proposed
marker for tubular disease, especially subtle industrial poisoning, acute
pyelonephritis, early acute tubular necrosis, and early transplant rejection.
Lactate dehydrogenase isozymes: In acute renal insufficiency the activity of
LDH1 and LDH2 is observed to increase. LDH1 and LDH2 isozymes are from renal
cortex.LDH4 and LDH5 isozymes found in kidney medulla.
Alanine aminopeptidase isozyme 3 (AAP3) in the blood plasma and urine is
observed as the specific sign of the affected kidney tissue.
Adenosine Deaminase Binding Protein is an enzyme from the brush borders of
the proximal tubule. Like NAG, its presence in urine indicates tubular disease.
171
Urinary alkaline phosphatase in urine comes from the proximal tubular brush
border, detects tubular necrosis too.
THE CHEMICAL COMPOSITION OF URINE OF HEALTHY ADULTS
Ions: Na+, K+. Ca2+, Mg2+, SO42-, HCO3 -, HPO42-, H2PO4-, PO43- and
1.
water.
2.
The main nitrogen-containing compounds are ammonia salts and
urea, other ones: uric acid, creatinine, amino acids, hippuric acid, stercobilin,
indican.
3.
Nitrogen free organic compounds such as acids: lactic, pyruvic,
citric, oxalic, acetoacetic, and others.
4.
Hormone derivatives such as 17-ketosteroids and others.
5.
Terminal products of xenobiotics transformation.
6.
Some vitamins and their derivatives.
THE PHYSICOCHEMICAL PROPERTIES OF THE URINE OF HEALTHY
AND DISEASED HUMANS
1. Diuresis (urine output)
It is the average volume of urine (ml) excreted by individual person under ordinary
dietary condition in 24 hours or per day. Normal diuresis: for men – 1500 ml/day;
for women – 1200 ml/day.
Polyuria state is indicated in patients when urine output is much higher than
normal (more then 3 L/day). It is considered at patients with chronic nephritis,
diabetes insipidus, chronic pyelonephritis.
Oligouria state is the diminished excretion of daily urine, and it is observed at
patients with febrile state, toxicosis, diarrhea, vomiting, and acute nephritis.
Anuria (nearly complete suppression of urinary excretion) is observed at patients:
1) under nervous shock; 2) at acute diffuse nephritis caused by poisoning with
lead, mercury or arsenic compounds.
172
2. The pH of urine
All the acids, ammonia salts and urea make special pH of urine; the average value
of it is about 5,3-6,5. The pH of urine depends on the diet of patient. Strong
vegetarians` urine in pH is higher then 6,5. After animal food intake the pH of
urine changes to value lower then 5, 3. The pH of urine may be decreased at
diabetes mellitus associated with ketoacidosis, at diseases accompanied with
extensive excretion of amino acids (aminoaciduria state). The alkaline urine is
observed in cystitis and pyelitis, at intake of some drugs, also as sequent to strong
vomiting. The pH of the urine is inversely proportional to the acidity of the urine .
3. The specific gravity of urine
The normal value must be in region 1,012 – 1,020 g/ml. The specific gravity of
urine may be very low (about 1,001-1,004 g/ml) in patients with diabetes insipidus.
At oligouria state it may be lower then normal, too. Polyuria state at patients with
diabetes mellitus may be accompanied with the increase of this index (higher then
1,020 g/ml) at the expense of glucose present in the urine.
4. The color of the urine
The urine of healthy humans is transparent, straw yellow or amber liquid. The
presence of pigments such as stercobilin, urochrome, uroerythrin gives those
colour for urine. Abnormal pigments observed in the urine at pathologic states can
change it to colour:
1)
dark (urobilin formed from excess urobilinogen that is not transformed in
the liver at liver parenchyma damage);
2)
green or blue (intensive putrefaction of proteins in the intestine causes the
accumulation of indoxyl sulpharic acid in the urine); uroglaucin at scarlatina state;
3)
dark brown like beer (there is the conjugated bilirubin presence in the urine);
4)
black (due to presence of homogentisic acid oxidation product at
Alkaptonuria state);
5)
red shade at presence of blood pigments, they include red blood cells
(hematuria state) and hemoglobin (hemoglobinuria state).These pigments are
observed at the damage of urinary tracts by kidney stones or at acute cystitis.
173
The urine may be not transparent when sediments are present in it. It may be at
pathologies associated with the damage of urinary tracts by kidney stones, with the
accumulation in the urine some salts (calcium oxalates), with the appearance of
epithelial cells in the urine and with excretes from vagina of women.
5. Special smell of the urine
The urine slight smell is associated with the presence of ammonia salts and urea in
it usually. But it may be changed at:
1) Maple syrup urine disease (like maple syrup odor);
2) Phenylketonuria (like mouse odor);
3) Intensive putrefaction of proteins in the intestine (the smell of rotten meat);
4) Glucosuria state at diabetes mellitus (special fruity odor);
5) The appearance of excretes from vagina of diseased women at pathologies
such as syphilis and gonorrhoea can also change the smell of the urine (like
the smell of rotten meat).
THE PATHOLOGICAL COMPONENTS OF THE URINE
Proteins of the urine
Proteins are found in minimal amounts (less 150 mg/day) in the urine of healthy
people and they can’t be detected by color reactions used for proteins. If the color
reaction for proteins is positive in the urine, this component is considered as
pathological and proves proteinuria state. This state is determined at patients with
acute glomerular nephritis; extra renal reasons: inflammation of urinary tracts,
affected prostate gland, at the burns and fever, at the trauma of urinary tract
(hemoglobinuria). Proteinuria state is accompanied with the change of
physicochemical properties of the urine: 1) hemoglobinuria is associated with
pink-red color of the urine; 2) the density of urine becomes higher then normal at
proteinuria state at the expense of proteins; 3) the urine has the big foam after
shaking.
174
Ketone bodies
In minimal amounts they are at healthy people but not detected by color reactions
in the urine. If the color reaction for ketone bodies in the urine is positive they are
considered as pathologic components. The high levels of them are accompanied
with long time starvation or with diabetes mellitus (severe form). The pH of urine
becomes lower then normal in this case.
Glucose
It is practically absent in the urine of healthy people, but is observed at patients
with diabetes mellitus (all types) when the levels of glucose in the blood are higher
then 9,5 mmole/L. Glucosuria state is observed in patients in this case. Polyuria
state in this case accompanied with the increase of urinary density (higher then
1,020 g/ml) at the expense of glucose present in the urine.
Bile pigments
Urobilin formed from excess urobilinogen and conjugated bilirubin are
pathological components and must be absent in the urine of healthy persons. Their
appearance in the urine first of all is the signal for the problems with liver function,
and is accompanied with the jaundice development in patient. The color of the
urine is changed at their presence (see above).
Creatine
It is practically absent in the urine of healthy adults, and is considered as
pathologic component. Creatine is determined in the urine at developed muscular
dystrophy in patients and at old people with the deficiency of motor function for
skeletal muscles in person.
175
EXERCISES FOR INDEPENDENT WORK. In the table with test tasks
emphasize keywords, choose the correct answer and justify it:
№
Test tasks:
1.
A 34-year-old patient was diagnosed
Explanations:
with chronic glomerulonephritis 3
years ago. Edema has developed
within the last 6 months. What
caused the edema?
A. Liver
dysfunction
of
protein
formation
B. Hyperosmolarity of plasma
C. Proteinuria
D. Hyperproduction of vasopressin
E. Hyperaldosteronism
2.
Examination of a 43 y.o. anephric
patient revealed anemia symptoms.
What
is
the
cause
of
these
symptoms?
A. Folic acid deficit
B. Vitamin B12 deficit
C. Reduced
synthesis of erythro-
poietin
D. Enhanced
destruction
of
erythrocytes
E. Iron deficit
3.
A biochemical urine analysis has
been performed for a patient with
progressive muscular dystrophy. In
the given case muscle disease can be
176
№
Test tasks:
Explanations:
confirmed by the high content of the
following substance in urine:
A. Urea
B. Porphyrin
C. Hippuric acid
D. Creatine
E. Creatinine
4.
Kidney insufficiency in patient is
accompanied with:
A. Excess levels of urea in the blood
plasma
B. Excess levels of potassium ions
in the blood plasma
C. Disturbed clearance
D. Disturbed filtration and
reabsorption processes
E. All that is placed above
5.
Point out the most important
compensatory mechanism in
metabolic acidosis:
A. Hyperventilation
B. Increased NH3 excretion by
kidneys
C. Increased filtration of phosphates
D. Increased HCO3- production
E. Urea production in the liver
6.
Point out main source of ammonia
in kidney tissue:
177
№
Test tasks:
Explanations:
A. Urea
B. Aspartate
C. Glutamine
D. Glutamate
E. Uric acid
7.
Choose normal amount of proteins
excreted in urine/24 hours:
A. Less than 150 mg
B. 200 mg - 225 mg
C. 450 mg – 500 mg
D. More than 800 mg
E. 150 mg – 250 mg
8.
Name organic compound which is
terminal for humans and not
reabsorbed in renal tubules:
A. Globulins
B. Glucose
C. Albumin
D. Creatinine
E. Bilirubin
9.
Choose the specific gravity region
(g/ml) for urine of healthy person:
A. 1.005-1.015
B. 1.030-1.040
C. 1.015-1.020
D. 1.030-1.040
E. Less then 1.010
178
№
Test tasks:
Explanations:
10. Creatinine levels in the urine and
blood are used to test kidney
function. Creatinine is useful for this
test because it is not significantly
reabsorbed nor secreted by kidney,
and metabolically it is:
A. Produced at a constant rate
B. Produced only in kidney
C. A storage form of energy
D. An acceptor of protons in renal
tubules
E. A precursor for phosphocreatine
11. Appearance of albumins in the urine
of diseased person may be at:
A. Acute nephritis
B. Chronical nephritis
C. Severe form of diabetes
mellitus
D. Pyelonephritis
E. All that is placed above
12. Choose the main biochemical tests
for diagnostics of kidney diseases:
A. Urea content in the blood
plasma and in the urine
B. Creatinine content in the blood
179
№
Test tasks:
Explanations:
and urine
C. Sodium ions content in the
blood and urine
D. N-acetyl-beta-D-glucoseaminidase activity (blood serum,
urine)
E. All that is placed above
13. What organic compounds
accumulate in final urine at severe
form of diabetes mellitus?
A. Albumins
B. Glucose
C. Ketone bodies
D. Bilirubin conjugated
E. All that is placed in positions A,
B, C
14. Kidney insufficiency development
will cause the infringements in those
processes:
A. Erythropoietin synthesis and
secretion
B. Calcitriol synthesis
C. Mineralization of bone tissue
D. Creatine synthesis
E. All that is placed
180
№
Test tasks:
15. The infringement
Explanations:
in glomerular
filtration mostly is associated with
appearance in the urine of this class
compounds. Name it:
A. Lipids
B. Proteins
C. Amino acids
D. Keto acids
E. Carbohydrates
16. Renal clearance may be calculated
using this compound concentration
value in the blood serum and in
urine of patient. Name it:
A. Inulin
B. Creatine
C. Free ammonia
D. Ammonia salt
E. Indican
17. Utilization of excess protons in renal
tubule lumen may be due to:
A. Aspartic acid
B. Creatinine
C. Uric acid
D. Ammonia
E. Water
181
№
Test tasks:
Explanations:
18. This compound impossible to find
out in the urine of healthy person:
A. Globulin
B. Alanine
C. Pyruvate
D. Oxaloacetate
E. Carbonic acid
19. Acute tubular necrosis is associated
with increase of this index in the
blood serum of patient. Name it:
A. Creatine
B. Free amino acids
C. Pyruvate
D. Cholesterol total
E. Urea
20. This vitamin derivative is produced
in renal tubules mainly to control
calcium ad phosphate ions levels in
the blood. Name it:
A. FAD
B. NAD+
C. Calcitonin
D. Calcitriol
E. Angiotensin II
182
LITERATURE
Basic:
1. Berezov T. T. Biochemistry : translated from the Russian / T. T. Berezov, B. E.
Korovkin. - М. : Mir, 1992. - 514 p.
2. Ferrier D. R. Biochemistry : Lippincott illustrated reviews / D. R. Ferrier ; ed.
by.: R. A. Harvey. - 6th ed. - India : Lippincott Williams & Wilkins, 2015. 560 p.
3. Murray R. K. Harper's Illustrated Biochemistry / R. K. Murray, D. K. Granner,
V. W. Rodwell. - 27th ed. - Boston [etc.] : McGraw Hill, 2006. - 692 p.
4. Satyanarayana U. Biochemistry : with clinical concepts & case studies / U.
Satyanarayana, U. Chakra Pani. - 4th ed. - India : Elsevier, 2015. - 812 p.
Additional:
1.
Deitmer J. W. Strategies for metabolic exchange between glial cells and
neurons / J. W. Deitmer // Respir. Physiol. – 2001. – N 129. – P. 71-81.
2.
Hames D. Instant Notes in Biochemistry / D. Hames, N. Hooper. – [2nd ed.].
– UK : BIOS Scientific Publishers Ltd, 2000. – 422 p.
3.
Hertz L. Intercellular metabolic compartmentation in the brain: past, present
and future / L. Hertz // Neurochemistry Int. – 2004. – N 2-3. – P. 285-296.
4.
Jurcovicova J. Glucose transport in brain - effect of inflammation / J.
Jurcovicova // Endocr. Regul. – 2014. – Vol. 1. – N. 48. P. 35-48.
5.
Koolman J. Color Atlas of Biochemistry: textbook / J. Koolman, K.-H.
Roehm. – 2nd ed. – Stuttgart-New York : Thieme, 2005. – 467 p.
6.
Kutsky R. J. Handbook of vitamins, minerals, and hormones / R. J. Kutsky.[2nd ed.]. - New York : Van Nostrand Reinhold, 1981. – 492 p.
7.
Lieberman M. Medical Biochemistry: textbook / M. Lieberman; A. Marks, C.
Smith. - 2nd ed. - New York : Lippincott Williams & Wilkins, 2007. – 540 p.
8.
Marks D. B. Biochemistry: The Chemical Reactions of Living Cells / D. B.
Marks, D. Metzler - [2nd ed., vol. 1,2] - USA : Elsevier Academic Press,
1994.- 1974 p.
183
9.
Marshall J. W. Clinical Chemistry : textbook / J. W. Marshall, S. K. Bangert.Fifth edition. – China : Mosby, 2004. – 422 p.
10. Molecular Biology of the Cell / B. Alberts [et al]. – [6th ed.]. – NY : Garland
Science, 2015. – 1465 p.
11. Newsholme E. A. Functional Biochemistry in Health and Disease / E. A.
Newsholme, T. R. Leech. - UK : John Wiley & Sons Ltd, 2010.-543 p.
12. Smith C. Basic Medical Biochemistry: A Clinical Approach: textbook / C.
Smith, A. Marks, M. Lieberman. - 2nd ed. - New York : Lippincott Williams
& Wilkins, 2009. - 920 p.
184
ANSWERS TO TESTS TASKS:
The role of water-soluble and fat-soluble vitamins in the metabolism of humans.
Vitamin similar substances. Antivitamins
1
2
3
4
5
6
7
8
9
10
E
C
B
B
C
A
E
A
C
A
11
12
13
14
15
16
17
18
19
20
A
A
A
D
C
A
E
E
E
D
21
22
23
24
25
26
27
28
29
30
C
B
D
B
A
C
E
E
A
A
31
32
33
34
35
36
37
38
39
40
A
A
D
E
A
E
B
D
B
C
Biochemistry of muscular and connective tissues
1
2
3
4
5
6
7
8
9
10
B
A
B
D
B
D
E
C
E
A
11
12
13
14
15
16
17
18
19
20
D
A
A
B
A
A
E
C
A
E
Biochemistry of nervous tissue
1
2
3
4
5
6
7
8
9
10
A
B
D
C
B
A
D
B
D
A
11
12
13
14
15
16
17
18
19
20
C
B
B
C
B
D
A
C
A
A
Biochemical functions of the liver at healthy and diseased people
1
2
3
4
5
6
7
8
9
10
D
D
B
E
C
D
A
C
E
C
11
12
13
14
15
16
17
18
19
20
B
A
C
A
B
B
D
D
A
C
185
Xenobiotic transformation in humans. Microsomal oxidation
1
2
3
4
5
6
7
8
9
10
A
D
A
C
C
E
E
B
A
A
11
12
13
14
15
16
17
18
19
20
C
D
E
D
D
B
E
C
D
A
Biochemistry of blood tissue. Proteins of blood plasma. Non-Protein components
of blood plasma at healthy and diseased people
1
2
3
4
5
6
7
8
9
10
E
B
E
B
E
A
A
C
B
C
11
12
13
14
15
16
17
18
19
20
D
C
A
D
D
D
A
A
A
C
21
22
23
24
25
26
B
D
B
A
A
A
ANSWERS TO TESTS TASKS:
The role of kidneys in the regulation of water and salts metabolism. The normal
and pathological components of urine
1
2
3
4
5
6
7
8
9
10
C
C
D
E
B
C
A
D
C
A
11
12
13
14
15
16
17
18
19
20
E
E
E
E
B
A
D
D
E
D
186
CONTENT
Introduction…………………………………………………………………...
3
The role of water-soluble and fat-soluble vitamins in the metabolism of
humans. Vitamin similar substances. Antivitamins ...................................
4
Biochemistry of muscular and connective tissues……………………......
28
Biochemistry of nervous tissue.................................................................
61
Biochemical functions of the liver at healthy and diseased people..................
83
Xenobiotic transformation in humans. Microsomal oxidation…………….…
108
Biochemistry of blood tissue. Proteins of blood plasma. Non-Protein
components of blood plasma at healthy and diseased people.....................
131
The role of kidneys in the regulation of water and salts metabolism. The
normal and pathological components of urine..................................................
162
Literature..........................................................................................................
183
Answers to tests tasks………………………………………………………...
185
187