Download chemical coordination and integration

CHemical coordination and Integration
CHEMICAL COORDINATION
AND
INTEGRATION
Chapter Outline
•
•
•
•
•
•
•
•
Introduction
Prerequisites
Learning objectives
Endocrine Glands and Hormones
Human Endocrine System
Hormones of Heart, Kidney and Gastrointestinal Tract
Mechanism of Hormone Action
Summary
www.sciencetuts.com
CHemical coordination and Integration
Introduction
Let us take one example to understand what is co-ordination and its importance. We are
familiar with team games – hockey, foot ball or cricket. For a team to be successful and win
the match, all the players in the team should play properly in their assigned positions in the
field and should follow the instructions of captain. They should co operate with other members
of their team. Instead, if each member of the team plays the game in his own way without
bothering about other players and ignoring the instructions of their captain the team will loose
the game and will never be winners. For a team to be successful and survive, the captain
should co-ordinate the game of all players of the team and the members of the team should cooperate and co-ordinate with each other. The same rule may also be applied for the functioning
of our body.
Prerequisites
In multi cellular organisms, there are several organs and organ systems. When all the organs
and organ system work independent of each other, then the organism may not live long. For
example, our eyes, ears, legs should coordinate with each other, when we are crossing a
street. Otherwise, we may hit another person on the street or even come in the way of a vehicle
and this may have serious consequences.
Similarly, when we are running, our leg muscles require more glucose and oxygen while our
stomach muscles do not require them in large amounts. If the blood is diverted more to stomach
and less to the muscles while you are running, our leg muscles will fatigue and we get tired
very soon. More over the supply of oxygen and glucose should be brought back to normal level
once we stop running. This requires co-ordinate effort between heart, liver, blood vessels, brain
and muscles.
All these examples indicate that to respond to a stimulus, functions of many organs must be
considered. Some of the responses are quick and some are very slow. Thus in living organism
there is finely tuned co ordination to respond to the environmental changes and to carry out
specific functions at a specific time in the life cycle. The functions of organisms are in harmony.
This harmony is maintained through perfect control system.
The neural system provides a rapid co-ordination among organs. Which is fast but short lived.
As the nerve fibres do not innervate all the cells of the body, a special kind of co-ordination
and regulation is provided. This function is carried by hormones. The neural system and the
endocrine system jointly co-ordinate and regulate the physiological functions in the body.
2
www.sciencetuts.com
CHemical coordination and Integration
Learning objectives
1.
2.
3.
4.
5.
To identify the location of different endocrine glands in the body.
To recognize the role of hormones.
To know the mechanism of hormone action.
To differentiate between endocrine system and Nervous system.
To compare endocrine and exocrine glands.
Endocrine Glands and Hormones
Glands are specialized tissues which secrete chemicals. Depending on how they release the
chemicals substances. Glands are of two types – Exocrine glands and Endocrine glands.
Endocrine glands
Have no ducts – so these are called as ductless glands. These glands secrete chemical
substances called HORMONES directly into blood. Blood carries hormones to all organs in the
body. Hormones act on the cells of other organs and increase or decrease the metabolism of
carbohydrates, proteins and lipids. They make the cells to synthesize new proteins or make
cells of the body to grow. They may even act on other endocrine glands and control their
function.
Tissues or organs on which hormones act are called TARGET TISSUES or ORGANS. Some
hormones have different effects on different tissues. Similarly, different hormones may act on
one target tissue. Hormones act at very specific sites in the body. Very small amount of hormone
(1/10, 00, 000 of a gram or even less) brings out large changes in the target tissue. Thus
hormones act as chemical messengers and trigger the chemical and physiological processes
of target cells. They are slow in action. Their deficiency and excess are harmful, often leading
to serious disorders.
3
www.sciencetuts.com
CHemical coordination and Integration
DIFFERENCE BETWEEN EXOCRINE AND ENDOCRINE GALANDS
ENDOCRINE GLANDS
EXOCRINE GLANDS
1
The glands are devoid of ducts
The glands possess ducts
2
They occur in isolation They do not occur in isolation
3
Their secretions are poured into
circulatory system
The glands pour their secretion over
target directly or through ducts
4
The target site is far away from
its endocrine gland
Target site is adjacent to the gland
5
Secretions consists of hormones
Secretions are enzymes, mucus,
lubricants excretory substances.
Endocrine system is also called hormonal system. Branch of science that is connected with the
study of endocrine glands, hormones and their effects is known as Endocrinology. Endocrine
system often operates in co-ordination with nervous system. In many cases nervous system
stimulates components of endocrine system. Nervous system is fast and is connected to
receptors as well as effectors. However the effect cannot reach every cell of the body. Endocrine
system is slower but influences all the cells of the target.
DIFFERENCE BETWEEN ENDOCRINE AND NERVOUS SYSTEM
ENDOCRINE SYSTEM
NERVOUS SYSTEM
1
Passage of information is through
chemicals like hormones
It is through electro-chemical
conduction
2
Sensory receptors are absents
Present
The system is slower
Fast
4
The system is not connected to the
target sites directly
The system is directly connected to
every part under its control
5
The response is slow of longer duration
produced by all cells of target tissues
The response is quick, of short duration and
limited to those cells that are innervated
3
6
The system controls growth and
development
It has no role in growth and development
4
www.sciencetuts.com
CHemical coordination and Integration
Human Endocrine System
Endocrine glands are present in different parts of the body. Pituitary, pineal, thyroid, adrenal, pancreas,
parathyroid, thymus and gonads are the organized endocrine glands in our body. In addition to these –
Gastrointestinal tract, liver, kidney, heart also produce hormones.
1. HYPOTHALAMUS
It lies at the floor of diencephalon. It regulates many body functions. It contains several groups of
neurosecretory cells which produce hormones. These hormones regulate the synthesis and secretion
of pituitary hormones (Fig 22.1). The hormones produced by hypothalamus are of 2 types. The
releasing hormones and the inhibiting hormones. Example: hypothalamic hormone called Gonadotropin
releasing hormone (GRH) stimulates pituitary synthesis and release of gonadotropins. Somatostatin
from hypothalamus inhibits the release of growth hormone from pituitary. These hormones originating
in the hypothalamic neurons pass through axons and are released from their nerve endings. These
hormones reach the pituitary gland through a portal circulatory system and regulate the functions of
anterior pituitary. The posterior pituitary is under the direct neural regulation of hypothalamus.
w
Pineal
Hypothalamus
Pituitary
Thyroid and Parathyroid
Thymus
Pancreas
Adrenal
Testis (in male)
Ovary (in female)
Location of endocrine glands
2. PITUITARY GLAND
Is very small. The size of a large pea seed. But it is
a very important gland and it controls the functions
of all the other endocrine glands in the body. It is
therefore called as MASTER GLAND of body. The
pituitary gland is located in a bony cavity called sella
tursica and is attached to hypothalamus by a stalk. It
has 3 parts – Anterior, middle and posterior. Posterior
lobe of pituitary is called Neurohypophysis while
anterior and middle pituitary lobes are collectively
called adenohypophysis.
Hypothalamus
Hypothalamic
neurons
Portal
circulation
Anterior
pituitary
Posterior pituitary
Pituitary gland
5
www.sciencetuts.com
CHemical coordination and Integration
A. ANTERIOR PITUITARY
I. Growth Hormone or Somatotropic Hormone (GH or STH)
The hormone stimulates body growth by increased anabolic activity, retention of calcium, synthesis of
more proteins, enlargement of long bones, muscles and visceral organs. Increased secretion produces
Gigantism (height above 2.15m) while deficient secretion produces Dwarfism (height 1.0-1.3m).
Excessive secretion of hormone in an adult causes Acromegaly (increase in size of bones of hand, feet
and face)
II. Prolactin: (Maternity hormone) It stimulates growth of mammary glands during pregnancy and
lactation afterwards.
III. Thyroid stimulating Hormone (TSH). It stimulates thyroid to produce and release its hormones.
IV. Adenocorticotropic Hormone : (ACTH) It activates adrenal cortex to produce its hormones.
V. Follicle stimulating hormone (FSH). It stimulates sperm formation in males, growth of ovarian
follicles and secretion of estrogens from them in females.
VI. Luteinisisng Hormone (LH) In females the hormone stimulates ovulation and secretion and
secretion of progesterone from corpus luteum. In males the hormones is also called interstitial cell
stimulating hormone (ICSH). It induces leyding cells of tests to secrete testosterone.
B. Middle lobe of pituitary
Melanocyte stimulating hormone (MSH). The hormone causes dispersal of melanin or pigment granules
in chromatophores causing darkening of skin.
C. Posterior lobe of pituitary
It produces two hormones which are actually neurosecretion products of hypothalamus.
I. Oxytocin: The hormone stimulates uterine contractions during child birth and milk ejection during
suckling of infant. Oxytocin is also called birth hormone and milk ejection hormone. Milk secretion is
under control of prolatcin.
II. Vasopressin or Antidiuretic Hormone (ADH). It is essential for reabsorption of water from distal
convoluted tubules, collecting tubules and collecting ducts for producing concentrated urine. Deficiency
of hormone causes disorder known as Diabetes insipidus. It produces a lot of urine (more than 1.5
Litres/day) at short intervals resulting in excessive thirst and dehydration.
At high concentration the hormone raises blood pressure (B.P) by causing constriction of arterioles.
3. PINEAL GLAND
It is a small stalked body located on the dorsal side of forebrain. The gland secretes hormone called
melatonin. It controls mood, sleep, regulates sexual cycle, body temperature. It also influences
metabolism, pigmentation, the menstrual cycle as well as our defense capability.
4. THYROID GLAND
It is the largest endocrine gland which is attached to trachea below larynx. It is bilobed or H-shaped.
Thyroid secretes thyroxin. Iodine is required for the production of this hormone. The thyroid gland is
composed of follicles and stromal tissues. Each thyroid follicle is composed of follicular cells, enclosing
a cavity. These follicular cells synthesise two hormones tetraiodothyronine or thyroxine (T4) and Triiodothyronine (T3).
6
www.sciencetuts.com
CHemical coordination and Integration
Deficiency of dietary iodine causes enlargement of thyroid which results swelling of neck. This disorder
due to hypothyroidism is called goitre. Hypothyroidism during pregnancy causes defective development
and maturation of growing baby leading to stunted growth (cretinism), mental retardation, low intelligence
quotient, abnormal skin, deaf-mutism etc. in adult women, hypothyroidism may cause irregular menstrual
cycle, myxedema or puffiness.
Due to cancer of thyroid gland or due to the development of nodules of thyroid glands, the rate of
synthesis and secretion of the thyroid hormones is increased to abnormal high levels leading to a
condition called hyperthyroidism which adversely affects body physiology. It also leads to protrusion of
eyes or exophthalmia, high metabolic rate and leanness. Common salt is compulsorily iodised
(with K i ) (potassium iodide) to provide required iodine to thyroid.
Thyroxine controls Basal Metabolic Rate (BMR). It
determines the consumption of energy, tendency
of the body to gain weight, physical activity, body
temperature, heart physical development, mental
development, muscular activity, nervous activity and
sexual development. The hormones also support
Thyroid
the process of RBC. It controls the metabolism of
carbohydrates, proteins and fats. Maintenance of water
and electrolyte balance is also influenced by thyroid
Trachea
hormones. Thyroid gland also secretes a protein
hormone called thyrocalcitonin (TCT) which regulates
the blood calcium levels.
5. PARATHYROID GLAND
Thyroid and Parathyroid
(a) Dorsal side
Four parathyroid glands are present on the back side of thyroid gland, one pair each in the 2 lobes of
the thyroid gland. The glands secrete parathormone. The hormone maintains optimum level of blood
calcium and phosphorus by reducing their excretion and mobilization from bones when required.
Parathyroid hormone increases the calcium levels in the
blood. PTH acts on bones and stimulates the process
of bone re absorption. It also stimulates reabsorption
of ca2+ by renal tubules and increases ca2+ absorption
from digested food. PTH is hyper calcemic hormone.
I.e. it increases the blood ca2+ levels. Along with
thyrocalcitonin (TCT), it plays a significant role in calcium
balance in the body. It is essential for proper functioning
of nerves and muscles. If sufficient amounts of this
hormone are not produced bones loose calcium and
become soft. If the hormone is in large quantities, the
muscles become very active and remain in contracted
state – a condition called Tetany.
7
Parathyroid
Thyroid and Parathyroid
(b) Ventral side
www.sciencetuts.com
CHemical coordination and Integration
6. THYMUS
Thymus gland is a soft, pinkish, lobular structure
located on the dorsal side of the heart and aorta.
The thymus plays a major role in the development
of immune system. This gland secretes a peptide
hormone called thymosins. Thymosin play a major role
in the differentiation of T- lymphocytes, which provide
cell – mediated immunity. The size is maximum during
puberty but begins to shrink and becomes microscopic
in old age. Thymus is degenerated in old individuals
resulting in decreased production of thymosins. As a
result, the immune responses of old persons become
weak.
Thymus
Thymus
7. ADRENAL GLAND
They are a pair of yellowish, flat, pyramid like glands which lie over the upper end of the kidneys. They
look like a cap on the kidney. Each gland has an outer yellow adrenal cortex and inner reddish brown
adrenal medulla.
Adrenal Medulla : secretes 2 hormones called adrenaline or epinephrine and non adrenaline or non
epinephrine. These are commonly called catecholamines.
In conditions of physical and mental stress – such as fall in blood sugar levels or when a person is
injured or exposed to cold conditions or suffering with pain. It is also secreted during anger, fear or grief.
It helps the body to face these conditions.
It is therefore called Emergency hormone or Fight hormone or 3F-hormone (Fight, fright and flight).
These hormones increase alertness, pupilary dilation, raising of hairs, sweating etc. These hormones
increases blood supply to heart and skeletal muscles. It constricts arterioles and blood supply to skin
and gastrointestinal tract. The bronchioles dilate. There is increased rate of breathing, oxygenation and
heart beat to meet any emergency. Catecholamines stimulate the breakdown of glycogen resulting in
increased concentration of glucose in blood. They also stimulate the breakdown of lipids and proteins.
Adrenal cortex : can be divided into 3 layers called zona reticularis (inner layer)
Zona fasiculata (middle layer)
Zona glomerulosa (outer layer)
Adrenal cortex secretes many hormones called corticoids
Adrenal Cortex
Adrenal
gland
(A)
Adrenal
Medulla
Kidney
Adrenal gland & Kidney
(B)
Parts of Adrenal gland
8
www.sciencetuts.com
CHemical coordination and Integration
a) Gluco corticoids : involved in carbohydrate metabolism. E.g. cortisol.
b) Mineralo corticoids : corticoids which regulate the balance of water and electrolytes in our body.
Eg: Aldosterone.
Gluco corticoids stimulate – gluconeogenesis, lipolysis and proteolysis and inhibit – cellular uptake and
utilization of amino acids. Cortisol is also involved in maintaining the cardiovascular system and kidney
functions. It also produces anti inflammatory reactions and suppresses the immune response. Cortisol
stimulates RBC production. Aldosterone acts at renal tubules and stimulates reabsorption of Na+ and
water and excretion of K+ and Po4 . Thus aldosterone helps in the maintenance of electrolytes, body
fluid volume, osmotic pressure and B.P. Small amounts of androgenic steroids are also secreted by
adrenal cortex which play a role in the growth of axial hair, pubic hair and facial hair during puberty.
8. PANCREAS
Pancreas is a mixed gland – A portion of pancreas
acts like exocrine gland and another portion acts like
an endocrine gland. The cells of endocrine pancreas
are called Islets of Langerhans representing 1 to 2% of
pancreatic tissue. They secrete 2 hormones – Insulin
and Glucagon.
I. Insulin
β-cells
α cells
Pancreas
The hormone is produced by β-cells of Islet of Langerhans. It is a peptide hormone, which plays a major
role in the regulation of glucose homeostasis. Insulin promotes the conversion of glucose to glycogen in
liver and muscle that is stored in these tissue for future use. Insulin is liberated when the blood glucose
levels are high, usually when food is digested and absorbed. If sufficient insulin is not produced glucose
level in blood increases and it is excreted through urine. This is called
DIABETES MELLITUS. Diabetes is identified by the presence of sugar in urine. Diabetic patients take
insulin injections regularly. Insulin also affects the metabolism of fats and proteins. Un attended diabetis
results in wasting of body tissue, reduced healing power, ketone bodies, blurred vision and kidney
problems. They may end up with gangrene and coma.
II. Glucagon
Is a peptide hormone secreted by α cells of islets of Langerhans. Glucagon acts on liver cells and
stimulates glycogenolysis resulting in an increased blood sugar – hyperglycemia. This hormone
stimulates the process of gluconeogenesis which also contributes to hyperglycemia. Glucagon reduces
the cellular glucose uptake and utilization. Thus glucagon is hyperglycemic hormone.
9. GONADS
A. Testic
Leyding cells of testes produce male sex hormone called TESTOSTERONE and ANDROGENS.
Androgens regulate the development, maturation and functions of male accessory sex organs like
epididymis, vas deferens, seminal vesicles, prostrate gland, urethra etc. These hormones stimulate
muscular growth , growth of facial and axillary hair,aggressiveness low pitch of voice etc. Androgens
play a major stimulatory role in the process of spermatogenesis. Androgens act on the central neural
system and influence the male sexual behaviour.
9
www.sciencetuts.com
CHemical coordination and Integration
These hormones produce anabolic effects on protein
and carbohydrate metabolism. The Leutinizing
hormone promotes the secretion of testosterone. In the
absence of testosterone, these male characters will
not develop and such a condition is called ENUCHISM.
B. Ovary
Testis
ovary is the primary female sex organ which produces
one ovum during each menstrual cycle. Ovary produces
two groups of steroid hormones called estrogen and
progesterone. Ovary is composed of ovarian follicles
and stromal tissues. The estrogen is synthesized
and secreted mainly by the growing ovarian follicles.
After ovulation, the ruptured follicle is converted to a
structure called corpus luteum which secretes mainly
progesterone.
Testis
Ovary
Ovary
Estrogens produce actions such as stimulation of growth and activities of female secondary sex organs,
development of growing ovarian follicles, appearance of female secondary sex characters, mammary
gland development, estrogens also regulate female sexual behavior.
Progesterone supports pregnancy. Progesterone also acts on mammary glands and stimulates the
formation of alveoli and milk secretion.
Hormones of Heart, Kidney and Gastrointestinal Tract
1. Heart
Atrial wall of heart secretes peptide hormone called
Atrial natriuretic factor (ANF) which decreases B.P
when B.P is increased. ANF is secreted which causes
dilation of blood vessels. This reduces B.P.
Heart
2. Kidney
The juxtaglomerular cells of kidney produce 2
hormones erythropoietin (stimulates bone marrow
to produce more RBC’s) and Renin acts on protein
angiotensinogen to form angiotensin. Angiotensin
raises B.P to increase ultra filtration.
Kidney
10
www.sciencetuts.com
CHemical coordination and Integration
3. Gastro – intestinal Tract
Endocrine cells present in different parts of gastro
intestinal tract secrete 4 major peptide hormones.
1) Gastrin : acts on gastric glands and stimulates the
secretion of Hcl and pepsinogen.
2) Secretin : acts on exocrine pancreas and stimulates
secretion of water and bicarbonate ions.
3) Cholecystokinin : acts on both pancreas and gall
bladder and stimulates the secretion of pancreatic
enzymes and bile juice.
4) Gastric inhibitory peptide : inhibits gastric
secretion and motility. Several non endocrine tissues
secrete hormones called growth factors.
These factors are essential for normal growth and
tissues and their repairing / regeneration.
Gastro – intestinal Tract
MECHANISM OF HORMONE ACTION
Hormones produce their effects on target tissues by binding to specific proteins called hormone
receptors located in the target tissues only. Hormone receptors present on the cell membrane of the
target cells are called membrane bound receptors and the receptors present inside the target cell are
called intercellular receptors, mostly nuclear receptors. Binding of a hormone to its receptors leads to
the formation of a hormone receptor complex. Each receptor is specific to one hormone only and hence
receptors are specific. Hormone – Receptor complex formation leads to certain biochemical changes in
the target tissues hence physiological functions are regulated by hormones which can be divided into
groups.
I.
Peptide, polypeptide, protein hormones (insulin, glucagon, pituitary hormones,
hypothalamic hormones etc)
II. Steroids (cortisol, testosterone, estradiol and progesterone)
III. Iodohyronines – thyroid hormones.
IV. Amino acid derivative – epinephrine.
Hormones which interact with membrane bound receptors normally do not enter the target cell,
but generate second messengers. (eg. Cyclic AMP, Ip3, Ca++ etc) which in turn regulate cellular
metabolism.
Hormones which interact with intra cellular receptors (steroid hormones, iodothyronines etc). mostly
regulate gene expression or chromosome function by the interaction of hormone – receptor complex
with genome. Cumulative biochemical actions result in physiological and development effects.
11
www.sciencetuts.com
CHemical coordination and Integration
Hormone(e.g FSH)
Receptor
Ovarian cell membrane
Response 1
Generate second messengers .
Cyclic AMP or Ca++
Biochemical responses
(A) Protein hormone
Physiological responses
(e.g., ovarian growth)
Uterine cell membrane
Hormones
(e.g., estrogen)
Nucleus
Genome
Proteins
Receptor-hormone
complex
physiological responses
(Tissue growth and differentiation)
(B) Steroid hormone
The mechanism of hormone action
12
www.sciencetuts.com
CHemical coordination and Integration
Summary
The endocrine glands secrete chemical substances called hormones which are released directly into
blood. The hormones provide chemical co-ordination, integration and regulation in the human body.
They regulate metabolism, growth and development of our organs. The endocrine system consists of
hypothalamus, pituitary, pineal, thyroid, parathyroid, thymus, Adrenal, pancreas and Gonads. Apart
from these, heart, kidney and gastro intestinal tract also produce hormones. Pituitary hormones
regulate growth and development of somatic tissues. Pineal body secretes melatonin and plays
important role in regulation of 24 hrs rhythms of our body. Thyroid helps in regulation of BMR (basal
metabolic rate), development and maturation of CNS, erythropoiesis, metabolism of carbohydrate,
proteins and fats menstrual cycle. Parathyroid hormone increases calcium levels and helps in ca lcium
homeostasis. Thymus gland secretes thymosins which helps in differentiation of T-lymphocytes and
provide cell mediated immunity. Adrenal gland consists of medulla and cortex. Adrenal medulla secretes
epinephrine and norepinephrine. These hormones increase alertness, pupilary dilation, sweating, heart
beat ,strength of heart contraction, rate of respiration, etc. Adrenal cortex secretes gluco corticoids and
mineralocorticoids. Glucocorticoids stimulate gluconeogenesis, B.P, erthropoiesis etc. Minerocorticoids
regulate water and electrolyte contents of the body. Pancreas secrete glucagon and insulin. Glucagon
stimulate glycogenolysis and gluconeogenesis resulting in hyperglycemia. Insulin deficiency results in
diabetes mellitus.
Testis secrete androgens which stimulate the development, maturation and functions of secondary
sexual characters in males. Ovary secretes estrogen and progesterone. Estrogen stimulates development
of secondary sexual organs in female. Progesterone play a role in maintenance of pregnancy,
mammary gland development and lactation. Atrial wall of heart produces ANF which decreases B.P.
kidney produces erythropoietin which stimulates erythropoiesis. Gastro intestinal tract secretes gastrin,
secretin, cholecystokinin and gastric inhibitory peptide. These hormones regulate the secretion of
digestive juices and help in digestion.
13
www.sciencetuts.com