Download Metabolism

METABOLISM
© Katarína Babinská, MD, PhD, MSc., Institute of Physiology, 2016
fuel – function – end products
• Food – „fuel for the body“
• GIT – brak down of the sunstances in food into simple,
absorbable molecules
 enter metabolic reactions – in the cells
= utilization of substances from food
METABOLISM
- chemical reactions within in
the cells of the body
- enzyme catalyzed reactions
Two aspects of metabolism
• chemical conversion of
substances for tissue synthesis
and operation of the body (e.g.
enzymes, hormones)
energy
A+B
C
• conversion of chemical energy
provided by chemical bonds of
nutrients into energy utilizable in
cells (ATP and other high
energy bonds) and its
utilization for vital functions
catabolism – „energy yielding metabolism“
– breakdown of substances (e.g.fat or glycogen stores in the body)
– energy (of the chemical bonds) is released in form of
• chemical energy - utilized for body functions (max 27 %)
• heat – maintenance of the constant body temperature
– required for homeostasis and normal
operation of metabolic functions
anabolism – „biosynthetic metabolism“
– utilisation of the available substrates for synthesis
(glycogen, structural proteins, hormones, enzymes, bone tissue, etc.)
– energy consumption
- both anabolism and catabolism occur continuously in changing proportion
- e.g. building up the body protein (anabolism) requires energy derived in catabolic processes
- depending on which processess prevail, the body is in
-
catabolic state (fasting)
-
anabolic state (food intake)
Metabolic reactions
enzyme – driven reactions
metabolic pathways – sequence of
predefined enzyme driven chemical
reactions (e.g. glycolysis, Krebs cycle,
Cori cycle, etc.)
enzyme
substance A +B
substance C
Energetics and metabolic rate
functions of the human body – require continuous supply of energy:
growth, movement, „beating“ of the heart, breathing, brain function, etc.
= synthesis of tissues, hormones, muscle contraction, active membrane transport, etc.
Metabolic rate
- is the amount of energy utilized (released) in the body
Units
• Joule (J)
•
calorie (cal)
– old, but still commonly used unit
•
•
1 cal = 4,18 J
1Cal = 1000 cal
-
matabolic rate is usually expressed in kJ/ 24 hours (1 hour, 1 min)
 metabolic rate in a moderately active person – approx. 8 000-10 000 kJ
 the metabolic rate of individual tissues and organs differs
- high metabolic activity: brain, liver, skeletal muscle
- low metabolic rate: fat tissue
http://www.nature.com/ijo/journal/v34/n2s/fig_tab/ijo2010234f6.html
The metabolic rate varies throughout the day
kJ
0
4
8
12
16
20
- sleep – the lowest metabolic rate (by 10-15 % than minimum when awake)
- awake/during the day – an increase in metabolic rate
24 (h)
Basal metabolic rate
Basal metabolic rate (BMR)
- lowest metabolic rate required for the maintenance of vital body functions
- metabolic rate in a person who is awake and who is in basal conditions
- basal conditions:
1. the person is awake
2. physical rest - lying position
3. emotional rest – elimination of emotional excitement
4. normal body temperature (~ 36-37° C)
5. neutral temperature of the environment: 20-23 °C
6. fasting state (fats or carbohydrates for 12 hours, proteins - 18 hours)
- basal conditions in real life - only just after we wake up
Main factors explaining the differences in BMR
1.
2.
3.
4.
Age
Gender
Composition and size of the body
Hormones
Age
-
increasing age - the metabolic rate
decreases
-
the highest metabolic rate (per 1 kg of
body weight) is in children – growth
rate
-
in aging – the body composition is
changed – less lean tissue, more fat
Body size and composition - body surface
- „larger body size – higher metabolic rate“
- the metabolic rate is directly proportional to the body surface
(better than to the weight or height)
This is due to thermoregulation:
- larger body size → bigger heat loss (through the skin →
→ more heat needs to be produced for thermic homeostasis
(heat is produced in metabolism)
Body composition:
- metabolic rate depends on the fat content in the body
- fat tissue - lower metabolic rate
- fat free mass (e.g. muscles) - higer metabolic rate
-
Gender
males – higher BMR than females (approx. by
5 – 7%)
-
explanation:
• body composition of males (vs. females)
- lower body fat content (metabolically less active)
- more muscles (metabolically more active)
• larger body size
• higher concentration of testosterone
(anabolic effect)
Hormones
Main metabolism regulating hormones include:
-
thyroid hormones T3, T4 (main role in metabolism regulation)
-
catecholamines
-
growth hormone
-
testosterone
Higher production – increased metabolic rate
E.g.
Stress – epinephrine – higher metabolic rate
Adaptation to cold climate – higher thyroxine production – elevated BMR
Adaptation to hot climate – lower thyroxine production – decreased BMR
Testosterone – higher BMR in males than in females
Main components of daily energy expenditure
(Values for a physically active individual)
Thermoregulation (6 %)
Specific– dynamic effect of food (6%)
Physical activity 25 – 30%
Arousal
Basal metabolic rate
(60%)
Sleeping
metabolic
rate
Factors that increase the metabolic rate
1. physical activity
- major factor that increases the metabolic rate
- the increase depends on DURATION and INTENSITY of the physical activity
(mild – moderate – vigorous)
Activity
Sitting activities (eating, computer games, studying)
Standing activities - light (washing dishes, cooking)
Walking slowly (a walk)
Walking at normal pace
Walking fast
Sport – light physical activity (bowling, table tennis. etc.)
Sport – medium physical activity (swimming, tennis, skating, aerobic, cycling)
Sport – heavy (football, athletics, jogging, hockey)
Increase of
BMR
1.4
1.7
2.8
3.2
3.4
3.3
5.5
6.6
strenous exercise – dramatically increases metabolic rate
- major factor contributing to the energy balance between E intake – E expenditure
- physical activity allows for voluntary regulation of energy expenditure
-
PAL – Physical activity level
-
indication of a person´s physical activity by a single number
is the ratio between the total daily energy expenditure and 24-hour basal
metabolic rate
-
energy expenditure in 24 h
___________________________
PAL =
basal metabolic rate
-for
adults, a PAL above 1.75 is considered to be compatible with a healthy lifestyle
PAL
Daily Activities
< 1.4
Hospital patient with limited physical mobility
1.4 - 1.69 Little physical activity at work or in leisure time, e.g. office worker
Lifestyle
Inactive
Sedentary
1.7 - 2.0
Moderate physical activity at work, e.g. in construction, or some jobs in Moderately
agriculture or the leisure industry.
Active
Office workers who work-out e.g. in gym for an 1 h/ day.
2.0 - 2.4
Considerable physical activity at work, e.g. outdoor occupations, fitness
trainers who run alongside clients. Office workers who take at least
moderate exercise for two or more hours/day.
> 2.4
Professional athlete or sports person
Very
Active
Extremely
Active
2. Thermogenic effect of food (specific – dynamic action of food)
- a term used for an increase of metabolic rate after food ingestion
= energy over BMR that is used for
- digestion
- absorption
- transport
- storage of nutrients
Nutrient
Increase in BMR
Duration of the effect
Carbohydrates
+ 5 –10 %
3-12 h
Fats
+ 5 –10 %
3-12 h
Proteins*
+30 %
12-24 h
Usual mixed diet
+6%
6-12 h
*stimulatory effect of some AA, also protein synthesis is an energy very demanding process
3. temperature of surrounding environment, climate
-
neutral temperature 20-23 °C (no extra energy expenditure for thermoregulation)
-
hot environment (over 23 °C) – extra energy is spent to remove the excess heat from
the body - sweating
-
cold environment (below 20 °C) – heat is produced by increased muscle activity: higher
muscle tone, shivering
4. body temperature
- increase of temperature by o 1°C – increase of metabolic rate by 10 %
- decrease of temperature (hypothermia) – decrease of metabolic rate
5. other factors – drugs, pregnancy, caffeine, etc. – slight increase
metabolic
rate
Cold environment – more
heat is produced by an
increase in metabolic rate
increase
Hot environment – extra
energy is spent to remove the
excess heat from the body
body
temperature
temperature
of the environment
Increase in body temperature
by o 1°C – increase of
metabolic rate by 10 %
neutral temperature
decrease
Decrease of body
temperature – decrease
of metabolic rate
lower
higher
Sources of energy and free energy
- Source of energy: food/nutrients – proteins, fats, carbohydrates
- energy is released from nutrients in oxidation
- energy value of nutrients – amount of energy liberated by
oxidation of 1 g of a nutrient in the human body (physiological free E)
- physical free energy– amount of heat liberated by burning
(oxidation) of 1 g of nutrients in calorimeter
free energy
carbohydrates
fat
protein
(alcohol
physical
17 kJ
38 kJ
23 kJ
29 kJ
P,F,C
physiological
17 kJ
38 kJ
17 kJ *
29 kJ)
Carbohydrates and fats
- fully oxidized in the body (CO2, H2O), therefore
- physiological free energy = physical free energy
Proteins
• not completely oxidized in the body
• end products of their oxidation include
– H2O, CO2 and energy
– also nitrogen containing substances (urea, creatinine,
creatine, ammonia, etc.)
P,F,C
• excreted from the body by urine -their bonds contain certain amount of energy
•
physiological free energy of proteins < physical free energy of proteins
free energy
carbohydrates
fat
protein
(alcohol
physical
17 kJ
38 kJ
23 kJ
29 kJ
physiological
17 kJ
38 kJ
17 kJ *
29 kJ)
Energy balance
E equilibrium: E intake = E expenditure
- optimal for a healthy adult individual
positive E balance: E intake > E expenditure
- excess energy is stored
- body fat (main form of stored energy – 75% of
energy supplies in the body)
- glycogen (1% of energy stores)
- leads to weight gain (may be positive or negative for
health)
negative E balance: E intake < E expenditure
- the energy deficit is compensated by depletion of stored forms of energy
(glycogen, fat, protein)
- leads to weight loss gain (may be positive or negative for
health)
Measurement of energy expenditure
1. calculation by formula
e.g. BMR = 293 . body weight (kg) 0,75
2. determination from tables (Harris – Benedict tables)
- depending onweight, height, gender, age
Value A – depending on age and height
Value B – depending on weight
BMR = Value A + Value B
3. direct calorimetry
- measurement is performed in special
insulated chambers
- heat released from the body is measured
4. Indirect calorimetry
principle:
- energy expenditure is calculated indirectly
- utilization of O2 and production of CO2 is measured
and based on their values BMR is calculated
Rationale of the method
- human metabolism is aerobic -energy is released by oxidation of substrates
- oxygen consumption and metabolic rate are in direct association
- oxygen cannot be accumulated in the body
A/ Closed method - calculation of energy expenditure is based on measurement of
the consumed O2
B/ Open method - calculation of energy expenditure is based on measurement of
both the consumed O2 and produced CO2 (more accurate method)
For calculation of energy expenditure we must determine:
amount of produced CO2
------------------------------------1. Respiratory quotient RQ =
amount of utilized O2
carbohydrates
RQ = 1
C6H12O6 + 6 O2  6 CO2 + 6 H2O
fats
RQ = 0,7
C12H31COOH + 23 O2  16 CO2 + 16 H2O
proteins
RQ = 0,8
mean value on mixed diet
RQ = 0,82
2. Energy equivalent (EE)
– is the amount of energy liberated while using 1 l of oxygen
– value derived from RQ – can be found in a table (average 20,2 kJ/ L)
– it depends on the type of oxidized fuel (differs for protein, fat, carbohydrates)
– oxidation of 1 mole of different nutrients requires different quantity of O2 and CO2
production is also different
Tab 8.4 Energy equivalents of 1 L of oxygen for RQ from 0.69 to 1.00
(RQ – respiratory quotient, EE – energy equivalent)
RQ
0.69
0.70
0.71
0.72
0.73
0.74
0.75
0.76
EE (kJ)
19.531
19.586
19.636
19.686
19.737
19.791
19.841
19.896
RQ
0.77
0.78
0.79
0.80
0.81
0.82
0.83
0.84
EE (kJ)
19.946
19.996
20.051
20.101
20.151
20.201
20.256
20.306
RQ
0.85
0.86
0.87
0.88
0.89
0.90
0.91
0.92
EE (kJ)
20.360
20.411
20.461
20.515
20.566
20.616
20.666
20.716
RQ
0.93
0.94
0.95
0.96
0.97
0.98
0.99
1.00
EE (kJ)
20.767
20.821
20.871
20.921
20.976
21.026
21.076
21.131
Metabolic rate and physical activity
Physical activity
• immediate increase in energy expenditure/ metabolic rate
• an immediate increase in demand for
a/ fuels
b/ oxygen
Metabolic
rate
physical
activity
kJ
resting
state
0
time (min)
Energy sources for the muscle in physical activity
1. Phosphagen system (ATP + PC)
a/ ATP
- first source of energy for the muscle contraction
- stores of ATP in muscles – sufficient for 1-3 sec.
b/ Phosphocreatine (PC)
- cannot be utilized directly
ATP
creatine
ADP+ P + E
phosphocreatinine
- serves for fast re-synthesis of ATP from ADP
ATP and PC supplies for 8 – 10 s
ADP+ADP
Main source of energy in short-lasting intense physical activity
2. Subsequently carbohydrates and fats are utilized in
a/ Anaerobic metabolism – carbohydrates only
b/ Aerobic metabolism
AMP+ ATP
Reaction of the body to physical activity
- physical activity = sudden increase of requirements for O2
- systems that help to supply O2 into the muscle are activated
increase of ventilation (tidal volume and frequency)
higher cardiac output per minute (frequency and stroke volume)
blood re-distribution into the muscle
....
- Gradual activation!
- balance (i.e. needs for O2
= supply of O2) is reached
in approx 3-5 minutes
Oxygen supply in physical activity
- due to gradual activation of systems involved
in O2 supply, the O2 availability increases gradually
- inbetween O2 from the stores is utilized
haemoglobin
- higher O2 uptake
- decrease of haemoglobin oxygen
saturation (venous blood)
A
96%
V
75 %
A
96%
O2 bound to myoglobin
utilization of physically dissolved O2
- stores of O2 are very limited - at the beginning of exercise O2 is not supplied in
quantity adequate to metabolic rate - oxygen deficit is established
V
50 %
Oxygen deficit
- is the difference between
the O2 requirements for
the physical activity and
O2 that is supplied
- consequence: energy must
be provided by anaerobic
metabolism
Anaerobic glycolysis
- only glucose can be utilized:
- glucose  pyruvate  lactate
- fast source
- less efficient
1 mol of glucose anaerobic: – 2 moles of ATP
aerobic – 36 moles of ATP
Steady state
-achieved approx. after
3-5 minutes of exercise
- O2 supplied into
working muscle is
adequate to metabolic
requirements
3. Aerobic metabolism
- utilization of glucose,
fatty acids
Recovery period
- physical activity is finished
- O2 consumption remains
higher and only gradually
decreases to resting values
Oxygen debt
-is repaid
= volume of O2 consumed
in recovery period above
baseline consumption
Excess O2 is used
- to replenish the O2 supplies (haemoglobin, myoglobin, O2 dissolved in blood)
- for re-conversion of lactate to glucose
- to replenish the stores of ATP, PC
Recovery (restoration) period
-heart rate, frequency of
breathing are dropping
down
- the restoration period is
finished when preexercise heart rate and
breathing frequency is
reestablished
Maximal oxygen consumption (maximal aerobic capacity)
-VO2max - is the maximum capacity of an individual's body to transport and use
oxygen during exercise
-reflects the physical fitness of the individual
- expressed either in litres of oxygen per minute (l/min) or as millilitres of oxygen per
kilogram of bodyweight per minute (ml/kg/min)
- in physical activities with oxygen
requirements exceeding VO2max
part of the energy is derived in
anaerobic processes
if maximum aerobic capacity is
exceeded in a heavy physical
activity, no steady state occurs
the physical activity requires
anaerobic metabolism all the time
replenishing of oxygen takes
longer time (i.e. the restoration
period is longer)
Physical activities can be
Dynamic activities
• activities with joint movements and rhythmic muscle contractions
(swimming, walking, training, house cleaning)
• physical work is performed
Static activities (also known as isometrics)
•
•
•
exerts muscles at high intensities without movement of the joints
no force is acting on a trajectory (e.g. when carrying a weight)
all the metabolized energy is transformed to heat
Efficency of the physical work
when an individual performs physical activity only part of the total energy
expenditure is used for external work (exercise), the remainder appears as heat.
Net efficiency of
the physical work
external work
=
_____________________________________________________________
net energy expenditure for the physical activity*
*energy expenditure that is above resting metabolic rate
Dynamic activities
- average efficiency 25% = 0,25
- i.e. 25 % of the metabolized energy is utilized for
performing the physical work and 75 % is transfromed to heat
Static activities
-efficiency 0%
-all the energy released in metabolism is converted into heat
Sources of energy for the human body
•
nutrients (derived from food or in stored form)
Carbohydrates
Fats
Cannot be utilized directly!
Proteins
- chemical energy of their carbon bonds - must be converted into a form that the
cells are able to utilize - high energy phosphate bonds
-adenosine triphosphate (ATP)
-cytidine triphosphate (CTP)
-phosphocreatinine (CrP)
- guanosino triphosphate (GTP,) etc.
Adenosine triphosphate (ATP)
- „universal energy currency“
- direct energy source for most cellular functions
- present in all cells
- last 2 bonds - high energy phosphate bonds
ATP + H2O → ADP + Pi + energy
ADP + H2O → AMP + Pi + energy
Krebs cycle
(citrate cycle, cycle of tricarboxylic acids)
cyclic metabolic pathway
crucial for energy metabolism
occurs in the matrix of mitochondria
exclusively in aerobic conditions
sequence of chemical reactions, in
which acetyl Co A is oxidized
Co A is derived from
– carbohydrates
– fats
– proteins
product: CO2 and reduced forms of
coenzymes NADH, FADH2
enter respiratory chain – ATP
formation (oxidative phosphorylation)
Digestion, absorption
and metabolism of carbohydrates
Carbohydrates and their digestion
starch
sacharose
lactose
polysaccharide
disaccharide
disacharid
monosaccharides
in food
Oral cavity
salivary a-amylase
Small intestine
pancreatic juice
• a-amylase
maltose
Small intestine
brush border
- enterocytes
glucose
frucose
•maltase
glucose
glucose

•saccharase
•lactase
glucose
fructose
glucose
galactose


Blood
Absorption of carbohydrates
a/ absorption into the enterocyte
glucose, galactose – Na+ cotransport
fructose – facilitated diffusion
-in the enterocyte conversion to glucose
b/ absorption from the enterocyte into blood
(passive mechanisms)
- diffusion
- facilitated diffusion
Main metabolic pathways of carbohydrates
•
liver – most of the galactose and fructose is converted into glucose
•
glucose - the main form of carbohydrate in the human body
• exclusive/preferred energy source for some tissues (brain, red blood cells)
• the blood level is strictly controlled (insulin, glucagon)
1. Breakdown of carbohydrates (catabolsim, yields energy)
Aerobic conditions:
a/ Glycolysis: 1x glucose ....  2 x pyruvate (this step does not require oxygen)
b/ pyruvate  AcCoA  Krebs cycle  oxidative phosphorylation
energy gain: 38 ATP
Anaerobic conditions:
Glycolysis: 1x glucose ....  2 x pyruvate  lactate
energy gain: 2 ATP
When O2 is available again:
lactate  pyruvate  glucose
Krebs cycle
.... other pathways of utilization
2. Formation and dergadation of glycogen (glycogenesis and glycogenolysis)
- storage form of carbohydrates
- formed only in
liver – can be released into blood, available for other tissues
muscles – cannot leave the muscle cells, serves only for muscle contraction
3. Conversion to fat
– in excess of glucose – if glycogen stores are fully replenished
4. Gluconeogenesis
– glucose formation from lactate, glucogenic aminoacids, glycerol (in liver)
Regulation of carbohydrate metabolism
insulin (anabolic)
glucagon, thyroxine, growth hormone, epinephrine, glucocorticoids (catabolic)
Digestion, absorption
and metabolism of fats
Fat digestion
fats
Stomach
• gastric lipase
Small intestine
- pancreatic juice
• pancreatic lipase
- bile ( no enzymes)
monoglycerides,
fatty acids, glycerol
Fat absorption
Lymphatic vessels
Blood
Absorption of fats
- duodenum to mid-jejunum
- absorbed by diffusion into the enterocytes
- resynthesis od triacylglycerides
- chylomicron formation
and release into blood
lumen
diffusion
triacylglycerols
cholesterol
phospholipids
proteins
enterocyte
blood
diffusion
86 %
3%
9%
2% - apoproteins
 fatty acids with 10 or less carbons in the chain
- transported directly into blood (by diffusion)
 fatty acids with more than 10 carbons in the chain
- absorbed into lymph, transported by lymph into blood
lymphatics
Main metabolic pathways of fats
1. Lipolysis
glycerol – glycolytic pathway
fatty acids: β-oxidation in mitochondria
product: AcCoA Krebs cycle  oxidative phosphorylation  ATP
energy yield (stearic acid) 147 ATP
2. Deposition of fats – in form of TAG in adipose tissue (less in the liver)
3. Ketone bodies formation - acetoacetate, β –hydroxbutyrate, aceton
- produced in reduced availability of glucose
- production in the liver – utilization in the peripheral tissues
- utilization in the Krebs cycle
4. Lipogenesis (fat synthesis from non-fat substrates)
Fatty acids: from AcCoA
glucose, some amino acids (+degraded lipids)
Glycerol: from glucose
Digestion, absorption
and metabolism of proteins
Protein digestion
proteins
Stomach
• pepsin
• chymosin
Pancreatic juice
(released into small intestine)
•trypsin
•chymotrypsin
•carboxypeptidase
polypeptides, peptides
Small intestine
(brush border of enterocytes)
•aminopeptidases
dipeptides, tripeptides, amino acids
Blood
Absorption of proteins
a/from the lumen to the enterocyte
1. Na+ - cotransport
2. primary active transport
- specific transporters for different AA (acidic,
basic, neutral), dipeptides, tripeptides
b/ form the enterocyte to blood
passive mechanisms
1.
2.
diffusion
pinocytosis
Main metabolic pathways of proteins
1. Protein synthesis
- after entry into the cells - the amino acids form cellular proteins
- in cells, only small amount of free amino acids is present
- limited capacity of cells to form proteins (no protein stores can be formed)
2. Protein breakdown
- degradation of amino acids - occurs almost entirely in the liver.
- deamination of AA - removal of the amino groups (-NH2)
A. resulting keto acids are oxidized to release energy.
liver
B. -NH2 → ammonia → urea (excretion by kidneys)
3.
Conversion to carbohydrates and fats
excess AA
- deamination – gluconeogenesis
- lipogenesis
Enegy intake and energy expenditure in 24 hours
Energy expenditure: continuous process
Energy intake: 3-5x /day
0
4
8
12
16
20
Storage forms of energy
adipose tissue 75 % of stores
- glycogen (1% of stores - liver, muscles)
- proteins – 24 % (waste of active tissues)
- high energy bonds: ATP, phosphocreatinine, etc.. – very limited supplies
-
Depending on substrate availability: catabolism or anabolism prevails
(fed state metabolism, fasting state metabolism)
24 (h)
Principal metabolic pathways during the
absorptive state
(Fed state metabolism)
Copyright 2009, John Wiley & Sons, Inc.
Fed state metabolism
• up to 4 hours after food ingestion
• food is digested, metabolic fuels are absorbed and enter the circulation
• regulation of metabolism is determined primarily by the influx of glucose
from the gut into blood
Hormonal regulation
• insulin is released (in response to increased glucose level),
• gucagon level drops down
• epinephrine and cortisol do not play significant role in fed state
metabolism
Fuel utilization
•
plentiful supply of glucose - becomes the main fuel for the tissues
•
insulin stimulates
– uptake od glucose by muscle - becomes the preferred fuel for the muscle
– synthesis of glycogen in both liver and muscle
– glucose uptake into adipose tissue for triacylglycerol synthesis
– uptake of AA leading to and increased rate of protein synthesis
•
most of the absorbed triacylglycerols travel to adipose tissue for storage
•
the fatty acid and TAG synthesis in liver is increased (in response to
increased glucose availability)
– exported in VLDL to periphery
– used as metabolic fuels in peripheral tissues
– stored in adipose tissue
Principal metabolic pathways during the
postabsorptive state
(Fasting state metabolism)
Copyright 2009, John Wiley & Sons, Inc.
Fasting state metabolism
• begins about 4 hours after last meal
• can extend to 4-5 days before entering the starvation state
Hormonal regulation
•
detemined primarily by the disappearance of glucose from the blood signalling the end of fuel absorption from the gut
•
drop in insulin blood level
•
rise in glucagon level
•
fasting is stressful – epinephrine plays a role in fasting state metabolism
Fuel utilization
Glucagon causes stimulation of:
– glycogen breakdown in the liver to release glucose into circulation
– lipase in the adipose tissue resulting in release of free fatty acids
– gluconeogenesis from amino acids and pyruvate
Reduced level of insulin causes
– reduced rate of glucose uptake by the skeletal muscle
– reduced AA uptake into muscle and lower protein synthesis, so that
AA are available for gluconeogenesis
•
tissues (other than brain and red blood cells) utilize preferentially fatty
acids to spare glucose for the brain and RBC
•
liver - synthesis of ketones (because of a greater capacity to oxidize fatty
acids then required to meet its own energy requirements)
– for use as a metabolic fuel for other tissues (including brain)
Humoral control of metabolism
Thyroxine
Epinephrine
- significant effect on metabolism
(increase) – delayed effect
-  lipolysis
-  glycoslysis
-  glycogenolysis
-  gluconeogenesis
-  lipolysis
Insuline
Glucagon
-  glycogenolysis
-  gluconeogenesis
-  glycogenesis
-  lipolysis
-  lipogenesis
-  glucose uptake by cells
-  glycogenesis
-  gluconeogenesis
-  glycogenolysis
-  lipogenesis,  lipolysis
-  AA uptake by cells,
-  prot.synthesis
Growth hormone
- glucose sparing - uptake by muscles
-  lipolysis
-  protein synthesis in muscles
Cortisol
-  gluconeogenesis
-  uptake of glucose, fatty acids and
amino acids
-  lipolysis
-  protein breakdown