Metabolic relationships
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Transcript of Metabolic relationships
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Metabolic relationships
Seminar No. 5
- Chapter 16 -
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Transformation of energy in human body
energy input = chemical energy of nutrients = work
+ heat
energy of nutrients = BM + phys. activity + reserves
+ heat
BM = basal metabolism
Reserves = chemical energy of adip. tissue, liver/muscle glycogen, and cca ⅓ of muscle proteins
work
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Basal metabolism depends on
• sex (in females by cca 10 % lower)
• age (diminishes with age)
• body temperature (increase by 1 C increases BM by 12 %)
• hormones thyroxine, adrenalin - increase BM
• long-term starvation – BM goes down (lowering diets,
anorexia nervosa)
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BM estimation (see p. 90)
4.2 MJ / m2 / day
0.1 MJ / kg / day
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Energy expenditure in various conditions (MJ/day)
BM - anorexia nervosa
BM - lowering diets
BM - females
BM - males
Light work
Medium hard work
Hard work
1-2
4-5
6-7
7-8
8-11
11-14
14-18
total energy
expenditure
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Main sources of nutrients
Nutrient Food source
Saccharides
Lipids
Proteins
starch, sugar (sucrose)
oils, lard, bacon, butter, margarines etc.
meat, egg, milk, (cottage) cheese, beans
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Energy content in nutrients
NutrientHeat of combustion (kJ/g)
Biological Physical
Lipids
Saccharides
Proteins*
38
17
17
38
17
24
* In calorimeter, AA are oxidized to CO2 + H2O + N2.
In human body, AA are catabolized to CO2 + H2O + urea.
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Recommended intake of nutrients
Saccharides 50-55 % (mainly starch)
Lipids 25-30 % (10 % PUFA)
Proteins 10-15 % (esenc. AA)
Essential FA: linoleic, α-linolenic
Conditionally esent. FA: arachidonic
Essential AA: Phe, Trp, Val, Leu, Ile, Met, Thr, Lys
Conditionally esent. AA: His, Arg, Ala, Gln
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Energy reserves in adult man (70 kg)
Nutrient Tissue Mass (g) Energy (MJ)
Glycogen
Glycogen
Glucose
Lipids
Proteins
liver
muscle
ECF
adip. t.
muscle
70
120
20
15 000
6 000
1,2
2,0
0,3
570
102/3=34
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Q. 1 (p. 95)
What is the performance of an active student in seminar if his body surface is 1.73 m2 ?
Express it in Watts.
Use the data from the chart on p. 90.
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A. 1
Energy expenditure of a student =
basal expenditure (= BM) + activity in seminar =
4.2 × 1.73 + 4 = 11.266 MJ/day =
11 266 000 J/day = (J/s) = 130 J/s = 130 W 86400
11266000
medium hard work~ 4 MJ/d
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Q.2 (p. 95)
The rate of energy expenditure in a fasting man (70 kg) without physical activity is 7 MJ/d.
How long do his energy stores last?
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A. 2
Energy stores: (data from table p. 90)
1.2 + 2.0 + 0.3 + 570.0 + 34.0 = 607.5 MJ
BM = 7 MJ/d
survival time = = 86.8 days7(MJ/day)
)MJ(5.607
1/3 of total muscle energy
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Body mass index 2(m)][height
(kg) mass BMI
BMI Classification
< 16
16-20
20-25
25-30
30-40
> 40
severe underweight
underweight
optimal weight
light obesity
marked obesity
severe obesity
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Basic facts on metabolism
• ATP is immediate source of energy in cells
• ATP is derived from metabolic oxidation of nutrients: glycolysis + β-oxidation of FA acetyl-CoA CAC resp. chain ATP
• ATP and glucose levels in body have to be reasonably constant
• glucose is necessary for brain and RBC
• glucose is necessary for utilization of lipids for energy: Glc pyruvate oxalacetate CAC
• glucose cannot be made from FA
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Relationships between nutrients
glucose lipids
FA glucose
glucogenic AA glucose
Glc (pyruvate, CAC intermed) C skeleton of non-essential AA
AA lipids
lipids AA
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Saccharides in well-fed state (insulin)
Glc
GIT
liver
Glc
glycogen
Glc in blood
lactate
ery
brainCO2
TAG
NADPH
adip. t.
glycerol-P
TAG
muscle
glycogen
CO2
GLUT 4 insulin dependent
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Glucose in liver (well fed state)
• Glc glycogen
• Glc pyruvate acetyl-CoA CAC energy
• Glc pyruvate acetyl-CoA FA TAG (VLDL)
• considerable amount of Glc just passes through into blood
• small portion of Glc is converted into specialized products
(pentoses + NADPH, galactose, glucuronate)
• excess of Glc lipids (VLDL) blood adipose tissue
obesity
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Glc in other tissues (well fed state )
• Glc is the only fuel for RBC (anaerobic glycolysis)
• Glc is prominent fuel for brain (aerobic glycolysis)
• Glc is source of energy + reserves (glycogen) in muscles
• Glc is source of glycerol-3-P for TAG synthesis in adipose
tissues
Glc glyceraldehyde-3-P + DHAP
glycerol-3-P
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Lipids in well-fed state (insulin)
AA
GIT
liver
Glc
TAG
adipose t.
FA + glycerol-P
TAG
muscle
CO2
AA
TAG
VLDL
FA
myocard
FA
chylomicrons
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Lipids in well-fed state (insulin)
• Exogen. TAG (CM) and endogen. lipids (VLDL) supply
peripheral tissues (muscles, myocard, kidney, adip. t.)
• FA are released from TAG by the action of LPL
• FA are fuel for muscles
FA acetyl-CoA CAC CO2 + energy
• In adipose tiss., FA are substrates for TAG synthesis
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Q.
Which extrahepatal tissues utilize glucose in well-fed state?
What is the role of insulin in this process?
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A.
• most tissues:
• RBC + brain (exclusively in well-fed state)
• muscles + adipose tissue + some other ...
• insulin stimulates the exposition of GLUT4 in muscles and adip. tiss. cell membranes
• Glc can enter these organs
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Q.
Why is glucose needed for adipose tissue?
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A.
• Glc is the source of energy (aerobic glycolysis)
• Glc is the source of NADPH +H+ for FA synthesis (pentose cycle)
• Glc is the source of glycerol-3-P for TAG synthesis
glycerol-3-P 1-acylglycerol-3-P 1,2-diacylglycerol-3-P
1,2-diacylglycerol TAG
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Q.
How can FA be formed from glucose?
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A.
• Glc 2 pyruvate (aerobic glycolysis)
• pyruvate acetyl-CoA (oxidative decarboxylation)
• acetyl-CoA + CO2 (biotin) malonyl-CoA (activation)
• [malonyl-CoA + acetyl-CoA]nx FA
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Q. (p. 91)
Why are KB not formed during resorption state?
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A.
• there is not enough substrate for KB synthesis
• insulin has anti-lipolytic action
not enough FA and acetyl-CoA
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Saccharides in fasting (glucagon)
GIT
liver
Glc
glycogen
Glc in blood
lactate(100%)
ery
brainCO2
muscle
glycogen
lactate(5-10%)
90% gluconeogenesis
10% gluconeogenesis
kidney
lactate(25%)
CO2
proteolysis
Ala
fosforolysis
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Glucose in fasting (glucagon)• blood Glc level is maintained by two processes:
• (1) liver glycogenolysis
(Glc)n + Pi (Glc)n-1 + Glc-1-P
Glc-6-P Glc
• (2) liver gluconeogenesis from lactate, AA, glycerol
• in muscles + brain, glycolysis is partly anaerobic
Glc (6C) 2 lactate (3C)
• the body starts to save glucose
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Substrates of gluconeogenesis
Lactate(60 %)
Alanine + other glucogennic AA (30 %)
Glycerol (10 %)
H3C CH
OH
COO
H3C CH
NH3
COO
CH2
CH
CH2
HO
OH
OH
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Lipids in fasting (glucagon)
GIT
liver
Acetyl-CoA
ketone bod. KB in blood
brainCO2
muscle
FA
CO2
adipose t.
FA + glycerol
TAG
FA-albumin
myocard
kidney
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Lipids in fasting (glucagon)
• glucagon stimulates lipolysis in adip. tiss. (HSL)
TAG 3 FA + glycerol
• FA are released to blood, bound to albumin, and trasferred to
muscles ( CO2 + energy)
to liver ( partly CO2 + energy for liver, partly KB for export)
• KB are metabolic fuel for muscles and partly for brain
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Ketone bodies
H3C C CH3
O
H3C CH CH2 CO
OH
OH
H3C C CH2
O
CO
O H- CO2
- 2H
+ 2H
-hydroxymáselná kyselina acetoctová kyselina aceton
Acid pKA
Acetoacetic
-Hydroxybutyric
3.52
4.70
acetic acid pKA = 4.75
formic acid pKA = 3.75
Compare:
acetone
non electrolyte
β-hydroxybutyric acid acetoacetic acid
which is stronger acid?
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Ketone bodies as the source of energy
H3C C CH2
O
COOH
sukcinyl-CoA sukcinát
H3C C CH2
O
C
SCoA
O
S
H
CoA
C
SCoA
O
H3C2CC
Energie
acetoacetát
acetoacetyl-CoA
thioly
sis
energy CAC
acetoacetate
succinate
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Q.
In which tissue are KB produced?
Which substrate is the source?
What is the cause of increased synthesis of KB?
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A.
• KB are produced only in liver from acetyl-CoA
• liver is not able to utilize KB
• the metabolic cause:
the shortage of oxaloacetate and excess of acetyl-CoA
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Q.
• How does lipoprotein lipase act on fat reserves in body?
• How does hormon sensitive lipase act on fat reserves in body?
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Feature LPL HSL
Substrate
Fat reserves are
Stimulation by
TAG in blood
increased
insulin (inducer)
TAG in adipose tissue
decreased
glucagon + adrenalin
A.
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Metabolic turn-over of saccharides in fasting (g/d)
glycogen
gluconeogenesis
liver
AA
glycerol16
144CNS
36Ery
lactate
36
Glc180
gluconeogenesis
liver
AA
glycerol15
44CNS
36Ery
lactate
50
Glc80
Early fasting
Prolonged starvation
75
20
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Metabolic turn-over of lipids in fasting (g/d)
gluconeogenesis
liver
glycerol KB
60
Early fasting
Prolonged starvation
TAG 160
FA 40
FA 160
FA120
muscles, myocard, kidney
gluconeogenesis
liver
glycerol KB
57
TAG 150
FA 38
FA 150
FA112
muscles, myocard, kidney
10 urine
CNS
47
xadip. t.
adip. t.
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Adaptation to prolonged starvation
• muscle proteolysis: 75 20 g/d decreases
• liver gluconeogenesis: 180 80 g/d decreases
• lipolysis: 160 150 g/d approx. the same
• KB production: 60 57 g/d approx. the same (dif. utiliz.)
• energy for brain: Glc (44 g/d) + KB (47 g/d)
• energy for muscle: FA
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Q.
Which are the main priorities of metabolism
during long starvation?
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A.
1. sparing glucose
2. sparing proteins
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Q.
How does a long term fasting affect
the acid-base balance?
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A.
• the accumulation of acetoacetate and β-hydroxybutyrate in
ECF leads to the decresase of pH acidosis
Acid pKA
Acetoacetic
-Hydroxybutyric
3.52
4.70