Department of Physiology, Faculty of Medicine, Masaryk University1
Energetic metabolism
Physiology II lecture (aVLFY0422p)
Tibor Stračina
Physiology II lecture (aVLFY0422p)2
The presentation is copyrighted work created by employees of
Masaryk University. Any unauthorized reproduction or distribution
of the presentation or individual slides is against the law.
Physiology II lecture (aVLFY0422p)3
Energetic metabolism
̶ Energy input (external an internal
sources)
̶ Energy output
̶ Energy stored
̶ INPUT = OUTPUT + STORAGE
ENERGY
INPUT ENERGY
OUTPUT
STORAGE
ENERGY
INPUT
ENERGIE
OUTPUT
STORAGE
Physiology II lecture (aVLFY0422p)4
Energy input
̶ Basic substrates: carbohydrates, fats a proteins
̶ Energy is obtained by burning (oxidizing) substrates
̶ carbohydrates 4,1 kcal/g
̶ fats 9,3 kcal/g
̶ proteins 5,3 kcal/g (in the body 4,1 kcal/g)
̶ Source of substrates: food intake or mobilization of reserves
Physiology II lecture (aVLFY0422p)5
Nutrient burning
GLYCOLYSIS b-OXIDATION
carbohydrate
C6H6O6
(2)pyruvate (2)acetyl-CoA(n/2)
2ATP
4xATP
4H
4H
Each acetyl-CoA
Citrate
cycle
8H
Fatty acid
CnH2nO2
ATP
2(n-2)H
2(n-2)H
O2 + ADP
Oxidative
phosphorylation
ATPH2O
2 CO2
GTP
protein
AA
Physiology II lecture (aVLFY0422p)6
Energy output
̶ Basal metabolism – energy expenditure to maintain homeostasis under
basal conditions (vital function) – ~75% of AEE in a person sitting at rest
̶ Specific dynamic effect of food – a small increase in energy expenditure
after eating– ~7% of AEE in a person sitting at rest
̶ Thermoregulation
̶ Spontaneous motoric activity– ~18% of AEE in a person sitting at rest
̶ Physical work (exercise)
Physiology II lecture (aVLFY0422p)7
Energy output: Basal metabolism
̶ The smallest amount of energy required to keep homeostasis (vital functions)
under the basal conditions
̶ Minimally 12 hours at rest (no physical activity, no stress)
̶ No intense physical activity in the last 24 hours
̶ Minimally 12 hours no food intake
̶ Thermoneutral environment
̶ BEE (basal energy expenditure) / BMR (basal metabolic rate)
Physiology II lecture (aVLFY0422p)8
Energy output:
Specific dynamic effect of food
̶ Energy required to process food and subsequently absorbed nutrients
̶ Depends on composition of diet
̶ For proteins, 30% of energetic content
̶ For carbohydrates, 6% of energetic content
̶ For fat, only 4% of energetic content
̶ For mixt diet, ~ 8-10% of energy contained in the food
̶ Specific dynamic effect of the food = thermic effect of the food
Physiology II lecture (aVLFY0422p)9
Energy output: Thermoregulation
̶ All thermoregulatory mechanisms (effectors) increase energy expenditure
̶ Energy is needed to warm up the body – to decrease heat loss and to
increase heat production
̶ Energy is needed to cool down the body – to increase heat loss (and to
decrease heat production)
Physiology II lecture (aVLFY0422p)10
Energy output:
Spontaneous motoric activity and exercise
̶ Muscle work increases energy expenditure
̶ AEE in supine position < AEE standing
̶ Such increase is proportional to intensity of the activity
̶ Sleeping 1.1x BEE; studying 1.4x; fast walking 2.4x; running 8.5-10x BEE
̶ After high-intensity exercise, energy expenditure is increased even after
the end of the exercise (tens of minutes to tens of hours)
̶ Oxygen debt (lactate metabolism), rebuilding of substrates in muscle (glycogen), reparation of muscles
Physiology II lecture (aVLFY0422p)11
Energy output: Somatic diseases
̶ Any somatic "damage" increases energy expenditure
̶ After surgery 1.1x BEE; sepsis 1.3x; multiple injuries 1.5x; burns 50-60% 1.8x BEE
̶ An increase in body temperature by 1°C increases energy expenditure by
10%
̶ Core body temperature of 38°C 1.1x BEE; temperature of 40°C 1.3x BEE
̶ Some diseases – specific effect on energy expenditure
̶ Hyperthyroidism, hypothyroidism, chronic inflammatory diseases, tumors
Physiology II lecture (aVLFY0422p)12
Energy storage and transfers
̶ Irregular energy intake and output – the need for energy storage
̶ Ready-to-use stock - macroergic compounds
̶ ATP
̶ creatin phosphate
̶ GTP, CTP, UTP, ITP
̶ Long-term storage – stock substrates
̶ Fat, proteins, glycogen
Physiology II lecture (aVLFY0422p)13
Adenosine trisphophate (ATP)
̶ universal macroergic compound
Synthesis
̶ circa 63 kg/day (128 mol/day)
̶ oxidative phosphorylation
̶ glykolysis – for short-term production only, production of lactate
̶ conversion from other macroergic compounds (creatine phosphate)
Use
̶ macroergic bond splitting – efficiency is not 100%, heat release
Physiology II lecture (aVLFY0422p)14
Storage substrates
̶ Triacylglycerols in fat tissue (75% of stores) – up to 2 months
̶ Source: FA from food and esterification with α-glycerol phosphate or synthesis of FA from acetyl-CoA from
glycolysis (conversion of sugars into a more efficient energy store = fat)
̶ Proteins in skeletal muscles and blood plasma (25% of stores)
̶ Possible conversion to sugars (glukoneogenesis; stimulated by glucocorticoids)
̶ Blood plasma proteins – quickly usable; leads to hypoproteinemia, drop of specific immunity
̶ Mobilization of muscle proteins leads to sarcopenia
̶ Carbohydrates in form of glycogen (less than 1% of stores)
̶ Important for the CNS and covering energy demands during short-term physical work
̶ Glycogen stored in the liver (about 25%) and in the muscles (about 75%)
̶ Liver glycogen - glycogenolysis - release of Glc into the blood
̶ Muscle glycogen - use only in muscles (glucose-6-phosphatase is missing)
Physiology II lecture (aVLFY0422p)15
Energy transfers between organs
̶ Only in the form of substrates (glucose, FA, AA, lactate, ketons, ...)
̶ Any transfer of substrates consumes some energy (synthesis and splitting of
stock substrates, transports, ...)
Fat tissue Muscles
Liver
Triacylglycerols
Free FA
FA
CO2
Muscle work
Lactate
Lactate
Pyruvate
Glucose
Glucose
ATP
H+
Physiology II lecture (aVLFY0422p)16
Measurement of energy expenditure
̶ Precise measurement – direct or indirect calorimetry
̶ Calculation based on anthropometric parameters (diverse formulas)
̶ Estimation based on the level of physical activity
Physiology II lecture (aVLFY0422p)17
Direct calorimentry
̶ Assumption: when ATP molecule is
split, some heat is released
̶ Heat production ≈ energy expenditure
̶ Heat production is measured directly
̶ Technically demanding
https://www.topendsports.com/health/tests/bmr-calorimeter.htm
Physiology II lecture (aVLFY0422p)18
Indirect calorimentry
̶ Assumption 1: the amount of ATP consumed is the same as the amount of ATP produced
̶ Assumption 2: each ATP is produced by consuming O2 and producing CO2
̶ O2 consumption and/or CO2 production is measured
̶ Open vs. closed system (Krogh respirometer - practical exercises)
̶ Energy equivalent of O2: the amount of energy released when consuming 1 liter of O2
̶ Sugars: 21.15 kJ/L
̶ Fats: 19.6 kJ/L
̶ Proteins: 19.65 kJ/L
̶ Mixed diet: 20.1 kJ/L
Physiology II lecture (aVLFY0422p)19
Respiratory quotient
̶ The ratio of the volume of CO2 produced and O2 consumed
̶ RQ = VCO2
/ VO2
̶ It provides information about the composition of the substrates that the organism metabolizes
̶ Sugars (glucose) RQ = 1
̶ Fats RQ = 0.7
̶ Mixed sources RQ ≈ 0.85
̶ After intensive exercise, RQ > 1 (paying the oxygen debt)
Physiology II lecture (aVLFY0422p)20
Calculation of basal energy expenditure (BEE)
̶ BEE from anthropometric parameters
̶ Harris-Benedict formulas: Men: BEE [kcal/day] = 66,5+ 13,75 × m + 5,003 × h − 6,755 × a
Women: BEE [kcal/day] = 665,1+ 9,563× m + 1,850× h − (4,676× a)
̶ Mifflina and St. Jeora formulas: Men: BEE [kcal/day] = 10 × m + 6,25 × h − 5 × a + 5
Women: BEE [kcal/day] = 10× m + 6,25× h − 5 × a − 161
m – body mass[kg]; h – high [cm];a – age [years]
̶ Resting energy expenditure (REE) from body composition
̶ Katch-McArdle formula: REE [kcal/day] = 370 + 21,6× FFM, FFM – fat-free mass
Department of Physiology, Faculty of Medicine, Masaryk University21
Physiology of Exercise
Physiology II lecture (aVLFY0422p)
Tibor Stračina
Physiology II lecture (aVLFY0422p)22
Work (physical activity, exercise)
Source: www.freepik.com. Photos created by freepik and standret
Physiology II lecture (aVLFY0422p)23
Skeletal muscle
̶ Contraction: isometric (static work) vs. isotonic (dynamic work)
̶ Blood flow depends on muscle tension
̶ Metabolic autoregulation: ↓pO2; ↑pCO2; ↓pH; ↑K+; ↑local temperature
̶ Metabolism: aerobic vs. anaerobic
̶ Muscle spindles – muscle tension – afferentation of exercise pressor reflex
Physiology II lecture (aVLFY0422p)24
Skeletal muscle metabolism
Adopted from: D.U.Silverthorn:
Human Physiology (An Integrated
Approach)
Physiology II lecture (aVLFY0422p)25
Energy substrate used by skeletal muscle
during exercise
̶ Low-intensity e.: fats
̶ High-intensity e.: glucose
Adopted from: D.U.Silverthorn:
Human Physiology (An Integrated
Approach)
Physiology II lecture (aVLFY0422p)26
Energy substrate use – aerobic vs. anaerobic
Adopted from: D.U.Silverthorn:
Human Physiology (An Integrated
Approach)
Physiology II lecture (aVLFY0422p)27
Reaction of the body to exercise
̶ Sympathetic NS (ergotropic system)
̶ Cardiovascular changes
̶ Respiratory changes
̶ Metabolic changes
̶ HOMEOSTASIS
Physiology II lecture (aVLFY0422p)28
Anticipation of exercise
̶ Reaction of the body (cardiovascular system)
̶ Prepare the body for the increased metabolism of the exercising skeletal
muscles
̶ Same as the early response to exercise
̶ Resembling fight-or-flight reaction
Physiology II lecture (aVLFY0422p)29
Cardiovascular response to exercise
̶ Increased cardiac output
̶ Increased venous return
̶ Vasoconstriction in inactive skeletal muscles, the GIT, skin, (kidneys)
̶ Vasodilation in active muscles (metabolic autoregulation)
̶ Epinephrine release (adrenal medulla)
̶ Thermoregulation
Physiology II lecture (aVLFY0422p)30
Increase of cardiac output. Cardiac reserve
̶ CO = SV x HR (SNS: positive inotropic and chronotropic effect)
̶ Cardiac reserve = maximal CO / resting CO (4 – 7)
̶ Coronary reserve = maximal CF / resting CF (~3.5)
̶ Chronotropic reserve = maximal HR / resting HR (3 – 5)
̶ Volume reserve = maximal SV / resting SV (~1.5)
CO – cardiac output; CF – coronary flow; HR – heart rate; SV – stroke volume
Physiology II lecture (aVLFY0422p)31
Cardiac reserve in healthy and failing heart
0
10
20
30
40
0 1 2 3 4 5
CO[L/min]
External power output[W/kg]
trained (athletic heart)
untrained
(physiological response)
heart failure
Physiology II lecture (aVLFY0422p)32
Changes of arterial blood pressure
PARAMETER AT REST DURING EXERCISE INCREASE (x)
Cardiac output
[L/min]
5 – 6 25 (35) 4 – 5 (7)
cardiac reserve
Heart rate
[1/min]
(45) 60-90 190 – 200 (220)
age-dependent
3 – 5
chronotropic reserve
Stroke volume
[mL]
75 115 ~1.5
volume reserve
Systolic BP
[mmHg]
120 static work ↑
dynamic work ↑↑
Diastolic BP
[mmHg]
70 static work ↑↑↑
dynamic work ─ / ↓
Mean arterial P (MAP)
[mmHg]
~90 static work ↑
dynamic work ─ / ↑
Muscle persufion
[mL/min/100g]
2 – 4 60 – 120 (180)
static vs. dynamic work
30
(10% COmax)
Physiology II lecture (aVLFY0422p)33
Respiratory response to exercise
̶ Respiratory centre - ↑ ventilation
̶ chemoreceptors: ↑ pCO2 + ↓ pH
̶ proprioceptors in lungs
̶ Sympathetic stimulation (stress – anticipation)
Physiology II lecture (aVLFY0422p)34
Respiratory response to exercise
PARAMETER AT REST DURING EXERCISE INCREASE (x)
Ventilation
[L/min]
6 – 12 90 – 120 15 – 20
respiratory reserve
Breathing frequency
[1/min]
12 – 16 40 – 60 4 – 5
Tidal volume (VT)
[mL]
0.5 – 0.75 ~2 3 – 4
Pulmonary artery blood flow
[mL/min]
5 – 6 25 – 35 4 – 6
O2 uptake (VO2)
[mL/min)]
250 – 300 ~3000 10 – 12 (25)
CO2 production
[mL/min]
~200 ~8000 ~40
Physiology II lecture (aVLFY0422p)35
Oxygen uptake by lungs
̶ Spiroergometry
̶ Resting VO2: ~3.6 mL O2 / (min x kg)
̶ VO2 max – objective index for aerobic power
̶ untrained middle age person: 30 – 40 mL O2 / (min x kg)
̶ elite endurance athletes: 80 – 90 mL O2 / (min x kg)
̶ HF / COPD patients: 10 – 20 mL O2 / (min x kg)
Adopted from:
https://studentconsult.inkling.com/read/boron-
medical-physiology-3e/chapter-60/figure-60-6
Physiology II lecture (aVLFY0422p)36
Determinants of VO2 max
1. Uptake of O2 by the lungs
̶ pulmonary ventilation
2. O2 delivery to the muscles
̶ blood flow (pressure gradient – cardiac output x resistence)
̶ haemoglobin concentration
3. Extraction of O2 from blood by muscle
̶ pO2 gradient: blood-mitochondria
Physiology II lecture (aVLFY0422p)37
Oxygen consumption during exercise
̶ Oxygen debt
Adopted from: D.U.Silverthorn:
Human Physiology (An Integrated
Approach)
Physiology II lecture (aVLFY0422p)38
Testing of fitness
̶ (Spiro)ergometry
̶ Standardised workload
̶ accurate: in W/kg
̶ comparative (simple, inaccurate): in MET
̶ metabolic equivalent (actual MR / resting MR)
̶ 1 MET = uptake of 3.5 ml O2/kg.min ≈ 4.31 kJ/kg.h
̶ sleeping ≈ 0.9 MET; slow walking ≈ 3-4 MET; fast running ≈ 16 MET
Physiology II lecture (aVLFY0422p)39
Indexes of fitness
̶ W170 [W/kg]
̶ VO2 max [mL O2 / (min x kg)]
̶ Aerobic / anaerobic threshold
̶ Fatigue
̶ Training
̶ Adaptation to exercise
Physiology II lecture (aVLFY0422p)40
The presentation is copyrighted work created by employees of
Masaryk University. Any unauthorised reproduction or distribution
of the presentation or individual slides is against the law.