L14 Metabolism and thermoregulation

Energy metabolism

All chemical reactions in the body which are involved in energy storage and usage

Catabolism

Anabolism

Catabolism

Breakdown, energy producing

Anabolism

Building, energy storage

ATP

Universal energy carrier

Capture free energy by catabolism of macronutrients

• Aerobic (O2)

• Anaerobic

Needed for labour/work or storage

Catabolism: glucose oxidation

Uptake of carbohydraes - glucos

Uptake of glucose: glucose transporters

Used for energy: glycolysis, Krebs, OXPHOS

Metabolized via other routes: glycerol, fatty acids, nucleotides

Storage: glycogen (glycogenesis), (mainly muscle, liver, but also brain)

Glycogen broken down to glucose (glycogenolysis)

Uptake of proteins - amino acids

Uptake: specialized transporters

Storage: assembled to proteins

Used: deamination NH3 (Krebs, OXPHOS)
Proteins degraded to amino acids (proteolysis) if necessary

Proteins always have a functional role

Uptake of fats - triglycerides

Lipoproteins in blood, broken down to free fatty acids and monoglycerol (lipoprotein lipase)

Uptake: diffusion into cell

Used: fatty acids broken down into acetyl CoA (Beta-oxidation) and oxidized Krebs, OXPHOS

Storage: fatty acids and glycerol assembled into triglycerides (lipogenesis)

Triglycerides broken down (lipolysis)

Metabolism of macronutrients

Proteins → amino acids
Glycogen → glucose
Triglycerides → glycerol + fatty acids

glycolysis

pyruvate

acetyl coa

krebs cycle

oxidative phosphorylation

proteolysis

proteins → amino acids

glycogenesis

glucose → glycogen

glycogenolysis

glycogen → glucose

lipogenesis

glycerol + fatty acids → triglycerides

lipolysis

triglycerides → glycerol + fatty acids

Gluconeogenesis

Needs ATP, liver (also kidneys, not muscle)

actie low blood glucose levels

metabolic process of creating glucose (sugar) from non-carbohydrate sources, such as lactate, glycerol, and amino acids

Glucose oxidation - pathway

1. Glycolysis

2. Pyruvate → acetyl CoA

3. Krebs cycle (TCA)

4. Electron transfer system

   1. Stepwise energy loss (final acceptor is O2)

5. Oxidative phosphorylation/chemi-osmotic coupling

   1. ATP generated using H+ production (glucose)

Maximal ATP production (glucose)

32ATP

Anaerobic situations (low oxygen)

No O2 available as an electron acceptor

• No activity of Krebs cycle and OXPHOS

• Accumulation of pyruvate and NADH → shutdown glycoglysis

Anaerobic glucose oxidation

• Pyruvate → lactate : 2ATP + 2NAD+

Inefficient ATP production

Cori cycle

Liver converts lactate into glucose

Efficiency ATP production

Aerobic

Anaerobiv

Aerobic 32.7%
Anaerobic 2%

Why choose anaerobic ATP production

It is much faster than aerobic respiration, useful in situations of sudden, high energy demand (e.g. sprinting)

Energy balance

Energy in = energy out

Energy in

• food, alcohol

energy out

• basal metabolism (bmr)

• thermogenesis

• physical activity

positive balance

in>out

• energy storage (fat)

negative balance

in<out

• energy liberation

Energy balance during the day

energy intake

energy use

energy intake - discontinuous

energy use - continuous with spikes

Absorptive phase

3-4 hours after meal

absorption nutrients from digestive tract

energy in > energy out

postabsorptive phas

between meals

no absorption of nutrients

energy in < energy out

summary of (post) absorptive phase

anabolism - positive energy balance

• storing nutrients/energy

• glycogenesis

• lipogenesis

catabolism - negative energy balance

• liberation of energy

• glycogenolysis

• lipolysis

• proteolysis

  • gluconeogenesis

hormonal regulation of energy balance

Anabolism	Metabolism	Catabolism
Glycogen ←	Glucose	← Glycogen
Triglycerides ←	Fatty acids	← Triglycerides
Protein ←	Amino acids	← protein
Insulin Sex steroids (Growth hormone) (Thyroxine)		(Glucagon) (Epinephrine) (Glucocorticoids) (Growth hormone) (Thyroxine)

Insulin

Sole hormone that actively reduces blood glucose levels

Anabolism

Glucagon

Catabolism

Insulin vs glucagon

Blood glucose mainly regulated via insulin and glucagon

Insulin lowers high blood sugar by helping cells take up glucose, while glucagon raises low blood sugar by signaling the liver to release stored glucose

Temperature balance

Heat production

• Thermogenesis

  • Metabolism

  • Muscle contraction

• Heat loss

  • Heat loss (Tb>To) or gain (Tb<To)

Heat exchange

Radiation

Evaporation

Convection

Conduction

Radiation

Sun and animals, mainly infrared

Evaporation

Conversion liquid to gas, heat loss

Convection

Heat exchange to moving gas or liquid

Conduction

Heat exchange between objects that are in contact

Thermoregulation

Strict regulation of the body temperature within the limits

Poikilothermic vs homeothermic animals

Poikilothermic animals

Body temperature is not regulated, but conform to the (outside) environment

Homeothermic animals

Body temperature regulated to be kept constant independent from environment

Thermoregulation: behaviour

Torpor: reduced activity

• conserving energy, 7 degrees celcius reduction of body temperature

• thermogenesis, movement (flying)

Hibernation

• reduced temperature, low → extended sleep, e.g. bear, high → real hibernation (hamster)

  • thermogenesis, shivering, non-shivering: brown fat

Thermoregulation: adaptations

Thermogenesis

Insulation

Evaporation: sweating

Thermoregulation: adaptations

Thermogenesis

Shivering - increased muscle activity: ATP production 33% efficient, 67% lost as heat

Non-shivering - mitochondrial uncoupling

Thermoregulation: adaptations

Sweating

Ecrine glands, from birth

• skin: mainly head, palms, soles

Aocrine glands, from puberty

• in hair follicles, e.g. armpits

sympathetic nervous system stimulates sweat production. ACh is the neurotransmitter

Thermoregulation via blood supply through the skin

cold zone, vasoconstriction → shivering

warm zone, vasodilation → sweating