Body Temperature Physiology

1. Body Temperature:

• Highest temperature: Liver

• Lowest temperature: Skin

• Core body temperature: Temperature in deep tissues. Measured rectally, orally, axially (most stable in rectum: 36.3 – 37.1°C, oral temperature is 0.2-0.5° lower, axillary is 0.5-1° lower).

• Peripheral body temperature: Temperature measured in the skin and limbs.

2. Sources of Heat Production:

• Chemical reactions: The main source of heat for the body.

• Basal metabolic rate: The minimum energy expenditure at rest, without movement, digestion, or thermoregulation.

• 75% of energy produced during muscle contraction: Is converted into heat energy.

3. How Heat is Produced:

• Basal metabolism: Includes basic metabolic activities of the body.

• Movement: Muscle activity consumes energy and produces heat.

• Digestion: The process of digesting food also generates heat.

• Body growth: The growth and development of the body also require energy consumption, which produces heat.

4. Heat Exchange:

• Methods:

• Direct heat transfer: Through direct contact between two objects.

• Convection: Through a flow of liquid or gas.

• Radiation: Through electromagnetic waves.

• Evaporation of water: Water evaporating from the body surface carries away heat.

• Water evaporation through:

• Sweat glands: Evaporation of sweat carries away heat.

• Respiratory tract and skin permeability: Water vapor from the lungs and skin also carries away heat.

• Most important method of heat elimination: Heat elimination through water evaporation via sweat glands.

• Heat transfer rate: Proportional to the square root of wind speed (v^1/2).

5. Heat Balance:

• Formula: Metabolic heat – evaporative heat +,- radiative heat +,- conductive heat.

• Positive balance: The amount of heat retained is high and body temperature increases.

• Negative balance: The body loses heat and body temperature decreases.

6. Thermoregulation:

• Conditioned reflex arc: Consists of 5 components: sensory organ, afferent pathway, center, efferent pathway, effector organ.

• Efferent pathway: Includes neural and humoral pathways.

7. Mechanisms for Combating Heat:

• Increased heat dissipation:

• Sweat secretion.

• Increased ventilation.

• Vasodilation of skin vessels.

• Reduced heat production:

• Decreased metabolism.

• Decreased muscle contraction.

• Inhibition of shivering.

• Inhibition of chemical heat production under the influence of catecholamines (adrenaline and noradrenaline).

• Increased Na+ reabsorption during sweat secretion occurs under the influence of aldosterone from the adrenal cortex.

8. Mechanisms for Combating Cold:

• Increased heat production:

• Increased metabolism.

• Increased thyroxine secretion.

• Heat production due to increased cellular metabolism under the influence of blood catecholamines and sympathetic stimulation (the heat generated in this metabolic process is the result of complete oxidation and does not produce ATP).

• Chemical heat production occurs mainly in fat, especially brown fat present in newborns, because the mitochondria of these cells contain only OXH enzymes (heat production without shivering).

• Brown fat: Present only in infants, not in adults, receives a large number of sympathetic fibers that control it.

• Thyroxine increases the overall metabolism of the body in the direction of oxidation, thus increasing heat production.

• Reduced heat loss:

• Vasoconstriction.

• Shivering.

• Piloerection.

9. Regulation of Energy Metabolism:

• Cellular level regulation factors: ADP.

• Thyroid hormones T3,T4: Promote oxidation in mitochondria -> increase energy metabolism.

• Adrenal medulla hormone adrenaline: Promotes glycogenolysis to glucose.

• Adrenal cortex hormone: Convert amino acids to glucose, convert the energy of amino acids into the energy of glucose (the only energy source for nerve cells).

• Pancreatic hormone glucagon: Breaks down glycogen into glucose.

• Pancreatic hormone insulin: Promotes glucose utilization in cells.

• GH from the pituitary gland: Reduces glucose utilization and mobilizes energy reserves in the form of lipids in adipose tissue.