Temperature Regulation

Question 1

Define body temperature

Answer 1

Balance between heat produced and energy used (heat production and heat loss). Different parts of the body have different temperatures.

Question 2

Define core temperature

Answer 2

Core region - head, thoracic and abdominal cavity (highest temperatures). It is precisely regulated by the blood, which is the major agent of heat exchange between core and shell.

Question 3

Define surface (shell) temperature

Answer 3

The skin (lowest temperature)

Question 4

What is the normal temperature range?

Answer 4

37°C +/- 0.5°C

Range: 35.8-38.2°C and fluctuations within the ranges are normal

Question 5

How does temperature increase affect cell function?

Answer 5

Increases enzymatic catalysis, depresses neurons and degrades proteins.

Question 6

How does temperature decrease affect cell function?

Answer 6

Reduced metabolic rate.

Question 7

What is the main integration centre for thermoregulation?

Answer 7

The preoptic region in the hypothalamus

Question 8

Explain the mechanism of neural control of body temperature

Answer 8

The hypothalamus receives afferent input from peripheral thermoreceptors (in shell) and central thermoreceptors (sensitive to blood temperature and located in body core). Hypothalamus responds by reflexively initiating the appropriate action - heat loss or heat production.

Central thermoreceptors alert the hypothalamus not to change temperature in the core.

Question 9

Name and explain the heat loss mechanisms

Answer 9

1. Dilation of cutaneous blood vessels - inhibition of vasomotor fibers serving blood vessels allows them to dilate and as they swell with warm blood, the shell loses heat by radiation, conduction and convection.
2. Enhanced sweating - evaporation due to overheating. Sympathetic fibers activate sweat glands to release large amounts of perspiration. (Perspiration is possible when air is dry)

Question 10

Name and explain heat promoting mechanisms

Answer 10

1. Constriction of cutaneous blood vessels - vasoconstriction by activation of sympathetic vasoconstrictor fibers supplying blood vessels.
2. Shivering - brain centers controlling muscle tone are activated and progress to stimulate stretch receptors in antagonistic muscles. Temperature raised by heat produced by skeletal muscle.
3. Increased metabolic rate - cold stimulates adrenal medulla to release epinephrine and norepinephrine in response to sympathetic nerve stimuli, increasing metabolic rate and heat production.
4. Enhanced thyroxine release - cold temperature leads to release of thyrotropin releasing hormone from hypothalamus of infants. The hormone activates anterior pituitary to release thyroid stimulating hormone, thyroid hormone increases metabolic rate and heat production rises.

Question 11

What are the mechanisms of heat exchange between skin and external environment?

Answer 11

1. Radiation - loss of heat in form of infrared waves
2. Conduction - energy transfer between objects in contact with each other
3. Convection - energy carried away from body by warm air
4. Evaporation - water leaving body as gas ; Water vapour