Page 59 - Physiology and Pathophysiology MNU 2024-2025 نظرى

Clinical pharmacy 2024/2025 Level 2 Pharm D Physiology and Pathophysiology (MD303)

TEMPERATURE REGULATION

A. Sources of heat gain and heat loss from the body

1. Heat-generating mechanisms—response to cold

a. Thyroid  metabolic rate and heat production by stimulating Na+, K+ adenosine
hormone triphosphatase (ATPase).

b. Cold activate the sympathetic nervous system and, via activation of βreceptors in

temperatures brown fat, increase metabolic rate and heat production.
c. Shivering the most potent mechanism for increasing heat production.

2. Heat-loss mechanisms—response to heat

a. Heat loss by radiation and convection increases when the ambient temperature increases.

. b. Heat loss by evaporation depends on the activity of sweat glands, which are under sympathetic

muscarinic control.

B. Hypothalamic set point for body temperature

1. Temperature sensors on the skin and in the hypothalamus “read” the core temperature and relay this

information to the anterior hypothalamus.

2. The anterior hypothalamus compares the detected core temperature to the set-point temperature

a. If the core temperature is below the set b. If the core temperature is above the set

point point
heat-generating mechanisms (e.g., increased mechanisms for heat loss (e.g., vasodilation of

metabolism, shivering, vasoconstriction of the cutaneous blood vessels, increased
cutaneous blood vessels) ➔ activated by the sympathetic outflow to the sweat glands) ➔

posterior hypothalamus. activated by the anterior hypothalamus.

3. Pyrogens increase the set-point temperature ➔ Core temperature will be recognized as lower than the
new set-point temperature by the anterior hypothalamus.

➔ As a result, heat generating mechanisms (e.g., shivering) will be initiated.

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