The
human body is designed to function most efficiently at 37ºC. If you
become too hot or too cold, there are ways in which your body
temperature can be controlled.
Too hot
When we get too hot:
- Sweat glands in the skin release more sweat. The sweat evaporates, removing heat energy from the skin.
- Blood vessels leading to the skin capillaries become wider - they dilate - allowing more blood to flow through the skin, and more heat to be lost.
Too cold
When we get too cold:
- Muscles contract rapidly - we shiver. These contractions need energy from respiration, and some of this is released as heat.
- Blood vessels leading to the skin capillaries become narrower - they constrict - letting less blood flow through the skin and conserving heat in the body.
The skin
The
hairs on the skin also help to control body temperature. They lie flat
when we are warm, and rise when we are cold. The hairs trap a layer of
air above the skin, which helps to insulate the skin against heat loss.
The hypothalamus is the part of the brain which monitors the body's temperature. It receives information from temperature-sensitivereceptors in the skin and circulatory system.
The hypothalamus responds to this information by sendingnerve impulses to effectors to
maintain body temperature. For example, if we become too cold, the hair
erector muscles contract. This raises the skin hairs and traps a layer
of air next to the skin.
Skin hairs lie flat when we are hot and stand upright when we are cold
Negative feedback mechanisms control body temperature. They include the amount of:
- shivering (rapid muscle contractions release heat)
- sweating (evaporation of water in sweat causes cooling)
- blood flowing in the skin capillaries
Negative feedback in temperature regulation
Vasoconstriction and vasodilation
The amount of blood flowing through the skin capillaries is altered byvasoconstriction and vasodilation.
| Too cold | Too hot | |
|---|---|---|
| Process | Vasoconstriction | Vasodilation |
| Arterioles | Get narrower | Get wider |
| Blood flow in skin capillaries | Decreases | Increases |
| Heat loss from skin | Decreases | Increases |
These diagrams show the processes that take place when vasoconstriction and vasodilation occur.
Vasoconstriction – a response to being too cold
Vasodilation – a response to being too hot
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