Control of body temperature

Last time

Before we start: last time, in Auxin and the growth of shoots and roots, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

Thirty-seven degrees

Whether you are in a freezing winter or a hot summer, your core temperature stays close to thirty-seven degrees. If it rises or falls by just a few degrees, enzymes stop working properly. Today: how your skin, blood vessels and muscles keep you at thirty-seven.

Why it matters

Thirty-seven degrees is close to the optimum temperature for human enzymes. If the body gets too hot, enzymes start to denature. If it gets too cold, reactions such as respiration slow down.

Control centre

Temperature receptors in the skin, and in the brain, detect changes. A part of the brain called the hypothalamus acts as the control centre. It sends impulses to effectors, such as skin blood vessels, sweat glands and muscles, to correct the change.

The skin

The skin has sweat glands, hair erector muscles, blood vessels near the surface, and a layer of fat below. The fat layer insulates, reducing heat loss. The blood vessels near the surface control how much heat is lost by radiation.

When too hot

Vasodilation: the arterioles supplying the skin capillaries widen. More blood flows near the skin surface, so more heat is lost by radiation. The skin looks red. Sweat glands make sweat. As it evaporates, it takes heat energy from the skin.

When too cold

Vasoconstriction: the arterioles supplying the skin capillaries narrow. Less blood flows near the surface, so less heat is lost. The skin looks pale. Shivering: muscles contract rapidly, and their respiration releases heat. Hair erector muscles raise the hairs, trapping a layer of insulating air. Sweating stops.

Hot or cold?

Here is the table to learn. Each response, too hot and too cold. The examiner always asks about vasodilation and vasoconstriction, so learn them exactly.

Behaviour helps too

When cold, we put on more clothes, curl up, and move to warmer places. When hot, we remove clothes, find shade, and drink cold water.