Controlling Body Temperature

Why must body temperature be kept around 37 °C?

So enzymes work at their optimum rate; too high or too low a temperature reduces enzyme activity.

Which part of the brain detects changes in body temperature?

The hypothalamus.

What happens when the body is too hot?

Sweat production increases, blood vessels in the skin dilate, and hairs lie flat to increase heat loss.

What happens when the body is too cold?

Shivering occurs, blood vessels in the skin constrict, hairs stand on end, and we may put on more clothes.

What is vasoconstriction?

Narrowing of blood vessels in the skin, which reduces blood flow and heat loss.

What is vasodilation?

Widening of blood vessels in the skin, which increases blood flow and heat loss.

How does sweating help control temperature?

Sweat evaporates from the skin, taking heat energy with it and cooling the body.

What type of control system is used to maintain body temperature?

A negative feedback system.

Why is shivering a useful response when cold?

Muscles contract rapidly, releasing heat from respiration and warming the body.

How does putting on a jumper help keep the body warm?

It traps a layer of air and reduces heat loss by conduction and convection.

What is the role of hairs on the skin in temperature control?

When standing on end they trap air, reducing heat loss; when lying flat they reduce insulation.

How does temperature change the rate of enzyme activity?

Activity increases up to an optimum temperature, then drops sharply as enzymes denature.

What might happen if the body gets too hot?

Enzymes denature, chemical reactions slow, and the person may become dehydrated or suffer heat stroke.

What might happen if the body gets too cold?

Metabolic reactions slow, and the person may become hypothermic and lose consciousness.

How does the hypothalamus bring about vasoconstriction when cold?

It sends nerve impulses to smooth muscles in the blood vessel walls, causing them to contract.

Why is sweating more effective in dry air?

Evaporation is faster when the air is not already saturated with water vapour.

How do hormones sometimes help in temperature control?

They can increase metabolic rate (e.g. thyroid hormones), producing more heat.

What is the role of the skin in temperature control?

It contains receptors, sweat glands, hairs, and blood vessels that respond to temperature changes.

How does exercise affect body temperature?

It increases respiration and heat production, so the body must increase heat loss (sweating, vasodilation).

Why is maintaining a stable core temperature called homeostasis?

Because it keeps the internal environment stable despite changes in the external environment.