Regulating body temperature

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-sensitive receptors in the skin and circulatory system.

The hypothalamus responds to this information by sending nerve 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 lying flat and uprightSkin 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 mechanism controlling body temperatureNegative feedback in temperature regulation

Vasoconstriction and vasodilation

The amount of blood flowing through the skin capillaries is altered by vasoconstriction and vasodilation.

Too coldToo hot
ArteriolesGet narrowerGet wider
Blood flow in skin capillariesDecreasesIncreases
Heat loss from skinDecreasesIncreases

These diagrams show the processes that take place when vasoconstriction and vasodilation occur.

VasoconstrictionVasoconstriction – a response to being too coldDiagram looks like a capital A. The horizontal is shunt vessel. Nerve impulses come from the hypothalmus and the arteriole becomes dilated whilst the shunt vessel narrows. A lot of heat is lost. Vasodilation – a response to being too hot