Body temperature and the thermoregulatory centre

Body temperature

Body temperature is one of the factors controlled by homeostasis. The human body maintains the temperature that enzymes work best at, which is around 37°C. This process is controlled by the thermoregulatory centre, which is contained in the hypothalamus in the brain. It contains receptors sensitive to the temperature of the blood. The skin also has temperature receptors and sends nervous impulses back to the thermoregulatory centre.

Too hot

When we get too hot, sweat glands in the skin release more sweat. The sweat evaporates, transferring heat energy from the skin to the environment.

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 to the environment. This is called vasodilation.

Too cold

When we get too cold, skeletal muscles contract rapidly and we shiver. These contractions need energy from respiration and some of this is released as heat.

Blood vessels, which lead to the skin capillaries, become narrower - they constrict – which allows less blood to flow through the skin and conserve the core body temperature. This is called vasoconstriction.

The hairs on the skin also help to control body temperature. The hairs lie flat when we are warm and rise when we are cold. If we are too cold, nerve impulses are sent to the hair erector muscles which contract. This raises the skin hairs and traps a layer of insulating air next to the skin.

The control of body temperature is an example of a negative feedback mechanism. It regulates 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 temperatureFlow chart showing how the body regulates a normal temperature of 37°C

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 cold

Generally, when the body temperature is too low, a variety of processes happen - vasoconstriction, sweating stops and shivering starts.

Diagram 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

When the temperature is too high, different processes happen - vasodilation and sweat production, which both transfer energy from skin to the environment, resulting in a cooling effect.

The two diagrams show the role of the blood vessels in maintaining body temperature. Hairs on the skin help to regulate temperature. When cold, the erector muscle of each hair forces them to stand upright. This traps a layer of warm air near the skin which provides insulation. When hot, hairs on the skin lie flat to reduce body temperature.

A diagram of skin and its component parts such as nerve endings and fatty tissue

Sweat glands also release sweat which travels to sweat ducts to sweat pores on the surface of the skin. When this sweat evaporates, it removes heat and cools the body down.