Homeostasis: Temperature Control (Cambridge (CIE) IGCSE Biology): Revision Note

The skin & homeostasis: extended

• Control of body temperature is a homeostatic mechanism

  • Homeostasis is the maintenance of a constant internal environment

  • This means that internal conditions within the body (such as temperature, blood pressure, water concentration and glucose concentration) need to be kept within set limits in order to ensure that reactions in body cells can function

• The human body maintains the temperature at which enzymes work best: around 37°C

• If body temperature increases too far above this, enzymes will denature and become less effective at catalysing reactions

The skin and temperature regulation

• The skin plays an important role in the control of body temperature

• Structures in the skin that are involved with temperature regulation include:

  • sweat glands

  • temperature receptors

  • capillaries

  • hairs

  • hair erector muscles

  • insulating fatty tissue

• When skin temperature changes, temperature receptors in the skin send nerve impulses to the brain via sensory neurones

• The brain responds to this information by sending nerve impulses to effectors in the skin that act to maintain normal body temperature, e.g.:

  • in response to an increase in body temperature:

    • sweat glands produce sweat which cools the skin by evaporation

    • blood vessels that supply the skin capillaries dilate

    • hairs on the skin surface lie flat

  • in response to a decrease in body temperature:

    • sweat gland stop producing sweat

    • blood vessels that supply the skin capillaries constrict

    • hairs on the skin stand up to trap an insulating layer of air

    • shivering generates heat in the muscles

Vasoconstriction & vasodilation: extended

• The blood vessels in and below the skin aid temperature regulation by vasoconstriction and vasodilation

Vasoconstriction

• When we are cold the blood vessels that supply capillaries in the skin constrict, or get narrower; this is known as vasoconstriction

• Vasoconstriction reduces blood flow to the skin, and so reduces the heat lost from blood by radiation at the skin surface

Vasodilation

• When we are hot the blood vessels that supply capillaries in the skin dilate, or get wider; this is known as vasodilation

• Vasodilation increases blood flow to the skin surface, and so increases heat lost at the skin by radiation