Temperature Regulation (WJEC GCSE Biology: Combined Science)

• The skin is our largest sense organ
• It contains many different receptors that enable us to detect various external stimuli, including touch, pressure, pain, heat and cold
• Structures within the skin also play an important role in regulating body temperature (an example of homeostasis):
  • Hair
  • Erector muscles
  • Sweat glands
  • Sweat ducts
  • Sweat pore
  • Blood vessels

Structure of skin diagram

Human skin contains structures involved in processes that can increase or reduce heat loss to the surroundings

Regulation of temperature

• Control of body temperature is a homeostatic mechanism
• It is important the human body maintains the temperature at which enzymes work best, around 37°C
• If body temperature increases over this temperature, enzymes will denature and become less effective at catalysing reactions such as respiration
• The structures of the skin play a role in the regulation of temperature within the body

When we are too hot

Blood vessel diameter

• When we are hot blood flow in capillaries increases because blood vessels close to the skin capillaries get wider - this is known as vasodilation
• This cools the body as blood (which carries heat around the body) flows at a faster rate close to the skin’s surface and so more heat is lost by radiation

Sweating

• Sweat is secreted by sweat glands
• This cools the skin by evaporation, which uses heat energy from the body to convert liquid water into water vapour

Heat loss from the skin diagram

When we are too cold

Blood vessel diameter

• When we are cold blood flow in capillaries slows down because arterioles leading to the skin capillaries get narrower - this is known as vasoconstriction
• This reduces the amount of heat lost from blood by radiation as less blood flows close to the surface of the skin

Erection of hairs

• The hair erector muscles in the skin contract, causing hairs to stand on end
• This forms an insulating layer over the skin's surface by trapping air between the hairs and stops heat from being lost by radiation

Shivering

• This is a reflex action in response to a decrease in core body temperature
• Muscles contract in a rapid and regular manner
• The metabolic reactions, such as respiration, required to power this shivering release sufficient heat to warm the blood and raise the core body temperature

Heat retention in the skin diagram