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Homeostasis

Homeostasis is the ability to maintain changes in the body’s internal environment within narrow bounds.

The internal environment is the set of conditions the cells inside the body are exposed to.

Body temperature and blood content are part of the internal environment.

Organisms can only function properly if their internal environment is within an optimal range. If the conditions change, homeostasis responds to return conditions to within this range.

Internal conditions can be affected by the external environment (everything outside an organism).

On a cold day, your body temperature would decrease if it wasn't kept stable by homeostasis.

Homeostasis is maintained using negative feedback loops. A negative feedback system detects changes in a condition and produces a response that opposes that change.

The body monitors changes in internal conditions (a) and responds to reverse them (b). Blood glucose concentration is controlled in this way.
The body monitors changes in internal conditions (a) and responds to reverse them (b). Blood glucose concentration is controlled in this way.

The body maintains a constant internal temperature by balancing the production and loss of heat.

Large changes in body temperature are very harmful.

Enzymes become inactive if the body temperature is too high or low. This inhibits cell metabolism and can cause cell death.

The hypothalamus is the thermostat in the brain. It monitors and adjusts body temperature.

  • It contains sensors that monitor blood temperature.
  • It receives information from the skin about external temperature.

Body heat is generated by respiration and lost through the skin. The hypothalamus controls these processes.

Decrease in body temperature Increase in body temperature
Respiration Respiration increases.

More heat is produced.

Involuntary muscle contractions cause shivering.

Respiration decreases.

Less heat is produced.

Sweating increases heat loss thought evaporation.

Skin Blood vessels in skin get narrower (vasoconstriction).

Less heat is lost.

Blood vessels in skin get wider (vasodilation).

More heat is lost.

Penguins huddle together to reduce heat loss.
Penguins huddle together to reduce heat loss.

The skin is an important regulator of heat loss and conservation.

The skin contains many specialised structures involved in thermoregulation. Directly below the skin is a layer of fatty tissue (subcutaneous fat). This insulates the skin but is not directly involved in thermoregulation.

Skin contains sweat glands, hairs, blood vessels and receptors.
Skin contains sweat glands, hairs, blood vessels and receptors.

Skin is able to change the level of insulation (heat conservation) it provides. These changes are directed by the hypothalamus.

Structure Cold day Hot day
Blood vessels Become narrower (vasoconstriction) Become wider (vasodilation)
Hairs Stand up

Layer of trapped air acts as insulator

Lie flat

Heat easily radiates from surface

Sweat glands Less sweat produced More sweat produced

Sweat cools the skin as it evaporates