Homeostasis

Biology · Coordination and control. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

Homeostasis is the maintenance of a constant internal environment. Conditions inside the body, such as temperature and blood glucose concentration, are kept close to a normal value even when conditions outside change. This matters because enzymes work best at a particular temperature, and cells need steady surroundings.

The normal value is called the set point. Control works by negative feedback. When a condition moves away from its set point, the body detects the change and makes a response that pushes it back. If it rises, it is brought down. If it falls, it is brought up. When the value is back at the set point, the response is switched off.

Rules to remember

Homeostasis: the maintenance of a constant internal environment.
Set point: the normal value that a condition is kept close to (about 37 °C for human body temperature).
Negative feedback: a change away from the set point causes a response that reverses the change.
Sequence: change → detected by receptors → corrective response → return to set point → response stops.
The value is never perfectly steady; it moves a little above and below the set point.

Common mistake

Negative feedback does not mean that a value always goes down. It means the response is opposite to the change, so a fall is corrected by a rise.

Worked example

During exercise a person's body temperature rises to 37.8 °C. Sweating starts, the temperature falls to 37.0 °C and sweating stops. Explain why this is negative feedback.

The set point is about 37 °C, so 37.8 °C is a change above the set point.
The change is detected and causes a response (sweating) that lowers the temperature.
The response is opposite in direction to the change, and it stops when the set point is reached.

Answer: It is negative feedback because the rise in temperature triggers a response that reverses the rise and returns the temperature to the set point.

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Homeostasis

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