Principles of HomeostasisAQA GCSE Biology: Revision notes

Homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function, in response to internal and external changes.

Homeostasis is essential because enzymes and other cell processes only work efficiently within a narrow range of conditions — outside this range, reactions slow down or enzymes may denature.

The human body uses homeostasis to control several internal conditions, including:

• Blood glucose concentration
• Body temperature
• Water levels

Control of these conditions can involve either nervous responses (fast, via electrical impulses) or chemical (hormonal) responses (slower, longer-lasting).

Every homeostatic control system, whether nervous or hormonal, includes the same three components:

1. Receptors — detect stimuli (changes in the environment or inside the body)
2. Coordination centres — such as the brain, spinal cord and pancreas; these receive and process information from receptors
3. Effectors — muscles or glands that bring about a response to restore optimum levels

Information generally flows through the body in this sequence: stimulus → receptor → coordinator → effector → response.

This pathway applies whether the coordination centre is part of the nervous system (fast, electrical) or the endocrine system (slower, via hormones in the blood) — the same basic pattern of detecting a change and acting to correct it underlies all homeostatic mechanisms in the body.