Knowledge Organiser: Homeostasis Introduction
Key Terms
- Homeostasis — regulation of internal conditions to maintain optimum conditions for function
- Receptor — detects a change (stimulus)
- Coordination centre — processes information; sends instructions to effector
- Effector — muscle or gland; carries out the corrective response
- Negative feedback — response opposes and reverses the original change
- Internal environment — conditions inside the body (temperature, glucose, water, pH)
- Optimum conditions — the specific temperature, pH, and glucose level at which enzyme activity (and therefore cell function) is at its maximum rate
Key Facts
- Body temperature maintained at 37°C (enzyme optimum)
- Blood glucose range: 4–8 mmol/L
- Blood pH range: 7.35–7.45
- Control loop: receptor → coordination centre → effector → response → return to normal
- Nervous system: fast, short-lived, specific target
- Endocrine system: slower, long-lasting, widespread effects
- Coordination centres: hypothalamus (temp), pancreas (glucose), kidneys (water)
The Control Loop
- 1. Condition deviates from normal
- 2. Receptor detects the change
- 3. Coordination centre processes signal
- 4. Effector produces corrective response
- 5. Response opposes the original change
- 6. Condition returns to normal range
- 7. Effector response switches off
Common Mistakes
- Saying the body "keeps conditions constant": Homeostasis maintains conditions within a narrow range — conditions fluctuate slightly around a set point. The body does not keep any variable perfectly constant; it uses negative feedback to return it to the normal range.
- Confusing receptor and effector: A receptor detects a change and sends a signal. An effector (muscle or gland) brings about the corrective response. Students often describe the effector doing the detecting or the receptor making the response.
- Forgetting to name all three components of a control system: Full marks require naming the receptor, coordination centre, AND effector. Omitting any one of these three components in a "describe the negative feedback loop" answer will lose a mark.
- Describing positive feedback as homeostasis: Homeostasis uses negative feedback, where the response opposes the original change. Positive feedback amplifies the change and is not part of homeostasis — do not confuse the two.
Memory Aid
- Receptor — detects the change and calls for help
- Coordination centre — receives the call and decides what to do
- Effector — carries out the correction
- Temperature (37°C — enzyme optimum)
- Water balance (osmotic regulation)
- Blood glucose (fuel for respiration)