By the end of this lesson
- Define homeostasis accurately.
- Explain negative feedback.
- Apply homeostasis to water and temperature.
BIG QUESTION
How can body conditions remain stable while the environment and metabolism keep changing?
Negative-feedback systems detect deviations and activate responses that oppose them.
Internal conditions fluctuate around a range
homeostasisKeeping the internal environment relatively constant, with factors such as body temperature and blood glucose concentration held within limits suitable for cell function. is maintenance of a relatively constant internal environment. It does not mean every value is perfectly fixed.
Stable conditions support enzyme activity, membrane function and cell water balance.
Negative feedback opposes change
Receptors monitor a variable and a coordination centre compares information with an appropriate range. Effectors then produce changes that reduce the deviation.
As the variable returns toward normal, the corrective signal decreases, preventing continual overcorrection.
Water content and temperature are examples
ADH-mediated kidney responses conserve or release water. Sweating and changes in skin blood flow alter heat transfer.
These systems coordinate multiple organs and can be overwhelmed by extreme conditions.
Two homeostatic variables
Both use feedback but different receptors and effectors.
| Variable | Example deviation | Corrective response |
|---|---|---|
| Blood water content | Too little water. | More ADH and renal water reabsorption. |
| Blood water content | Too much water. | Less ADH and more dilute urine. |
| Body temperature | Too high. | Sweating and skin vasodilation. |
| Body temperature | Too low. | Reduced skin blood flow and increased heat production. |
Language that earns precision
- homeostasis
- Maintenance of a relatively constant internal environment.
- set range
- Acceptable interval around which a regulated variable fluctuates.
- negative feedback
- Response that counteracts a deviation from normal.
- coordination centre
- Part of a control system that processes receptor information and directs effectors.
Common misconceptions
Claim: Homeostasis keeps values exactly constant.
Correction: Variables fluctuate within regulated ranges.
Claim: Negative feedback means a harmful response.
Correction: “Negative” means it opposes the original change.
Claim: One organ controls homeostasis alone.
Correction: Receptors, coordination systems and effectors across organs cooperate.
Match the answer to the command word
Use relatively constant internal environment.
State the deviation, detector, effector and opposing outcome.
Recall, apply, then justify
Explain how negative feedback maintains body water content.
Hint
Use dehydration and ADH as the example.
Suggested marking points
- A fall in blood water content is detected by osmoreceptors.
- More ADH is released.
- Collecting ducts reabsorb more water.
- Blood water content rises toward normal.
- The ADH signal then decreases.
Explain why homeostasis is important for cells.
Hint
Think enzymes and water movement.
Suggested marking points
- Enzymes require suitable temperature/chemical conditions.
- Cells require controlled water and ion balance.
- Stable internal conditions allow metabolic reactions and membranes to function effectively.
Explain why fever can be described as regulated temperature elevation rather than simple homeostatic failure.
Planning hint
The control target can temporarily change.
What a strong design includes
- Immune signals can alter the hypothalamic temperature set point.
- Normal temperature is then below the temporary target.
- Heat-conserving/producing responses occur.
- Body temperature rises toward the new target.
- When the set point returns, sweating/vasodilation can lower temperature.
- Extreme fever can still become harmful or overwhelm regulation.