A level-readyAll subjects · Biology · WBI15 (Unit 5)
Homeostasis, feedback and thermoregulation
Your internal conditions are kept within narrow limits by feedback. Temperature control by the hypothalamus is a key example, especially during exercise.
Homeostasis and negative feedback
Homeostasis is maintaining a stable internal environment within narrow limits, such as core temperature, blood glucose, blood pH and water potential. It is a dynamic equilibrium: conditions fluctuate slightly around a set point rather than staying perfectly constant.
In negative feedback, a change from the set point is detected by receptors, a control centre coordinates a response, and effectors reverse the change, returning conditions towards the set point. Separate mechanisms that raise and lower a value give finer control.
Positive feedback
In positive feedback, a change triggers responses that increase the change further. It does not keep conditions stable, but it is useful for rapid, one-off events, such as:
- the opening of more voltage-gated Na+ channels during an action potential
- oxytocin increasing contractions of the uterus during birth
Thermoregulation
Thermoreceptors in the skin, and in the hypothalamus (which monitors the temperature of the blood), send information to the thermoregulatory centre in the hypothalamus. It sends impulses through the autonomic nervous system.
| Too hot (for example during exercise) | Too cold |
|---|---|
| Vasodilation: arterioles to the skin widen, more heat lost by radiation | Vasoconstriction: arterioles to the skin narrow, less heat lost |
| Sweating: evaporation of sweat removes heat | Little or no sweating |
| Hair erector muscles relax, hairs lie flat | Hair erector muscles contract, hairs trap air |
| Lower metabolic rate | Shivering and higher metabolic rate (thyroxine, adrenaline) generate heat |
Worked example
Explain how negative feedback returns body temperature to normal during exercise.
- Respiration in muscles releases heat; blood temperature rises.
- Thermoreceptors in the hypothalamus detect the rise.
- The thermoregulatory centre triggers vasodilation and sweating.
- More heat is lost, temperature falls back towards the set point, and the responses decrease.
Answer: The rise is detected and reversed by heat-loss mechanisms: negative feedback.
Check yourself
- What is negative feedback?
- A change triggers responses that make it bigger
- A change is detected and responses reverse it, returning towards the set point
- The body ignores small changes
- Hormones are released continuously regardless of conditions
Show answer
A change is detected and responses reverse it, returning towards the set point. Negative feedback opposes the change.
- Which is an example of positive feedback?
- Sweating when body temperature rises
- ADH release when blood is concentrated
- Shivering when cold
- Opening of more Na+ channels as a neurone depolarises
Show answer
Opening of more Na+ channels as a neurone depolarises. Depolarisation causes more channels to open, increasing depolarisation.
- Which part of the brain contains the thermoregulatory centre?
- Cerebellum
- Hypothalamus
- Medulla oblongata
- Cerebral cortex
Show answer
Hypothalamus. The hypothalamus monitors blood temperature.
- How does vasodilation help cool the body?
- Capillaries move closer to the skin surface
- Blood flow to the skin decreases
- Arterioles in the skin widen, so more blood flows near the surface and loses heat
- It increases the metabolic rate
Show answer
Arterioles in the skin widen, so more blood flows near the surface and loses heat. More blood near the surface radiates more heat.
- How does sweating cool the skin?
- Evaporation of water from sweat removes heat energy
- Sweat reflects sunlight
- Sweat contains cold chemicals
- Sweat stops blood flow to the skin
Show answer
Evaporation of water from sweat removes heat energy. Evaporation uses heat from the skin.
- Why is homeostasis described as a dynamic equilibrium?
- Conditions never change at all
- Conditions change randomly with no control
- Conditions fluctuate slightly around a set point rather than staying exactly constant
- Only positive feedback is involved
Show answer
Conditions fluctuate slightly around a set point rather than staying exactly constant. Small fluctuations are continually corrected.
- Which response helps raise body temperature?
- Shivering
- Sweating
- Vasodilation
- Hairs lying flat
Show answer
Shivering. Muscle contractions in shivering release heat from respiration.
Sources
Last updated 7 November 2026. Spotted a mistake? Tell us.