Homeostasis and thermoregulationSpec 7.17
In short
Homeostasis is the maintenance of a stable internal environment within narrow limits, a state of dynamic equilibrium. It keeps conditions suitable for enzymes and cells, including during exercise. The hypothalamus detects changes in blood temperature and coordinates responses such as sweating, vasodilation, vasoconstriction and shivering.
Homeostasis is the maintenance of a stable internal environment (for example body temperature, blood glucose concentration, blood water potential and pH) within narrow limits, by negative feedback. It is a state of dynamic equilibrium: conditions continually change slightly and are continually corrected, so they fluctuate around a set point.
It is important because enzymes work best at a particular temperature and pH, and cells need a stable water potential and a constant supply of glucose and oxygen for respiration. During exercise, muscle respiration increases heat production, CO₂ concentration and the demand for glucose and oxygen, so conditions must be corrected to prevent damage.
Thermoregulation and the hypothalamus
The hypothalamus contains thermoreceptors that detect the temperature of the blood flowing through it (core temperature). Thermoreceptors in the skin also send information to the hypothalamus. The hypothalamus acts as the coordination centre and sends impulses to the effectors.
| Response | If core temperature rises (e.g. exercise) | If core temperature falls |
|---|---|---|
| Skin arterioles | Vasodilation: more blood flows near the surface, so more heat is lost by radiation | Vasoconstriction: less blood flows near the surface, so less heat is lost |
| Sweat glands | Sweat secreted: evaporation of water takes heat from the skin | Little or no sweat |
| Skeletal muscles | No shivering | Shivering: rapid involuntary contractions release heat from respiration |
| Hair erector muscles | Relax: hairs lie flat (little effect in humans) | Contract: hairs stand up, trapping an insulating layer of air |
| Metabolic rate | Reduced | Increased (e.g. by hormones such as adrenaline and thyroxine) |
| Behaviour | Seek shade, remove clothing | Seek warmth, add clothing |
In exercise, say that heat released by respiration in muscle raises core temperature, the hypothalamus detects it, and effectors such as sweat glands and skin arterioles lower it again (negative feedback).
Written and checked against the Edexcel International A Level Biology (YBI11) specification · Updated October 2026