The body regulates core temperature through thermoregulation, a negative feedback process coordinated by the hypothalamus. If temperature moves away from its normal range around , physiological and behavioural responses reduce the deviation and restore homeostasis.
Thermoreceptors in the skin detect changes in external temperature, while thermoreceptors in the hypothalamus monitor the temperature of the blood. Sensory information is sent to the hypothalamus, which acts as the thermoregulatory control centre by comparing the detected temperature with the body's set point.
If a deviation is detected, the hypothalamus activates effectors, including sweat glands, skeletal muscles and smooth muscle in skin arterioles. Their responses alter heat loss or heat production:
| Thermal condition | Main responses | Effect on core temperature |
|---|---|---|
| Core temperature rises | Vasodilation increases blood flow near the skin; sweating increases evaporative heat loss; metabolic heat production may decrease | More heat is transferred to the environment, so temperature falls toward the set point |
| Core temperature falls | Vasoconstriction reduces blood flow near the skin; shivering produces heat through rapid muscle contractions; metabolic rate may increase | Heat loss decreases and heat production increases, so temperature rises toward the set point |
Behavioural responses also support thermoregulation. Examples include moving into shade, removing clothing, drinking fluids, adding clothing or reducing exposure to cold.
A common misconception is that sweating cools the body simply because sweat is produced. Cooling occurs when sweat evaporates, using thermal energy from the skin; sweat that drips off without evaporating provides little cooling. Similarly, vasodilation does not produce cold blood, it increases heat transfer by moving more warm blood close to the skin.
In an IB SEHS response on A.1.2 Maintaining homeostasis, identify the stimulus, receptor, hypothalamic control centre, effector and corrective response. Explicitly explain how the response reverses the original change, demonstrating negative feedback rather than merely listing mechanisms.
