Physiology · Temperature, exercise and metabolism
Body temperature regulation !
- Regulation
- Exam priority: high
The brain keeps the body core near 37 °C: it sweats and opens skin vessels when hot, shivers and closes them when cold.
Updated 2026-11-01
Also called: Thermoregulation
See it in 3D: Hypothalamus · Skin
What it is
The preoptic area of the anterior hypothalamus compares core temperature with a set point (≈37 °C) and integrates input from skin and visceral thermoreceptors. When hot, it boosts heat loss through the skin; when cold, it cuts heat loss and makes more heat. The skin is the radiator and skin blood flow is the valve.
How it works, step by step
- Thermoreceptors in skin, spinal cord and viscera, plus warm-sensitive preoptic neurons, report temperature.
- If core temperature rises above the set point, sympathetic vasoconstrictor tone falls and warm blood floods the skin.
- Sympathetic cholinergic fibres switch on sweating; evaporation removes ≈0.58 kcal per gram of water.
- If temperature falls, norepinephrine closes skin arterioles and arteriovenous anastomoses, and hairs stand up.
- Motor neurons receive a rhythmic drive (shivering) that can raise heat production several-fold.
- Over longer periods norepinephrine activates brown fat (UCP1) and thyroid hormone raises the basal metabolic rate.
Responses to heat and cold
| Response | Heat | Cold |
|---|---|---|
| Skin vessels | Vasodilation | Vasoconstriction |
| Sweating | Increases (up to 1–2 L/h when acclimatized) | Suppressed |
| Heat production | Falls slightly | Shivering, non-shivering thermogenesis |
| Behaviour | Seek shade, less activity | Wrap up, curl up |
| Acclimatization (days–weeks) | Earlier, more dilute sweat (aldosterone) | Limited in humans |
Clinical notes
- Newborns: large surface area and little insulating fat; they rely on brown fat and cool quickly.
- Older adults, high spinal cord injury and anticholinergic drugs impair sweating or vasoconstriction and raise the risk of heat stroke or hypothermia.
- Hypothyroidism: cold intolerance; hyperthyroidism: heat intolerance with warm, moist skin.
Test yourself
Think of the answer, then tap the question to see it.
Why does the body heat up on a 38 °C, 90%-humidity day in Cartagena despite heavy sweating?
With air hotter than skin only evaporation cools, and high humidity stops sweat evaporating: it drips off without removing heat.
Which transmitter drives eccrine sweat glands, and what does that mean for anticholinergic drugs?
Acetylcholine from sympathetic postganglionic fibres acting on muscarinic receptors; anticholinergics dry the skin and favour hyperthermia.
How does brown fat make heat without muscle contraction?
UCP1 lets protons return to the mitochondrial matrix bypassing ATP synthase, so the gradient's energy is released as heat.
See it in 3D
The structures of Durgical's 3D anatomy where it happens.
Related topics
- Fever
- Heat exhaustion and heat stroke
- Hypothermia and cold injury
- Energy metabolism and basal metabolic rate
Related conditions
In Biochemistry
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: 24.6 Energy and Heat Balance (OpenStax (Rice University), 2022); 1.5 Homeostasis (OpenStax (Rice University), 2022); 5.3 Functions of the Integumentary System (OpenStax (Rice University), 2022); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 74). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).
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Representative model, for educational purposes only.