Thermoregulation is the process that keeps body temperature within a narrow, healthy range even when the environment changes. In humans, the normal core temperature is about 37 degrees Celsius, and enzymes, nerves, and muscles work best near this value. If the body becomes too hot or too cold, cells can be damaged and organs may stop working properly.
Thermoregulation matters because it links anatomy, physiology, physics, and homeostasis in one feedback-controlled system.
The hypothalamus in the brain acts as the main control center by comparing body temperature to a set point. Temperature receptors in the skin and body core send information to the hypothalamus, which triggers responses such as sweating, shivering, vasodilation, and vasoconstriction. Heat moves between the body and the environment by radiation, conduction, convection, and evaporation.
These responses form negative feedback loops because they reverse the original temperature change and help return the body toward normal.
Key Facts
- Normal human core body temperature is about 37 degrees Celsius.
- Negative feedback: stimulus causes responses that reduce the original change.
- Heat balance can be summarized as heat stored = heat gained - heat lost.
- Evaporation of sweat removes heat because liquid water absorbs energy as it becomes vapor.
- Vasodilation increases blood flow near the skin, increasing heat loss.
- Vasoconstriction decreases blood flow near the skin, reducing heat loss.
Vocabulary
- Thermoregulation
- Thermoregulation is the control of body temperature within a narrow range that supports normal cell function.
- Hypothalamus
- The hypothalamus is a brain region that monitors temperature and coordinates responses to heating or cooling.
- Negative feedback
- Negative feedback is a control process in which a response reduces the original stimulus and returns a system toward a set point.
- Vasodilation
- Vasodilation is the widening of blood vessels, often near the skin, which allows more heat to leave the body.
- Vasoconstriction
- Vasoconstriction is the narrowing of blood vessels, often near the skin, which helps conserve body heat.
Common Mistakes to Avoid
- Thinking sweating cools the body only because sweat is wet is wrong because cooling mainly happens when sweat evaporates and carries heat away.
- Confusing vasodilation with vasoconstriction is wrong because vasodilation increases skin blood flow and heat loss, while vasoconstriction reduces skin blood flow and conserves heat.
- Assuming the skin temperature and core temperature are always the same is wrong because skin temperature changes more quickly with the environment, while core temperature is more tightly regulated.
- Describing thermoregulation as positive feedback is wrong because most body temperature control is negative feedback that opposes a rise or drop in temperature.
Practice Questions
- 1 A student has a core temperature of 39.0 degrees Celsius. If normal core temperature is 37.0 degrees Celsius, how many degrees above normal is the student, and which two thermoregulation responses should increase?
- 2 During exercise, a person loses 600 g of sweat that completely evaporates. If evaporating 1 g of water removes about 2.4 kJ of heat, how much heat is removed in kJ?
- 3 Explain why a person standing in cold wind loses heat faster than a person standing in still cold air, even if the air temperature is the same.