Control of body temperature (biology only) — AQA GCSE Biology
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Control of body temperature (biology only) explained
The thermoregulatory centre in the brain acts as the body's thermostat.
Read the full explanation
It receives information about blood temperature from receptors within itself and about skin temperature from receptors in the skin. It compares this information with a set point, around 37 °C, and coordinates responses through the nervous system. When too hot, it triggers vasodilation and sweating; when too cold, vasoconstriction, shivering and less sweating. These responses change heat loss or heat production to bring temperature back to the set point. This is an example of negative feedback, and it keeps enzymes working at their optimum.
The thermoregulatory centre contains receptors sensitive to the temperature of the blood.
Inside the thermoregulatory centre are receptors that detect the temperature of the blood flowing through the brain. Because blood circulates from the core, its temperature reflects the body's internal temperature, so these receptors give a direct measure of core temperature. They are separate from temperature receptors in the skin, which detect external temperature and warn the brain about changes in the environment. The centre combines both sets of information to decide whether to activate cooling or warming responses. This dual input allows the body to respond both to internal changes, such as during exercise, and to external changes, such as entering a cold room.
The skin contains temperature receptors and sends nervous impulses to the thermoregulatory centre.
Temperature receptors in the skin detect changes in external temperature. When stimulated, they generate nervous impulses that travel along sensory neurones to the central nervous system. These impulses reach the thermoregulatory centre, a region of the brain that monitors and coordinates body temperature. The thermoregulatory centre itself contains receptors sensitive to the temperature of the blood flowing through the brain. By combining this information, it compares core and skin temperatures. If it detects a deviation from the normal set point, it initiates corrective responses through the nervous system. For example, touching a cold railing stimulates skin receptors, sending impulses to the centre before core temperature changes.
If the body temperature is too high, blood vessels dilate (vasodilation) and sweat is produced from the sweat glands.
When the thermoregulatory centre detects that core body temperature has risen above the normal set point, it triggers two coordinated cooling responses. Vasodilation occurs when the smooth muscle in the walls of arterioles supplying the skin capillaries relaxes, so the arterioles widen and more blood flows through the skin capillaries. This increases the volume of blood close to the skin surface, so more energy is transferred by radiation and convection to the surroundings. At the same time, sweat glands secrete sweat onto the skin surface. As sweat evaporates, it takes latent heat from the skin, removing energy and cooling the body. For example, during exercise on a hot day, a person's skin may redden and become wet with sweat as both responses operate together to lower core temperature.
Both these mechanisms cause a transfer of energy from the skin to the environment.
Vasodilation and sweating both increase the rate at which energy is transferred from the skin to the surroundings, helping to lower core body temperature. In vasodilation, more blood flows through capillaries near the skin surface, so a greater volume of warm blood is exposed to the cooler environment; energy is transferred by radiation and convection from the skin to the air. In sweating, sweat glands release sweat onto the skin; as the water in sweat evaporates, it absorbs latent heat from the skin, so energy is transferred from the skin to the water vapour and then to the environment. For example, on a hot day a runner may have flushed skin and visible sweat; both features increase energy loss and help prevent overheating. The mechanisms work together and are reversed when body temperature falls.
If the body temperature is too low, blood vessels constrict (vasoconstriction), sweating stops and skeletal muscles contract (shiver).
When the thermoregulatory centre detects that core body temperature has fallen below the normal set point, it triggers responses that reduce energy transfer to the environment and increase energy release in the body. Vasoconstriction occurs when smooth muscle in the walls of skin arterioles contracts, narrowing the vessels and reducing blood flow through skin capillaries; less energy is therefore transferred from the skin to the surroundings. Sweat production stops, so evaporative cooling is reduced. Skeletal muscles contract rapidly and repeatedly in shivering; the increased respiration in muscle cells releases energy as heat, warming the blood and raising core temperature. For example, standing outside in cold weather may cause pale skin, dry skin and shivering as the body attempts to conserve and generate energy. These responses continue until the set point is restored.
(HT only) Students should be able to explain how these mechanisms lower or raise body temperature in a given context.
The hypothalamus monitors blood temperature and triggers responses that either lower or raise body temperature. When too hot, sweating increases and evaporation of sweat removes latent heat from the skin; vasodilation widens skin arterioles so more blood flows near the surface and radiates heat. When too cold, shivering contracts muscles rapidly, releasing heat from respiration; vasoconstriction narrows skin arterioles, reducing heat loss; sweating stops and hairs stand erect to trap insulating air. In a context such as a marathon runner on a hot day, explain each mechanism by linking the stimulus, the response and the resulting heat transfer, rather than listing responses alone.
Your focus
- State the location and role of the thermoregulatory centre.
- Describe how it coordinates cooling and warming responses.
- Explain why a stable core temperature is important for enzymes.
Show all 21 objectives
- Identify what the thermoregulatory centre receptors detect.
- Contrast blood receptors with skin temperature receptors.
- Explain why blood temperature indicates core temperature.
- Identify the skin as the location of temperature receptors.
- Describe the pathway of a nervous impulse from a skin receptor to the thermoregulatory centre.
- Explain the role of the thermoregulatory centre in coordinating temperature control.
- Describe vasodilation and sweat production as responses to overheating.
- Explain how vasodilation and sweating transfer energy from the skin to the environment.
- Relate the cooling responses to the action of the thermoregulatory centre.
- Explain how vasodilation transfers energy from the skin to the environment.
- Explain how sweating and evaporation transfer energy from the skin to the environment.
- Compare the two cooling mechanisms in terms of energy transfer.
- Describe vasoconstriction, cessation of sweating and shivering as responses to cooling.
- Explain how each response helps to conserve energy or generate heat.
- Relate the responses to the role of the thermoregulatory centre in negative feedback.
- Describe how sweating, vasodilation, shivering and vasoconstriction change heat loss or heat production.
- Explain, using a named context, how each response helps restore core body temperature.
- Link thermoregulation to negative feedback and the role of the hypothalamus.
Control of body temperature (biology only) exam tips
Marking Points
- The thermoregulatory centre is in the brain and monitors body temperature.
- It contains receptors sensitive to the temperature of the blood and receives impulses from temperature receptors in the skin.
- It coordinates responses such as vasodilation, vasoconstriction, sweating and shivering.
- Responses are negative feedback that returns temperature to about 37 °C.
- Stable temperature keeps enzymes at their optimum for metabolism.
- Receptors in the thermoregulatory centre detect blood temperature.
- Blood temperature reflects core body temperature because blood circulates from the core.
- Skin receptors detect external temperature and provide separate information.
- The centre integrates both inputs before triggering a response.
- This allows responses to internal and external temperature changes.
- Temperature receptors in the skin detect changes in the external environment.
- Stimulation of a temperature receptor generates a nervous impulse.
- The impulse travels along a sensory neurone to the central nervous system.
- Impulses are relayed to the thermoregulatory centre in the brain.
- The thermoregulatory centre itself contains receptors that are sensitive to the temperature of the blood flowing through the brain.
- The thermoregulatory centre coordinates responses that restore core body temperature to its normal set point.
- Vasodilation involves widening of arterioles that supply skin capillaries.
- More blood flows through skin capillaries, increasing energy transfer to the environment.
- Sweat glands produce sweat, which is released onto the skin surface.
- Evaporation of sweat transfers energy from the skin to the surroundings.
- Both responses are coordinated by the thermoregulatory centre when body temperature is too high.
- The responses continue until core body temperature returns to its normal set point.
- Vasodilation increases blood flow through skin capillaries, so more energy is transferred by radiation and convection.
- Sweating leads to evaporation of water from the skin surface.
- Evaporation of sweat transfers latent heat from the skin to the environment.
- Both mechanisms reduce core body temperature by increasing energy loss to the surroundings.
- The rate of energy transfer depends on the temperature difference between the skin and the environment.
- The responses are examples of negative feedback restoring the normal set point.
- Vasoconstriction narrows arterioles supplying skin capillaries, reducing blood flow to the skin surface.
- Reduced blood flow decreases energy transfer from the skin to the environment.
- Sweat production stops, so evaporative cooling is reduced.
- Shivering involves rapid contraction of skeletal muscles.
- Increased muscle respiration releases energy that warms the body.
- The responses are coordinated by the thermoregulatory centre as part of negative feedback.
- Identify the stimulus as a rise or fall in core body temperature detected by the hypothalamus.
- For cooling, link sweating to evaporation of water from the skin surface, which transfers latent heat away from the body.
- For cooling, link vasodilation to increased blood flow through surface capillaries, increasing heat loss by radiation.
- For warming, link shivering to rapid muscle contraction and increased respiration, which releases heat energy.
- For warming, link vasoconstriction to reduced blood flow near the skin surface, decreasing heat loss by radiation.
- Explain that these responses are coordinated by the nervous system as negative feedback, restoring core temperature towards a set point.
Examiner Tips
- 💡Name the centre and its location in every answer.
- 💡Link each response to more or less heat loss.
- 💡Use the phrase negative feedback when explaining return to normal.
- 💡Distinguish blood receptors from skin receptors clearly.
- 💡Explain why blood temperature represents core temperature.
- 💡Use the term core temperature accurately.
- 💡Use the phrase nervous impulse rather than signal or message when describing communication along neurones.
- 💡Name the thermoregulatory centre and state its location in the brain to show precise knowledge.
- 💡Link the receptor, sensory neurone and thermoregulatory centre in a logical sequence when explaining the pathway.
- 💡Use the terms vasodilation and sweat glands accurately, and link each to its cooling effect.
- 💡Explain the mechanism in terms of energy transfer rather than simply saying the body cools down.
- 💡When describing vasodilation, refer to arterioles widening and increased blood flow through skin capillaries.
- 💡Use the phrase transfer of energy rather than heat loss alone, and specify radiation, convection or evaporation where relevant.
- 💡Link each mechanism to the direction of energy transfer: from skin to environment.
- 💡Compare the two mechanisms briefly to show they both achieve cooling by different routes.
- 💡Use the terms vasoconstriction, sweating stops and shivering precisely, and link each to reduced energy loss or increased energy release.
- 💡Explain shivering in terms of muscle contraction and increased respiration, not just movement.
- 💡When describing vasoconstriction, refer to narrowing of arterioles and reduced blood flow through skin capillaries.
- 💡Use the context given in the question, such as exercise in hot weather or standing in cold water, and apply each mechanism to that situation.
- 💡Write cause-and-effect chains: stimulus, detection by hypothalamus, response, effect on heat gain or loss.
- 💡Use precise terms such as vasodilation, vasoconstriction, evaporation and latent heat rather than vague words like 'blood moves'.
Common Mistakes
- Saying the skin controls temperature; correction: the thermoregulatory centre in the brain coordinates the response.
- Thinking sweating cools the body by producing cold; correction: evaporation of sweat transfers energy away.
- Confusing vasodilation with vasoconstriction; correction: dilation widens vessels to lose heat, constriction narrows them to conserve heat.
- Saying the receptors detect skin temperature; correction: they detect blood temperature, while skin receptors detect external temperature.
- Thinking the receptors are in the blood vessels; correction: they are in the thermoregulatory centre in the brain.
- Believing only one source of information is used; correction: both blood and skin inputs are combined.
- Stating that the skin sends hormones to the thermoregulatory centre; the correct idea is that nervous impulses travel along neurones.
- Claiming that the thermoregulatory centre is in the skin; it is a region of the brain, and the skin only contains the receptors.
- Saying that temperature receptors detect core body temperature directly; skin receptors detect skin and environmental temperature, while receptors within the thermoregulatory centre monitor blood temperature.
- Confusing vasodilation with vasoconstriction; vasodilation widens vessels and increases blood flow to the skin when too hot.
- Stating that sweat itself cools the body; it is the evaporation of sweat that transfers energy away from the skin.
- Claiming that blood vessels move closer to the skin surface; the vessels dilate, and the increased blood flow through existing skin capillaries causes the effect.
- Saying that energy is destroyed or lost completely; energy is transferred to the environment, not destroyed.
- Describing sweating as releasing coldness; sweat cools by evaporation transferring energy away from the skin.
- Ignoring the role of blood flow in vasodilation and only mentioning sweating when asked about both mechanisms.
- Confusing vasoconstriction with vasodilation; vasoconstriction narrows vessels and reduces blood flow when too cold.
- Stating that shivering produces energy directly; muscle contraction increases respiration, which releases energy as heat.
- Saying that sweating stops because sweat glands freeze; sweating stops because the thermoregulatory centre inhibits the sweat glands.
- Saying sweating cools the body because sweat is cold; the correction is that evaporation of sweat removes latent heat from the skin.
- Confusing vasodilation with vasoconstriction; the correction is that vasodilation widens arterioles to lose heat, while vasoconstriction narrows them to conserve heat.
- Stating that shivering creates heat without linking it to respiration; the correction is that rapid muscle contraction increases respiration, which releases heat energy.