Thermoregulation - TCE Biology (Tasmania)
“Analyse thermoregulation in humans, including stimulus-response models, feedback loops and the associated messages and organ structures”
Humans keep core body temperature near 37 degrees Celsius by negative feedback. Thermoreceptors in the skin and the hypothalamus detect changes, and the hypothalamus acts as the control centre, sending nerve impulses to effectors. When too hot: skin arterioles dilate (vasodilation) and sweat glands produce sweat, increasing heat loss. When too cold: skin arterioles constrict (vasoconstriction), skeletal muscles shiver, piloerector muscles raise the hairs and sweating stops, reducing heat loss and increasing heat production. Behaviour, such as finding shade or adding clothes, also helps.
Jump to a section
What this dot point is asking
Thermoregulation is part of criterion 6 (Section C of the TASC exam). The external assessment specifications include the mechanisms in the skin (vasodilation, vasoconstriction, piloerector muscles, sweat glands) and the role of the hypothalamus as detector. The role of the thyroid gland and TSH is excluded.
Why temperature matters
Enzymes work best within a narrow temperature range. If body temperature rises too high, enzymes begin to denature; if it falls too low, enzyme-controlled reactions (including respiration) slow down. Humans are endotherms: most of their body heat comes from their own metabolism.
The feedback loops
When body temperature rises (exercise, a hot day)
| Element | Structure | Action |
|---|---|---|
| Receptors | Thermoreceptors in the skin; the hypothalamus (monitors blood temperature) | Detect the rise |
| Control centre | Hypothalamus | Sends nerve impulses to effectors |
| Effectors | Skin arterioles | Vasodilation: more blood near the skin surface, more heat lost |
| Sweat glands | More sweat; evaporation removes heat | |
| Piloerector muscles | Relax, so hairs lie flat | |
| Result | Temperature falls back towards normal; stimulus reduced |
When body temperature falls (cold weather)
| Element | Structure | Action |
|---|---|---|
| Receptors | Thermoreceptors in the skin; the hypothalamus | Detect the fall |
| Control centre | Hypothalamus | Sends nerve impulses to effectors |
| Effectors | Skin arterioles | Vasoconstriction: less blood near the surface, less heat lost |
| Skeletal muscles | Shivering: rapid contractions release heat from respiration | |
| Piloerector muscles | Contract, raising hairs (goosebumps) | |
| Sweat glands | Sweating stops | |
| Result | Temperature rises back towards normal; stimulus reduced |
In vasodilation and vasoconstriction, the arterioles supplying the skin widen or narrow. The blood vessels do not move closer to or further from the skin surface.
Structural and behavioural responses
Endotherms also use structural features and behaviour to control heat exchange:
- Structural: body fat and fur or hair provide insulation.
- Behavioural: seeking shade or shelter, changing clothing, huddling, reducing activity in the heat.
In furry mammals, raising the hairs traps a layer of insulating air; in humans the effect is small because body hair is sparse.
A runner on a 35 degree day
- Muscle activity releases heat and the surroundings are hot, so core temperature rises (stimulus).
- Skin thermoreceptors and the hypothalamus detect the rise.
- The hypothalamus sends nerve impulses to skin arterioles and sweat glands.
- Vasodilation increases blood flow near the skin; sweat evaporates, removing heat.
- If the runner cannot replace the water lost in sweat, the blood becomes more concentrated, and water balance mechanisms (ADH) are triggered too, which links to osmoregulation.
Marker's note: name the receptor, control centre, pathway (nervous) and each effector, then close the loop.
- Saying blood vessels move towards the skin
- The arterioles dilate or constrict; they do not move.
- Forgetting the receptor and control centre
- Name the thermoreceptors and the hypothalamus explicitly.
- Bringing in the thyroid
- The thyroid and TSH are excluded from the TASC exam.
Exam-style questions
Questions in the style of TASC exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
Original6 marksA bushwalker is caught in cold, windy weather on kunanyi / Mount Wellington and her core body temperature begins to fall. Use a stimulus-response model to explain how her body responds.Show worked answer →
One mark for each element correctly applied, up to six.
- Stimulus
- Core body temperature falls below the normal range.
- Receptors
- Thermoreceptors in the skin detect the cold, and the hypothalamus detects the fall in blood temperature.
- Control centre
- The hypothalamus sends nerve impulses to effectors.
- Effectors and responses
- Skin arterioles constrict (vasoconstriction), so less blood flows near the surface and less heat is lost; skeletal muscles contract rapidly (shivering), releasing heat; piloerector muscles contract, raising hairs; sweating stops.
- Behaviour
- She puts on more layers and moves out of the wind.
- Negative feedback
- As core temperature returns to normal, the stimulus is removed and the responses decrease.
Original3 marksExplain how vasodilation of skin arterioles helps to cool the body.Show worked answer →
Explanation (3 marks). Arterioles supplying the skin widen (1), so more warm blood flows through capillaries close to the skin surface (1), and more heat is lost from the skin to the surroundings by radiation, conduction and convection, and helps evaporate sweat (1).