Disease and response · GCSE Biology
Thermoregulation
Control body temperature for GCSE Biology: thermoregulatory centre, sweating, vasodilation, vasoconstriction, shivering, hair erection, and why enzymes need a set point near 37 °C.
Too hot: sweat and vasodilation, more heat lost. Too cold: shivering, vasoconstriction, less sweating, hairs up. The hypothalamus (thermoregulatory centre) is the thermostat. Enzymes denature if it fails.
The important bits
What you need to know
- 1
Human core temperature is kept near 37 °C so that enzymes stay at their optimum. Too high: denaturation. Too low: collisions too slow, metabolism fails.
- 2
Receptors in the skin and in the thermoregulatory centre of the brain (hypothalamus) detect temperature. The centre coordinates effectors.
- 3
If too hot: sweat glands secrete sweat; evaporation transfers heat from the skin. Blood vessels supplying the skin capillaries dilate (vasodilation), more blood flows near the surface, more heat is transferred to the surroundings by radiation.
- 4
If too cold: sweating stops. Blood vessels supplying the skin capillaries constrict (vasoconstriction), less blood near the surface, less heat lost. Skeletal muscles shiver: respiration transfers heat. Erector muscles raise hairs to trap an insulating layer of air (more useful in furry mammals; limited in humans).
- 5
Vasodilation is not the blood vessel moving to the skin, and it is not the same as sweating. Name the mechanism and the effect on heat transfer.
- 6
This is negative feedback: once temperature returns to the set point, the responses switch off.
- 7
Exercise produces extra heat from respiration (exothermic). The same cooling responses then prevent overheating. Fever is a raised set point during infection — Triple may mention it; do not treat a fever as failed homeostasis without that idea.
- 8
Hypothermia and heat stroke are the clinical ends. For GCSE, stick to named effectors and heat loss or gain.
Quotations worth analysing
Short evidence. Real method.
“Vasodilation: blood vessels supplying the skin capillaries dilate, so more heat is lost by radiation.”
Name dilation, more blood in the skin, more heat transferred to the surroundings. “Blood goes to the skin” is sloppy but on the right track.
“Evaporation of sweat transfers heat from the skin.”
Evaporation is the key word. Sweat sitting on the skin without evaporating (humid day) cools less.
“Shivering transfers heat from increased respiration in muscles.”
Link to the respiration equation being exothermic. Huddling and extra clothes are behavioural responses some papers accept.
Go deeper
How do I get full marks on “explain how the body cools down”?
Detect: thermoregulatory centre and skin receptors. Sweat: glands release water plus salts; evaporation uses heat from the skin, so core temperature falls. Vasodilation: arterioles to skin capillaries widen, more blood flow near the surface, more heat radiated (and convected) away. Mention both. Do not write that pores open as the main story, or that blood vessels “move up”. Hairs lie flat, reducing the trapped-air layer. Then negative feedback: when 37 °C is restored, sweating and dilation reduce. If the question is exercise, add that respiration is transferring extra heat, so these responses increase. A humid environment reduces evaporation, so cooling is less effective — a neat extra if data show two climates.
Go deeper
What is the exact wording for vasoconstriction versus vasodilation?
Vasodilation: vessels supplying skin capillaries dilate → more blood in skin → more heat loss. Vasoconstriction: those vessels constrict → less blood in skin → less heat loss (core stays warmer). The capillaries themselves are often said to “open” or “close” in textbooks; mark schemes prefer the supplying arterioles. Never say the blood vessel travels through the body to a new place. Never say vasoconstriction “keeps heat in the blood” without locating the skin. Pair each with shivering or sweating so a six-mark has two cooling and two warming mechanisms. Hair erection traps air; in humans it is goosebumps and a weak insulator, but still teach it because diagrams show erector muscles.
Go deeper
Why is 37 °C a homeostasis number, not a trivia fact?
It is the optimum for human enzymes such as those of respiration and of the brain. A few degrees up and proteins begin to denature — active sites fail, metabolism collapses, it can be fatal. A few degrees down and reaction rates crash, brain and heart fail. So temperature control is enzyme protection, the same idea as the enzyme graphs. Blood glucose and water control also protect cells and enzymes (osmosis, respiration fuel). A strong exam sentence: “Homeostasis of temperature keeps enzymes at their optimum so respiration can transfer energy at a suitable rate.” That joins three topics in one line, which is what grade 8 answers do.
See the idea in action
A runner’s core temperature rises because respiration is exothermic. Receptors and the thermoregulatory centre detect the rise. Sweat evaporates, transferring heat from the skin. Vasodilation increases blood flow through skin capillaries, so more heat is lost by radiation. When temperature returns towards 37 °C, these responses reduce (negative feedback). If the same person sat in a cold wind, vasoconstriction, shivering (heat from extra respiration) and reduced sweating would be used instead. Writing “the blood moves to the skin” without dilation or heat loss would be a weaker line.
Exam technique
Turn knowledge into marks
Always name the mechanism (vasodilation, sweating, shivering, vasoconstriction) and the effect on heat transfer. Mention 37 °C and enzymes. Do not say blood vessels move up and down through the skin.
Common mistakes
Do not give these marks away
- 01
Saying blood vessels move to the surface, rather than dilate or constrict.
- 02
Forgetting evaporation when discussing sweat, or mixing up vasodilation (cool) with vasoconstriction (warm).
- 03
Omitting the thermoregulatory centre, or never linking temperature to enzyme optimum.
What happens when body temperature is too high?
AVasoconstriction and shivering
BSweating and vasodilation so more heat is transferred to the surroundings
CADH makes urine more concentrated
DInsulin stores heat as glycogen
Show the answer
Sweating and vasodilation so more heat is transferred to the surroundings. Evaporation of sweat and extra blood flow in the skin increase heat loss. Vasoconstriction and shivering are for when the body is too cold. ADH and insulin control water and glucose, not this cooling response.
Quick questions
If this is the bit you searched
How does the body cool down GCSE Biology?
Sweating (evaporation transfers heat) and vasodilation (more blood in the skin, more heat lost by radiation). The thermoregulatory centre coordinates this.
What is vasoconstriction?
Blood vessels supplying skin capillaries narrow, so less blood flows near the surface and less heat is lost — used when you are too cold.
Why is body temperature kept at about 37 °C?
It is the optimum for human enzymes. Too hot and enzymes denature; too cold and metabolic reactions are too slow.
How does shivering warm you?
Muscle contraction increases the rate of respiration, which is exothermic, so more heat is transferred to the body.