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Learn4BI1Paper 2B · Paper 2 (all content)Structure and functions in living organismsHormones and homeostasis
Structure and functions in living organisms · Subtopic 14 of 21

Hormones and Homeostasis

Hormones are chemicals made by endocrine glands and carried in the blood to target organs. They act more slowly than nerves but for longer. Adrenaline (adrenal glands) prepares the body for action; insulin (pancreas) lowers blood glucose by making the liver and muscles take up glucose and store it as glycogen; glucagon raises it. Homeostasis keeps internal conditions constant using negative feedback. Body temperature is controlled by the brain: when too hot, sweating and vasodilation; when too cold, shivering and vasoconstriction. In Type 1 diabetes, the pancreas makes no insulin.

Cambridge 5090 Paper 1Cambridge 5090 Paper 2Cambridge 0610 Papers 2, 4Cambridge 0610 Papers 1, 3Edexcel 4BI1 Paper 1BEdexcel 4BI1 Paper 2B≈ 45 minRevision 1 · updated 2026-10-30
Section 1 of 14

Learning objectives

  • Compare nervous and hormonal control.
  • Describe the roles of adrenaline, insulin and glucagon.
  • Explain negative feedback in blood glucose and temperature control.
  • Describe Type 1 diabetes and its treatment.
Pause and think

Why do you feel your heart pounding seconds after a sudden fright, and why does the feeling last a while?

Section 2 of 14

Core idea

Start hereA thermostat inside you

Whether you're in a snowstorm or a desert, your core temperature stays within about half a degree of 37 °C. Your body is constantly correcting itself.

The big idea

Hormones carry chemical messages in the blood. Homeostasis uses negative feedback: any change from the set point triggers a response that reverses it.

1. Negative feedback

Blood glucose control

Two hormones pull in opposite directions.

Worked exampleOverheating

A runner's core temperature rises to 38.5 °C.

Goal
Describe the responses.
Strategy
Brain detects the rise and triggers cooling.
  1. sweating\text{sweating}
    Evaporation takes heat from the skin.
  2. vasodilation\text{vasodilation}
    Arterioles near skin widen, more heat lost by radiation.
  3. hairs lie flat\text{hairs lie flat}
    Less insulating air trapped.
AnswerTemperature falls back towards 37 °C.
✓ CheckResponses reverse the change: negative feedback ✓.
Key takeawayNerves vs hormones Nerves: electrical, fast, brief, precise. Hormones: chemical in blood, slower, longer-lasting, widespread.
Pause and think

Why must people with Type 1 diabetes balance insulin with food and exercise?

Summary

  • Hormones in blood.
  • Insulin/glucagon.
  • Temperature control by feedback.
Key words
Homeostasis
Keeping internal conditions constant.
Negative feedback
A change triggers a response that reverses it.
Vasodilation
Widening of blood vessels near the skin.
HistoryBanting and Best. In 1921 Frederick Banting and Charles Best extracted insulin from dog pancreases. Within a year, children dying of diabetes were being saved by injections.
Fun factGoosebumps. Goosebumps are tiny muscles raising your hairs. In furry ancestors this trapped warm air; in humans it's mostly leftover wiring.
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