Homeostasis: how the body keeps conditions stable
TutorAura guide · Updated
Homeostasis is the regulation of the internal conditions of a cell or organism to keep them at the best levels for enzymes and cells to work, despite changes inside and outside the body. In humans, it controls blood glucose concentration, body temperature and water levels. Automatic control systems do the work, using nerves and hormones.
Key takeaways
- Homeostasis keeps internal conditions stable for enzyme action and cell function.
- Control systems have receptors, coordination centres and effectors.
- Negative feedback reverses a change back towards normal.
- Insulin lowers blood glucose; glucagon raises it.
Control systems
| Part | What it does | Examples |
|---|---|---|
| Receptors | Detect a change (a stimulus) | Temperature receptors in the skin |
| Coordination centres | Receive and process the information | The brain, the spinal cord, the pancreas |
| Effectors | Bring about a response to restore normal levels | Muscles and glands |
Information is carried by the nervous system (fast, short-lived electrical impulses) or the endocrine system (slower, longer-lasting hormones carried in the blood).
Negative feedback
In negative feedback, a change from the normal level triggers a response that reverses it. If a level rises too high, the body acts to lower it; if it falls too low, the body acts to raise it. The result is that conditions stay within a narrow range, like a thermostat switching heating on and off.
Controlling blood glucose
The pancreas monitors and controls blood glucose concentration.
- Too high (after a meal): the pancreas releases insulin. Glucose moves from the blood into cells, and liver and muscle cells convert excess glucose into glycogen for storage.
- Too low (higher tier): the pancreas releases glucagon, which makes the liver convert glycogen back into glucose and release it into the blood.
Insulin and glucagon work together as a negative feedback cycle.
Diabetes
| Type 1 | Type 2 | |
|---|---|---|
| Cause | The pancreas produces too little insulin | Body cells no longer respond properly to insulin |
| Result | Uncontrolled high blood glucose | Uncontrolled high blood glucose |
| Treatment | Insulin injections | A carbohydrate-controlled diet and exercise; sometimes medication |
| Risk factor | Usually starts in childhood | Obesity is a major risk factor |
Controlling body temperature
The thermoregulatory centre in the brain monitors blood temperature and receives impulses from temperature receptors in the skin.
| Too hot | Too cold |
|---|---|
| Sweating: evaporation of sweat transfers energy away from the skin | Shivering: muscles contract, and respiration releases heat |
| Vasodilation: blood vessels near the skin widen, so more heat is lost | Vasoconstriction: blood vessels near the skin narrow, so less heat is lost |
| Sweating stops |
Blood vessels don't move closer to or further from the skin; they widen or narrow.
Controlling water
The kidneys filter the blood and reabsorb the water, glucose and ions the body needs. Excess water, ions and urea leave in urine. If the blood is too concentrated, the pituitary gland releases more ADH (anti-diuretic hormone), which makes the kidney tubules reabsorb more water, so less, more concentrated urine is produced. (Water balance and ADH are separate science content in some specifications.)
Common mistakes
- Mixing up glucagon (a hormone) and glycogen (a stored carbohydrate).
- Saying insulin "turns glucose into glycogen" in the blood. It causes cells to take up glucose, and liver and muscle cells store it as glycogen.
- Saying blood vessels "move". They dilate or constrict.
Practice questions
- Which organ releases insulin?
- Describe what happens when blood glucose concentration is too high.
- Explain how vasoconstriction helps when you're cold.
- What is the main difference between type 1 and type 2 diabetes?
Answers: 1. The pancreas. 2. The pancreas releases insulin; glucose moves into cells, and the liver and muscles store excess as glycogen, lowering blood glucose. 3. Blood vessels near the skin narrow, so less blood flows near the surface and less heat is lost. 4. In type 1 the pancreas makes too little insulin; in type 2 cells don't respond properly to insulin.
Frequently asked questions
What is homeostasis?
Homeostasis is the regulation of internal conditions, such as blood glucose, temperature and water, to keep them at the best levels for cells and enzymes, despite changes inside and outside the body.
What is negative feedback?
A control mechanism in which a change from the normal level triggers a response that reverses it, bringing the level back to normal.
What does insulin do?
Insulin, released by the pancreas, lowers blood glucose by making glucose move into cells, where liver and muscle cells store excess as glycogen.
Sources
- GCSE Biology (8461) specification: subject content. AQA.
- Cambridge IGCSE Biology 0610 syllabus for 2026, 2027 and 2028. Cambridge International.
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