Homeostasis
Homeostasis is keeping the internal environment of the body constant, even when the outside conditions change. It includes body temperature (about 37 °C), blood sugar level, water content and pH. Homeostasis works by negative feedback: a change is detected, and the body acts to reverse it.
Temperature control
The brain contains a temperature centre that checks the blood. If the body is too hot, blood vessels in the skin widen (vasodilation) to lose heat, and sweat glands release sweat. If the body is too cold, the vessels narrow (vasoconstriction), sweating stops, hairs stand up and muscles shiver to make heat.
| Condition | Skin blood vessels | Sweat | Other responses |
|---|---|---|---|
| Too hot | Widen | More | Hairs lie flat |
| Too cold | Narrow | None | Shivering, hairs stand up |
Blood sugar
After a meal rich in carbohydrates the blood glucose rises. The pancreas releases the hormone insulin, which makes the liver and muscles take up glucose and store it as glycogen. When glucose falls, the hormone glucagon makes the liver release glucose. In diabetes the body does not make enough insulin, or does not respond to it.
A healthy person releases insulin quickly, but a person with untreated diabetes does not. Choose the amount of sugar eaten.
Key terms
- Homeostasis
- Keeping the internal environment constant.
- Negative feedback
- A response that reverses a change.
- Insulin
- A hormone from the pancreas that lowers blood glucose.
- Diabetes
- A condition where blood glucose is not controlled.
Summary
- Homeostasis keeps body conditions steady by negative feedback.
- Skin blood vessels, sweating and shivering control body temperature.
- Insulin lowers and glucagon raises blood glucose.
- Diabetes is a failure of blood glucose control.