Homeostasis — Cambridge IGCSE Biology

Revision notes

4 short notes, in the order of the specification. Each one in short:

1. Homeostasis and negative feedback

   Homeostasis is the maintenance of a constant internal environment, such as body temperature and blood glucose concentration. It is controlled by negative feedback. When a level moves away from its set point, receptors detect the change and effectors act to reverse it, so the level returns towards the set point. The response then reduces or stops.

2. Controlling blood glucose

   Blood glucose concentration is controlled by hormones from the pancreas acting on the liver. Insulin decreases blood glucose: it is secreted when glucose is too high, and the liver converts glucose to glycogen and stores it. Glucagon is secreted when glucose is too low, and the liver converts glycogen back to glucose and releases it into the blood.

3. Type 1 diabetes

   Supplement

   Type 1 diabetes is a condition in which the pancreas produces little or no insulin, so blood glucose concentration rises after a meal and stays too high. It is treated with insulin injections, usually at mealtimes, by monitoring blood glucose to give the right dose, and by managing the diet, especially the amount of carbohydrate eaten.

4. The skin and temperature control

   Supplement

   Temperature control keeps human body temperature constant at about 37 °C, coordinated by the brain. When too hot, sweat evaporates and takes heat from the body, and vasodilation widens the arterioles supplying skin surface capillaries so more heat is lost. When too cold, shivering releases heat, vasoconstriction reduces blood flow near the surface, and raised hairs trap insulating air.