6. Homeostasis

What you need to know...
  • What is homeostasis?
  • How is homeostasis of body temperature achieved?
  • How is homeostasis of blood glucose concentration achieved?

Living things must be able to keep their internal environment constant despite changes in the environment. We call this homeostasis

Homeostasis of Temperature

This thermogram shows a heat picture of a polar bear. This picture shows that despite the very cold surroundings the polar bear is able to maintain a body temperature of 370C. This ability to maintain a constant body temperature is common to all mammals including humans.

Humans maintain a constant body temperature of 370C. This means that the body temperature is always kept at the best temperature for enzymes. So how do we achieve this? Think about how our body reacts to being cold. We get pale skin, we shiver and get goosebumps. These are all methods that the body uses to warm itself up again. The pale skin is a result of blood being diverted away from our skin. This means that less heat is lost from the blood through our skin. Shivering is a very fast contraction of our muscles. When our muscles are working they create heat and this warms our body. Lastly goosebumps are a result of tiny muscles attached to the hairs on our skin pulling the hair into an upright position. This traps an insulating layer of air and helps minimise any heat lost from the body.

Think again about how our body reacts to being hot. We get red in the face and we sweat. The red face is a result of blood being diverted to our skin to maximise heat being lost through our skin. Sweating is a clever way to maximise heat lost from our skin. Sweat glands in our skin secrete a liquid onto our skin. This liquid evaporates from the skin and takes heat energy away.
We can show these mechanisms in a diagram as below:




Homeostasis of Blood Glucose Concentration
You may need to look back at unit 1 to remind yourself why glucose is so important to our body. In short, the cells of our body need a constant supply of glucose for the process of respiration. In respiration, our cells break down glucose to release energy. This energy can be used to power all the chemical reactions in our cells. If our blood glucose is too low our cells cannot get the energy they need. If our blood glucose concentration is persistently too high this damages our blood vessels and organs. It is therefore vital to keep a perfect balance.
The job of keeping our blood glucose concentration under control is down to the liver and pancreas. Excess glucose is stored in the liver and released again as we need it. The pancreas monitors the blood glucose concentration and releases hormones which tell the liver to either store glucose or release it. 
People with type 1 diabetes do not have the hormone which causes blood glucose to be stored in the liver. This hormone is called insulin. People with diabetes need to test their blood glucose concentration regularly and inject insulin with every meal. This insulin is made by genetic engineering. You learned about this process in unit 1.