Homeostasis Basics

What is homeostasis? 

Changes in your external enviroment can affect your internal enviroment- the blood and tissue fluid that surrounds your cells. Homeostasis is the maintenance of a constant internal enviroment. It involves control systems that keep your internal enviroment roughly constant. Keeping your internal enviroment constant is vital for cells to function normally and to stop them being damaged. 

Its particularly important to maintian the right core body temperature. This is because temperature affects enzyme activity, and enzymes control the rate of metabolic reactions.

Temperature

The rate of metabolic reactions increases when the temperature is increased. More heat means more kinetic energy, so molecules move faster. This makes the substrate molecules more likely to collide with enzymes' active sites. The energy of these collisions also increases, which means each collision is more likely to result in a reaction. 

But, if the temperature gets too high, the reaction essentially stops. The rise in temperature makes the enzyme's molecules vibrate more. This vibration breaks some of the hydrogen bonds that hold the enzyme in it's 3D shape. The active site changes and the enzyme and substrate are no longer complamentary. At this point, the enzyme is denatured and no longer functions as a catalyst.

If the temperature is too low enzyme activity is reduced, slowing the rate of metabolic reactions. The highest rate of enzyme activity happens at their optimum temperature- about 37 degrees C.

Negative Feedback

Homeostatic systems involve receptors, a communication system and effectors. Receptors detect whena level is too high or too low, and the information is communicated via the nervous system or the hormonal system to effectors. The effectors respond to counteract the change- bringing the level back to normal. The mechanism that restores the level to normal is called a negative feedback mechanism.

Negative feedback only works within certain limits- if the change is too big then the effectors may not be able to counteract it, e.g. a huge drop in body temperature caused by prolonged exposure to cold weather may be too large to counteract. 

Positive Feedback

Some changes trigger a positive feedback mechanism, which amplifies the change. The effectors respond to futher increase the level away from the normal level. 

Positive feedback is not involved in homeostasis because it does not keep your internal enviroment constant. Positive feedback is useful to rapidly activate processes in the body. 

Example

During the formation of a blood clot after an injury, platelets become activated and release a chemical- this triggers more platelets to be activated, and so on. This means platelets very quickly form a blood clot at the injury site.