Homeostasis Basics

Homeostasis is the maintenance of a constant internal environment.

1. Changes in your external environment can affect your internal environment - the blood and tissue fluid that surrounds your cells.

2. Homeostasis involves control systems that keep your internal environment roughly constant (within certain limits).

3. Keeping your internal environment that keep your internal environment constant is vital for cells to function normally and stop them being damaged.

4. It’s particularly important to maintain the right core body temperature and blood pH. This is because temperature and Ph affect enzyme activity, and enzymes control the rate of metabolic reactions

If body temperature is too high enzymes may become denatured. The enzyme’s molecules vibrate too much, which breaks the hydrogen bonds that hold them in their 3D shape. The shape of the enzyme’s active site is changed and it no longer works as a catalyst. This means metabolic reactions are less efficient.

If body 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 (around 37 degrees in humans).

If blood pH is too high or too low (highly alkaline or acidic) enzymes become denatured. The hydrogen bonds that hold them in their 3D shape are affected so the shape of the enzyme’s active site is changed and it no longer works as a catalyst. This means metabolic reactions are less efficient.

The highest rate of enzyme activity happens at their optimum pH - usually around pH 7 (neutral), but some enzymes work best at other pHs, e.g. enzymes found in the stomach work best at a low pH.

5. It’s important to maintain the right concentration of glucose in the blood because cells need glucose for energy. Blood glucose concentration also affects the water potential of the blood - this is the potential (likelihood), of water molecules to diffuse out of or into a solution:

If blood glucose concentration is too high the water potential of blood is reduced to a point where water molecules diffuse out of cells into the blood by osmosis. This can cause the cells to shrivel up and die.

If blood glucose concentration is too low, cells are unable to carry out normal activities because there isn’t enough glucose for respiration to provide energy.

1. Homeostatic systems involve receptors, a communication system and effectors.

2. Receptors detect when a level is too high or too low, and the information is communicated via the nervous system or the hormonal system to effectors.

3. The effectors respond to counteract the change - bringing the level back to normal.

4. The mechanism that restores the level to normal is called a negative feedback mechanism.

5. Negative feedback keeps things around the normal level e.g. body temperature is usually kept within 0.5 degrees above or below 37 degrees.

6. Negative feedback only works within certain limits though - 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.