Homeostatis

1.  The body temperature mustn't get too high or low.

2. Water content mustn't get too high or low, or too much water could move in and out of cells and damage them due to osmosis 

3.  If the ion content of the body is wrong, the same thing could happen.

4.  The blood sugar level must stay within certain limits.

5. Carbon dioxide is a product of respiration. It is toxic in high quantities so it has to be removed.

6. Urea is a waste product made from excess amino acids that also has to be removed.

• Must be controlled carefully
• All enzymes work best at a certain temperature.
•   The enzymes within the human body work best at around 37C.
•  If the body gets too hot or too cold, the enzymes will not work properly and important reactions can bedisrupted.
• This can lead to death in extreme cases.
• There is a thermoregulatory centre in the brain which acts like a personal thermostat.
•  It contains receptors that are sensitive to the temperature of the blood flowing through the brain.
•   The thermoregulatory centre also receives impulses from the skin, giving info about skin temperature.
•  If you are getting too hot or too cold, your body can try and respond to this to try and cool you down or warm you up.

•    Hair lies flat on the skin.
•     Sweat is produced by sweat glands and evaporates from the skin, which removes heat.
•  The blood vessels supplying the skin dilate, so more blood flows closer to the surface. This makes it easier to heat to be transferred from the blood to the environment.

•  Hairs stand up to trap an insulating layer of air.
• No sweat is produced.
•  Blood vessels supplying skin capillaries constrict to close off the skin's blood supply.
•  You also shiver too, which means your muscles contract automatically.
•  This needs respiration, which releases some energy as heat.