homeostasis

Homeostasis is the maintanence of a constant internal enviroment.

Certian things inside your body must be kept constant so that no damge is done. Body levels that need to be controlled for example are your temperature, water content of the body, ion content of the body and blood gluecose content. 

All of the metabolic reactions within your body are controlled by enzymes. Enzymes within the human body work at around 37 degrees and if it gets too high or low the enzymes will denature (stop working as they have lost shape). So the body tries to maintain a temperature of 37 degrees. 

Part of the brain monitors your temperature through the temperature of the blood within the brain and recieves messages from receptors located within the skin that provide knowledge about skin temperature. 

Ions are taken into the body via food and then absorbed into the blood. If food contains too many ions then the excess needs to be removed. 

Some of the ions are lost in sweat. The kidneys remove the excess from the blood and it is then gotten rid of in the urine.

The body needs to control the water levels coming and going out. Water is taken in through food and drink and lost in these ways:

• through the skin as sweat
• by the lungs in breath
• through the kidneys as urine 
• through faeces 

The balnce between sweat and urine depends on what the conditions are like and what you're doing. 

On a cold day or if you're not exercising you dont sweat as much and so you will produce more urine which will be pale as it is more diluted as you haven't lost as much water as you usually would in sweat.

On the other hand however on a day that you're exercising on it's hot you will produce less urine but more sweat. Your urine will be darker in colour as it is less diluted as you have lost water through sweat. If you exercise you will also lose more water through yur breath as you breathe faster.

By eating foods which contain carbohydrates you are putting gluecose into the blood from the gut. The normal metabolism of your body's cells removes gluecose from the blood, if you do more exercise more gluecose is removed from your blood. 

This is because gluecose is an energy source for your cells, a hormone called insulin helps maintain the correct level of gluecose in your blood and so your cells are supplied with energy constantly.