Homeostasis

Homeostasis means the maintenance of a constant internal environment.

The body needs to keep certain things the same to stay healthy. There are six things that need to be controlled:

1) Body Temperature

2) Water levels - if not, too much water could enter/leave cells by osmosis

3) Ion content

4) Urea

5) Carbon dioxide

6) Blood Sugar

The human body is kept at a constant 37 C, which is the best temperature for enzymes to work at. If the body gets too hot or too cold, the enzymes won't work.

When you're too hot:
=> hairs lie flat
=> sweat is produced, which evaporates from the skin and removes heat
=> blood vessels dilate, so more blood runs to the skin. This makes it easier for heat to be lost to the surrounding air.

When you're too cold:
=> hairs stand up, trapping an insulating layer of air
=> no sweat
=> blood vessels constrict, so less blood runs to the skin
=> shivering causes the muscles to respire, producing heat

The kidneys are pretty important to homeostasis as they control three main things:

=> water content
=> ion content
=> urea

1) Water is released from the body in three ways: urine, sweat and the air we breathe out. The kidneys monitor our water content, so on days when we don't sweat much, our urine is more dilute and pale. When we sweat lots, our urine is concentrated and darker.

2) Excess ions are released into the bloodstream. The kidneys filter the blood and release any excess ions in urine.

3) Urea is the waste product created by the liver when they store excess food as fat. It is released into the bloodstream and filtered out by the kidneys.

Blood sugar levels are controlled by the pancreas.

When there is too much glucose in the blood, the pancreas detects this and secretes insulin. This is detected by the liver, which stores glucose rather than releasing it, so blood sugar levels drop.

When there is too little glucose in the blood, the pancreas detects this and does not secrete insulin. The liver does not store the glucose, so blood glucose levels increase.

There are two different types of diabetes.

Type 1: the pancreas does not produce insulin. It is controlled by insulin injections before a meal.

Type 2: the pancreas does release insulin, but the liver no longer responds. It is controlled by diet.

Diabetes was discovered when Banting and Best managed to successfully locate insulin after removing the pancreases from dogs.

Nowadays, insulin is produced by genetic engineering. Enzymes cut the insulin-producing gene from a healthy pancreas and it is inserted into bacteria. The bacteria then multiply and produce human insulin.

The alternative is a pancreas transplant, but there is a shortage of donors and there is a risk of rejection.