"Excellent. Answered all those questions I had that are never covered in text books, such as how big is a piece of DNA?"
Homeostasis describes the functions of your body which work to keep your internal environment constant within a very narrow range. Two important aspects of homeostasis are balancing the blood sugar levels and maintaining the body temperature.
Your body is made up of millions of cells which need the conditions inside your body to be as constant as possible so they can work properly. However everything you do tends to change your internal conditions.
You take millions of new molecules into your body when you eat and digest food. Your blood sugar levels soar after you have a meal - but your cells use up the glucose fast when you exercise hard. You release heat energy every time you move about, the amount of water you take into and lose from your body varies all the time and your cells are constantly producing poisonous waste (see Homeostasis - the kidneys and water balance.)
The blood sugar levels in your body are coordinated by hormones, chemicals which regulate and balance the working of organs and cells. Hormones are made in endocrine glands and are carried around the body to their target organs in the blood stream.
Some hormones have long term effects, for example, the hormones that control how you grow and the changes that happen at puberty. Other hormones have shorter term effects. The hormones insulin and glucagon which control your blood sugar levels are like this.
It is important that the core temperature of your body stays within a very small range for the enzymes in the cells of your body to work properly. Your skin is one of the most important organs in the control of body temperature.
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