The atmosphere of body cells inside the body are called internal environment. The function of homeostasis is to maintain this internal environment constant. Certain procedures are required to maintain things stable and these may be called homeostatic procedures. Conditions that are controlled by homeostasis are blood glucose level, temperature, water content of the body, and the amount of carbon dioxide and urea being carried by the blood. Body cells are enclosed and immersed in fluid. This fluid, which is the tissue fluid, is made from blood. This gives the cells mineral salts like glucose. As cells require glucose all the time as energy for respiration, the level of glucose must not be allowed to drop. If the level goes too high, it is also harmful. The hormone insulin helps keep the blood glucose level stable by raising the uptake into cells and increasing the conversion of glucose into glycogen in the liver. (Homeostasis: www.tiscali.co.uk/).

             In human temperature the thermoregulatory center in the hypothalamus manages homeostasis. It gets input from two sets of thermo receptors: receptors in the hypothalamus itself check the temperature of the blood as it goes through the brain, and receptors in the skin check the external temperature. Both pieces of information are required so that the body can make suitable modifications. The thermoregulatory center propels signal to many different effectors to modify body temperature. The thermoregulatory center is a component of the autonomic nervous system, so the different reactions are all instinctive. The accurate reactions to high and low temperatures are given in the table below. It is to be noticed that some of the reactions to low temperature actually produce heat, while others just preserve heat. Likewise some of the reactions to cold vigorously cool the body down, while others just lessen heat production or transmit heat to the surface. Thus based on the internal and external temperatures, the body has a variety of reactions.