Homeostasis involves mechanisms which detect the state of the internal environment and correct the situation to restore that environment to its optimal state. Hoever, there is a significant time lag between mechanisms operating to restore equilibrium and the body registering their effect. For example, by the time a person has eaten enough to restore energy levels, only a small amount of food has been digested. Therefoere the receptors responsible for detecting nutrient levels have insufficient 'data' to turn off eating.
There are two seperate systems in the body for turning eating on and off. In humans, glucose levels play an important role in producing feeling of huner. Hunger increases and glucose levels decrease. A decline in glucse in the blood activates a brain area called the lateral hypothalamus, resulting in feelings of hunger. The person then eats food, causing the glucose levels to rise again, and this activates the ventromedial hypothalamus and leads to feelings of satiety. This in turn inhibits further feeding.
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