Hunger

When we eat , we must satiation obtain adequate amount of carbohydrates, fats, amino acids, vitamins and minerals. This amount supplied us fuel and reservoirs in our body.These reservoirs are short and long term. Short term reservoirs base on carbohydrates and long term stores fats. The short term is located in the cells of liver and muscles and is field with complex insoluble carbohydrates called Glycogen. This is the conversion of glucose into glycogen in a liver functioning process. While the long term reservoirs consist of adipose tissues (fatty tissues). This is filled with fats or "triglycerides" which are the complex molecules that contain 'glycerol' or 'glycine' combined with 3 fatty acids.

1) Stearic acid.
2) Oliec acid.
3) Palmit acid.

Adipose tissue is found beneath the skin and abdominal cavity. It consists of cells absorbing nutrients from the blood, converting them into triglycerides and storing them. This is called the Metabolism of eating and the phase through all process occur is called absorptive phase.
The brain lives on glucose and the rest of the body lives on fatty acids. The brain contain detectors that monitor the availability of glucose inside the blood brain barrier (the vessels which bear blood and supplies blood to the brain) and the liver contain the detectors that monitor the availability of nutrients (glucose and fatty acids) outside the blood brain barrier.
Hypoglycemia is a potent stimulus for hunger. If a dramatic fall in the level of glucose occur due to some factors. That is known to be glucoprivation (hypoglycemia) or the deprivation of glucose in the cells which stimulate eating hunger. Hunger is also associated lipoprivation which means a fall in the level of fatty acids.

Satiety Signals

There are two sources.
Short term Satiety signals
Eyes, nose, mouth, stomach, dudemum, liver. Each part signals to brain that indicate the food has injusted and processing on the way toward absorption.
Long term Satiety signals
These signals are associated with the calories by modulating the sensitivity of brain mechanism involved in hunger.

Some Other Factors

1) Head factors
These factors refers to the several sets of receptors located in the head, eye, nose, throat and tongue.
2) Gastric factors
The stomach contain receptors that detect the presence of food.
3) Intestinal factors
Intestines contain also some detectors which are sensitive to the presence of glucose, amino acids and fatty acids. Their axons send statiey signals to the brain.
4) Liver factors
Liver receives nutrients from the intestine and send signals to the brain.

Brain Stem
Brain stem contains neural circuits that are able to control food and satiation or physiological hunger signals such as glucose signals by means of decrease in glucose metabolism or food in the digestive system. In the brain stem the area "Posterma" and "nucleus of the solitary track" region (AP/NST) receives signals from tongue, stomach, small intestine and liver and sends information to the lateral "Para brachial nucleus" of the pones which passes the information to many regions of the brain. These signals help to control food intake.
Para Brachial Nucleus
A nucleus in the pons that receives gustatory information and informations from the liver and digestive system and relays it to the forbrain.

Hypothalamus

The two important portions of hypothalamus the lateral and ventro medial nucleus controlled hunger and satiety signals.

5-HT (NTM)

It inhibit eating especially carbohydrates.