Biological bases of hunger and thirst needs-Hunger: The stimuli of hunger include stomach contractions, which signify that the stomach is empty, a low concentration of glucose in the blood, a low level of protein and the amount of fats stored in the body. The liver also responds to the lack of bodily fuel by sending nerve impulses to the brain. The aroma, taste or appearance of food may also result in a desire to eat.

They all in combination act with external factors (such as taste, colour by observing other’s eating, and the smell of food, etc.) to the help one understands that she/he is hungry. Thus, it can be said that our food intake is regulated by a complex feeding satiety system located in the hypothalamus, liver and other parts of the body as well as the external cues available in the environment.

Thirst: When we are deprived of water for a period of several hours, the mouth and throat become dry, which leads to dehydration of body tissues. Drinking water is necessary to wet a dry mouth. The processes within the body itself control thirst and drinking of water. Water must get into the tissues sufficiently to remove the dryness of mouth and throat.

Motivation to drink water is mainly triggered by the conditions of the body: loss of water from cells and reduction of blood volume. When water is lost by bodily fluids, water leaves the interior of the cells. The anterior hypothalamus contains nerve cells called ‘osmoreceptors’, which generate nerve impulses in case of cell dehydration. These nerve impulses act as a signal for thirst and drinking.

Some researchers assume that the mechanism which explains the intake of water is also responsible for stopping the intake of water. Others have pointed out that the role of stimuli resulting from the intake of water in the stomach must have something to do with stopping of drinking water. However, the precise physiological mechanisms underlying the thirst drive are yet to be understood.