Motivation of Hunger
Hunger is one of the types of biogenic motives along with thirst and sex. Normally, it starts when we feel pangs in stomach and contractions begin for food. Generally an individual feel hungry when level of sugar increases in blood. This is the reason why persons with diabetes have higher level of hunger than on-diabetic people.
Role of Hypothalamus: According to Set-point theory, hypothalamus plays an important role in regulating and controlling hunger and stop eating behaviours. The hypothalamus wants to maintain an optimum level of body weight of the individual. Thus, it permits us for eating when the individual drop below or lose the desirable level of body weight and decreases the rate of metabolism. Similarly, it tells the individual to stop further eating s/he reaches the set point of body weight and increases metabolic rate.
Physiological mechanisms in hunger:
Biologically, hypothalamus is the centre of origin of all kinds of biological motives including hunger to be triggered by several internal physiological and biochemical mechanisms. The feeling of hunger is conveyed by the receptors of liver to the lateral part of hypothalamus region of brain for origin and related eating behaviour. In fact, when the person doesn't consume anything for long time, the level of leptin decreases significantly, this, in turn, leads to ghrelin to be released to initiate feeling of hunger to consume food. In addition, researches have also suggested that an increased level of ghrelin may cause a sudden increase in appetite to be evoked by merely the sight at or smell of food. Similarly, when a person starts eating for gratification, the adipocytes cause the release of the same leptin in body, the increased level of which causes reduction in the motivation of the individual for further eating. Thus, the increase in level of leptin conveys message that the stomach is full and no more eating is required at that point of time. However, any possible change in level of stress is likely to influence the release of hormone. It suggests us to understand that hunger may continue to occur even in stressful life situations.
Role of Cholecystokinin (CCK):
The CCK is a kind of neuropeptide hormone in our visceral system which facilitates the digestion and metabolism of protein and fat. It is produced in the small intestine and generated thereafter secreted in the adjoining part between liver and stomach, i.e., duodenum. The CCK causes the pancreas and gall bladder to secrete digestive enzymes and bile respectively in state of hunger. The CCK also take part in suppressing hunger after satiation by sending its signals throughout the central nervous system in general, as well as, to the vetromedial region of hypothalamus in brain in particular. It mediates digestion in duodenum by inhibiting secretion of gastric acid, as well as, triggering pancreas to release digestive enzymes, iron and water to digest fat, protein and carbohydrates of consumed food within thirty minutes after eating. During this interval of thirty minutes, the stomach digests food through emptying itself by passing the consumed meal on to the duodenum. Here, when CCK is released and becomes functioning, the duodenum becomes occupied in digesting the food and conveys the stomach to stop sending more until it permits. Thus, when the stomach stops releasing food into duodenum, the CCK informs the brain that the individual's stomach does require further immediate eating.