A good number of factors operate together as a complex mechanism for regulating food intake (Fig. 11.12).
Food intake regulation. Since eating is a voluntary act so conscious sensation (hunger and appetite), indicating whether food is needed or not, is a prerequisite for the regulation of food intake (eating). Hunger is aroused by the physical need of the food whereas appetite is the emotional (psychic) desire to which may or may not be associated with the need of food.
Hunger, i.e., desire for taking food is controlled by a centre in the hypothalamus i.e. lateral hypothalamic area. There is another centre, i.e. ventromedial hypothalamic nuclei (Fig. 11.11) in tuber cinerium called satiety centre, which inhibit the hunger centre when it is satisfied with the amount of food appropriate to calorific requirement resulting loss of desire for taking food.
Reversely when the satiety centre is not satisfied with the amount of food appropriate to calorific requirement, then this centre is not satisfied to inhibit the centre so the hunger centre is not inhibited resulting the desire for food.
Appetite, on the other bind, is conditional and not dependent to calorific need.The mode of activation of these centres has not been established as yet. Several theories have been put forward suggesting the regulatory activity of the appetite centre or appestat.
They are as follows:
i. Concentration of Blood Glucose:
Low glucose concentration stimulates the lateral hypothalamic nucleus producing increased hunger and food intake. When glucose concentration increases after intake of food, the ventromedial centre of the hypothalamus is satisfied and hunger centre is inhibited, thus the animal stops eating.
ii. Temperature Variation of Blood:
Low temperature from normal stimulates food intake and vice versa.
iii. The Proportionate Amounts:
The proportionate amounts of active fat in fat cells to passive fat also act in a regulatory manner.
iv. The Concentration of Serum Amino Acids:
The concentration of serum amino acids also regulates the hunger centre.
Other factors also play some part. The hypothalamic hunger centre receives projection from the cortex. So it is under voluntary control. Emotional stress, such as worry, tension etc., also play a major part (Fig. 11.12).
The satisfaction achieved by food intake and its regulatory role are partly dependent also on the digestive tract. The feeling of fullness after a heavy meal may depend on the distention of the stomach, which may be brought about by proprioception. Other nervous projections may also play a part.