Physiologists used to think that hunger originated from the stomach and was caused by gastric emptying. However, later experiments found that hunger did not disappear after the nerve innervating the stomach was removed, that is, animals still had feeding behavior. At the same time, it was observed that patients whose stomachs were mostly removed were as hungry as normal people. It shows that the stomach has no direct effect on hunger, but it will cause stomach contraction when hungry. People often say that "hungry stomachache" is the truth. So how did hunger come about? First of all, some patients with pituitary or hypothalamic tumors will have symptoms such as refusing to eat or overeating. This suggests that there are structures related to hunger or satiety in pituitary or hypothalamus. From June 65438 to June 0964, scientists proved through experiments that after a certain area of hypothalamus was injured in rats, animals would obviously increase their food intake, which led to obesity. After about 40 days, their weight is more than twice that of normal animals of the same age. However, animals in this area refused to eat when they were stimulated by electricity, which proved that this area can make animals feel full, which is called satiety center in physiology. Similarly, it is proved that there is another area in the hypothalamus. Animals fasted after being damaged and eventually starved to death, which stimulated the animals in this area to increase their food intake. Physiologically, it is called the feeding center. Appetite refers to the preference or aversion to a certain food, which is a psychological state, greatly influenced by senses and emotions, and also related to habits or life experiences. In addition to hypothalamus, other areas of the brain also play a major role in the formation of appetite. For example, if the amygdala is destroyed, animals will lose the ability to choose food. Appetite will directly or indirectly affect food intake.

At present, it is considered that the nerve cells in the feeding center and satiety center of hypothalamus are very sensitive to the changes of glucose concentration or lipid concentration in blood. When the glucose content in blood increases, satiety will be felt by satiety center through blood circulation, otherwise it will cause food intake.

When the stomach expands, it will inhibit the feeding center or reduce appetite through hormones released in the stomach and nerves innervated. Overeating in early childhood will raise the threshold of satiety center when the brain is not fully developed, which means that these children must eat more food than normal children to feel full, which will inevitably lead to childhood obesity. Of course, due to genetic factors, the threshold of natural satiety center is higher, which is also one of the reasons for childhood obesity. It is worth noting that if you lose weight by excessively inhibiting diet during growth and development, it will do great harm to your body, which will easily lead to the decrease of the excitability of the feeding center, and may lead to anorexia in severe cases.

It doesn't matter if it is proved by science. Study hard and you will be able to finish this math problem.