Quizzing my self. What is hunger?

Appetite goes hand in hand with hunger and wanting to eat. The mechanism that controls ones appetite involves the GI tract, CNS, ANS, and of course hormones. The main effector organ is the hypothalamus which controls many homeostasis events along with hunger. The hypothalamus sends signals throughout the body through the pituitary gland by stimulating or inhibiting the pituitary hormones. When the hypothalamus senses a certain stimuli it reacts appropriately; with appetite, a positive/negative feedback response from hormones involved with the digestive tract, a message will be sent to the hypothalamus to stimulate a response via neurons. Hormones such as: leptin, ghrelin, and cholecystokinin (CCK) are all GI tract hormones and regulate appetite. Leptin gives a signal to decrease appetite and increase metabolism; ghrelin hormone increases prior to eating and decreases afterwards; and CCK suppresses hunger and plays a role in digestion and satiety. Digestion starts with the intake of food at the mouth, then through the esophagus where it progresses to the GI tract. Before food enters the mouth, a sense of knowing ones going to eat causes a sensory input which stimulates the vagus nerve, increasing its outflow thereby increasing gastrin release in the stomach as well as an increase in saliva in the mouth. Once food has passed to the stomach the gastrin actions are as follows: an increase in churning, HCl secretion (which increases digestive activity of proteases), pepsinogen release, and growth of stomach mucosa. Gastrin also stimulates fluid and bicarbonate secretion in the bile of the liver and gallbladder contraction. From the stomach the food enters the small intestine through the duodenum and due to an increase in H+ from the production of HCl an increase in the hormone secretin takes place. Secretin increases bicarbonate secretion from the pancreas and stimulates CCK release. CCK which is also produced in the small intestine increases bile secretion and causes the ‘full feeling’ which is associated with satiety. With the release of CCK another hormone GIP is an important factor and inhibits acid secretion and gastric motility of the stomach, bicarbonate/enzyme secretion of the pancreas, as well as the liver and gallbladder functions stated previously. Insulin production is increased to take the glucose and store it as glycogen in cells. Two other hormones involved in the GI tract are: motilin, which increases motility and pepsinogen secretion and VIP, which increase blood flow to viscera in preparation for absorption. Satiety as mentioned earlier is the ‘full feeling’ which occurs due to the negative feedback from CCK. This is why you can eat a lot of food really fast and not feel full until 20 min. later because the food hasn’t reached the point where the hormone CCK is produced.