Appetite is our desire for food. The digestive system extracts as much nutrition as possible from meals. This means that our intake of calories is regulated by our appetite and not by the digestive system. Appetite is controlled by hunger and satiety centers in the hypothalamus. It is influenced by hormones produced by the GI tract and adipose tissues. The cerebral cortex and limbic system have additional input to appetite centers. The sight, smell, and taste of food increases gastric and salivary secretions. These gastric secretions prepare the stomach for incoming food.
Stomach hormones (ghrelin) are secreted during fasting to increase appetite. Leptin (produced by adipocytes) and GI hormones are secreted in the fed state to decrease appetite. Appetite hormones modulate the release of factors that lead to feelings of hunger or satiety. Orexigenic molecules stimulate appetite and decrease in the fed state. Anorexigenic molecules suppresss appetite and increase in the fed state.
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