Ghrelin is a hormone that is produced by the enteroendocrine cells of the gastrointestinal tract, especially the stomach; the enteroendocrine cells respond to stimuli by producing hormones, such as ghrelin, and release them in the bloodstream.
Ghrelin is often called the hunger hormone because it increases food intake, in fact, its levels in the blood are higher when one is hungry.
The Function of Ghrelin
Ghrelin is one of the main participants in the process of energy homeostasis, which is a biological process that regulates the balance between energy input, such as adjusting hunger signals, and energy output, such as dividing the use of energy between fat storage, short-term heat loss, etc. It has been shown in studies that this hormone is dose-dependent, meaning the more of it in the blood, the higher the food intake, by making the meals more frequent, not bigger. The result of these functions is the bodyweight of a person, which is under constant change based on metabolic signals and needs, with ghrelin’s aim to reduce our sensitivity to gastric distension, reducing our ability to understand we are full.
The hunger hormone, besides, also activates the cholinergic–dopaminergic reward link, which is a circuit that reinforces aspects of natural rewards, such as food and alcohol.
It has been shown that ghrelin levels increase in the body before a meal and drastically decrease after it; its decrease is stronger in response to proteins and carbohydrates, compared to lipids.
Some preliminary studies are showing how this hormone participates in the regulation of the circadian rhythms, which is a natural, internal process, that regulates our sleep-wake cycle, and repeats itself roughly every 24 hours.
Levels of ghrelin in obese individuals are lower than those in leaner individuals, suggesting that it is not a contributor to obesity (except in the cases of Prader-Willi syndrome).
The name ghrelin comes from its role as Growth Hormone-Releasing peptide.
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