Ghrelin, the pre-meal hunger hormone
Ghrelin, a peptide hormone (a short chain of amino acids), is released from an empty stomach and stimulates appetite, the urge to eat, so hunger rises before a meal.
Remember
Ghrelin is the pre-meal hunger signal of the empty stomach: it rises before a meal, and stretch of the stomach wall switches it off.
Memory aid
ghrelin sounds like a growl
Ghrelin sounds like a growl, the sound of an empty stomach, which links it to hunger before a meal.
Ghrelin is released from the wall of the stomach when the stomach is empty. It is often nicknamed the hunger hormone, a handy plain-language reminder.
Ghrelin travels in the blood to the arcuate nucleus, a cluster of nerve cells found at the base of the hypothalamus. There it activates the stimulatory neurones (the nerve cells that increase appetite), so hunger rises and the person is prompted to eat.
When the stomach has been empty for a long time, there is no stretch of its wall to hold ghrelin back, so it rises and drives hunger. In people, ghrelin shows a rise before a meal and a fall after a meal. Once eating begins, the food stretches the stomach wall, which inhibits (holds back) further ghrelin release, and the urge to eat fades. This is negative feedback: hunger leads to eating, and the eating then switches the hunger signal off.
Other hormones work in opposition to ghrelin. Peptide YY (from the small intestine), leptin (from fat cells), insulin (from the pancreas) and cholecystokinin (from the duodenum) all favour satiety (feeling full). Of ghrelin, peptide YY, insulin, leptin and cholecystokinin, only ghrelin raises appetite.
Key facts
- Source
- ghrelin is released from the wall of the stomach when the stomach is empty.
- Action
- it activates the stimulatory neurones in the arcuate nucleus, so hunger increases.
- Timing
- in people, ghrelin rises before a meal and falls after a meal.
- Switch-off
- stretch of the stomach wall by food inhibits further ghrelin release.
- Opposing signals
- peptide YY, insulin, leptin and cholecystokinin all favour satiety (feeling full).
Exam traps
- Leptin reflects the size of the fat stores and suppresses appetite, so it is not the signal that rises before a meal.
- Peptide YY is released from the small intestine after a meal and acts as a satiety signal that reduces food intake, so it does not drive hunger before eating.
- Insulin is released from the pancreas when blood glucose rises after eating, so it belongs to the time after a meal and is not the hormone that drives hunger before eating.
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