2.2 Pre-absorptive information
The stretch receptors in the stomach send signals to the brain. Combined with the early phase of digestion in the duodenum, gut hormones are released. Cholecystokinin (CCK) is produced by cells in the wall of the small intestine. This affects the brain, reducing the feelings of hunger. CCK is stimulated particularly by the presence of protein and fat digestion products in the duodenum. Peptides such as PYY and ghrelin signal to the brain that the stomach is full.
In Week 1 you were introduced to ghrelin. Can you remember what it does?
As the level of ghrelin increases, you feel hungry. As ghrelin decreases, there is a feeling of satiety (fullness). At the same time, the level of PYY increases, causing satiety.