Hormones of GIT and their role in digestion

1. Hormonal Control Of Digestion
Hormones have a key role in food digestion, By influencing the secretions of different
enzymes in different parts of the GIT. The gut is the body’s largest hormone-producing
organ, releasing more than 20 different peptide hormones, some of which target the
brain to regulate appetite and influence the pleasure of eating.
Hormones – chemicals that ‘excite’
Hormones are chemical substances produced by specialised cells in the body known
as endocrine cells. Once released, the hormone enters the bloodstream and is
transported to its specific site of action.
Once the target cell has been stimulated, it responds in a variety of different ways such
as producing new proteins, activating or deactivating enzymes within the cell or
allowing the passage of substances into or out of the cell.
Gut hormones
The gut hormones work in association with the gut’s extensive nervous system (enteric
nervous system) and play a co-ordinating role in the control of appetite, the digestion of
food, the regulation of energy balance and the maintenance of blood glucose levels.
The gut continuously sends information to the brain regarding the quality and quantity
of the food that is consumed.
The role that some of these hormones play is outlined below:
1. Ghrelin is produced in the stomach, and its function is to tell the brain that the
body has to be fed. It increases appetite.
2. Gastrin is produced in the stomach when it is stretched. It stimulates the release
of gastric juice rich in pepsin and hydrochloric acid.
3. Secretin is produced in the duodenum and has the effect of stimulating the
pancreas to produce alkaline secretions as well as slowing the emptying of the
stomach.
4. Cholecystokinin (CCK) is produced in the duodenum. It reduces appetite,
slows down the emptying of the stomach and stimulates the release of bile from the
gall bladder.
5. Peptide YY (PYY) is produced in the last part of the small intestine known
as the ileum as well as parts of the large intestine. It plays a role in slowing down the
passage of food along the gut, which increases the efficiency of digestion and
nutrient absorption after meal.

2. 6. Glucagon-like peptide 1 (GLP-1) is produced in the small intestine
and colon and has multiple actions including inhibition of gastric emptying and
appetite as well as the stimulation of insulin release.
7. PYY3-36 Pancreatic peptide peptide released by cells in
the ileum and colon in response to feeding. In the blood, gut, and other
elements of periphery, PYY acts to reduce appetite; similarly, when injected
directly into the central nervous system,, i.e., it reduces appetite.
Figure 1 Hormonal control of Digestion