Gastro-intestinal (GI) Hormones are so named because these are secreted mainly from the different parts of our digestive system or gastro-intestinal tract. In few cases GI hormones are also secreted from our central nervous system (brain) and those GI hormones are called “Brain-Gut Peptides”. Like other hormones GI hormones also have the following important properties :-

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a) These are non-antigenic and may act quickly or slowly.

b) These have no cumulative effects.

c) These hormones can react in very low concentration.

d) These are chemical messengers which are soluble in blood and water. 

These hormones are only chemically proteinaceous in nature. The GI endocrine pathway is distributed variously within the mucosal epithelial tissue system throughout the all areas of our digestive system.

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The important GI intestinal hormones of human has been described below :- 

1) Duocrinin : This hormone is secreted from the mucosal part of Duodenum. It helps to secrete mucous from Bruner’s glands (Bruner’s glands are tubular branched glands located in the duodenum and secrete mucous along with bicarbonates, also protect small intestine from acidic chime). 

2) Villikinin : This hormone is secreted from small intestine and helps to move villi and thus helps in absorption of digested food materials. 

3) Gastrin : This hormone is secreted fro the G-cells of islets of Langerhans of Pancreas and also from duodenum. This hormone has a key role in the secretion of Gastric enzymes (mainly Pepsin) as well as pancreatic enzymes. Also, it helps to grow the gastric mucosa. 

4) Cholecystokinin : This hormone is secreted from Duodenum and also from Jejunum. This hormone is specially responsible for the controlling of Gall bladder action as well as secretion of bile from the same. Regular contraction of gall bladder helps to activate the secretion of bile from it.

5) Pancreozymin : This hormone is secreted from Duodenum and Jejunum part of the small intestine. It helps in pancreatic secretion, that is, pancreatic lipase, trypsin etc. enzymes are secreted under the control of that hormone. 

6) Neurotensin : This is only secreted from Ileum of small intestine and prohibits the motor activity of stomach. 

7) Enterocrinin : This hormone is secreted from intestinal mucosa and controls the secretion of intestinal hormones from intestinal mucosa. 

Secretin : This hormone is secreted from duodenum and Jejunum part of small intestine. It is a special hormone because it inhibits the secretion of stomach but on the other hand it stimulates pancreas to secrete enzymes as well. So, this hormone acts inversely with the stomach but suitably with pancreas. 

9) Enteroglucagon : This hormone is secreted from Pancreas, Ileum of small intestine and colon of large intestine. It helps in the growth of intestinal mucosa. 

10) Motilin : This hormone is secreted from Enterochromaffin cells of Gut. This hormone stimulates the secretion of pepsin and also helps in the movement of different part of Gastro-intestinal tract.

Discussion : From the above informations it is clear that our digestive system is a source of several endocrine activities and it behaves like a ‘Highly developed centre of hormonal control’ in our gastro-intestinal tract. Whole of our digestive system including Stomach, Liver, Pancreas, Gall bladder, small intestine and also large intestine are involved with this special endocrine system. Though the actual mode of activities of GI hormones is not properly understood, but further studies or research works have been going on to know more about the GI hormonal activities.