Four major peptides hormone are secreted by the endocrine cells present in the gastro-intestinal tract :

It secretes the following hormones :

1. Gastrin : This hormone acts on the gastric gland and stimulate them to secrete hydrochloric acid and pepsinogen. 

2. Secretin : It acts on the exocrine pancreas and stimulates secretion of water and bicarbonates.

3. Cholecystokinin (CCK) : It stimulates gall bladder to release bile and stimulates pancreas to secrete pancreatic juice.

4. Gastric inhibitory peptide (GIP) - inhibts gastric secretion and motility.