View source for 4. Pathophysiology of GIT-peptides

Gastrointestinal hormones or peptides regulate the secretion of digestive juices and the function of the Langerhans islets. They have some common features:

* They are all peptides
* They are produced in cells of the wall of hollow organs
* They participate in the “gut-brain axis”
* Several of them may derive from the same gene
* They may act via endocrine, paracrine, autocrine or neurocrine transmission

Gastrin is produced by G-cells in the gastric antrum and stimulates gastric motility and the HCl secretion by the parietal cells. This transmission is endocrine. HCL secretion can also be enhanced by the vagus nerve and histamine relase. It’s inhibited by negative feedback when too much HCl is secreted.

Secretin is produced in the intestinal mucosa and increases the quantity and bicarbonate content of pancreatic juice. It inhibits HCl secretion.

Cholecystokinin (CCK) stimulates bile secretion and pancreatic enzyme production. It also inhibits HCl secretion.

Vasoactive intestinal peptide (VIP) stimulates intestinal and pancreatic secretions. It also inhibits HCl secretion.

Somatostatin (SST) inhibits the production of secretin and HCl.

Gastric inhibitory peptide (GIP) inhibits the secretion of only HCl.

Motilin increases intestinal motility.

GLP-1 and GIP together form a group called the incretins. They increase the secretion of insulin.

Serotonin is a neurotransmitter and not a peptide, however it’s present in the <abbr>GI</abbr> tract where it regulates intestinal motility.