Question

1) Below is a chart of the 5 GI peptides involved in GI motility. Research the actions of these peptides and list their effects in the chart below. Again your textbook will have information on these peptides.

Five GI hormones and their effects:

Hormone	Effect
Gastrin From G cells in the pyloric antrum
Cholecystokinin (CCK) From I cells in the duodenum and jejunum
Secretin From S cells in the duodenum
Glucose Dependent Insulinotropic Peptide (GIP) From cells in the duodenum and proximal jejunum
Motilin From cells in the duodenum and jejunum; released about every 90 minutes during the post-absorptive state

Answer 1

1) Gastrin hormone is responsible for the production and secretion of gastric acid (mainly HCl) from the stomach mucosa and digestive enzymes from the pancreas. It stimulates contraction smooth muscles of GIT and increases blood circulation and water secretion in the stomach and intestine.

2) Cholecystokinin -  It is secreted from mucosal epithelial cells in the duodenum. It helps in digestion by delaying the gastric emptying and stimulate the production of bile in the liver as well as its release from the gall bladder. Bile helps in the emulsification of fat which is necessary for its digestion and absorption. It also increases the release of fluid and enzymes from the pancreas to break down fats, proteins, and carbohydrates.

3) Secretin- It is released from the cells in the duodenum and proximal jejunum in response to acid in the intestine which comes from the stomach with the food. It stimulates the pancreas to release water and bicarbonate in order to protect the intestinal lining by diluting and neutralizing the acid. It also inhibits the secretion of gastrin from the gastric mucosa.

4) Glucose Dependent Insulinotropic Peptide (GIP)- It is also known as Gastric inhibitory polypeptide and its main function is to stimulate insulin secretion from the pancreas in response to infusions of glucose. It also inhibits gastric motility and secretion of acid from the stomach. It has also effects on the bones. GIP affects bone by causing the proliferation of osteoblasts and inhibits osteoclastic bone resorption.

5) Motilin - the main function of motilin is to increase the migrating motor complex that acts on the movement of the gastrointestinal tract called hunger contraction and it is released about every 90 minutes during the post-absorptive state. This stimulates the contraction of the fundus and antrum and facilitates gastric emptying. It also helps in the production of pepsin. It also helps in the release of pancreatic polypeptide and somatostatin.