Some Major Hormones of the Gut Page!

 

Homer says there are a lot of gastrointestinal hormones to learn in a short time!  The best approach is to i) familiarize yourself with the names of the hormones below, ii) get a handle on the general actions of the hormones and iii) not be totally unfamiliar with these hormones should they come up in discussion with your colleagues!  The first 5 are the most important!  DOH!

Gastrin:  Gastrin is secreted by the antral mucosa of the stomach in response to the presence of food in the stomach or in response to vagal stimulation associated with the taste, smell, sight or feel of food!  Gastrin is also secreted by the intestinal mucosa in response to the arrival of acidic chyme and undigested protein from the stomach!

gastrin affects the stomach:  Gastrin increases gastric motility, acid secretion and enzyme secretion to aid in the mixing and breakdown of the stomach contents.  Gastrin increases the tone of the gastroesophageal sphincter to prevent reverse movement of food from the stomach into the esophagus.  Gastrin increases the motility of the small intestine and gall bladder in preparation for the arrival of food from the stomach into the small intestine.  Finally, gastrin decreases the tone of the ileocecal valve to assist in the passage of food from the small intestine to the colon; opening the ileocecal valve makes it easier to move out the old to make room for the new!  In this sense, gastrin indirectly assists in the movement of food from the stomach into the small intestine!

Secretin:  Secretin is secreted by the mucosa of the duodenum in response to acidic chyme from the stomach; recall that the chyme arriving from the stomach has a pH of 1-3!

secretin affects the stomach:  Secretin decreases motility of the stomach, and increases the tone of the cardiac (gastroesophageal) and pyloric sphincters.  By tightening up the pyloric sphincter and decreasing gastric motility and secretion, secretin reduces the rate of secretion of stomach contents into the small intestine, preventing chyme from arriving too quickly or all at once.

secretin affects the exocrine pancreas:  Secretin promotes the production of alkaline buffers by the exocrine pancreas.  These buffers are used to neutralize acidic chyme arriving in the duodenum from the stomach!

secretin affects the liver:  Secretin promotes the production of bile by the liver.  Recall that bile will be used to dilute and neutralize acidic chyme arriving in the duodenum from the stomach and assist in the emulsification of fats.  The liver produced between 600 and 1000 mL of bile daily!

secretin affects the submucosal glands:  Secretin stimulates the submucosal glands (Brunner's glands) of the small intestine to produce large quantities of alkaline mucus to protect the duodenum from acidic chyme arriving from the stomach!

Gastric inhibitory peptide (GIP):  GIP is secreted by the mucosa of the duodenum in response to the arrival of acidic chyme and fat and carbohydrates, especially glucose.

GIP affects the stomach:  GIP moderately decreases gastric motor activity to slow emptying of the stomach.

GIP affects the endocrine pancreas:    At physiological levels, GIP stimulates insulin secretion.

Cholecystokin (CCK):  CCK is secreted by the mucosa of the jejunum in response to the arrival of fats and proteins from the stomach.

CCK affects the stomach:  CCK decreases gastric secretion and motility and increases tone of the pyloric sphincter to reduce the rate of stomach emptying!

CCK affects the gall bladder:  CCK increases contractility of the gall bladder to expel bile and relaxes the hepatopancreatic sphincter.

CCK affects the pancreas:  CCK promotes production of digestive enzymes by the exocrine pancreas; proteolytic trypsin, chymotrypsin and carboxy-peptidases, starch degrading amylases and fat degrading lipases.

Vasoactive intestinal polypeptide (VIP):  VIP is secreted by the duodenum in response to the arrival of chyme from the stomach.

VIP affects the stomach:  VIP reduces acid production by the stomach, helping to protect the stomach from acid digestion as stomach contents are moved into the small intestine!

VIP affects the duodenum:  VIP stimulates the submucosal glands to produce lots of alkaline mucus to protect the small intestine from acidic chyme arriving from the stomach.  VIP also promotes capillary dilation in the small intestine to promote absorption of nutrients.

Enterocrinin:  Enterocrinin is secreted from the duodenum in response to the arrival of chyme from the stomach.

enterocrinin affects the duodenum:  Enterocrinin promotes the production of large amounts of alkaline mucus by the submucosal glands of the small intestine.  The mucus protects the intestine from acidic chyme arriving from the stomach.

Much less likely to be the topic of conversation at a formal dinner party are the following hormones:

Motilin:  This intestinal peptide increases contractility (motility) of the small intestine.

Vilikinin:  This intestinal peptide increases the activity of the villi and microvilli of the intestine.

Somatostatin:  This intestinal peptide decreases gastric emptying to slow passage of food into the intestine.

David Currie.
Copyright 2000. All rights reserved.
Revised: July 29, 2007