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Hormones of the Gastrointestinal Tract

There are different hormones related to gastrointestinal system which plays important role in digestion of the food. These hormones are related to each other and in different pathological condition, their production may increase or decrease leading to derangement of digestive process. Some important hormones are Gastrin, Cholecystokinin (CCK), Secretin, Somatostatin, and Motilin.

GASTRIN

Gastrin is peptide hormone produced by G cells (flask shaped cells), from the antrum of the stomach.  Also found in duodenum and jejunum.

Gastrin secretion is stimulated by

@CAPE-Down

 Gastrin secretion is inhibited by

@GAS
Calcium (blood borne) GIP/VIP

Glucagon/Calcitonin
Amino acids
Peptides Acidic environment
Epinephrine (blood borne)
Distension (Gastric)/ Discharge (vagal) Secretin/Somatostatin
 
Action of gastrin on parietal cells

  1. Gastrin causes insertion of K+/H+ ATPase pump into apical membrane of parietal cells.
  2. Stimulates the secretion of HCI

Action of gastrin on ECL (Entero Chromaffin Like) cells

  1. Stimulates the release of histamine by acting on CCK-B receptors on ECL cells.
Bivek014 (1)

SUMMARY OF MAJOR HORMONES OF THE GASTROINTESTINAL SYSTEM

 

CHOLECYSTOKININ (CCK)

Cholecystokinin (CCK) – Pancreozymin (PZ)  is peptide hormone produced by I cells of the small intestine (duodenum > jejunum, ileum) and stimulates the digestion of protein and fats.

Action: (@GRID)

  1. Gall bladder contraction
  2.  Relaxation of sphincter of Oddi
  3. Increased pancreatic enzyme secretion
  4. Decreased gastric emptying

CCK receptors are of two types mainly, CCK- A and CCK- B, CCK- A primarily located in GIT, and CCK- B primarily located in CNS. CCK also acts in hypothalamus inducing satiety and it augments effect of secretin for production of alkaline pancreatic juice. It also exerts tropic effect on pancreas.

CCK secretion in enhanced by lipid >>> peptones, amino acids, CCK releasing factors.

SECRETIN

Secretin is peptide hormone (27 amino acids) produced by S cells of duodenum and jejunum. It is stored as prosecretin. It stimulates secretion of fluid and bicarbonate from the pancreas. It acts through cAMP causing increase secretion of watery alkaline pancreatic juice.

Action include (@CIDS)

  1. Contraction of pyloric sphincter.
  2. Increased secretion of pancreatic enzymes along with CCK.
  3. Decreased secretion of gastric acid.
  4. Stimulate pancreatic growth (exocrine portion) along with CCK.

Secretin secretion is enhanced by amino acids, bile acid, fats, increased duodenal acidity and it is inhibited by Somatostatin.

SOMATOSTATIN

Somatostatin /Growth hormone inhibitory hormone

There are two forms of Somatostatin ( 14 and 18). Somatostatin 14 is primarily located in hypothalamus and Somatostatin 18 in GIT. Secretion is more in gastric lumen as compared to circulation and it acts through G protein coupled receptor. In GIT , it is secreted by D cells present in stomach, duodenum and pancreatic islet and is released in response to acid in stomach.

It decreases:

  1. Gall bladder contraction /Bile flow
  2. Pancreatic secretion ( both endocrine and exocrine)
  3. Intestinal secretion
  4. Gastric acid secretion
  5. Motility
  6. Absorption of glucose amino acids, triglycerides.

It increases:

  1. Fluid absorption.

It inhibits secretion from:

  1. Gastrin /Secretin
  2. VIP/GIP
  3. Insulin/Glucagon
  4. Motilin/Growth hormone

MOTILIN  

  • Motilin is 22 amino acids polypeptide secreted by enterochromaffin cells and Mo cells in the stomach, small intestine, and colon.
  • Produces contraction of smooth muscle in the stomach and intestines in injection.
  • Major regulator of the migrating motor complexes (MMCs) that control gastrointestinal motility between meals.

Note: Keep updates on schematic diagrams in next 72 hours and other gastrointestinal hormones.

Dr Bivek Singh

Academic coordinator” MBBS”

Author ” A Journey into the human body”

Author ” Pharmacology Simplified”

biveksingh@hotmail.com 

 

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