Gastro-intestinal Hormones - Human Physiology

This presentation provides a comprehensive overview of gastrointestinal hormones and their role in regulating digestion, absorption, and appetite. It covers the major gut hormones such as gastrin, secretin, cholecystokinin (CCK), ghrelin, motilin, gastric inhibitory peptide (GIP), somatostatin, and peptide YY (PYY), along with their sources, functions, mechanisms of action, and clinical significance. Special emphasis is given to the gut-brain axis and the endocrine regulation of digestive processes, making this resource valuable for students, researchers, and healthcare professionals.

1. Gastro-intestinal Hormones SANJIDH SAJ A S

2. Gastrointestinal hormones The hormones which are secreted from the localized areas of the gastrointestinal area is called Gastrointestinal Hormones. Some of the hormones, of course, are not exclusively secreted from the gastro-intestinal areas but also from other areas too. These hormones regulate the motor and secretory activities of the digestive organs. The hormones are polypeptide in nature, a structural resemblance between the chemical nature of these hormones themselves, and also other polypeptide hormones like glucagon and caerulein (amphibian skin secretion) has been noted. Their secretions are mostly conditioned by the presence or absence of specific food materials in the lumen of the gastro-intestinal tract, rather than by other glandular products in the circulation. By appropriate stimuli, these hormones are secreted quickly and also destroyed rapidly following withdrawal of the appropriate stimuli.

3. GI Hormones are broadly classified into 3 categories: Gastrin family that includes cholecystokinin and gastrin Secretin family that includes GIP, secretin and VIP Other polypeptides

4. Types of Gastrointestinal Hormones 1. Gastrin 2. Cholecystokinin 3. Secretin 4. Motilin 5. GIP 6. VIP 7. Ghrelin 8. Somatostatin 9. Peptide YY

5. Gastrin It stimulates the secretion of HCl and pepsin by the stomach. It is secreted from G cells present in the pyloric gland. It is a polypeptide hormones found in forms such as G34, G17 and G14, G17. They have half-life of around three minutes. The inactivation of gastrin occurs in small intestine and kidney. It also stimulates chief and oxyntic glandular cells to secrete pepsinogen and acid (HCl), pancreas to secrete bicarbonate containing fluid and enzymes, duodenal mucosa for the release of secretin. It also stimulates insulin secretion after protein intake. It also produces contraction of gastro- oesophageal sphincter.

6. 3 forms occur in blood and tissues 1. Big gastrin (G-34) 2. Little gastrin (G-17) 3. Mini gastrin (G-14) Maximum gastrin secretion occurs at pH 5.7

7. Zollinger Ellison syndrome Here Gastrin is produced at excessive levels. Often by a gastrinoma(gastrin producing tumour usually benign) of the duodenum or the pancreas. It occurs in autoimmune gastritis the immune system attacks the parietal cells leading to hypochlorhydria(low stomach acidity) This results in elevated levels in an attempt to compensate for increased pH in the stomach. Eventually all parietal cells are lost and achlorhydria results leading to a loss of negative feedback on gastrin secretion.

8. Cholecystokinin (CCK) Cholecystokinin was previously called pancreozymin . It is synthesized and secreted by enteroendocrine cells in the duodenum, the first segment of the small intestine. But it is now clear that it is a single hormone and is secreted from the mucosa of the upper small intestine when foodstuffs ( especially dilute acids, lipids, fatty acids, peptones, etc.) come in contact with it. Cholecystokinin depending on post-translational modification of the 150-amino acid precursor, preprocholecystokinin consists of varied numbers of amino acids. CCK peptide hormone exists in several forms and is labelled as CCK58, CCK33, CCK22 and CCK8. CCK12 depending on number of amino acids it contains.

9. Cholecystokinin hormone has got action on the contraction of the gall bladder; it also releases stored bile into the intestine, and stimulates the secretion of pancreatic juice by secreting enzyme-rich pancreatic juice. It inhibits gastric acid secretion and gastric emptying. It increases the secretion of enterokinase. It increases the action of secretin in producing alkaline juices. It stimulates the secretion of calcitonin and glucagon. It also enhances the motility of colon and small intestine. Regulation of Secretion of Cholecystokinin or Pancreozymin (CCK) Products of digestion, peptides, amino acids and fats increases cholecystokinin secretion. Cholecystokinin

10. Secretin It is secreted by the duodenal mucosa due to presence of chyme from stomach; the release of pancreatic juice but not enzymes is stimulated. In addition to hydrochloric acid, fatty acids, hydrolyzed protein, etc. even water are effective stimulant. Secretion is ineffective by mouth and is destroyed in the body due to the action of an enzyme " secretinase “. The jejunum cells are responsible for its synthesis. It contains 27-amino acid residues and is a polypeptide hormone. It increases the secretion of bicarbonate by duct cells of pancreas and biliary duct. It also potentiates the secretion of CCK to produce enzyme rich pancreatic secretion. Secretin mainly increases the secretion of bicarbonate by the biliary duct and duct cells of pancreas.

11. It increases the secretion of bicarbonate by duct cells of pancreas and biliary duct. It also potentiates the secretion of CCK to produce enzyme rich pancreatic secretion. Secretin mainly increases the secretion of bicarbonate by the biliary duct and duct cells of pancreas. The decreased gastric acid secretion may cause contraction of pyloric sphincter. Increased acid in upper small intestine and products of protein digestion increases secretin secretion. Bile salts in intestine stimulates secretin production.

12. Motilin It is secreted by cells in the stomach, duodenal and colon mucosa; some of these cells are enterochromaffin cells. It contains 28 amino acids. It regulates intestinal motility in inter-digestive phase. It prepares the intestine for next meal. It also regulates the migrating motor complexes.

13. Ghrelin It is secreted by the cells in stomach. It regulates intake of food. Ghrelin secretion is increased on fasting and decreased after ingestion of food. It also stimulates growth hormones secretion.

14. GASTRIC INHIBITORY POLYPEPTIDE (GIP) GIP is produced by cells in the mucosa of the duodenum and jejunum. It is released in response to presence of glucose and fat in the gut. It consists of 42 amino acids. It stimulates insulin secretion and in high doses inhibits gastric juice secretion and its motility.

15. VASOACTIVE INTESTINAL PEPTIDE (VIP) VIP is released from jejunum in response to fatty meals. It contains 28 amino acids. It increases secretions of electrolytes and water from intestine, inhibits secretion of gastric juices, dilates peripheral blood vessels and brings over relaxation of intestinal smooth muscle including the sphincters.

16. Somatostatin Somatostatin is also known as growth hormone inhibiting hormone (GHIH). It is released from cells in the pancreatic islets and GIT mucosa. It inhibits gastric acid secretion and motility, inhibits gall bladder contraction, and also inhibits the absorption of glucose, amino acids and triglycerides. It also inhibits the secretion of gastrin, secretin, Vaso -active intestinal peptides, gastro-intestinal peptides and motilin.

17. Peptide YY PYY is found in L cells in the mucosa of gastrointestinal tract, especially in ileum and colon. Also, a small amount of PYY, about 1-10%, is found in the esophagus, stomach, duodenum and jejunum. It is secreted by the jejunum in response to fatty acid in diet. It inhibits gastric acid juice secretion and gastric motility. Peptide YY

18. References CC Chatterjee’s Human Physiology Vol 1, 12th edition, CBS Publishers Guyton and Hall Textbook of Medical Physiology, 12 th edition

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