Gastric Secretions Sarah and Susan 07/10/2014

Stomach Anatomy

The Pyloric Sphincter A ring of smooth muscle and connective tissue between the gastric antrum and the duodenum. Has 2 Functions: Allows the regulated emptying of gastric contents at a rate consistent with the ability of the duodenum to process chyme. Prevents the regurgitation of duodenal contents back into the stomach

Gastric Juice How many litres of gastric juice are produced by the stomach each day? 300ml 500ml 1L 3L 5L

Gastric Juice What are the main components of gastric juice? (4) Hydrochloric acid (HCl) 2. Mucus 3. Enzymes: pepsinogens, gastric lipase 4. Intrinsic Factor

What are the major types of secretory epithelial cells in the stomach? Surface mucous cell Mucous neck cell Parietal cell Chief cell G cell Enterochromaffin-like (ECL) cell Delta (D) cell Mucus HCl and IF Pepsinogen Gastrin Histamine Somatostatin

Mucus What is it? What is the Gastric Mucosal Barrier? A mixture of glycoproteins and glycopolysaccharides. What is the Gastric Mucosal Barrier? Mucus and the alkaline secretions entrapped within it. It protects the stomach against acid, proteolytic enzymes and mechanical damage.

Hydrochloric Acid Produces a gastric luminal pH of 1-2 Stimuli of acid secretion also promotes increased mucus and HCO3- secretion. Stimulated by: gastrin acetylcholine histamine Inhibited by: somatostatin prostaglandins E2 and I2 enteric hormones

Inhibition of Gastric Acid Secretion ECL cell Somatostatin - SSR Cholinergic nerve Blood vessel Muscarinic-R Gastrin-R + + Histamine ACh Gastrin + - Somatostatin + + Muscarinic-R H2-R Gastrin-R + PGE2-R - SSR PGE2 - Parietal cell K+ H+ Cl- P C AA H+ Cl- K+

The Parietal Cell 1. Truncated pyramidal shape, with apex oriented towards gastric lumen. 2. Canaliculi (envaginations of luminal membrane) lined with ion pumps: increased surface area 3. Many mitochondria: provides energy for H+ pump

The Parietal Cell 4 CO2 and H2O are converted into H+ and HCO3- by carbonic anhydrase H+ is pumped into the lumen by a H+/K+-ATPase transporter HCO3- leaves the cell and enters the bloodstream via antiport with Cl-. Cl- diffuses passively into the lumen via a Cl- channel. 2 1 3

Intrinsic Factor Glycoprotein secreted by parietal cells Intrinsic factor production is the only indispensable function of the stomach. Is essential for the absorption of vitamin B12 in the intestines.

Pepsinogen Pepsin secretion parallels acid secretion. Parietal Cell HCl Chief Cell Pepsinogen Pepsin Protein Peptide Pepsin secretion parallels acid secretion. Pepsin is active only at low pH.

Gastric Hormones Hormone Production Site Gastric Functions Gastrin G cells in antrum of stomach Stimulates Acid Secretion Stimulates Gastric Motility Inhibits Gastric Emptying Stimulates Intestinal Motility Histamine ECL cells in gastric mucosa Increases Local Blood Flow Somatostatin D cells in antrum and body of stomach Inhibits Gastrin Inhibits Acid Secretion

What is the one indispensable function of the stomach? SECRETION OF INTRINSIC FACTOR