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STOMACH ANATOMY Stomach consists of three parts 1. FUNDUS 2. BODY 3. PYLORUS - Pyloric antrum and Pyloric canal.

GASTRIN 1. It is secreted by Gastrin cells. 2. Inactive Progastrin gets converted to its active form gastrin in the presence of HCl. ACTIONS a) Stimulates the secretion of gastric acid. b) Stimulates pepsin secretion. c) Growth of mucosa of stomach, small and large intestine. d) Stimulates motility of stomach e) Stimulates secretion of insulin and glucagon. FACTORS AFFECTING SECRETION Factors increasing gastrin secretion 1. Digested protein products 2. Increased vagus activity 3. Calcium and epinephrine in blood Factors that Decrease gastrin secretion 1. Presence of the Acid in the pyloric antrum 2. Presence of : Secretin Vasoactive Intestinal Peptide Gastric Inhibitory Peptide Glucagon

GASTRIC JUICE 1. DAILY SECRETION: 2.5 – 3 L / DAY. 2. PH - 1 -2, acidic. 3. Composition: 1) Electrolytes 2) Enzymes: pepsinogen, lysozymes, rennin, gastric lipase. 3) Mucus 4) Intrinsic factor 5) Water

MECHANISM OF SECRETION OF HCL z z z z z z z

H+ is secreted in gastric lumen against concentration gradient by H – K ATP are present in the apical membrane of parietal cells. On stimulation of Parietal cells, H+ is secreted in the lumen in exchange for K .This is mediated by H+ - K ATPase. Cl is also secreted into gastric lumen down its electrochemical gradient. In the parietal cell H2CO3 is formed from CO2 and H2O by carbonic anhydrase enzyme. H2CO3 dissociates into H and HCO3 This H+ is secreted into gastric lumen HCO3 enters interstitial fluid in exchange for Cl that passes to gastric lumen.

REGULATION OF GASTRIC ACID A. NERVOUS B. HUMORAL A. Nervous regulation 1. Local autonomic reflexes via cholinergic neurons. 2. Impulses from CNS via X nerve; vagus nerve. Vagal stimulation: Increases secretion of gastric juice by z Release of GRP (Gastrin Releasing Peptide) z Release of Ach that increases acid and pepsinogen secretion. B. Humoral regulation Mediated by release of hormone gastrin. Psychic stimuli and food increases secretion of gastric juice.

Vagal activity causes: • Direct stimulation of gastric juice by pancreatic cells. • Release of gastrin from the gastrin cells of pyloric antrum.

PHASES OF GASTRIC JUICE SECRETION: 1. Cephalic phase. 2. Gastric influence. 3. Intestinal influences. Cephalic phase Gastric phase Intestinal phase. Before food enters Once food enters When food enters stomach stomach duodenum Vagal mediated Local reflexes, and Reflex and hormonal gastrin mediated feedback effects from intestinal mucosa 30 50 % of gastric 50 – 60 % of total Much less than both juice Factors effecting gastric emptying: INHIBITED BY: 1. CCK 2. Secretin 3. GIP 4. Vagotomy STIMULATED BY: 1. Gastrin 2. Excitement APPLIED: 1. PEPTIC ULCER: Breach in the epithelium of gastric mucosa of stomach or duodenum. Total gastrectomy: removal of whole stomach.