Basics of Gastric Acid Secretion

Basics of Gastric Acid Secretion for Esproute

1. Physiology of Gastric Acid Secretion

2. Introduction Parietal cells : Predominate in the oxyntic glands, secrete hydrochloric acid and intrinsic factor Chief cells : Located at the base of the oxyntic glands, are responsible for secreting the digestive enzyme precursor pepsinogen Neuroendocrine cells containing hormonal and paracrine signaling agents that regulate the activity of the parietal cell reside within the glands. These include D cells, enterochromaffin-like (ECL) cells, A-like cells and enterochromaffin (EC) cells Oxyntic Gland Area: 80% Pyloric Gland Area: 20% Stomach

3. Gastric Gland Stomach mucosa’s epithelial lining consists of number of gastric pits, leading to gastric gland

4. Gastric Gland: Secretions Cell Types Substances Secreted Function Parietal Cells HCL Intrinsic Factor Kills microbes & activates pepsinogen Binds vitamin B12 to help it absorption Chief Cells Pepsinogen (converted to pepsin by acid) Gastric Lipase Protein Digestion Fat Digestion G Cells Gastrin Stimulates acid secretion ECL Cells Histamine Stimulates acid secretion Mucus-neck Cells Mucus & Bicarbonate Protection from acid D Cells Somatostatin Inhibits acid secretion

5. Gastric Gland: Gastric Juice Pale yellow in colour , pH is 1-3 Per day secretion is 2-3 liters It is a colourless, watery, acidic, digestive fluid produced in the stomach Gastric Juice HCl Electrolytes Mucus, Water Intrinsic factor Bicarbonate Gastric glands secretes a complex digestive fluid referred to as gastric juice

6. Gastric Gland: Gastric Juice Functions Hydrochloric Acid ( HCl ) Converts pepsinogen to pepsin for chemical digestion Provides optimal pH environment for pepsin Destroys some bacteria Stimulates the small intestinal mucosa to release Secretin and CCK Promotes the absorption of Ca 2+ and Fe 2+ in small intestine

7. Gastric Gland: Gastric Juice Functions Pepsinogen (precursor of pepsin) Digestion of proteins Mucus Forms a protective barrier: Mucus-bicarbonate barrier Intrinsic factor Combines with vitamin B 12 to make it absorbable

8. Parietal Cell Proton Pump (H + K + -ATPase) : Membrane protein in the parietal cells Parietal Cell

9. How is Gastric Acid produced? Sight, smell, taste and eating of food leads to release of biochemical substances Biochemicals get attached to respective receptors on parietal cell Activation of proton pump and release of HCl Step 1 Step 2 Step 3 Gastrin Histamine Acetylcholine

10. Proton Pump Inhibitors: Mechanism Proton Pump Inhibitors Block H + K + -ATPase Inhibit acid production

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