GASTRIC JUICE AND IT'S FUNCTIONS

 

MECHANISM OF HCl SECRETION: The gastric mucosa has different types of cells:

(a) The mucous secreting surface epithelial cells,

(b) The oxyntic or parietal cells which secrete acid, and

(c) The chief cells or peptic cells that secrete enzymes.

The HCl secreted by the parietal cells is of high concentration about 0.15 M with a pH as low as 0.8. Acids,Bases and the pH,

THE K⁺/H⁺ATPase: The parietal cells transport protons against a concentration gradient at the extracellular fluid pH of 7.4. It is an energy-requiring process. The K⁺ activated ATPase is necessary for the production of HCl. It is located on the luminal side of the plasma membrane. The H⁺ ions are generated within the cell by ionization of carbonic acid. The carbonic anhydrase is active in the parietal cells. Proton pump inhibitors  One molecule of ATP is hydrolyzed for every molecule of H⁺ secreted. The hydrolysis of ATP is coupled with an exchange of K⁺ for H⁺. The hydrogen ions are then secreted into gastric lumen. Side by side with the H⁺ to K⁺ exchange, a bicarbonate to chloride exchange is also taking place. When the bicarbonate level within the cell increases which is formed from Carbonic acid (H2CO3), it is reabsorbed into bloodstream, in exchange for Cl^– . The chloride is then secreted into the lumen to form HCl. This would account for the alkaline tide of plasma and urine, following hydrochloric acid secretion, immediately after meals.

REGULATION OF ACID SECRETION: Gastrin, the gastrointestinal peptide hormone secreted by G cells, stimulates secretion of HCl. The secretion of gastrin is cut off by acidic pH by a feedback regulatory control. The most potent stimulus for acid secretion is histamine, which acts through specific H2 receptors on the gastric mucosa. ANTIHISTAMINES

OTHER CONSTITUENTS OF GASTRIC SECRETIONS: The major enzyme present in gastric juice is pepsin, which is responsible for digestion of proteins. One of the functions of HCl is to activate the zymogen pepsinogen to pepsin by partial proteolysis. In addition, the HCl helps in the absorption of iron and calcium. The gastric juice also contains a glycoprotein required for the absorption of B12, the Castle's intrinsic factor.

RELATED;

1. PEPTIC ULCER DISEASE

2.  NAUSEA AND VOMITING

3.  ANATOMY AND PHYSIOLOGY

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