VPB 121: Veterinary Physiology - II (2+1)

GASTRIC JUICE - COMPOSITION

• It is a colourless fluid, containing HCl, enzymes and mucus. Concentration of HCI in the stomach content varies with the nature of food, stage of digestion, amount of saliva to be neutralized etc

Hydrochloric acid

• It is actively secreted by the parietal/oxyntic cells of the fundic glands involves expenditure of energy, which is derived from the oxidative metabolism.  
• Diffusion of CO₂ from the plasma into parietal cells
• Higher concentration of carbonic anhydrase in the parietal cells
• Chemical reaction of CO₂ with cellular water in the presence of “carbonic anhydrase”
• Formation of carbonic acid ( H₂CO₃ ) in the parietal cells
• Dissociation of H₂CO₃ in to HCO₃^- + H⁺
• Diffusion of HCO₃^– ions into plasma with a exchange of Cl^- ion from the plasma
• During active digestion, the concentration of HCO₃ increases very high and increases the pH of blood, called as alkaline tide.
• Active exchange of H⁺ and K⁺ ions between parietal cell and luminal surface of the stomach by of H⁺ - K⁺ ATPase, enzyme present in the luminal surface of the stomach
• H⁺ ion is actively secreted into the luminal surface of the parietal cell with a exchange of K⁺ ions into the parietal cell
• Reaction of K⁺ ions with Cl^- ion and formation of KCl in the parietal cell
• Release of KCl into the luminal surface
• Reaction of KCl with H⁺ ion and the formation of K⁺ ion and HCl

Functions of HCl

• Activates pepsinogen, the inactive form of enzyme into active pepsin, hydrolysing enzyme of protein
• Slight hydrolysis of sucrose
• Also function as antiseptic in the stomach.