Hydrochloric Acid Is Secreted by the Parietal Cells

The HCl present in the gastric lumen is secreted by the parietal cells of the corpus and fundus. The mechanism of HCl production is depicted in Figure 27.6. An H+/K+-ATPase in the apical (luminal) cell membrane of the parietal cell actively pumps H+ out of the cell in exchange for

Plasma Parietal cell Lumen

Plasma Parietal cell Lumen

Parietal Cell Hcl Production
The mechanism of HCl secretion by the gastric parietal cell.

K+ entering the cell. The H+/K+-ATPase is inhibited by omeprazole. Omeprazole, an acid-activated prodrug that is converted in the stomach to the active drug, binds to two cysteines on the ATPase, resulting in an irreversible inacti-vation. Although the secreted H+ is often depicted as being derived from carbonic acid (see Fig. 27.6), the source of H+ is probably mostly from the dissociation of H2O. Carbonic acid (H2CO3) is formed from carbon dioxide (CO2) and H2O in a reaction catalyzed by carbonic anhydrase. Carbonic anhydrase is inhibited by acetazolamide. The CO2 is provided by metabolic sources inside the cell and from the blood.

For the H+/K.+ -ATPase to work, an adequate supply of K.+ ions must exist outside the cell. Although the mechanism is still unclear, there is an increase in K+ conductance (through K+ channels) in the apical membrane of the parietal cells simultaneous with active acid secretion. This surge of K+ conductance ensures plenty of K+ in the lumen. The H+/K+-ATPase recycles K+ ions back into the cell in exchange for H+ ions. As shown in Figure 27.6, the basolateral cell membrane has an electroneutral Cl~/HCO3~ exchanger that balances the entry of Cl_ into the cell with an equal amount of HCO3~ entering the bloodstream. The Cl_ inside the cell then leaks into the lumen through Cl" channels, down an electrochemical gradient. Consequently, HCl is secreted into the lumen.

A large amount of HCl can be secreted by the parietal cells. This is balanced by an equal amount of HCO3~ added to the bloodstream. The blood coming from the stomach during active acid secretion contains much HCO 3 , a phenomenon called the alkaline tide. The osmotic gradient created by the HCl concentration in the gland lumen drives water passively into the lumen, thereby, maintaining the iso-osmolality of the gastric secretion.

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Responses

  • marco
    How hydrochloride acid produce in parietal cell?
    8 years ago
  • helen
    How HCl is secreted into the stomach lumen?
    7 years ago
  • david
    How is hydrochloric acid secreted into the lumen by parietal cells?
    7 years ago
  • filiberta
    How is hcl secreted by parietal cell?
    1 year ago
  • Anthony
    Which is not a function of the HCl secreted by the parietal cells?
    9 months ago

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