HCL SECRETION
HCL secretion occurs within parietal cells, during this process many activities are achieved.
1-HCL Characteristics.
The gastric juice contains 1 to 5% of free HCL, between 30 to 150mEq of hydrogen ion per liter, its pH is close to 1, it is therefore more acidic than all biological fluids.
2-Factors Of HCL Secretion.
Acid secretion occurs during meal intake and digestion.
— This delivery requires a lot of energy. This is formed by oxidative mechanism.
— Ions, chlorine and potassium come from parietal cells, mucus cells and interstitial fluid.
— Chlorine passage from the internal environment to the gastric cavities is active transport linked to cellular metabolism.
— Potassium ion does not quantitatively influence HCL secretion.
— Hydrogen ion is secreted by the parietal cells, and comes mainly from carbonic acid.
3- Deep Insight Of HCL Secretion.
The parietal cells are found between the lumen and Plasma. The parietal cells have two channels called canaliculi, in their apical side are directed toward the lumen region, but in their baso lateral region, the parietal cells are facing the plasma region.
— When the cell is not activated, the lumen side is an environment of higher concentration of sodium ions, and low concentration of hydrogen.
— An activation of bordering cells provokes 3 main opening channels. One channel towards the luminal side and 2 other channels directed into the plasma side:
— Proton / potassium ATP (proton pump).
— Chloride channels.
— Potassium channels.
— Chloride bicarbonate exchanger or anti-porter.
— Sodium potassium pump.
— During this activation, we also observe, a decrease in concentration of calcium ions and an increase of concentration of proton or hydrogen ions in the luminal area; and simultaneously passage of three ions chloride, potassium and hydrogen through the plasma region.
— When the carbon dioxide and water entered into the cell, they combine with each other and form the carbonic acid in the presence of an enzyme called carbonic anhydrase. They will be dissociated into proton and bicarbonate. This hydrogen positive, will be the source for the proton channel, to be transferred through the proton pump towards the lumen region.
— Thus, one ATP molecule is used to transfer this proton from the cytoplasmic side towards the luminal region, and of potassium ion in the plasma region, by using the hydrogen potassium ATPase.
— In the luminal side, two compounds (the proton and chloride), are appeared separately, to be combined and build the HCL.
— In the baso-lateral region, exist a chloride bicarbonate exchanger, it is an anti-porter, its main role is to transfer one bicarbonate ion from the cytoplasmic side towards the external side, and simultaneously it transfers the chloride ion from the outside towards the inside of the parietal cell. Thus, the chloride ion is formed, to serve as a source for the chloride channel.
— In the sodium potassium pump, we see a transfer of three Na positive to the outside and two K positives to the inside.
— When this bicarbonate is transferred from the cytoplasmic site towards the external side, it causes an increase in the alkalinity of the blood, but in the lumen side, we observe an increase in acidity.
