HOW PARIETAL CELLS SECRETE HCL ?
Initially, the parietal cell only contains water that dissociates to give hydroxide and hydrogen ions.
1-Parietal Cell And HCL.
The parietal cell is the most important cell in the stomach. Within its environment, it built huge works. It starts from hydrogen potassium exchange and ends in HCL secretion.
2- Electrolytes Concentration.
The main electrolytes found in your stomach are:
-H ions, from 0 to 143 and 160 mEq /l.
-Cl, from 100 to 170 mEq /l.
- Na varies from 10 to 100–120 mEq /l.
- K+ between 10 and 20 mEq/l,
-Ca (0.7 to 3 mEq/l.
-Mg2+ (0.1 to 2.5 mEq /l.
-Bicarbonates (20 to 30 mEq /l.
-Phosphates, sulfates, and iodides in small quantities.
3- HCL Finality.
— Initially, the parietal cell, only contains water that dissociates to give hydroxide and hydrogen ions.
— Potassium enters the parietal cell at the same time as the hydrogen ions.
Note :
— Hydrogen ion cannot pass into the lumen, because it contains high energy. For this reason, it needs a H-K pump.
— Carbon dioxide, which also has a higher concentration in plasma, can use simple diffusion to get inside the parietal cell with reduced energy. Thus, it can connect with hydroxide and form bicarbonate.
— Bicarbonate has a higher concentration inside the cell, so it can easily move outward to the plasma medium.
— In the plasma environment, there exist two ions: chlorine, and sodium.
— Chlorine also can not penetrate the parietal cell easily because of its high energy. To do this, it requires ATP to pass through the channel.
— Chlorine enters the lumen through the channel, binds with hydrogen, and generates HCL.
— Potassium returns to the lumen to actualize its contraction outside to facilitate the transfer of hydrogen ions in the future.
4- Hydrogen-Potassium Pump.
— The parietal cell has two main receptors: M3 called muscarinic receptors and H2.
— The first chemical messenger of acetylcholine binds to the M3 receptor and generates a second chemical messenger, which is the calcium ion.
— The calcium ion in return activates a protein kinase C.
— This kinase transports phosphate to ADP and builds ATP.
— ATP is broken down and the hydrogen-potassium pump is activated.
5-G Cell.
G-cell has two ways to secrete HCL.
*The First Way is direct.
— Gastrin secreted by G cell has a receptor called CCK5 on the parietal cell. When connected to this receptor, it generates calcium ions and activates protein kinase-C. This kinase transports phosphate to ADP and ATP is built. Once ATP is broken down , the hydrogen-potassium pump is activated.
*The Second Way is indirect.
— Gastrin activates the ECL (enterochromaffin-like cell) and generates histamine.
— Histamine connects to its own receptor called H2, generates a second chemical messenger, C-AMP, and activates protein kinase-A. The same process is built : a transport of phosphate to ADP and transformation to ATP . When this energy is broken down , the hydrogen-potassium pump is at work.
