How does are body produce hcl (stomach acid)sergius - 28-11-2004 at 03:31
HCl is the major component of the secretion in the stomach that aids in the digestion and protection against food-borne microbes. HCl secretion is
tightly regulated by neural and hormonal mechanisms.
The acid-secreting parietal cell is located in the oxyntic gland, adjacent to other cellular elements important in the gastric secretory process. This
unique cell also secretes intrinsic factor (IF) essential for the absorption of vitamin B12.
The parietal cell expresses receptors for several stimulants of acid secretion including histamine, gastrin and acetylcholine. Each of these are G
protein–linked, seven transmembrane–spanning receptors. Binding of histamine to the H2 receptor leads to activation of adenylate cyclase and an
increase in cyclic AMP. Activation of the gastrin and muscarinic receptors results in activation of the protein kinase C/phosphoinositide signaling
pathway. Each of these signaling pathways in turn regulates a series of downstream kinase cascades, which control the acid-secreting pump, H+,
K+-ATPase. The discovery that different ligands and their corresponding receptors lead to activation of different signaling pathways explains the
potentiation of acid secretion that occurs when histamine and gastrin or acetylcholine are combined.
More importantly, this observation explains why blocking one receptor type (H2) decreases acid secretion stimulated by agents that activate a
different pathway (gastrin, acetylcholine). Parietal cells also express receptors for ligands that inhibit acid production (prostaglandins,
somatostatin, and EGF).
The enzyme H+, K+-ATPase is responsible for generating the large concentration of H+. It is a membrane-bound protein that consists of two subunits
(alpha and beta). The active catalytic site is found within the alpha subunit; the function of the beta subunit is unclear. This enzyme uses the
chemical energy of ATP to transfer H+ ions from parietal cell cytoplasm to the secretory canaliculi in exchange for K+. The H+,K+-ATPase is located
within the secretory canaliculus and in nonsecretory cytoplasmic tubulovesicles. The tubulovesicles are impermeable to K+, which leads to an inactive
pump in this location. The distribution of pumps between the nonsecretory vesicles and the secretory canaliculus varies according to parietal cell
activity. Under resting conditions, only 5% of pumps are within the secretory canaliculus, whereas upon parietal cell stimulation, tubulovesicles are
immediately transferred to the secretory canalicular membrane, where 60 to 70% of the pumps are activated. Proton pumps are recycled back to the
inactive state in cytoplasmic vesicles once parietal cell activation ceases.
(Excerpted from Harrison's Principles of Internal Medicine)
SergiusBlind Angel - 28-11-2004 at 08:12
Very intereseting, we have the answer for the H+ ion, now we would need the Cl- ions? Does it come directly from the blood? or the salt that we eat
(the Na+,Li+,K+ ions are absorbed somewhere leaving the Cl- ions that "ligand" with them?)andresderis - 8-12-2005 at 09:04
by the Na+/H+ pump in parietal cells in gastric epitelium.
the extracellular Cl ions are always in major concentrations that inside of cell
Edit by chemoleo:
Please, use the edit function in the future, instead of doubleposting. Also it'd help to be a bit clearer in your posts.
Quote:
the extracellular Cl ions are always in major concentrations that inside of cell
Compared to that inside the cell???
[Edited on 8-12-2005 by chemoleo]bereal511 - 8-12-2005 at 21:29
I found a diagram of the current model for parietal cell manufacturing of hydrochloric acid in my father's old medical textbooks. I don't have a
scanner, so I tried my best to render it into paint . Although it's not in the
diagram, the lumen exchanges most of the potassium ions with the hydrogen ions, forming a solution predominantly of hydrochloric acid with a miniscule
amount of sodium and potassium chloride.
. Although it's not in the
diagram, the lumen exchanges most of the potassium ions with the hydrogen ions, forming a solution predominantly of hydrochloric acid with a miniscule
amount of sodium and potassium chloride.