Alternative definition : KEGG: Gastric acid is a key factor in normal upper gastrointestinal functions, including
protein digestion and calcium and iron absorption, as well as providing some protection
against bacterial infections. The principal stimulants of acid secretion at the level
of the parietal cell are histamine (paracrine), gastrin (hormonal), and acetylcholine
(ACh; neurocrine). Stimulation of acid secretion typically involves an initial elevation
of intracellular calcium and cAMP, followed by activation of protein kinase cascades,
which trigger the translocation of the proton pump, H , K -ATPase, from cytoplasmic
tubulovesicles to the apical plasma membrane and H secretion into the stomach lumen.;