Your stomach is a stretchy acid mill between gullet and gut
The stomach sits in the left upper abdomen as a hollow muscular bag between esophagus and duodenum. After the cephalic phase of smell and chewing, its gastric phase uses acid and enzymes to turn meals into chyme that the pyloric sphincter meters onward—normally holding about a litre, sometimes expanding toward two to four.
Anatomy is directional: the diaphragm rides above, the pancreas nestles behind, and the greater omentum drapes from the greater curvature. Two sphincters—lower esophageal at the cardia and pyloric at the exit—contain contents while parasympathetic and sympathetic plexuses tune both secretion and motility. Empty it is often J-shaped; partly filled it becomes pear-like; in newborns capacity may be only about thirty millilitres.
Four regions march from cardia through fundus and body to pylorus. The wall stacks mucosa, submucosa, a distinctive three-layer muscular coat with an inner oblique sheet absent elsewhere in the gut, then subserosa and serosa. That oblique layer churns food while the antrum contracts more forcefully than the fundus, producing the strongest peristalsis of the tract.
Arterial arcs include left and right gastric vessels along the lesser curve, gastroepiploic arteries along the greater curve, and short gastrics from the splenic artery feeding the fundus. Lymph drains toward the cisterna chyli. The organ is less a passive sack than a regulated reactor that chemically digests, shapes microbiota cues, and hands carefully timed chyme to the small intestine.
The chemistry happens in the lining. Each gastric pit collects juice from somewhere between two and seven glands. In the fundus and body, parietal cells release hydrochloric acid plus intrinsic factor, while chief cells supply pepsinogen, an inert precursor that the acid switches on as pepsin so proteins get cut into polypeptides. The resulting pH of roughly 2 also kills or suppresses bacteria. Near the exit, G cells in the pyloric glands add the hormone gastrin, and a smooth groove along the lesser curvature lets drinks bypass the churning and slip quickly toward the pylorus. Genetically the organ is busy too: nearly seven in ten human protein-coding genes are active there, yet only about twenty are highly stomach-specific.
Source: Stomach
