stomachs

The stomach is a sac-like organ of the upper gastrointestinal tract between the esophagus and the small intestine. It functions to mechanically digest food through contractions and chemically digest proteins, beginning the process of digestion before chyme moves to the duodenum. In an adult, the stomach can hold about 1 to 1.5 liters when full.

It is divided into regions: cardia, fundus, body, and antrum, with the pyloric region controlling exit to the duodenum via the pyloric sphincter. The inner lining forms rugae when the stomach is empty. The mucosa contains gastric glands: parietal (oxyntic) cells that secrete hydrochloric acid and intrinsic factor; chief (peptic) cells that produce pepsinogen; mucous cells that secrete protective mucus; and various enteroendocrine cells, including G cells that secrete gastrin.

Hydrochloric acid denatures proteins and activates pepsinogen to pepsin. The stomach also secretes intrinsic factor, essential for vitamin B12 absorption. Gastric mixing produces a semi-liquid chyme; the pyloric sphincter regulates emptying into the duodenum. Secretion and motility are regulated by neural (vagus nerve) and hormonal signals, including gastrin, somatostatin, and other enteric hormones. The gastric mucosa is protected by mucus, bicarbonate, tight junctions, and prostaglandins.

Common conditions affecting the stomach include gastritis, peptic ulcers, and gastric cancer. Delayed gastric emptying, or gastroparesis, can follow diabetes or viral illness. Treatments target acid production, motility, and mucosal protection, such as proton pump inhibitors and antacids; NSAIDs can disrupt protective mechanisms.