Stomach

The stomach is the most dilated part of the digestive tract: a J-shaped, muscular, hollow organ that can hold roughly 2 to 3 liters. It acts as both a temporary food reservoir and a powerful blender, beginning the chemical breakdown of protein.

Structure and Location

The stomach sits in the upper abdomen, left of the midline, just below the diaphragm and connected above to the esophagus and below to the small intestine. It has four regions: the cardia (where the esophagus enters), the dome-shaped fundus, the central body (the largest part), and the funnel-shaped pylorus, which empties into the duodenum through the pyloric sphincter. Its inner curve is the lesser curvature and its outer curve is the greater curvature.

Unlike the rest of the gut, the stomach wall has three muscle layers: an inner oblique layer (unique to the stomach), a middle circular layer, and an outer longitudinal layer. This extra layer lets the stomach churn food vigorously. The middle circular layer thickens at the outlet to form the pyloric sphincter, which controls how fast contents leave.

Function

The lining contains gastric glands with specialized cells. Parietal cells secrete hydrochloric acid (creating a strongly acidic environment that kills microbes) and intrinsic factor, a protein needed to absorb vitamin B12 later in the gut. Chief cells release pepsinogen, which the acid converts into pepsin to digest protein. Mucous cells coat the lining to protect it from self-digestion. Together these turn a meal into chyme, a semi-liquid that is released in controlled spurts into the small intestine. The main blood supply comes from branches of the celiac trunk.

Clinical Relevance

Common disorders include peptic ulcers (often linked to Helicobacter pylori infection or NSAID use), gastritis, GERD, and gastric cancer. Because intrinsic factor is made here, severe stomach disease or surgery can cause vitamin B12 deficiency. This page is educational and is not medical advice.