Stomach

The stomach is a muscular organ forming part of the digestive system (the pathway through which food is broken down inside the body). It is located in the upper part of the abdominal cavity, between the oesophagus (the food passage) and the small intestine. Its primary function is to store food for a period, break it down chemically, and then pass it gradually on to the small intestine.

The stomach wall has muscular layers that churn food until it becomes a liquid-like substance called chyme. At the same time, glands inside the stomach release hydrochloric acid and enzymes that begin to break down protein.

Anatomy

The stomach is typically divided into several parts: the section joining the oesophagus (the cardia), the upper distended part (the fundus), the central body (corpus), and the lower section near the small intestine (the pylorus). Two muscular rings control movement: one before the stomach, preventing food from returning to the oesophagus, and one after the stomach, regulating the passage of chyme. When empty, the interior of the stomach bears folds (rugae) that allow it to expand when food is taken in.

Digestive function

Different glands release different secretions. Parietal glands release hydrochloric acid, making the stomach highly acidic. Chief glands release pepsinogen, which the acid converts into pepsin—the enzyme that breaks down protein. Other glands release mucus and bicarbonate, which protect the stomach wall from being burned by the acid. The hormone gastrin increases acid secretion when food is eaten.

Absorption and regulation

The stomach itself is not the primary site of nutrient absorption; most absorption occurs in the small intestine. However, certain small molecules—such as water, alcohol, and certain medicines—can pass through the stomach wall. The stomach also produces a substance needed for the absorption of vitamin B12 further down the intestine.

Health conditions

Conditions affecting the stomach include inflammation of the stomach lining (gastritis), stomach ulcers, and reflux of acid back into the oesophagus. The bacterium Helicobacter pylori is associated with stomach ulcers and some stomach cancers. Medicines that reduce acid production and antibiotic treatment are part of routine management.