- The stomach is a muscular, hollow organ that forms a crucial component of the digestive system, located in the upper left quadrant of the abdomen, just beneath the diaphragm.
- Shaped somewhat like a J, the stomach connects the esophagus to the small intestine and functions as a reservoir where food is stored, broken down, and prepared for further digestion and absorption. It plays a central role in the mechanical and chemical digestion of food, transforming ingested material into a semi-liquid substance known as chyme.
- Anatomically, the stomach is divided into several distinct regions: the cardia, where food enters from the esophagus; the fundus, which acts as a storage area; the body or corpus, which is the main digestive chamber; and the pylorus, which regulates the passage of chyme into the duodenum of the small intestine via the pyloric sphincter. The inner lining of the stomach is highly folded into structures called rugae, which allow the stomach to expand significantly after food intake.
- The stomach wall consists of four layers: mucosa, submucosa, muscularis externa, and serosa. The mucosa contains millions of gastric glands, which secrete a combination of hydrochloric acid (HCl), digestive enzymes (primarily pepsin), and mucus. HCl creates an acidic environment (pH 1.5–3.5) that helps denature proteins, kill ingested pathogens, and activate enzymes. Pepsinogen, an inactive enzyme secreted by chief cells, is converted into pepsin in the presence of acid, enabling the breakdown of protein into smaller peptides. Mucus, secreted by goblet cells, forms a protective barrier on the stomach lining, preventing self-digestion and damage from gastric acid.
- The stomach also plays a role in mechanical digestion through strong peristaltic contractions of its muscular walls. These contractions churn and mix food with gastric juices to enhance enzymatic breakdown. This process, known as gastric motility, ensures thorough digestion before chyme moves into the small intestine. The stomach also produces intrinsic factor, a glycoprotein necessary for the absorption of vitamin B12 in the small intestine.
- Regulation of stomach activity is coordinated by neural and hormonal mechanisms. The vagus nerve stimulates gastric secretions in response to the sight, smell, or thought of food—a phase known as the cephalic phase. Hormones such as gastrin, secreted by G cells in the antrum of the stomach, further stimulate acid production and motility in response to food intake.
- Several disorders can affect stomach function, including gastritis, peptic ulcers, acid reflux (GERD), and gastric cancer. These conditions often arise from imbalances in gastric acid secretion, infection by Helicobacter pylori, or the breakdown of protective mucosal barriers. Diagnostic tools such as endoscopy, barium swallow studies, and biopsy are used to assess stomach health.
