The human stomach plays a central role in the digestive system, breaking down ingested food received from the esophagus and preparing it for further digestion and nutrient absorption in the intestines. This muscular organ temporarily stores food, allowing for controlled release into the digestive tract.
Structure of the Stomach
The stomach is a muscular, hollow organ located in the upper left abdomen, nestled between the esophagus and the small intestine. It typically has a J-shaped or comma-shaped appearance. An empty stomach is roughly the size of a fist but can expand considerably to hold up to 1.5 liters or more of food and fluid.
The stomach is broadly divided into four main regions. The cardia is the initial section where food enters from the esophagus, followed by the dome-shaped fundus, which often stores undigested food and gases. The largest part is the body, or corpus, where the bulk of initial digestion occurs. Finally, the funnel-shaped pylorus connects the stomach to the duodenum, the first part of the small intestine.
Two muscular rings, or sphincters, regulate food flow. The lower esophageal sphincter, also known as the cardiac sphincter, controls food entry from the esophagus into the stomach and prevents reflux. At the stomach’s exit, the pyloric sphincter regulates the passage of partially digested food into the small intestine. The stomach wall is comprised of several layers, including an inner mucosa, submucosa, and a muscular layer with three sub-layers of muscle that enable its churning actions.
The Digestive Powerhouse
The stomach performs both mechanical and chemical digestion to transform ingested food into a semi-liquid mixture called chyme. Mechanical digestion involves strong muscular contractions, known as churning, which mix and physically break down food into smaller particles. These contractions are facilitated by the stomach’s muscular layer, which includes an inner oblique layer not found in other parts of the gastrointestinal tract.
Chemical digestion in the stomach relies on the secretion of gastric juices, produced by specialized cells within the stomach lining. These juices contain hydrochloric acid, which creates a highly acidic environment with a pH between 1.5 and 3.5. This acidity serves multiple purposes, including killing most bacteria ingested with food and denaturing proteins, making them more susceptible to enzymatic breakdown.
Another component of gastric juice is pepsin, an enzyme specifically responsible for initiating protein digestion. Pepsin breaks down large protein molecules into smaller polypeptide chains. The stomach also secretes a protective layer of mucus, which coats the inner lining and shields it from the corrosive effects of the hydrochloric acid and digestive enzymes, preventing self-digestion.
Common Stomach Conditions
Several conditions can affect the stomach, impacting its function and leading to discomfort. Acid reflux, often referred to as gastroesophageal reflux disease (GERD) when chronic, occurs when stomach acid frequently flows back into the esophagus. This backward flow can irritate the esophageal lining, causing symptoms like heartburn.
Gastritis refers to the inflammation of the stomach lining. This inflammation can result from various factors, including bacterial infections, regular use of certain pain relievers, or excessive alcohol consumption. Depending on the cause, gastritis can be acute, appearing suddenly, or chronic, developing gradually over time.
Peptic ulcers are open sores that develop on the inside lining of the stomach, the small intestine, or sometimes the esophagus. These ulcers often form when the protective mucus layer is reduced, allowing stomach acid to damage the underlying tissue. A common cause of peptic ulcers is infection with the bacterium Helicobacter pylori, though long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs) can also contribute.