Stomach Health Article

Definition

The stomach is a muscular J-shaped organ of the digestive tract. It temporarily stores and mixes food; it also secretes gastric juice into the lumen (the hollow inside the stomach) and a hormone called gastrin into the blood.

Description

The stomach is located in the upper left quadrant of the abdomen, just beneath the diaphragm. It is positioned between the esophagus (the passage between the mouth and stomach) and the small intestine. There is a sphincter (circular muscle) between the esophagus and the stomach, which allows food to pass into the stomach and prevents chyme (the semi-fluid mass into which food is converted by gastric enzymes) from flowing backwards into the esophagus. The pyloric valve is situated between the stomach and the small intestine, which allows chyme to pass into the small intestine and back into the stomach.

The stomach is divided into three general areas. The upper portion of the stomach near the esophagus is called the fundus; the middle section of the stomach is called the body; and the bottom portion of the stomach where the pyloric sphincter is located is called the antrum. When the stomach is completely distended (expanded), it measures about 10 in (26 cm) by about 4 in (10 cm). It can hold about one quart of semiliquid chyme.

The wall of the stomach is made up of four layers: the mucous, submucous, muscular, and peritoneal layers. The mucous and submucous layers are made up of ridges called rugae. Within the ridges are gastric glands made up of mucous cells, parietal cells, chief cells, and G-cells. Each of these cells secretes a chemical that aids in the process of digestion.

The muscular layer is actually composed of three different layers of smooth muscle, each with fibers running in a different direction: horizontal, vertical, and diagonal. The muscles are responsible for mixing the chyme and moving it through the stomach to the small intestine.

The peritoneal layer is the outer layer of stomach tissue. It is part of the peritoneum that lines the inside of the abdomen, covering most of the organs. It does not play a role in digestion.

The stomach has a large supply of blood vessels for the absorption of nutrients from digested food. Branches of the vagus nerve supply both sensory and nervous fibers to the stomach.

Food storage

The stomach's primary role is to act as a temporary receptacle for food. While the food is in the stomach, it is mixed with gastric juices that are secreted by cells in the mucosal layer.

There are three general phases regulating gastric juice secretion. The first, or cephalic, phase occurs before food is actually eaten. The thought, smell and sight of food cause the brain to send signals to the stomach to increase its gastric secretions. The second phase is the gastric phase, which occurs when food enters the stomach. The food causes the stomach to stretch, which in turn sends nervous impulses to the brain. The brain sends return impulses back to the stomach to begin secreting gastrin. Gastrin then stimulates the release of other gastric juices. The third phase is called the intestinal phase, which occurs when food enters the small intestine. This phase results in a decrease in the movement of chyme into the small intestine, ensuring that the small intestine does not receive too much chyme at one time.

The stomach secretes 2–3 quarts (liters) of gastric juices every day. There are several types of specialized cells in the stomach that secrete gastric juices. Like the pancreas, the stomach has both exocrine and endocrine glandular functions. Exocrine secretory glands contain three types of secretory cells: chief cells, parietal cells and mucous cells. Endocrine cells called G-cells are scattered throughout the mucosa.