Stomach
The stomach is a J-shaped organ of the GI tract directly inferior to the diaphragm in
the abdomen. The stomach connects the esophagus to the duodenum, the first part
of the small intestine.
Gross anatomy:
The stomach has four main regions:
Cardia is the smallest part of the stomach. It consists of the superior, medial
portion of the stomach within 3 cm (1.2 in.) of the junction between the
stomach and the esophagus. The cardia contains abundant mucous glands.
Their secretions coat the connection with the esophagus and help protect that
tube from the acid and enzymes of the stomach.
Fundus is the portion of the stomach that is superior to the junction between
the stomach and the esophagus. The fundus contacts the inferior, posterior
surface of the diaphragm.
Body is the area of the stomach between the fundus and the curve of the J is
the body, the largest region of the stomach. The body acts as a mixing tank
for ingested food and secretions produced in the stomach. Gastric glands in
the fundus and body secrete most of the acid and enzymes involved in gastric
digestion.
Pylorus forms the sharp curve of the J. The pylorus is divided into a pyloric
antrum (antron means cavity), which is connected to the body, and a pyloric
canal, which empties into the duodenum, the proximal segment of the small
intestine
Rugae: When the stomach is empty, the mucosa lies in large folds, known as rugae
(wrinkles), which can be seen with the unaided eye. As the stomach fills, these
temporary features increase the surface area of stomach and let the gastric lumen
expand.
Lesser curvature: The concave medial border of the stomach is called the lesser
curvature.
Greater curvature: The convex lateral border is called the greater curvature.
A muscular pyloric sphincter regulates the release of chyme into the duodenum.
Size: The size of the stomach varies from person to person. It may expand when full
and deflates when empty. In an average stomach, the lesser curvature is
approximately 10 cm (4 in.) long, and the greater curvature measures about 40 cm
(16 in.)
Location: The stomach typically extends between the levels of vertebrae T7 and L3.
Histology:
The stomach wall is composed of the same basic layers as the rest of the GI tract,
with certain modifications.
1) Mucosa: The mucosa of the stomach consists of:
The surface of the mucosa is a layer of simple columnar epithelial cells
called surface mucous cells.
Lamina propria (areolar connective tissue), and
Muscularis mucosae consists of an irregular layer of smooth muscles
2) Sub mucosa: The submucosa contains areolar connective tissue and blood
vessels.
3) Muscularis externa: The muscularis has three layers of smooth muscle
(rather than the two found in the esophagus and small and large intestines): an
outer longitudinal layer, a middle circular layer, and an inner oblique layer.
The oblique layer is limited primarily to the body of the stomach.
4) Serosa: The serosa is composed of simple squamous epithelium
(mesothelium) and areolar connective tissue; the portion of the serosa
covering the stomach is part of the visceral peritoneum.
Gastric glands: Epithelial cells extend down into the lamina propria, where they
form columns of secretory cells called gastric glands. Several gastric glands open
into the bottom of narrow channels called gastric pits. Secretions from several
gastric glands flow into each gastric pit and then into the lumen of the stomach.
The gastric glands contain three types of exocrine gland cells that secrete their
products into the stomach lumen:
Surface mucous cells surround the gastric pit or outer region of gastric gland.
Both mucous neck cells and surface mucous cells secrete mucus.
Chief cells (or zymogenic cells), are most abundant near the base of a gastric
gland. These cells secrete pepsinogen (an inactive proenzyme) and gastric
lipase. Acid in the gastric lumen converts pepsinogen to pepsin, an active
proteolytic, or protein-digesting enzyme.
Parietal cells are especially common along the proximal portions of each
gastric gland. These cells secrete hydrochloric acid and intrinsic factor. This
glycoprotein helps absorb vitamin B12 across the intestinal lining.
Stem cells
Enteroendocrine cells: Three types of enteroendocrine cell are located in
gastric glands, which include the G cell, which is located mainly in the pyloric
antrum and secretes the hormone gastrin into the bloodstream. D cells which
release somatostatin, a hormone that inhibits the release of gastrin.
Enterochromaffin-like (ECL) cells release histamine.
Cells of gastric gland
Histology of stomach
