Gastric mucosa
Encyclopedia
The gastric mucosa is the mucous membrane
layer of the stomach
which contains the glands and the gastric pits
. In men it is about 1 mm thick and its surface is smooth, soft, and velvety. It consists of epithelium
, lamina propria
, and the muscularis mucosae
.
In its fresh state, it is of a pinkish tinge at the pyloric end and of a red or reddish-brown color over the rest of its surface. In infancy it is of a brighter hue, the vascular redness being more marked.
It is thin at the cardiac extremity, but thicker toward the pylorus. During the contracted state of the organ it is thrown into numerous plaits or rugae
, which, for the most part, have a longitudinal direction, and are most marked toward the pyloric end of the stomach, and along the greater curvature. These folds are entirely obliterated when the organ becomes distended.
When examined with a lens, the inner surface of the mucous membrane presents a peculiar honeycomb appearance from being covered with funnel-like depressions or foveolae of a polygonal or hexagonal form, which vary from 0.12 to 0.25 mm. in diameter. These are the ducts of the gastric glands, and at the bottom of each may be seen one or more minute orifices, the openings of the gland tubes. Gastric glands are simple or branched tubular glands that emerge on the deeper part of the gastric foveola, inside the gastric areas and outlined by the folds of the mucosa.
There are three types of glands: cardiac glands (in the proximal part of the stomach), oxyntic glands (the dominating type of gland), and pyloric glands.
The cardiac glands mainly contain mucus producing cells.
The bottom part of the oxyntic glands is dominated by zymogen (chief) cells that produce pepsinogen (an inactive precursor of the pepsin enzyme). Parietal cells, which secrete hydrochloric acid are scattered in the glands, with most of them in the middle part. The upper part of the glands consist of mucous neck cells; in this part the dividing cells are seen.
The pyloric glands contain mucus-secreting cells.
Several types of endocrine cells are found in all regions of the gastric mucosa. In the pyloric glands contain gastrin producing cells (G cells); this hormone stimulates acid production from the parietal cells. ECL (enterochromaffine-like) cells, found in the oxyntic glands release histamine, which also is a powerful stimulant of the acid secretion.
The A cells produce glucagon
, which mobilizes the hepatic glycogen
, and the enterochromaffin cells that produce serotonin, which stimulates the contraction of the smooth muscles.
The surface of the mucous membrane is covered by a single layer of columnar epithelium . This epithelium commences very abruptly at the cardiac orifice, where there is a sudden transition from the stratified epithelium
of the esophagus
. The epithelial lining of the gland ducts is of the same character and is continuous with the general epithelial lining of the stomach.
Mucous membrane
The mucous membranes are linings of mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion. They line cavities that are exposed to the external environment and internal organs...
layer of the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
which contains the glands and the gastric pits
Gastric pits
Gastric pits are indentations in the stomach which denote entrances to the tubular shaped gastric glands. They are deeper in the pylorus than they are in the other parts of the stomach. The human stomach has several million of these pits which dot the surface of the lining epithelium...
. In men it is about 1 mm thick and its surface is smooth, soft, and velvety. It consists of epithelium
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
, lamina propria
Lamina propria
The lamina propria is a constituent of the moist linings known as mucous membranes or mucosa, which line various tubes in the body ....
, and the muscularis mucosae
Muscularis mucosae
The lamina muscularis mucosae is the thin layer of smooth muscle found in most parts of the gastrointestinal tract, located outside the lamina propria mucosae and separating it from the submucosa....
.
In its fresh state, it is of a pinkish tinge at the pyloric end and of a red or reddish-brown color over the rest of its surface. In infancy it is of a brighter hue, the vascular redness being more marked.
It is thin at the cardiac extremity, but thicker toward the pylorus. During the contracted state of the organ it is thrown into numerous plaits or rugae
Rugae
Rugae is a term used in anatomy that refers to a series of ridges produced by folding of the wall of an organ. Most commonly the term is applied to the internal surface of the stomach...
, which, for the most part, have a longitudinal direction, and are most marked toward the pyloric end of the stomach, and along the greater curvature. These folds are entirely obliterated when the organ becomes distended.
When examined with a lens, the inner surface of the mucous membrane presents a peculiar honeycomb appearance from being covered with funnel-like depressions or foveolae of a polygonal or hexagonal form, which vary from 0.12 to 0.25 mm. in diameter. These are the ducts of the gastric glands, and at the bottom of each may be seen one or more minute orifices, the openings of the gland tubes. Gastric glands are simple or branched tubular glands that emerge on the deeper part of the gastric foveola, inside the gastric areas and outlined by the folds of the mucosa.
There are three types of glands: cardiac glands (in the proximal part of the stomach), oxyntic glands (the dominating type of gland), and pyloric glands.
The cardiac glands mainly contain mucus producing cells.
The bottom part of the oxyntic glands is dominated by zymogen (chief) cells that produce pepsinogen (an inactive precursor of the pepsin enzyme). Parietal cells, which secrete hydrochloric acid are scattered in the glands, with most of them in the middle part. The upper part of the glands consist of mucous neck cells; in this part the dividing cells are seen.
The pyloric glands contain mucus-secreting cells.
Several types of endocrine cells are found in all regions of the gastric mucosa. In the pyloric glands contain gastrin producing cells (G cells); this hormone stimulates acid production from the parietal cells. ECL (enterochromaffine-like) cells, found in the oxyntic glands release histamine, which also is a powerful stimulant of the acid secretion.
The A cells produce glucagon
Glucagon
Glucagon, a hormone secreted by the pancreas, raises blood glucose levels. Its effect is opposite that of insulin, which lowers blood glucose levels. The pancreas releases glucagon when blood sugar levels fall too low. Glucagon causes the liver to convert stored glycogen into glucose, which is...
, which mobilizes the hepatic glycogen
Glycogen
Glycogen is a molecule that serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue...
, and the enterochromaffin cells that produce serotonin, which stimulates the contraction of the smooth muscles.
The surface of the mucous membrane is covered by a single layer of columnar epithelium . This epithelium commences very abruptly at the cardiac orifice, where there is a sudden transition from the stratified epithelium
Stratified epithelium
Stratified epithelium can refer to:* Stratified squamous epithelium* Stratified cuboidal epithelium* Stratified columnar epithelia...
of the esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
. The epithelial lining of the gland ducts is of the same character and is continuous with the general epithelial lining of the stomach.