Gastric glands

Glands in lining of the human stomach

Gastric glands are glands in the lining of the stomach that play an essential role in the process of digestion. Their secretions make up the digestive gastric juice. The gastric glands open into gastric pits (foveolae) in the mucosa. The gastric mucosa is covered in surface mucous cells (foveolar cells) that produce the mucus necessary to protect the stomach epithelial lining from gastric acid secreted by parietal cells in the glands, and from pepsin a secreted digestive enzyme. Surface mucous cells follow the indentations and partly line the gastric pits. Other mucus secreting cells are found in the necks of the glands. These are mucous neck cells that produce a different kind of mucus. There are two types of gastric gland, the exocrine oxyntic gland, and the endocrine pyloric gland. The major type of gastric gland is the oxyntic gland that is present in the fundus and the body of the stomach making up about 80 per cent of the stomach area. These glands are often referred to simply as the gastric glands. The oxyntic gland contains the parietal cells that produce hydrochloric acid and intrinsic factor, and chief cells that produce pepsinogen and gastric lipase. The pyloric gland is found in the pyloric region, the remaining 20 per cent of the stomach. The pyloric glands are mainly in the pyloric antrum. The pyloric gland secretes gastrin from its G cells. Pyloric glands are similar in structure to the oxyntic glands but have hardly any parietal cells.

The gastric glands are glands in the lining of the stomach that play an essential role in the process of digestion. All of the glands have mucus secreting foveolar cells (also known as surface mucous cells) that line the stomach and partly line the gastric pits, and mucus secreting mucous neck cells in the necks of the gastric glands. Mucus lines the entire stomach as gastric mucosa protecting the stomach lining from the effects of hydrochloric acid produced by the parietal cells and released from the oxyntic glands. Gastric glands are mostly exocrine glands and are all located beneath the gastric pits within the gastric mucosa. The gastric mucosa is pitted with innumerable gastric pits which each house 3 5 gastric glands. Mucous neck cells produce mucus, parietal cells secrete hydrochloric acid and intrinsic factor, chief cells secrete pepsinogen and gastric lipase. Gastric juice contains water, hydrochloric acid, intrinsic factor, pepsinogen, and salts. Adults produce around two to three litres of gastric juice per day. They are fewer in number than the other gastric glands and are more shallowly positioned in the mucosa. There are two kinds either simple tubular with short ducts or compound racemose resembling the duodenal Brunner's glands. The fundic glands (or oxyntic glands), are found in the fundus and body of the stomach. They are simple almost straight tubes, two or more of which open into a single duct. Oxyntic means acid secreting and they secrete hydrochloric acid (HCl) and intrinsic factor.

There are millions of gastric pits (also known as foveolae) in the gastric mucosa and their necessary narrowness determines the tubular form of the gastric gland. More than one tube allows for the accommodation of more than one cell type. The form of each gastric gland is similar; they are all described as having a neck region that is closest to the pit entrance, and basal regions on the lower parts of the tubes. The epithelium from the gastric mucosa travels into the pit and at the neck the epithelial cells change to short columnar granular cells. These cells almost fill the tube and the remaining lumen is continued as a very fine channel. Cells found in the gastric glands include mucous neck cells, chief cells, parietal cells, G cells, and enterochromaffin like cells (ECLs). The first cells of all of the glands are mucus secreting foveolar cells that line the gastric pits. The mucus produced here is less acidic than that produced by the mucous neck cells. Fundic glands found in the fundus and also in the body have another two cell types–gastric chief cells and parietal cells (oxyntic cells). Foveolar cells (surface mucous cells) are mucus producing cells which cover the inside of the stomach, protecting it from the corrosive nature of gastric acid. These cells line the gastric mucosa and follows into the gastric pits. Mucous neck cells are located within gastric glands, interspersed between parietal cells. These are shorter than their surface counterpart and contain lesser quantities of mucin granules in their apical surface. Chief cells (zymogen cells/peptic cells) – They are found in the basal regions of the gland and release proenzymes or zymogens – pepsinogen (precursor to pepsin), and prorennin (precursor to rennin or chymosin). Prorennin is secreted in young mammals (childhood stage). It is not secreted in adult mammals. Chief cells also produce small amounts of gastric lipase. Gastric lipase contributes little to digestion of fat. Parietal cells ("parietal" means "relating to a wall"), also known as oxyntic cells are most numerous on the side walls of the gastric glands. The parietal cells secrete hydrochloric acid (gastric acid). This needs to be readily available for the stomach in a plentiful supply, and so from their positions in the walls, their secretory networks of fine channels called canaliculi can project and ingress into all the regions of the gastric pit lumen. Another important secretion of the parietal cells is intrinsic factor. Intrinsic factor is a glycoprotein essential for the absorption of vitamin B12. Enteroendocrine cells – They are usually present in the basal parts of the gastric glands, which is differentiated into three cell types – enterochromaffin like cells (ECL cells), G cells, and D cells. Enterochromaffin like cells (ECL cells) – They release serotonin and histamine. These cells store and release histamine when the pH of the stomach becomes too high. The release of histamine is stimulated by the secretion of gastrin from the G cells. D cells – D cells secrete somatostatin. Somatostatin suppresses the release of hormones from the digestive tract.

Fundic gland polyposis is a medical syndrome where the fundus and the body of the stomach develop many fundic gland polyps. Pernicious anemia is caused when damaged parietal cells fail to produce the intrinsic factor necessary for the absorption of vitamin B12. This is the most common cause of vitamin B12 deficiency.