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 (surface mucous cells) and mucous neck cells. Mucus lines the entire stomach, and protects the stomach lining from the effects of hydrochloric acid released from other cells in the glands.[1]
There are two types of gland in the stomach, the oxyntic gland, and the pyloric gland. The major type of gastric gland is the oxyntic gland that is present in 80 per cent of the stomach, and is often referred to simply as the gastric gland. The oxyntic gland is an exocrine gland and contains the parietal cells that produce hydrochloric acid, and intrinsic factor. Intrinsic factor is necessary for the absorption of vitamin B12.[1]
The other type of gland in the stomach is the pyloric gland found in the pyloric region taking up the remaining 20 per cent of the stomach area. The pyloric gland secretes gastrin from its G cells. Pyloric glands are similar in structure to the oxyntic glands but are endocrine glands with hardly any parietal cells.[1]
Types of gland
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 gastric pits, and mucus-secreting mucous neck cells in the necks of the gastric glands. Mucus lines the entire stomach protecting the stomach lining from the effects of hydrochloric acid released from other cells in the glands.
Histology of normal fundic mucosa. Fundic glands are simple, branched tubular glands that extend from the bottom of the gastric pits to the muscularis mucosa; the more distinctive cells are parietal cells. H&E stain.Histology of normal antral mucosa. Antral mucosa is formed by branched coiled tubular glands lined by secretory cells similar in appearance to the surface mucus cells. H&E stain.
The cardiac glands are found in the cardia of the stomach which is the part nearest to the heart, enclosing the opening where the esophagus joins to the stomach. Cardiac glands primarily secrete mucus.[5] 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 duodenalBrunner's glands.[citation needed]
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.[5]
Transverse section of fundic glandDiagram depicting the major determinants of gastric acid secretion
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.[8] 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).[9] 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, the main component of 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 castle's intrinsic factor. Intrinsic factor is a glycoprotein essential for the absorption of vitamin B12. The parietal cells also produce and release bicarbonate ions in response to histamine release from the nearby ECLs, and so serve a crucial role in the pHbuffering system.[10]
Enteroendocrine cells or argentaffin 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.[1] Histamine promotes the production and release of HCL from the parietal cells to the blood and protons to the stomach lumen. When the stomach pH decreases (becomes more acidic), the ECLs stop releasing histamine.
G cells – They secrete gastrin hormone. Gastrin stimulates the gastric glands to release gastric juice. These cells are mostly found in pyloric glands in the antrum of the pylorus; some are found in the duodenum and other tissues. The gastric pits of these glands are much deeper than the others and here the gastrin is secreted into the bloodstream not the lumen.[11]
D-cells – D-cells secrete somatostatin. Somatostatin suppresses the release of hormones from the digestive tract.
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.
^ abcdHall, John E. (2011). Guyton and Hall textbook of medical physiology (Twelfth ed.). Philadelphia, Pa. pp. 777–780. ISBN9781416045748.((cite book)): CS1 maint: location missing publisher (link)
^"gastric pits, that each open into four or five gastric glands", Quantitative Human Physiology2E, 2017, Joseph Feher
^"Secretions from several gastric glands flow into each gastric pit" Principals of Anatomy & Physiology 15th Ed 2017, Gerard Tortora & Bryan Derrickson
^ abDorland's (2012). Dorland's Illustrated Medical Dictionary (32nd ed.). Elsevier. p. 777. ISBN978-1-4160-6257-8.
^Dorland's (2012). Dorland's Illustrated Medical Dictionary (32nd ed.). Elsevier. p. 762. ISBN978-1-4160-6257-8.
^ abKelsey E. McHugh, M.D., Thomas P. Plesec, M.D. "Stomach - General - Histology". PathologyOutlines.((cite web)): CS1 maint: multiple names: authors list (link) Topic Completed: 28 May 2020. Minor changes: 28 December 2020
^Pocock, Gillian (2006). Human Physiology (3rd ed.). Oxford University Press. p. 388. ISBN978-0-19-856878-0.
