GASTRIC GLANDS: CHARACTERISTICS, FUNCTIONS, HISTOLOGY - BIOLOGY - 2025

The gastric glands or fundic glands are glands located in the fundus (a stomach region) that are mainly responsible for the secretion of gastric juices, electrolytes and water.

Despite the foregoing, the term "gastric gland" can also be used to refer to other glands in adjacent regions of the stomach such as the cardia and the pyloric region, that is, the cardial glands and the pyloric glands, respectively.

Diagram of a gastric or fundic gland (Source: Boumphreyfr via Wikimedia Commons)

These internal structures of the stomach mucosa fulfill various functions, but the most important is to contribute to the digestion of food, since the cells contained in them secrete enzymes and hormones essential for the hydrolysis of proteins and lipids.

Histologically, the gastric glands are subdivided into three main regions known as the isthmus, neck, and base, each of which has special cells that fulfill a defined secretory function.

Due to its importance, numerous pathologies are associated with the gastric glands or with defects in the cells that compose them. These include achlorhydria, pernicious anemia, and peptic ulcer disease, for example.

characteristics

The gastric glands, as mentioned, are located in the stomach, which is the most dilated portion of the digestive tract, located immediately below the diaphragm.

The stomach can be segmented, from the histological point of view, into three portions or regions, according to the type of gland each has. These regions are known as the cardial region (cardia), pyloric region (antrum), and fundus region (fundus).

The cardia corresponds to the orifice or the upper region of the stomach that connects with the esophagus (it is located at the mouth of the stomach), while the fundus extends on the horizontal plane, crossing the inner esophageal orifice and immediately below the cardia; this is the largest portion of the stomach.

The pyloric or anthropyloric region is funnel-shaped and ends in the pylorus, which represents the boundary between the stomach and the duodenum, the first portion of the small intestine, and is a thin and narrow terminal sphincter.

The cardial glands delimit the cardial region histologically, while the pyloric region is characterized by the pyloric glands or antral glands and the fundic region by the fundic glands or gastric glands.

Regulation of development

The differentiation of the cells typical of each type of stomach gland depends on a gradient of morphogens, that is, substances capable of inducing specific cellular morphogenetic changes such as Wnt, “Hedgehog”, bone morphogenetic protein and transforming growth factor β.

These morphogens have characteristic expression patterns that can be disrupted or affected in different ways by inflammatory stimuli or by pathological conditions such as cancer.

Histology

- Fundic or gastric glands

The gastric glands of the fundus are located in almost the entire stomach mucosa, with the exception of the cardia and the pyloric antrum, which are much smaller portions.

This type of glands has a simple and branched tubular shape that extends from the bottom of the foveoles or gastric crypts (holes in the gastric mucosa) to the muscular of the mucosa, which is the outermost layer of the mucosa and is characterized by the presence of smooth muscle cells arranged circularly in an inner and an outer layer.

Both the cells of the gastric mucosa and the cells of the fundic glands multiply at a special site known as the isthmus, which is located in a small segment between the foveola and the gland.

The cells that are destined for the mucosa migrate towards the crypts or foveoles, while those that are destined for the glands migrate towards the opposite side. Thus, many gastric glands can lead to the same crypt.

Structure

The gastric glands can be divided into two structural portions: the neck and the base or fundus.

The neck is the longest and narrowest region, while the base or bottom is a wider and wider portion. From the base, "branches" may project or divide and roll up close to the muscularis mucosa.

The gastric glands are composed of five different cell types: (1) the mucous cells of the neck, (2) the main or adelomorphic cells, (3) the parietal, delomorphic or oxyntic cells, (4) the enteroendocrine cells and (5) undifferentiated cells.

Mucous cells of the neck

They are located in the neck region of each fundic gland. They are short cells, with a spheroid-shaped nucleus and characterized by not producing much mucinogen in their apical region. The mucus they secrete is more fluid, compared to that produced by the cells of the superficial mucosa of the stomach.

Main or adelomorphic cells

These are secretory cells that have an abundant endoplasmic reticulum in their basal region, which gives them a "basophilic" appearance.

Its apical region, on the contrary, rich in secretory granules or zymogen granules (as they are loaded with enzyme precursors), is rather "eosinophilic" in appearance. The secretion of pepsinogen and lipase enzymes is carried out by the main cells.

C élulas parietal, delomorfas or oxínticas

These cells are also found in the neck region of the gastric glands, but in the region between the mucosa of the neck and the deepest part of these. They are abundant in the upper and middle part of the neck.

Parietal cells are generally large, often have a pair of nuclei, and when histological sections are seen, they have a triangular appearance. They have abundant mitochondria and numerous cytosolic granules.

The "base" of the parietal cells is attached to the basal lamina, while the "vertex" projects into the glandular lumen. These cells have a system of "intracellular canaliculi" capable of communicating with the internal region of the gastric gland to which they belong.

They are responsible for the secretion of hydrochloric acid (HCl) and are stimulated by different substances such as gastrin, histamine and acetylcholine. They also secrete the so-called intrinsic factor, a glycoprotein complexed with vitamin B12 that stimulates the secretion of gastric acid.

Enteroendocrine cells

They are distributed throughout the fundic gland, but are especially abundant in its basal portion. They are small cells, supported on the basal lamina and are responsible for the release of hormones towards the glandular lumen.

Undifferentiated cells

This type of cell is responsible for the multiplication of the other cell types present in the gastric glands, some authors consider them "stem cells" of the other glandular cells.

- Cardial glands

These glands are found in the cardia which, as discussed, is a small region of the stomach located between the esophagus and the fundus. Like the fundic glands, these are also responsible for the secretion of gastric juice.

They have a tubular morphology, sometimes branched, and are essentially composed of mucus-secreting cells and some enteroendocrine cells.

The cells that are responsible for mucus secretion have a flattened nucleus in the basal portion of the cells and have cytosols with abundant mucinogen granules.

- Pyloric glands

These glands are located in the pyloric antrum, which consists of the distal portion of the stomach, between the fundus and the entrance to the small intestine (to the region of the duodenum). Like the other gastric glands, these are tubular, coiled, and branching.

They have secretory cells similar to the superficial mucous cells of the stomach and secrete quite viscous and cloudy substances. They have, in turn, enteroendocrine cells and parietal cells, responsible for the secretion of hormones and gastric acids, respectively.

Features

The gastric glands, referring specifically to the glands present in the fundic region of the stomach, are primarily responsible for the secretion of gastric juices.

These glands have been found to produce about 2 liters of gastric juices per day, in addition to large amounts of water and various electrolytes.

The gastric juices secreted into the stomach lining by the gastric glands are made up of, among other things, hydrochloric acid, enzymes, mucus, and a special type of protein known as "intrinsic factor."

Hydrochloric acid (HCl) provides the characteristic pH to gastric juice (between 1 and 2 pH units) and is produced in concentrations close to 160 mmol / L. Its function is to start the digestion, by hydrolysis, of the proteins consumed with food and also to eliminate contaminating bacteria.

This acid also contributes to the activation of the pepsin zymogen (pepsinogen), which is an extremely important enzyme from the digestive point of view, since it hydrolyzes proteins to smaller portions through the breaking of peptide bonds.

Mucus serves to protect the cells of the intestinal mucosa against the secretion of gastric acids and is produced by different types of cells. Together with bicarbonate molecules, the mucus establishes a protective physiological barrier with a neutral pH.

Intrinsic factor, on the other hand, is an essential glycoprotein for the absorption of vitamin complexes.

Gastrin is another of the constituent elements of gastric juices that is a product of the secretion of the fundic glands and works on the hormonal stimulation of digestion. This can act locally on the epithelial cells of the stomach, or reach the bloodstream and send stimulating signals out of the digestive system.

Related diseases

Many diseases are related to the gastric glands, among which are:

- Peutz-Jeghers syndrome: evident as the proliferation of non-carcinogenic tumors in the stomach and as a failed differentiation of the cells responsible for the secretion of peptides in the pyloric glands.

- Achlorhydria: lack of hydrochloric acid-producing parietal cells that lead to the appearance of pernicious anemia due to lack of intrinsic factor synthesis (lack of vitamin B12).

- Peptic ulcer disease: it is a pathological condition that can be chronic or recurrent, also characterized by the lack of intrinsic factor production. It produces a loss of the epithelium and a scarring of the gastric mucosa, which reduces the number of functional cells in the stomach.

References

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