Gastric glands

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Gastric glands
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Gastric glands shown at c and their ducts at d
Details
Identifiers
Latin glandulae gastricae
Anatomical terminology

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.

Contents

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.

Types of gland

Illustration of stomach wall showing gastric mucosa and the gastric glands 2415 Histology of StomachN.jpg
Illustration of stomach wall showing gastric mucosa and the gastric glands

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. [1] 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.

Histology of mucosa showing gastric glands. H&E stain Histology of normal antral mucosa.png
Histology of mucosa showing gastric glands. H&E stain

Gastric glands are mostly exocrine glands [2] and are all located beneath the gastric pits within the gastric mucosa. [3] The gastric mucosa is pitted with innumerable gastric pits which each house 3-5 gastric glands. [4] The cells of the exocrine glands (oxyntic glands) are mucous neck cells, chief cells, and parietal cells. [4] Mucous neck cells produce mucus, parietal cells secrete hydrochloric acid and intrinsic factor, chief cells secrete pepsinogen and gastric lipase. [4]

The other type of gastric gland is the pyloric gland which is an endocrine gland that secretes the hormone gastrin produced by its G cells.

Gastric juice

The secretions of the different exocrine gastric gland cells produce a watery, acidic fluid into the stomach lumen called gastric juice. [5] [6] Gastric juice contains water, hydrochloric acid, intrinsic factor, pepsinogen, and salts. Adults produce around two to three litres of gastric juice per day. [5] The composition of the fluid varies according to the time of eating, and the rates of activity of the various cells. The cells are more active after eating. The composition of the gastric juice electrolytes is related to its rate of secretion: when secretion increases, the concentration of sodium decreases, and the concentration of hydrogen increases. There is always a higher level of potassium ions in the fluid than in the plasma. [5]

Location

The glands are named for the region of the stomach that they occupy.

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. [7] 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.[ 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. [7]

The pyloric glands are located in the antrum of the pylorus. They secrete gastrin produced by their G cells. [8]

Types of cell

Diagram depicting the major determinants of gastric acid secretion Determinants of Gastric Acid Secretion.svg
Diagram 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. [9] 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).

Gastric chief cell Histology of gastric chief cell.png
Gastric chief cell
Parietal cell Parietal cell.png
Parietal cell

Clinical significance

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.

Additional images

See also

List of distinct cell types in the adult human body

Related Research Articles

<span class="mw-page-title-main">Stomach</span> Digestive organ

The stomach is a muscular, hollow organ in the upper gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach is involved in the gastric phase of digestion, following the cephalic phase in which the sight and smell of food and the act of chewing are stimuli. In the stomach a chemical breakdown of food takes place by means of secreted digestive enzymes and gastric acid.

Digestion is the breakdown of large insoluble food compounds into small water-soluble components so that they can be absorbed into the blood plasma. In certain organisms, these smaller substances are absorbed through the small intestine into the blood stream. Digestion is a form of catabolism that is often divided into two processes based on how food is broken down: mechanical and chemical digestion. The term mechanical digestion refers to the physical breakdown of large pieces of food into smaller pieces which can subsequently be accessed by digestive enzymes. Mechanical digestion takes place in the mouth through mastication and in the small intestine through segmentation contractions. In chemical digestion, enzymes break down food into the small compounds that the body can use.

<span class="mw-page-title-main">Pylorus</span> Part of the stomach that connects to the duodenum

The pyloruspyloric region or pyloric part connects the stomach to the duodenum. The pylorus is considered as having two parts, the pyloric antrum and the pyloric canal. The pyloric canal ends as the pyloric orifice, which marks the junction between the stomach and the duodenum. The orifice is surrounded by a sphincter, a band of muscle, called the pyloric sphincter. The word pylorus comes from Greek πυλωρός, via Latin. The word pylorus in Greek means "gatekeeper", related to "gate" and is thus linguistically related to the word "pylon".

<span class="mw-page-title-main">Gastrin</span> Mammalian protein found in Homo sapiens

Gastrin is a peptide hormone that stimulates secretion of gastric acid (HCl) by the parietal cells of the stomach and aids in gastric motility. It is released by G cells in the pyloric antrum of the stomach, duodenum, and the pancreas.

<span class="mw-page-title-main">Gastric acid</span> Digestive fluid formed in the stomach

Gastric acid or stomach acid is the acidic component – hydrochloric acid of gastric juice, produced by parietal cells in the gastric glands of the stomach lining. With a pH of between one and three, gastric acid plays a key role in the digestion of proteins by activating digestive enzymes, which together break down the long chains of amino acids of proteins. Gastric acid is regulated in feedback systems to increase production when needed, such as after a meal. Other cells in the stomach produce bicarbonate, a base, to buffer the fluid, ensuring a regulated pH. These cells also produce mucus – a viscous barrier to prevent gastric acid from damaging the stomach. The pancreas further produces large amounts of bicarbonate and secretes bicarbonate through the pancreatic duct to the duodenum to neutralize gastric acid passing into the digestive tract.

<span class="mw-page-title-main">Parietal cell</span> Epithelial cell in the stomach

Parietal cells (also known as oxyntic cells) are epithelial cells in the stomach that secrete hydrochloric acid (HCl) and intrinsic factor. These cells are located in the gastric glands found in the lining of the fundus and body regions of the stomach. They contain an extensive secretory network of canaliculi from which the HCl is secreted by active transport into the stomach. The enzyme hydrogen potassium ATPase (H+/K+ ATPase) is unique to the parietal cells and transports the H+ against a concentration gradient of about 3 million to 1, which is the steepest ion gradient formed in the human body. Parietal cells are primarily regulated via histamine, acetylcholine and gastrin signalling from both central and local modulators.

<span class="mw-page-title-main">Brunner's glands</span> Duodenal submucosal cells secreting bicarbonate-rich mucus

Brunner's glands are compound tubuloalveolar submucosal glands found in that portion of the duodenum proximal to the hepatopancreatic sphincter.

<span class="mw-page-title-main">Atrophic gastritis</span> Medical condition

Atrophic gastritis is a process of chronic inflammation of the gastric mucosa of the stomach, leading to a loss of gastric glandular cells and their eventual replacement by intestinal and fibrous tissues. As a result, the stomach's secretion of essential substances such as hydrochloric acid, pepsin, and intrinsic factor is impaired, leading to digestive problems. The most common are vitamin B12 deficiency possibly leading to pernicious anemia; and malabsorption of iron, leading to iron deficiency anaemia. It can be caused by persistent infection with Helicobacter pylori, or can be autoimmune in origin. Those with autoimmune atrophic gastritis (Type A gastritis) are statistically more likely to develop gastric carcinoma, Hashimoto's thyroiditis, and achlorhydria.

<span class="mw-page-title-main">Enterochromaffin-like cell</span>

Enterochromaffin-like cells or ECL cells are a type of neuroendocrine cell found in the gastric glands of the gastric mucosa beneath the epithelium, in particular in the vicinity of parietal cells, that aid in the production of gastric acid via the release of histamine. They are also considered a type of enteroendocrine cell.

<span class="mw-page-title-main">Enterochromaffin cell</span> Cell type

Enterochromaffin (EC) cells are a type of enteroendocrine cell, and neuroendocrine cell. They reside alongside the epithelium lining the lumen of the digestive tract and play a crucial role in gastrointestinal regulation, particularly intestinal motility and secretion. They were discovered by Nikolai Kulchitsky.

In human anatomy, there are three types of chief cells, the gastric chief cell, the parathyroid chief cell, and the type 1 chief cells found in the carotid body.

<span class="mw-page-title-main">G cell</span> Type of cell in the stomach and duodenum that secretes gastrin

A G cell or gastrin cell is a type of cell in the stomach and duodenum that secretes gastrin. It works in conjunction with gastric chief cells and parietal cells. G cells are found deep within the pyloric glands of the stomach antrum, and occasionally in the pancreas and duodenum. The vagus nerve innervates the G cells. Gastrin-releasing peptide is released by the post-ganglionic fibers of the vagus nerve onto G cells during parasympathetic stimulation. The peptide hormone bombesin also stimulates gastrin from G cells. Gastrin-releasing peptide, as well as the presence of amino acids in the stomach, stimulates the release of gastrin from the G cells. Gastrin stimulates enterochromaffin-like cells to secrete histamine. Gastrin also targets parietal cells by increasing the amount of histamine and the direct stimulation by gastrin, causing the parietal cells to increase HCl secretion in the stomach. G-cells frequently express PD-L1 during homeostasis which protects them from Helicobacter pylori-induced immune destruction

<span class="mw-page-title-main">Enteroendocrine cell</span> Cell that produces gastrointestinal hormones

Enteroendocrine cells are specialized cells of the gastrointestinal tract and pancreas with endocrine function. They produce gastrointestinal hormones or peptides in response to various stimuli and release them into the bloodstream for systemic effect, diffuse them as local messengers, or transmit them to the enteric nervous system to activate nervous responses. Enteroendocrine cells of the intestine are the most numerous endocrine cells of the body. They constitute an enteric endocrine system as a subset of the endocrine system just as the enteric nervous system is a subset of the nervous system. In a sense they are known to act as chemoreceptors, initiating digestive actions and detecting harmful substances and initiating protective responses. Enteroendocrine cells are located in the stomach, in the intestine and in the pancreas. Microbiota play key roles in the intestinal immune and metabolic responses in these enteroendocrine cells via their fermentation product, acetate.

<span class="mw-page-title-main">Gastric chief cell</span> Type of gastric gland cell

A gastric chief cell, peptic cell, or gastric zymogenic cell is a type of gastric gland cell that releases pepsinogen and gastric lipase. It is the cell responsible for secretion of chymosin (rennin) in ruminant animals and some other animals. The cell stains basophilic upon H&E staining due to the large proportion of rough endoplasmic reticulum in its cytoplasm. Gastric chief cells are generally located deep in the mucosal layer of the stomach lining, in the fundus and body of the stomach.

<span class="mw-page-title-main">Gastric pits</span> Indentations in the stomach

Gastric pits are indentations in the stomach which denote entrances to 3-5 tubular 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. Surface mucous cells line the pits themselves but give way to a series of other types of cells which then line the glands themselves.

<span class="mw-page-title-main">Gastric mucosa</span> Mucous membrane layer of the stomach

The gastric mucosa is the mucous membrane layer of the stomach, which contains the gastric pits, to which the gastric glands empty. In humans, it is about one mm thick, and its surface is smooth, soft, and velvety. It consists of simple secretory columnar epithelium, an underlying supportive layer of loose connective tissue called the lamina propria, and the muscularis mucosae, a thin layer of muscle that separates the mucosa from the underlying submucosa.

The proventriculus is part of the digestive system of birds. An analogous organ exists in invertebrates and insects.

<span class="mw-page-title-main">Foveolar cell</span> Mucus-producing cells in stomach lining protective against gastric acid

Foveolar cells or 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 the gastric pits. Mucous neck cells are found in the necks of the gastric glands. The mucus-secreting cells of the stomach can be distinguished histologically from the intestinal goblet cells, another type of mucus-secreting cell.

The nervous system, and endocrine system collaborate in the digestive system to control gastric secretions, and motility associated with the movement of food throughout the gastrointestinal tract, including peristalsis, and segmentation contractions.

<span class="mw-page-title-main">Human digestive system</span> Digestive system in humans

The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion. Digestion involves the breakdown of food into smaller and smaller components, until they can be absorbed and assimilated into the body. The process of digestion has three stages: the cephalic phase, the gastric phase, and the intestinal phase.

References

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PD-icon.svgThis article incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)