The gastric glands are tube-like, branched structures present at the inner lining of the stomach. They are the basic secretory unit of the stomach and are composed of various cell components that perform specific functions. The gland originates at the opening of the stomach’s lumen, the gastric pits, which is itself present at the gastric mucosa of the stomach. The pit has pale-staining mucous droplets due to the presence of mucous-secreting cells. The base contains the isthmus and neck of the gland. The gastric glands are mostly exocrine in nature and help in the synthesis and secretion of gastric juices along with protective mucous.
Types of Gastric Glands
Depending on the region in the stomach, gastric glands location is divided into 3 major parts.
1. Cardiac Glands –
They are located close to the cardiac orifice. They generally contain cardiac glands. They are comparatively very few in number and are positioned in the mucosa shallowly. They are of two kinds, firstly, simple tubular (like those of pyloric ends) and short ducted, and secondly, compound racemose resembling the duodenal glands.
Their basic function is to secrete mucus.
2. Fundic Glands –
They are located in the fundus or body of the stomach. These glands are straight, parallel, tube-like structures. Two or more of such tubes open into a common duct. These tubes are at most one-sixth the length of the entire gland. These glands are much shorter than the pyloric glands. They are lined by columnar epithelium.
Their function is to produce digestive enzymes.
3. Pyloric Glands –
They are the endocrine glands located in the antrum, the pyloric portion of the stomach. They consist of two or three short, wavy closed tubes that open into a common duct. These tubes are half the length of the entire duct. The duct is lined by columnar cells and the tubes by short, granular cubical cells.
They secrete gastrin (produced by G cells) and mucus.
The mucus produced by the Cardiac glands and the Pyloric glands coats the stomach, dilutes the acids and enzymes, and thus protects the esophagus and the duodenum from self-digestion.
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Types of Cells
Each tube of gastric glands consists of multiple types of gastric cells. The various types of cells in gastric glands involve the 5 major cell types –
1. Mucous Neck Cells (or Foveolar Cells) –
They are smaller in size compared to the surface mucus cells having round nuclei and apical secretory granules. These cells are involved in the secretion of mildly alkaline mucus (which is different from the mucus secreted by the epithelial mucus cells). They are found in the isthmus and neck of the glands.
2. Stem Cells –
They are found in the isthmus or neck of the gland. These cells are involved in the replacement of damaged cells.
3. Parietal Cells (or Oxyntic Cells) –
These cells are round, large, or pyramidal in shape having rounded nuclei at the center. Oxyntic cells secrete Hydrochloric acid (HCl) which is the most important component of gastric acid, that activates other enzymes. These cells also secrete intrinsic factors (which helps in Vitamin B12 absorption). These are highly acidophilic that is, they stain pink colour. They are found in the Fundic glands and the walls of the tubes.
4. Chief Cells (or Zymogenic Cells) –
They are involved in the secretion of gastric lipase, rennin, and pepsinogen. They are basophilic in nature, that is, they stain blue colour. They are found in the Fundic glands, in lower regions of the gastric glands, and the basal regions of the gland.
5. Enteroendocrine Cells –
These are non-clustered singly cells that are associated with the production of gastrin, which regulates the gastric activity and also releases them into the blood.
The mucous cells, chief cells, and parietal cells compose the exocrine glands and make the gastric juices while the secretions of endocrine cells move into the bloodstream.
Did You Know?
Gastric cancer cannot be discovered in its initial stages as the symptoms are quite general like viral infection or indigestion.
The gastric acid or Hydrochloric acid in the stomach is strong enough to dissolve metals.
The production of gastric juices is constant but their secretion is stimulated. Neural and hormonal mechanisms regulate the secretion of gastric juices from the gastric glands. The three phases that stimulate gastric secretion are,
Cephalic phase, where the thought of food or its smell initiate gastric secretion
Gastric phase, where the food in the stomach initiates gastric secretion
Intestinal phase, where chyme (acid in the small intestine) initiates gastric secretion
Also, psychological factors like sadness or fear may reduce the secretion of gastric enzymes.