They are the basic secretory units of the stomach and contain a variety of component cells located in characteristic locations.
Also called fundus gland, gastric follicle. It is any of the branched tubular glands in the mucosa of the fundus and body of the stomach, containing parietal cells that secrete hydrochloric acid and zymogenic cells that produce pepsin.
The various cells of the glands secrete mucus, pepsinogen, hydrochloric acid, intrinsic factor, gastrin, histamine, and bicarbonate.
The gland begins in the gastric fossa, the opening to the lumen of the stomach.
The fossa itself contains mainly mucous-secreting cells, visible due to its pale staining mucous droplets. The isthmus and the neck of the gland lead to the lowest portion, its base.
Parietal cells, which secrete HCl and intrinsic factor, are found mainly in the isthmus and neck regions and appear highly eosinophilic, while the main cells responsible for pepsinogen secretion are found closer to the base of the gland and appear granular and basophilic.
The stomach, which receives food from the esophagus, is located in the upper left quadrant of the abdomen. The stomach is divided into the regions:
The minor and major curvatures are on the right and left sides, respectively, of the stomach.
The stomach wall is lined with millions of gastric pits that release gastric juice into the lumen of the stomach.
Gastric juice is an acidic solution that works to break down food into a creamy paste called chyme.
The gastric fossae are lined by several different cell types that contribute to the overall function of the stomach:
- Goblet cellss: Goblet cells (GC) are specialized epithelial cells that line multiple mucosal surfaces and have a highly valued role in maintaining the barrier through mucus secretion. Additionally, GCs secrete antimicrobial proteins, chemokines, and cytokines that demonstrate roles in innate immunity beyond barrier maintenance. It was recently appreciated that GCs can form goblet cell-associated antigen passages (GAP) and deliver luminal substances to underlying lamina propria (LP) antigen-presenting cells (APC) in a manner capable of inducing adaptive immune responses. SLNs on other mucosal surfaces share characteristics with intestinal SLNs that form GAP, suggesting that GAP formation may not be restricted to the intestine,
- Parietal cells : Parietal cell autoantibodies are cytolytic to parietal cells in vitro and infusion of a fraction of human serum IgG containing gastric parietal cell antibodies induced hypochlorodria and gastric parietal cell atrophy. However, whether the endogenous autoantibody is pathogenic in vivo remains uncertain because it is directed only against an inaccessible gastric H / K + + ATPase sequestered in inner and apical secretory membranes of parietal cells. Studies of mouse models of autoimmune gastritis indicate that gastritis can be adopted adoptively by Th1CD4 T cells but not by sera containing autoantibodies to H / K + ATPase parietal g cells.
- G cells: secrete gastrin Gastrin G cells located in the antral region of the stomach and the duodenum of the small intestine. Gastrin is also expressed to a limited extent in certain neurons, the pituitary. Its predominant physiological function is to regulate gastric acid secretion and the growth and differentiation of normal gastric epithelial cells. The secretion of acid by the parietal cells, located in the gastric body, facilitates the digestion of proteins, the adsorption of iron, calcium and vitamin B, and reduces the risk of bacterial infection.
- D cells: secrete somatostatin (inhibits the release of stomach acids to reduce heartburn)
- Major cells : secrete pepsinogen (inactive protease precursor that is activated by acidity to form active pepsin)
The mucous lining of the stomach is a simple columnar epithelium with numerous tubular gastric glands. The gastric glands open to the surface of the mucosa through small holes called the gastric fossae. Four different types of cells make up the gastric glands:
- Mucous cells.
- Parietal cells.
- Main cells.
- Endocrine cells.
The secretions of the exocrine gastric glands, composed of the mucous, parietal and main cells, form the gastric juice. Endocrine cell products are secreted directly into the bloodstream and are not part of the gastric juice.
Endocrine cells secrete the hormone gastrin, which functions in the regulation of gastric activity.
The secretion of digestive juices is controlled by nervous and hormonal mechanisms.
These mechanisms control both the volume of secretions produced and the specific content (for example, enzymes, acids, etc.)
The sight and smell of food trigger an immediate response whereby gastric juice is secreted by pre-ingestion of the stomach.
When food enters the stomach, it causes distention, which is detected by stretch receptors in the lining of the stomach.
Signals are sent to the brain, triggering the release of digestive hormones for sustained gastric stimulation
Gastrin is secreted into the bloodstream from the gastric pits of the stomach and stimulates the release of stomach acids.
If the pH of the stomach drops too low (becomes too acidic), intestinal hormones (secretin and somatostatin) inhibit gastrin secretion.
When digested food (chyme) passes into the small intestine, the duodenum also releases digestive hormones:
Secretin and cholecystokinin (CCK) stimulate the pancreas and liver to release digestive juices.
Pancreatic juices contain bicarbonate ions that neutralize stomach acids, while the liver produces bile to emulsify fats.
Regulation of gastric secretions
Regulation of gastric secretion is achieved through neuronal and hormonal mechanisms. Gastric juice is produced all the time, but the amount varies depending on regulatory factors. The regulation of gastric secretions can be divided into cephalic, gastric and intestinal phases.
The thoughts and smells of food begin the cephalic phase of gastric secretion; the presence of food in the stomach initiates the gastric phase; and the presence of acid chyme in the small intestine begins the intestinal phase.
Relaxation of the pyloric sphincter allows the chyme to pass from the stomach to the small intestine. The rate at which this occurs depends on the nature of the chyme and the receptivity of the small intestine.