Like the walls of the digestive tract, the walls of the stomach are also made up of several overlapping tunics. There gastric mucosa it is the innermost layer of the organ; as such, it faces directly on the lumen of the stomach, in close contact with the products of digestion. Proceeding outwards, under the mucosa, the remaining tunics meet: the submucosa, the muscular and the serosa (peritoneal serous lining).
At the gastric level, the most developed tunics are the muscular and mucous membranes. The first is made up of three different layers of fibers, the outermost of which are oriented longitudinally, the intermediate ones circularly and the innermost ones obliquely. The contraction of the gastric muscles is essential to favor the mixing of the bolus and the emptying of the stomach.
The gastric mucosa internally covers the organ cavity and in turn can be divided into three layers: epithelium, lamina propria and muscolaris mucosae. The surface epithelium, cylindrical simple, is the same throughout the mucosa of the stomach and consists of columnar cells that secrete mucus and bicarbonate, while the glandular component - which has its roots in the connective tissue of the lamina propria - differs in the various sectors.
The secretion of mucus and bicarbonate is essential to protect the gastric mucosa from the insult of the acid digestive juices secreted by one's glands. When this protective layer is eroded by "hydrochloric acid, a" more or less extended area of the mucous membrane undergoes the digestion of the gastric juice; the injured area is called a gastric ulcer.
In living things, the gastric mucosa takes on pink shades at the end of the pylorus and reddish or reddish-brown on the rest of the surface; in childhood the shades are brighter and the vascular redness more marked.
About a millimeter thick, with a soft and velvety surface, the gastric mucosa observed under the microscope appears to be crossed by numerous grooves, which divide it into small polygonal areas. In the centers of these islands, slightly depressed and called gastric pits, the ducts of the glands located in depth open.
The gastric glands are divided, by position and structure, into three different types:
cardial glands (located in the proximal region of the stomach),
glands of the fundus and of the body (the most abundant), called oxintiche or fundiche
and pyloric glands.
The cardial region presents the homonymous cardial glands of the tubulo-acinar type, predominantly mucous secretion.
The body-bottom region has simple tubular glands, called oxintic. This glandular component, which is entrusted with the production of important digestive factors, is made up of different types of cells:
the parietal cells (which make up the upper portion of the gland and secrete hydrochloric acid and intrinsic factor);
the principal or zymogene cells (located in the lower portion of the gland, they secrete pepsinogen, an important proenzyme for the digestion of proteins which transforms into pepsin in contact with hydrochloric acid);
the endocrine cells, which mainly secrete histamine, serotonin and somatostatin;
and the mucosecerning cells of the collar (they constitute the precursors of the cells of the mucous surface).
Pepsinogen, hydrochloric acid and mucus are the main constituents of gastric juice.
In the gastric mucosa of the antrum and pylorus there are glands with a prevalent mucous secretion, called pyloric glands. The glandular component of this region is in turn subdivided into mucoserning cells, gastrin secreting G cells (hormone sensitive to the amino acid and peptide stimulus, favors the synthesis of hydrochloric acid), enterochromaffin cells secreting serotonin (stimulates the contraction of smooth muscle) and endocrine cells of different types that produce hormones such as somatostatin (D cells), glucagon (A cells) and histamine (another stimulant of gastric secretion). The endocrine cells, however, are not located exclusively in the region of the antrum and pylorus, but a little in the entire gastric mucosa.
(bottom e
body)
Main
Mucous membranes
Enterochromaffins
Endocrine
Pepsinogen
Mucus
Serotonin
Antral and
Pyloric
Mucous membranes
G.
D.
Enterochromaffins
Endocrine
Gastrin
Somatostatin
Histamine
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