Stomach

The stomach (gaster, ventriculus) is an enlarged portion of the digestive tract, located between the esophagus and duodenum. In the stomach, food is delayed 4-6 hours. At this time, it is mixed and digested by the action of gastric juice containing pepsin, lipase, hydrochloric acid, mucus. In the stomach is also the absorption of sugar, alcohol, water, salts. In the mucous membrane of the stomach, an anti-anemic factor (Castle factor) is formed, binding vitamin B ₁₂ and promoting its adsorption by the intestinal wall.

The form of the stomach, its position, dimensions constantly vary depending on the amount of food taken, the position of the body and the type of build. In people of the brachymorph type of constitution, the stomach has the shape of a horn (cone), located almost transversely. In the case of a dolichomorph type of constitution, the stomach resembles an elongated stocking located almost vertically and then steeply curving to the right. In the mesomorphic type of constitution, the stomach has the shape of a hook. Its long axis runs from left to right and from behind to the front and is almost in the frontal plane.

The stomach is located in the upper part of the abdominal cavity. Three quarters of it is in the left hypochondrium region, one quarter - in the epigastrium. The entrance to the stomach is located to the left of the spine at the level of X-XI (sometimes XII) of the thoracic vertebrae. The exit from the stomach is determined to the right of the spine at the level of the XII thoracic or I lumbar vertebra. Often, especially in obese people, gastric emptying is observed with a shift of its borders down (gastroptosis).

The length of an empty stomach in an adult is 18-20 cm, width - 7-8 cm. Moderately filled stomach has a length of 24-26 cm, width - 10-12 cm. The capacity of the stomach varies from 1.5 to 4 liters.

The stomach has a front wall (paries anterior), directed anteriorly and somewhat upward, and a posterior wall (paries posterior), turned posteriorly and downwards. The place of the esophagus in the stomach is called the cardiac opening (ostium cardiacum). Next to it is a cardiac chasping (pars cardiaca), or cardia of the stomach. To the left of her, the stomach expands, forming the bottom (the vault) (fundus, s.fornix) which goes downwards and to the right into the body of the stomach (corpus ventriculi). The left convex edge directed downward is called the large curvature of the stomach (curvatura ventriculi major), the right concave margin is the small curvature of the stomach (curvatura ventriculi (gastrica) minor). The narrowed right side of the stomach - the pyloric part (pars pilorica), or the gatekeeper, is divided into two divisions. Distinguish the wide part - the pylorus cave (antrum pyioricurn) and the narrowed part - the canalis channel (canalis pyloricus), which passes into the duodenum. The border between the gatekeeper and duodenum on the surface of the organ is a circular groove, corresponding to the orifice of the pyloric canal (ostium pyloricurn) and the ring muscle - the pyloric sphincter.

The small curvature of the stomach on the border of the body and the pylorus part forms a shallow angular notch (incisure angularis). On the large curvature there is a notch separating the cardial part from the bottom of the stomach.

The anterior wall of the stomach with hook-shaped form in the region of the cardial part, bottom and body is in contact with the diaphragm, in the region of low curvature, with the visceral surface of the left lobe of the liver. A small portion of the body of the stomach, having a triangular shape, directly lays on the anterior abdominal wall. Behind the stomach is a glandular bag - a narrow slit-shaped space of the peritoneal cavity that separates the stomach from the organs located in the retroperitone. Behind the stomach is also the retroperitoneum of the upper pole of the left kidney, the adrenal gland and the pancreas. The posterior surface of the stomach in the region of great curvature is due to the transverse colon and its mesentery, in the upper part of this curvature (the bottom of the stomach) to the spleen.

The stomach is displaced when breathing and filling the neighboring hollow organs (transverse colon). The least moving zones are the entrance and outlet sections of the stomach. The position of the stomach is provided by the presence of fixative ligaments (folds of the peritoneum). The hepatic-gastric ligament (lig.hepatogastricum) begins at the gates of the liver and goes to a small curvature of the stomach. The gastric-ligament ligament (lig.gastrocolicum) comes from the large curvature of the stomach to the transverse colon. Gastro-splenic ligament (lig. Gastrolienale) is directed from the beginning of the large curvature and the left side of the stomach bottom to the gates of the spleen.

The walls of the stomach consist of a mucous membrane, a submucosal base, a muscle and serous membranes.

The mucosa (tunica mucosa) has a thickness of 0.5-2.5 mm. Along its small curvature, from the cardial to the pivot-hole, 4-5 longitudinal folds are sent, facilitating the progress of the food mass (the stomach path). In the region of the bottom and body of the stomach there are transverse, longitudinal and oblique folds. The location and dimensions of the folds of the stomach (plicae gastricae) are constantly changing in different physiological conditions (autologous mucosa). With the passage of the pyloric canal into the duodenum, the mucous membrane forms a circular fold-pyloric valve (valvula pylorica). On the surface of the mucous membrane are gastric fields (aureae gastricae). They have a polygonal shape, vary in size from I to 6 mm and give the surface of the stomach a peculiar granular appearance. Each field is separated from the neighboring furrow. On the surface of the stomach fields there are numerous gastric dimples (foveolae gastricae), into which the excretory ducts of the glands of the stomach open. At 1 mm ^{2 of the} surface of the gastric mucosa there are up to 60 gastric pits.

The mucous membrane is covered with a single-layered cylindrical epithelium. The apical part of these cells is filled with granules. In the basal part of the epithelial cells there is an ovoid nucleus, an endoplasmic segment. Above the core is the Golgi complex. In the propria of the mucous membrane, along with the vessels, nerves, lymphoid nodules, various cells (immunocytes, smooth myocytes, etc.) are the glands of the stomach.

Gastric glands simple, tubular in shape, unbranched. Distinguish own (base), pyloric and cardiac glands of the stomach. The deepest located bottom of the gland (its body) passes into the cervix (excretory duct), and then to the isthmus. Isthmus of 4-5 glands opens into the gastric fossa. The total number of gastric glands is about 35 million.

Own (main, base) stomach glands have a length of 0.65 mm, diameter - 30-50 microns. The length of the gland is 2-3 times greater than the depth of the gastric fossa. The neck is one-third the body of the gland. In the lamina propria of the mucous membrane, the main glands are fixed with a connective tissue in the region of the cervix. In their glands there are four types of cells: the main exocrine cells, parietal (lining), mucous (accessory) cells (mucocytes) and endocrine cells.

The main cells (glandulocytes) are found mainly in the bottom and body of the gland; they produce pepsinogen and chymosin. Between the main cells are single parietal and endocrine cells. The main cells have a cylindrical shape. In the apical part of their cytoplasm, granules of protein secretion are contained. On the plasma membrane of the apical part, there are many short microvilli. The main cells are characterized by a developed complex of Golgi, a granular endoplasmic reticulum, a significant amount of ribosomes. Under the Golgi complex, a nucleus is located.

The parietal cells (glandulocytes) are larger than the main ones. Parietal cells have a rounded or ellipsoidal nucleus, many mitochondria. These cells are characterized by the presence of branched intracellular secretory canals that open into the lumen of the gland. In the lumens of the tubules, the inactive complex of hydrochloric acid and protein synthesized by the cell is located. Getting on the mucous membrane of the stomach, this complex breaks up into hydrochloric acid and protein.

Mucous cells are smaller than the main and parietal glandulocytes. The cell form is elongated, the nucleus is located basally, the organoids have a supranuclear position. A relatively small amount of mucous granules is located in the apical part of the cytoplasm. Characteristic are the weak development of the Golgi complex and the endoplasmic reticulum, a significant content of mitochondria.

Endocrine cells in the gastric glands have morphological and biochemical features. More than 10 varieties of these cells are described. Enterochromaffin, or EC cells, the most numerous, produce serotonin and melatonin. Enterochromaffin-like (ECL) cells secrete histamine. A-cells synthesize glucagon, D-cells - somatostatin, D1-cells - vasoactive intestinal polypeptide, G-cells - gastrin, P-cells - bombesin, etc. Common for endocrine cells of different types are secretory granules under the nucleus in the basal part of the cytoplasm, the supernuclear location of the Golgi complex. The secretion of the endocrine glands is released through the basal and basolateral parts of the cell membrane into the intercellular space.

The peloric glands are located in the pyloric region, especially near the small curvature, and also near the large curvature. The anatomical boundaries of the pyloric part of the stomach and the zone of location of these glands do not coincide. The glands of this group in the form of wide strands can lie in the region of the bottom of the stomach. The majority of pyloric glands are mucocytes, between which parietal and endocrine cells are detected. The main cells in these glands are absent.

The cardial glands are located in the region of the cardia of the stomach. The length of the area of their localization fluctuates individually. These glands contain predominantly mucocytes; there are also parietal and endocrine cells.

The muscular plate of the mucous membrane (lamina muscularis mucosae) is formed by three layers of smooth myocytes: the inner and outer layers are oriented circularly, the middle layer is oriented longitudinally. Individual thin muscle bundles penetrate into the thickness of their own plate of the mucous membrane. Reduction of smooth muscle elements contributes to the formation of folds of the mucosa and the secretion of secretions from the gastric glands.

The submucosa (tela submucosa) is well developed. Its loose fibrous connective tissue is rich in elastic fibers, contains vessels and nerves, numerous lymphoid nodules and various cellular elements.

The tunic muscularis is formed by a smooth muscle tissue that forms three layers. The outer layer of the musculature has a longitudinal orientation, the middle layer is circular, and the inner layer is oblique. Longitudinal muscle bundles are located predominantly near the small and large curvature of the stomach; separate longitudinal beams are present in the area of the pylorus. Thickening of the circulatory layer in the region of the cardia forms the cardiac sphincter. Its thickness is related to the shape of the stomach. At the stomach in the form of a stocking, the sphincter is thicker and narrower, while in the horn-shaped stomach this sphincter is thinner, but wider. The circular layer is most developed in the pyloric section, where it forms a pyloric sphincter (m.sphincter pylorici) 3-5 mm thick. With its reduction, the exit from the stomach into the duodenum is closed. The oblique muscular fascicles lie beneath the circulatory musculature. The obliquely oriented bundles of myocytes are thrown across the cardial part to the left of the cardial opening and are fan-dropped down and to the right in the thickness of the anterior and posterior walls of the stomach in the direction of great curvature, where they are interlaced in the submucosa. Between the muscle layers there is an intermuscular neural plexus. The musculature of the stomach maintains its tone, creates a constant pressure in the lumen of the stomach and carries out in it the mixing of the food masses (peristalsis). As a result of the mixing of food masses with gastric juice, chyme is formed-liquid slurry, which is removed in separate portions from the stomach into the duodenum.

Outside, the stomach is covered with the peritoneum (intraperitoneal position). Only narrow strips, located on a small and large curvature, are devoid of serous cover. The serous membrane is separated from the muscular subserous base.

Innervation of the stomach: a gastric plexus formed by vagus nerves and sympathetic nerve fibers of the celiac plexus.

Gastric blood supply: the left gastric artery (from the celiac trunk), the right gastro-omental artery (from the gastroduodenal artery), the right gastric artery (from the internal hepatic artery), the left gastro-omental artery and the short gastric arteries (from the splenic artery). Gastric and gastro-omental arteries anastomose, forming around the stomach arterial ring. Venous outflow: left and right gastric, left and right gastro-omental veins (inflows of the portal vein).

Outflow of lymph of the stomach: right and left gastric, right and left gastro-omentum, pyloric lymph nodes.

X-ray anatomy of the stomach. The form of the stomach is extremely variable. Taking into account the digestive and motor functions, the stomach can distinguish a digestive sac (saccus digestorius) and an excretory (evacuator) canal (canalis egestorius). The digestive bag corresponds to the vault and body of the stomach, and the output channel to the gatekeeper and the doorkeeper. Radiographic examination using barium sulfate shows the relief of the folds of the mucosa and peristaltic waves.

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