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Other Terms: Ventriculus, Gaster, Estomac, Magen, Estómago, Sikmura
The left half of the anterosuperior surface is in contact with the diaphragm, which separates it from the base of the left lung, the pericardium, and the seventh, eighth, and ninth ribs, and intercostal spaces of the left side. The right half is in relation with the left and quadrate lobes of the liver and with the anterior abdominal wall. When the stomach is empty, the transverse colon may lie on the front part of this surface. The whole surface is covered by peritoneum. The posteroinferior surface is in relation with the diaphragm, the spleen, the left suprarenal gland, the upper part of the front of the left kidney, the anterior surface of the pancreas, the left colic flexure, and the upper layer of the transverse mesocolon. The transverse mesocolon separates the stomach from the duodenojejunal; flexure and small intestine. The posteroinferior surface is covered by peritoneum, except over a small area close to the cardiac orifice. This area is limited by the lines of attachment of the gastrophrenic ligament, and lies in apposition with the diaphragm and frequently with the upper portion of the left suprarenal gland.
The stomach is the most dilated part of the digestive tract. It is located between the end of the esophagus and the beginning of the small intestine. It lies in the epigastric, umbilical, and left hypochondriac regions of the abdomen. It occupies a recess bound by the upper abdominal viscera and completed in front and on the left side by the anterior abdominal wall and the diaphragm. The shape and position of the stomach are so greatly modified by changes within itself and in the surrounding viscera that no one form can be described as typical. The chief modifications are determined by the amount of the stomach contents, the stage which the digestive process has reach, the degree of development o the gastric musculature, and the condition of the adjacent intestines.
Relations and Parts
The stomach contains two openings, two curvatures, and two surfaces. The opening by which the esophagus communicates with the stomach is known as the cardiac orifice. The cardiac orifice is situated on the left of the middle line at the level of the tenth thoracic vertebra. The short abdominal portion of the esophagus is called the cardiac antrum. It is conical in shape and curved sharply to the left. The right margin of the esophagus is continuous with the lesser curvature of the stomach. The left margin joins the greater curvature at an acute angle, termed the cardiac incisor. The pyloric orifice communicates with the duodenum and its position is usually indicated on the surface of the stomach by the duodenopyloric constriction. This orifice lies to the right of the mid line at the level of the upper border of the first lumbar vertebra. The lesser curvature extends between the cardiac and pyloric orifices. It forms the posterior border of the stomach. It descends as a continuation of the right margin off the esophagus in front of the fibers of the right crus of the diaphragm. Then, turning to the right, it crosses the first lumbar vertebra and ends at the pylorus. The angular incision is a well-marked notch located nearer to its pyloric end. This incision varies somewhat in position with the state of distension of the viscus. It serves to separate the stomach into a right and a left portion. The lesser curvature gives attachment to the two layers of the hepatogastric ligament. Between these two layers are the left gastric artery and the right gastric branch of the hepatic artery. The greater curvature is directed mainly forward. It is four or five times as long as the lesser curvature. Starting from the cardiac orifice at the cardiac incisor, it forms an arch backward, upward, and to the left. The highest point of the convexity is on a level with the sixth left costal cartilage. From this level, it may be followed downward and forward. A slight convexity is located to the left as low as the cartilage of the ninth rib. It then turns to the right, to the end of the pylorus. Directly opposite the angular incisor of the lesser curvature, the greater curvature presents a dilatation, which is the left extremity of the pyloric part. This dilatation is limited on the right by the intermediate sulcus. The portion between the intermediate sulcus and the duodenopyloric constriction is termed the pyloric antrum. At its commencement, the greater curvature is covered by peritoneum continuous with that covering the front of the organ. The left part of the curvature gives attachment to the gastrosplenic ligament. The two layers of the greater omentum are attached to the anterior portion of the greater curvature. The greater omentum is separate from each other by the gastroepiploic vessels. A plane passing through the angular incision on the lesser curvature and the left limit of the opposed dilatation on the greater curvature divides the stomach into a body and a pyloric portion. The left portion of the body is known as the fundus and is marked off from the remainder of the body by a plane, passing horizontally through the cardiac orifice. The pyloric portion is divided by a plane through the intermediate sulcus at right angles to the long axis of this portion. The part to the right of this plane is the pyloric antrum.
Layers of the Stomach
The wall of the stomach consists of four layers: tunica mucosa, tela submucosa, tunica muscularis, and the tunica serosa. The tunica mucosa is thick and its surface is smooth, soft, and velvety. It is composed of simple columnar epithelium. During the contracted state of the organ, it is thrown into numerous gastric rugae. For the most part, the rugae have a longitudinal direction. They are most marked along the pyloric end of the stomach, along the greater curvature of the stomach. The function of the gastric rugae is to increase surface area, and provide a high friction surface to mix and blend the bolus. They are entirely obliterated when the organ becomes distended. The tela submucosa consists of loose connective tissue. It connects the mucosa and muscularis layers. It is the vascular layer of the stomach. The tunica muscularis is situated immediately beneath the tunica serosa, with which it is closely connected. It consists of three sets of smooth muscle fibers: longitudinal, circular, and oblique. The longitudinal fibers are the most superficial and are arranges in two sets. The first set consists of fibers continuous with the longitudinal fibers of the esophagus. The second set commences on the body of the stomach and passes to the right, its fibers becoming more thickly distributed as they approach the pylorus. Some of the more superficial fibers of this set pass on to the duodenum, but the deeper fibers dip inward and interlace with the circular fibers of the pyloric sphincter. The circular fibers form a uniform layer over the whole extent of the stomach beneath the longitudinal fibers. At the pylorus, they are most abundant. They are aggregated into a circular ring. They project into the lumen and help to form the pyloric sphincter. They are continuous with the circular fibers of the esophagus but are sharply marked off from the circular fibers of the duodenum. The oblique fibers are internal to the circular layer. They are limited chiefly to the cardiac end of the stomach. Here, they are disposed as a thick uniform layer, covering both surfaces, some passing obliquely from left to right, other from right to left, around the cardiac end. The oblique fibers perform mixing movements. The tunica serosa is derived from the peritoneum. It is composed of mesothelium. It covers the entire surface of the organ except along the greater and lesser curvatures at the points of attachment of the greater and lesser omentum. Here, the two layers of peritoneum leave a small triangular space, along with the nutrient vessels and nerves pass. On the posterior surface of the stomach, there is also a small area uncovered by peritoneum, where the organ is in contact with the under surface of the diaphragm.
There are three kinds of gastric glands: pyloric, cardiac, and the fundic glands. They are tubular and are formed of a delicate basement membrane, consisting of flattened transparent endothelial cells lined by epithelium. The pyloric glands are found in the pyloric portion of the stomach. They consist of two or three short closed tubes opening into a common duct. These tubes are wavy and are about one-half the length of the duct. The duct is lined by columnar cells, continuous with the epithelium lining the surface of the mucous membrane of the stomach. The tubes are lined by shorter and more cubical cell which are finely granular. The cardiac glands are few. They occur close to the cardiac orifice. There are two kinds: simple tubular and compound racemose glands. The simple tubular glands resemble those of the pyloric end of the stomach. The compound racemose glands resemble the duodenal glands. The fundic glands are found in the body and fundus of the stomach. They are simple tube, two or more of which open into a single duct. The duct in these glands is shorter than in the pyloric variety. The gland tubes are straight and parallel to each other. At the point where they open into the duct, the epithelium alters and consists of short columnar of polyhedral granular cells. The lumen becomes suddenly constricted and is continued down as a very fine channel. They are known as the chief cell of the gland. Between these cells and the basement membrane, larger oval cells are found. These cells are studded throughout the tube at intervals, giving it a beaded appearance. These are known as the parietal cells. They are connected with the lumen by fine channels which run into their substance.
The nerves are the terminal branches of the right and left vagi. The former is distributed upon the back and the latter upon the front part of the organ. A great number of branches from the celiac plexus of the sympathetic are also distributed to it. Nerve plexuses are found in the tela submucosa and between the muscular layers of the intestine. From these plexuses, fibrils are distributed to the muscular tissue and the mucous membrane.
The arteries supplying the stomach are: the left gastric, the right gastric and right gastroepiploic branches of the hepatic, and the left gastroepiploic and short gastric branches of the splenic. They supply the tunica muscularis, ramify in the tela submucosa, and are finally distributed to the mucous membrane. The arteries break up at the base of the gastric tubules into a plexus of fine capillaries which run upward between the tubules, anastomosing with each other. They end in a plexus of larger capillaries, which surround the mouths of the tubes and also form hexagonal meshes around the ducts.
The veins arise from the arterial hexagonal meshes around the duct. They pursue a straight course downward, between the tubules, to the submucous tissue. They end either in the splenic and superior mesenteric veins or directly in the portal vein.
The lymphatics are numerous. They consist of a superficial and a deep set. They pass to the lymph glands found along the two curvatures of the stomach.