The main function of the stomach is to process and transport food. After feeding, the contractile activity of the stomach helps to mix, grind and eventually evacuate small portions of chyme into the small bowel ,while the rest of the chyme is mixed and ground.

Its characteristic shape is shown, along with terms used to describe the major regions of the stomach. The right side of the stomach is called the greater curvature and the left the lesser curvature.

The lesser curvature (curvatura ventriculi minor), extending between the cardiac and pyloric orifices, forms the right or posterior border of the stomach. It descends as a continuation of the right margin of the esophagus in front of the fibers of the right crus of the diaphragm, and then, turning to the right, it crosses the first lumbar vertebra and ends at the pylorus. Nearer its pyloric than its cardiac end is a well-marked notch, the incisura angularis, which 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, and between these two layers are the left gastric artery and the right gastric branch of the hepatic artery.

The greater curvature (curvatura ventriculi major) is directed mainly forward, and is four or five times as long as the lesser curvature. Starting from the cardiac orifice at the incisura cardiaca, 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, with a slight convexity 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 incisura angularis 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 a slight groove, the sulcus intermedius, which is about 2.5 cm, from the duodenopyloric constriction. The portion between the sulcus intermedius 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 gastrolienal ligament, while to its anterior portion are attached the two layers of the greater omentum, separated from each other by the gastroepiploic vessels

Surfaces.—When the stomach is in the contracted condition, its surfaces are directed upward and downward respectively, but when the viscus is distended they are directed forward, and backward. They may therefore be described as anterosuperior and postero-inferior

Antero-superior Surface.—The left half of this 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 Postero-inferior 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. These structures form a shallow bed, the stomach bed, on which the viscus rests. The transverse mesocolon separates the stomach from the duodenojejunal flexure and small intestine. The postero-inferior 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 main divisions of the stomach are the following:

Cardia

The cardia is the portion of the stomach surrounding the cardioesophageal junction, or cardiac orifice (the opening of the esophagus into the stomach). Tumors of the cardioesophageal junction are usually coded to stomach.

Fundus

The fundus is the enlarged portion to the left and above the cardiac orifice.

Body

The body, or corpus, is the central part of the stomach.

Pyloric antrum

The pyloric antrum is the lower or distal portion above the duodenum. The opening between the stomach and the small intestine is the pylorus, and the very powerful sphincter which regulates the passage of chyme into the duodenum is called the pyloric sphincter.

The stomach is suspended from the abdominal wall by the lesser omentum. The greater omentum attaches the stomach to the transverse colon, spleen and diaphragm.

The common mesentery suspends the small intestine. The parietal peritoneum lies over the duodenum and other structures, such as the abdominal aorta. Because they lie behind the peritoneum, they are called retroperitoneal structures.

The figure below shows the anatomy of the stomach.

1. Body of stomach
2. Fundus
3. Anterior wall
4. Greater curvature
5. Lesser curvature
6. Cardia
9. Pyloric sphincter
10. Pyloric antrum
11. Pyloric canal
12. Angular notch
13. Gastric Canal
14. Rugal folds

Macroscopic anatomy of the stomach.

The stomach wall , like the wall of most other parts of the digestive canal, consists of three layers: the mucosal (the innermost), the muscularis and the serosal (the outermost). The mucosal layer itself can be divided into three layers: the mucosa (the epithelial lining of the gastric cavity), the muscularis mucosae (low density smooth muscle cells) and the submucosal layer (consisting of connective tissue interlaced with plexi of the enteric nervous system). The second gastric layer, the muscularis, can also be divided into three layers: the longitudinal (the most superficial), the circular and the oblique 

 The longitudinal layer of the muscularis can be separated into two different categories: a longitudinal layer that is common with the esophagus and ends in the corpus, and a longitudinal layer that originates in the corpus and spreads into the duodenum.

Figure  Structure of Gastric Muscularis: A — the longitudinal layer (the area where the longitudinal fibers split is marked with a black circle); B - the circular layer; C - the oblique layer.

The area in the corpus around the greater curvature, where the split of the longitudinal layers takes place, is considered to be anatomically correlated with the origin of gastric electrical activitY

The circular layer of the muscularis is continuous with the circular layer of the esophagus, but is absent in the fundus

The thickness of the circular layer increases in the antrum and especially in the pyloric sphincter

. It does not continue into the duodenum. The oblique layer of the muscularis is clearly seen in the fundus and near the lesser curvature of the corpus, but the oblique fibers disappear distally (towards the antrum). The outermost main layer is the serosa .

Figure . Cross section of gastric wall. Nerve plexi provide the interface between the mucosa and the muscularis, as well as between the longitudinal and circular layers of the muscularis 

 with the exception that the stomach has an extra oblique layer of smooth muscle inside the circular layer, which aids in performance of complex grinding motions.

In the empty state, the stomach is contracted and its mucosa and submucosa are thrown up into distinct folds called rugae; when distended with food, the rugae are "ironed out" and flat. The image below shows rugae on the surface of a dog’s stomach.

 

There are differences in the distribution of these cell types among regions of the stomach - for example, parietal cells are abundant in the glands of the body, but virtually absent in pyloric glands. The micrograph to the right shows a gastric pit invaginating into the mucosa (fundic region of a raccoon stomach). Notice that all the surface cells and the cells in the neck of the pit are foamy in appearance - these are the mucous cells. The other cell types are farther down in the pit and, in this image, difficult to distinguish.

Arteries of the Stomach

The arteries that supply the stomach are branches of the celiac trunk or artery. This is the first unpaired branch of the abdominal aorta, arising just after the aorta passes behind the diaphragm.
The branches of the celiac artery are three

left gastric

splenic

common hepatic

The branches to the stomach arise from the above:

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