Stomach and its Structure

The stomach is a muscular, hollow pouch like structure situated on the left side of the abdomen, thus helping in the digestion of the food. It is present nearly in every animal which chews food. In humans, it is located between the esophagus and the small intestine, from esophagus it enters stomach through a narrow section called esophageal sphincter. On the entrance of the food, it releases a large number of enzymes which combines with food, making chyme, thus helping in the digestion, usually 2nd step of digestion occurs here and useful contents get absorb into the blood for further processing. In adults, it has a capacity to store about 1500ml of the chyme.
The stomach is relatively fixed at both ends but very mobile in between. It tends to be high and transversely arranged in the short, obese person ( steer-horn ) and elongated vertically in tall, thin person ( J-shaped stomach ). Its shape undergoes considerable variation in the same person and depends on the volume of contents, the position of the body and the phase of respiration.

Structure of the Stomach

In humans, the stomach is divided into following parts:

Fundus: It is a dome-shaped structure, located left side of the cardiac orifice projecting upward and full of gas.

Body: It extends from the cardiac orifice to the incisura angularis, a constant notch in the lesser curvature of the stomach.

Pyloric antrum: This extends from the incisura angularis to the pylorus. 

Pylorus: This is the tubular structure of the stomach. The thick muscular wall is called the pyloric sphincter, and the cavity of the pylorus is called pyloric canal. 

Openings: The stomach has two openings the cardiac orifice and the pyloric orifice. The cardiac orifice is the region where the esophagus enters the stomach, that prevents the regurgitation of the stomach contents into the esophagus. The pyloric orifice is formed by the pyloric canal, which is about a 2.5cm long tube. The pylorus is located in the transpyloric plane, which can be recognized by the presence of the slight constriction on the surface of the stomach.

Lesser and greater Curvature: It extends from the cardiac orifice to the pylorus, forming right border of the stomach, which is suspended from the liver by the lesser omentum, The greater curvature is longer than the lesser curvature, which extends from the left of the cardiac orifice, over the dome of the fundus, and along the left border of the stomach to the pylorus.

Function

In addition to the secretion of the enzymes, it performs following functions too:

1. It stores meals (within the grown up it has an ability of approximately 1500ml ).
2. It mixes the meals with gastric secretions to shape semi-fluid chyme.
3. It controls the rate of transport of the chyme to the small gut in order that efficient digestion and absorption can take place.

Layers of the Stomach 

As we discussed earlier that the human stomach is hollow, muscular organ, which is consist of the layers packed on each other, providing strength to the stomach. It is consist of the following layers:

• Mucosa

This is the innermost structure of the stomach and has three layers the mucosal epithelium, the lamina propria, and the muscularis mucosa, collectively called lumen of the stomach.

• Submucosa

This surrounds the mucosa and contains loose connective tissue, blood vessels, and the nerves.

• Muscularis Externa

It consists of the connective tissues whose fibers move in a different direction from each other to strengthen the stomach, which is as follow, the oblique, circular and the longitudinal muscle.

• Serosa

It lies next to the muscularis externa and includes a dense network of the blood vessels.

Anatomical Relation

Anteriorly: Anterior to the stomach, the anterior abdominal wall, the left costal margin, the left pleura and lung, the diaphragm, and the left lobe of the liver are located.

Posteriorly: The lesser sac, the diaphragm, the spleen, the left suprarenal gland, the superior part od the kidney, the splenic artery, the pancreas, the transverses mese-colon, and the transverses colon.

Blood Supply

• Arteries

The arteries are derived from the celiac artery and supply blood to the stomach.

The left gastric artery: It supplies the lower third of the esophagus and the upper right part of the stomach.

The right gastric artery: It supplies the lower right part of the stomach.

The short gastric artery: It supplies blood to the fundus of the stomach.

The left gastroepiploic artery: It supplies blood to an upper part of the greater curvature.

The right gastroepiploic artery: It supplies blood to the lower part of the greater curvature of the stomach.

• Veins

The veins drain into the portal circulate, The left and right gastric veins drain at once into the portal vein. The short gastric veins and the left gastroepiploic veins be a part of the splenic vein. The right gastroepiploic artery then joins the superior mesenteric vein.