Stomach is a muscular bag forming the dilated portion of the alimentary canal. It is roughly J-shaped and is situated in the upper part of abdomen.
Location of stomach:
The stomach is located in the upper part of abdomen. It extends from beneath the left costal margin to the epigastric and umbilical regions of the abdomen. Much of it lies under cover of the lower ribs and is thus protected by them.
The stomach is relatively fixed at both of its ends but is mobile in between. In short and obese people, it tends to be high and transversely arranged (Steer-Horn Stomach). On the other hand, in tall and thin people, it is elongated and vertically arranged (J-Shaped Stomach).
Structure of stomach:
The stomach is a roughly J-shaped bad and has two orifices, two curvatures and two surfaces.
The orifices are cardiac orifice and pyloric orifice.
- Cardiac orifice: It lies near the heart where the esophagus enters the stomach. This orifice is not guarded by any anatomic sphincter, however, a physiologic mechanism exists through which the regurgitation of food into the esophagus is prevented. In this mechanism, the lower circular smooth muscle fibers of the esophagus serve as a physiologic sphincter.
- Pyloric orifice: It is formed by the pyloric canal (about 1 inch long). The canal joins the first part of small intestine, the duodenum, and creates an exit route for chyme. Unlike the cardiac orifice, the pyloric orifice is guarded by a proper sphincter, known as pyloric sphincter. This sphincter consists of the circular muscle coat of stomach, which is much thicker in this region. The pyloric sphincter controls the rate of discharge of contents of stomach into the duodenum.
The two curvatures are lesser curvature and greater curvature.
- Lesser curvature: It forms the right border of the stomach and extends from the cardiac orifice to the pylorus. It is suspended from the liver by the lesser omentum.
- Greater curvature: It is much longer than the lesser curvature and 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. From its upper part extends the gastrosplenic omentum (ligament) and from its lower part extends the greater omentum.
The two surfaces are anterior surface and posterior surface.
Parts of stomach:
The stomach is divided into the following parts;
- Fundus: It is the dome-shaped superior part of stomach that projects upward and to the left of the cardiac orifice. It is usually full of gas.
- Body: The body of stomach extends from the level of the cardiac orifice to the level of the incisura angularis (a constant notch in the lower part of the lesser curvature).
- Pyloric antrum: It extends from the incisura angularis to the pylorus and lies between the body and the pylorus.
- Pylorus: It is the last tubular part of the stomach and has a thick muscular wall which forms the pyloric sphincter. The cavity of pylorus is known as pyloric canal. The pylorus lies on the transpyloric plane and its position can be recognized by a slight constriction on the surface of stomach.
The mucous membrane lining the stomach is thick and vascular. It is thrown into numerous folds, known as rugae, which are predominantly longitudinal in direction. On distention of the stomach, these folds flatten out. It contains the glands and the gastric pits.
Wall of stomach:
The wall of stomach is muscular and contains three layers of fibers: Longitudinal, Circular and Oblique.
- Longitudinal fibers: These are the most superficial fibers of the muscular wall of stomach. They are concentrated along the curvatures.
- Circular fibers: They lie beneath the longitudinal fibers and encircle the body of the stomach. They are greatly thickenend at the pylorus to form the pyloric sphincter. There only a few circular fibers found in the region of fundus.
- Oblique fibers: They form the innermost muscle coat of wall of stomach. They loop over the fundus and pass down along the anterior and posterior walls, running almost parallel with the lesser curvature.
Relations of stomach:
- Anterior abdominal wall
- Left costal margin
- Left pleura and lung
- Left lobe of liver
- Lesser sac
- Left suprarenal (adrenal) gland
- Upper part of left kidney
- Splenic artery
- Transverse meoscolon
- Transverse colon
Blood supply of stomach:
The stomach receives an extensive blood supply. The details of arteries and veins of stomach are described below:
Arteries of stomach:
The arteries are direct or indirect braches of the celiac artery and are 5 in number;
- Left gastric artery: It arises directly from the celiac artery and passes upward and to the left to reach the esophagus. Afterwards, it descends along the lesser curvature of the stomach. It supplies the lower 1/3 of esophagus and the upper right part of stomach.
- Right gastric artery: It arises from the hepatic artery at the upper border of the pylorus and runs to the left along the lesser curvature of stomach. It supplies the lower right part of the stomach and ends by anastomosing with the left gastric artery.
- Short gastric arteries: These are small arteries arising from the splenic artery at the hilum of spleen. They pass forward in the gastrosplenic omentum (ligament) to supply the fundus of stomach.
- Left gastroepiploic artery: Like the short gastric arteries, it also arises from the splenic artery at the hilum of spleen and passes in the gastrosplenic omentum. It supplies the upper part of the greater curvature of stomach.
- Right gastroepiploic artery: It arises from the gastroduodenal branch of hepatic artery and passes to the left to supply the stomach along the lower part of greater curvature.
Veins of stomach:
The veins drain into the portal circulation. They are also five in number and correspond to the arteries. The right and left gastric veins drain directly into the portal vein. The short gastric veins and the left gastroepiploic vein drain into the splenic vein. The right gastroepiploic vein drains into the superior mesenteric vein.
Lymph drainage of stomach:
The lymph vessels of stomach follow the arteries into the left and right gastric nodes, right and left gastroepiploic nodes and the short gastric nodes. Eventually, all lymph from the stomach reaches the celiac nodes, which are located around the root of celiac artery on the posterior abdominal wall.
Nerve supply to stomach:
Stomach receives nerve supply from both sympathetic and parasympathetic nervous systems. The sympathetic fibers are derived from the celiac plexus and the parasympathetic fibers from the right and left vagus nerves.
The vagus nerves, in the thorax, form the anterior and posterior vagal trunks. The anterior vagal trunk is formed predominantly by the left vagus nerve. It enters the abdomen on anterior surface of esophagus and supplies mainly the anterior surface of the stomach. The posterior vagal trunk is predominantly formed by the right vagus nerves. It enters the abdomen on the posterior surface of esophagus and supplies mainly the osterior surface of stomach.
The sympathetic innervation of the stomach carries pain-transmitting nerve fiber. On the other hand, the parasympathetic fibers are secretomotor to the gastric glands and motor to the muscular wall of stomach.
The pyloric sphincter receives motor fibers from the sympathetic system and inhibitory fibers from the parasympathetic system.
Functions of Stomach:
Stomach has three main functions;
Storage of food: It stores food for a variable amount of time (depending on the nature of food) in order to make it appropriate for digestion and absorption in the small intestine. The storing capacity of stomach in an average adult is about 1500 ml.
Mixing of food: It mixes the food with its own secretions (gastric secretions) to form a semifluid chyme.
Controlling the rate of delivery of chyme: The stomach also controls the rate of delivery of chyme to the small intestine so that efficient digestion and absorption can take place.