Stomach is a roughly J shaped muscular tube and the most dilated part of the digestive tract. It occupies in the upper part of the abdomen and much of it lies under cover of the lower ribs. It is relatively fixed at two ends but is very mobile in between. It stores food approximately 30 ml in infant, 1000 ml in puberty and 1500 ml in adult.
|CONTENTS OF THIS PAGE|
|1. Orifices of stomach
2. Curvatures of stomach
3. Surfaces of stomach
4. Parts of stomach
5. Diagram of stomach
6. Structure of stomach
7. Functions of stomach
8. Blood supply of stomach
9. Lymphatic drainage of stomach
10. Nerve supply of stomach
11. Development of stomach
Orifices of stomach
Stomach has two orifices – cardiac orifice and pyloric orifice.
- Cardiac orifice – It is where the esophagus enters the stomach. A physiological sphincter presents at cardiac orifice that prevents regurgitation of stomach contents into esophagus.
- Pyloric orifice – The opening from the stomach into the duodenum is the pyloric orifice. The circular muscle coat of the stomach is much thicker here and forms an anatomic pyloric sphincter that controls the rate of discharge of stomach content into duodenum.
Curvatures of stomach
Stomach has two curvatures – lesser curvature and greater curvature.
- Lesser curvature – It forms the right border of the stomach. The most dependent part of the lesser curvature is known as incisura angularis. Lesser curvature gives attachment to two layers of lesser omentum.
- Greater curvature – It forms the left border of the stomach. Greater curvature is 4 to 5 times longer than lesser curvature. It gives attachment to gastro-phrenic ligament, gastro-splenic ligament and anterior two layers of greater omentum.
Surfaces of stomach
Stomach has two surfaces – anterior surface and posterior surface.
- Anterior surface – It is entirely covered with the peritoneum of the greater gac and is related to the anterior abdominal wall, left lobe of liver, the diaphragm beneath the left costal margin, and the left pleura and lung.
- Posterior surface – It is covered with the peritoneum of the lesser gac and is related to a number of structures which form the so-called stomach bed. The stomach bed consists of left crus of the diaphragm, left adrenal gland, left kidney, splenic artery, pancreas, transverse megacolon and sometimes left colic flexure.
Parts of stomach
Stomach has three parts – fundus, body and pyloric part. Fundus is upper dome-shaped part and is filled with gas. Body extends from the level of the cardiac orifice to the level of the incisura angularis (a notch in the lower portion of lesser cuvature). The pyloric part lies below the incisura angularis and subdivided into pyloric antrum, pyloric canal and pylorus. A slight groove called sulcus intermedius divides the pyloric part into pyloric antrum and pyloric canal. The pylorus is the ending portion of the pyloric part.
Diagram of stomach
The wall of the stomach has four layers from outwards to inwards – serous, muscular, submucous and mucous. Serous layer is derived from the peritoneum. Muscular layer has outer longitudinal muscle, middle circular muscle and inner oblique muscle fiber. At the pyloric orifice the circular muscle fibers become thickened to form a ring and join with the deep fibers of the longitudinal muscle to form pyloric sphincter. Submucous layer consists of loose areolar tissue and contains blood vessels, lymph vessels and nerves. Mucous layer is thick, soft and velvety, and presents a number of temporary longitudinal mucous folds called rugae. These rugae disappear when stomach is distented. The mucous layer consists from outwards to inwards – muscularis mucosae, lamina propria and surface epithelium. Lamina propria contains blood vessels, nerves and gastric glands. The surface epithelium is lined by simple columnar epithelium.
Functions of stomach
- Stomach stores large quantities of food until it can be accommodated in duodenum. On average, the food is retained in the stomach for about 3-4 hours. Carbohydrate retained for short time, protein retained for prolong time and fat retained in the stomach for more prolong time.
- It secretes hydrochloric acid that kills the swallowed microorganisms and also creates an acidic media in the stomach which is essential for protein digestion.
- It allows digestion of proteins into proteoses, peptones and polypeptides with the help of enzyme pepsin in an acidic media.
- Stomach mixes the food with gastric secretions until it forms a murky, milky semifluid mixture called chyme.
- It controls the rate of delivery of chyme to the small intestine so that proper digestion and absorption can take place.
- It secretes intrinsic factor that helps in absorption of Vitamin B12 by the ileum.
Blood supply of stomach
The stomach is supplied by the arteries arise directly or indirectly from the celiac trunk. The supplying arteries of stomach are:
- Left gastric artery – It is a branch of celiac trunk and reaches the lesser curvature. It is the principal artery of the stomach that supplies its upper two-third portion.
- Right gastric artery – It is a branch of common hepatic artery, reaches the lesser curvature and anastomoses with the left gastic artery.
- Short gastric artery – These are three or four in number and branches of splenic artery. It supplies the fundus of the stomach.
- Left gastro-epiploic artery – It is a branch of splenic artery and reaches the greater curvature.
- Right gastro-epiploic artery – It is a branch of gastro-duodenal artery, reaches the greater curvature and anastomoses with the left gastro-epiploic artery.
The veins of the stomach correspond to the arteries and drain directly or indirectly into the portal vein. The draining veins of stomach are:
- Left gastric vein – It drain directly into portal vein.
- Right gastric vein – It drain directly into portal vein.
- Short gastric vein – It drain into splenic vein.
- Left gastro-epiploic vein – It drain into splenic vein.
- Right gastro-epiploic vein – It drain into superior mesenteric vein.
Lymphatic drainage of stomach
The lymph from the stomach drain into the following groups of regional lymph nodes:
- From the part of the stomach to the left of a vertical line drawn from the cardiac orifice – drain into pancreatico-splenic lymph nodes.
- From the upper two-third of the right part of the stomach – drain into left gastric lymph nodes.
- From the lower one-third of the right part of the stomach – drain into right gastro-epiploic lymph nodes.
- From the pyloric part of the stomach – drain into three groups of lymph nodes such as hepatic, pyloric and left gastric lymph nodes.
Efferent vessels from these lymph nodes drain into celiac group of pre-aortic lymph nodes.
Nerve supply of stomach
The stomach is supplied by both the sympathetic and parasympathetic nerve fibers.
Sympathetic – Sympathetic nerve fibers arises from the celiac plexus. The stimulation of sympathetic nerve causes constriction of the pyloric sphincter and relaxation of the rest of the stomach muscle. Its sensory fibers convey pain from stomach.
Parasympathetic – Parasympathetic nerve fibers arises from the vagus nerve. The stimulation of parasympathetic nerve causes relaxation of the pyloric sphincter and constriction of the rest of the stomach muscle. Its stimulation also causes secretion from gastric glands (secreto-motor). The parasympathetic sensory fibers convey the sensation of hunger and nausea.
Development of stomach
It is developed in the 4th week of embryonic life from the lower part of the foregut as a fusiform dilatation. At first the stomach is placed in the midline with an anterior concave border and a posterior convex border, and having left surface and right surface. During the development, stomach rotates 900 clockwise around its longitudinal axis, causing its left surface to face anteriorly and its right surface to face posteriorly, and the anterior concave border forms lesser curvature and the posterior convex border forms greater curvature. During further growth, stomach further rotates around its anteroposterior axis, causing its upper part moves to the left and downward from the midline, and its lower part moves to the right and upward from the midline. Thus, the stomach assumes its final position.