Stomach

Structure/Morphology

The stomach has four primary regions: the cardia, fundus, body, and pylorus. It is bounded by two sphincters: the lower esophageal sphincter and the pyloric sphincter.

The cross-sectional microarchitecture of the stomach demonstrates mucosa, submucosa, and muscular (inner oblique, middle circular, and outer longitudinal) layers with a thin outer serosal covering.

The muscular layer of the stomach is distinct. In addition to the circular and longitudinal layers of muscle found throughout the digestive tract, there is a third layer of muscle fibers, the oblique fibers, that lies between the circular layer and the submucosa. This third layer assists in the mixing of chyme.

The cardia is the portion of the stomach immediately inferior to the lower esophageal sphincter. It contains a high number of mucous secreting cells.

The fundus is the superior portion of the stomach that sits below the left diaphragm. It is the site where food that has recently entered the stomach sits, before being churned through the body of the stomach as chyme. The angle between the left side of the lower esophagus and the fundus is the cardiac notch.

The body is the main portion of the stomach in which peristaltic waves of contraction and the resulting mixing breaks food down into chyme. It ends on the lesser curvature and meets the pylorus at the angular notch.

The pylorus is the inferior portion of the stomach that begins at the angular notch and ends at the pyloric sphincter. It consists of both the pyloric antrum, a region where the body of the stomach narrows, and the pyloric canal, the distal most portion of the stomach that ends at the pyloric sphincter. Larger food particles are deflected back out of the pylorus to continue mixing, while chyme that is sufficiently digested passes through the pylorus and pyloric sphincter and into the duodenum.

Anatomical Relations

The stomach lies between the esophagus and duodenum. It is intraperitoneal and sits primarily in the left upper quadrant, with the junction between the esophagus and cardia located at roughly the T11 vertebral level and just left of the midline.

The stomach expands greatly when full of food, and so its location varies with size and position. Roughly, it sits inferior to the diaphragm and liver, and superior to the pancreas and transverse colon, resting against the anterior abdominal wall and posteriorly against the transverse mesocolon.

The proximal most part of the stomach, the cardia, sits just below the distal muscular thickening of the esophagus, the lower esophageal sphincter, and the esophageal hiatus of the diaphragm. Internally, the cardia opens into the fundus and body of the stomach.

The fundus of the stomach sits superiorly and forms a dome shape space. It rests largely against the inferior surface of the left lobe of the liver and the left diaphragm. Internally it’s continuous with the cardia and the body of the stomach. Externally, it connects to the end of the esophagus at the cardiac notch.

The body of the stomach forms the bulk of the stomach and is defined on its sides by the greater and lesser curvatures. It is along the lesser curvature that the left and right gastric vessels run within a mesentery called the lesser omentum. This mesentery connects the liver to the stomach and separates the greater and lesser sacs of the abdomen.

The greater curvature of the stomach defines the lateral wall of the body of the stomach and contains the gastroomental vessels. It is found inferiorly against the transverse colon and is the site at which the greater omentum, running from the stomach to the transverse colon, attaches.

The inferior border of the body of the stomach is marked externally by the end of the lesser curvature at the angular notch. Internally, the body ends inferiorly at the pyloric antrum. The superior and inferior borders of the body of the stomach are not well defined on the greater curvature.

The pylorus is the inferior narrowing of the stomach that connects the body to the pyloric sphincter. The initial portion is the pyloric antrum, where the stomach narrows down. This leads to the pyloric canal, the distal most portion of the stomach that ends at the pyloric sphincter. The pylorus is found inferior to the liver and roughly on the midline. Externally, the pylorus begins at the angular notch on the lesser curvature.

Function

The stomach serves several functions: sterilization of food, physical and enzymatic digestion, production of intrinsic factor, and temporary storage of masticated food so delivery to the small intestine can be regulated.

Several different cells in the mucosa of the stomach secrete hydrochloric acid and enzymes to sterilize and break down food. Mucous and bicarbonate secreting cells protect the walls of the stomach from damage due to the low pH.

Peristaltic contractions of the smooth muscle in the muscular layer physically grind food particles and mix them with gastric juices to produce chyme. Larger particles are retained in the stomach while sufficiently digested liquid components are allowed to pass through the pyloric sphincter and into the duodenum.

Parietal cells in the stomach produce intrinsic factor, which is essential for absorption of vitamin B12. Its absence results in pernicious anemia.

Very little absorption occurs in the stomach, principally a minor amount of several small molecules, water, alcohol, and aspirin.

Arterial Supply

The arterial supply to the stomach is by the celiac trunk and its branches. The left and right gastric arteries serve the lesser curvature and adjacent portions of the body of the stomach. The left and right gastroomental arteries serve the greater curvature and adjacent regions of the body of the stomach. The short gastric arteries serve the fundus.

The left gastric artery is the primary artery serving the cardia while the right gastric and gastroomental arteries both serve the pylorus.

Venous Drainage

The venous drainage of the stomach is to the portal circulation.

Both the left and right gastric veins typically drain to the portal vein, the short gastric veins and left gastroomental vein to the splenic vein, and the right gastroomental vein to the superior mesenteric vein.

Blood from the left gastric veins can be shunted through anastomoses with the esophageal veins to the azygos system in cases of portal hypertension.

Innervation

Innervation of the stomach includes the autonomic nervous system, visceral sensory afferents, and the enteric nervous system.

Sympathetic innervation is derived from the sympathetic chain. Sympathetic fibers originated at the T5-L9 spinal cord levels emerge from the sympathetic chain via the greater splanchnic nerve. They synapse with postsynaptic sympathetic neurons in the celiac ganglion. Axons from these postsynaptic sympathetic neurons follow the vasculature of the celiac trunk to innervate the vasculature and muscles of the stomach.

Parasympathetic innervation is provided entirely by the vagus nerve. The left and right vagal trunks, shortly after entering the abdomen along the esophagus, give off gastric branches that distribute to the anterior and posterior stomach, respectively.

Visceral sensory afferent nerves send axons from the stomach back to the CNS along the greater splanchnic and vagus nerves.

The enteric system consists of two plexuses of densely packed small neurons. They control mucosal and peristaltic function in the gastrointestinal tract.

Lymphatic Drainage

Lymphatic drainage from the stomach parallels the arterial supply and drains primarily into celiac nodes. Intermediate lymph nodes are found along the greater and lesser curvatures of the stomach (gastroomental and gastric nodes respectively), the upper and lower pylorus (pyloric nodes), and a ring around the cardia. The posterior stomach drains through the pancreaticosplenic nodes along the splenic artery.

From the celiac lymphatic nodes, lymph drains into the cisterna chyli and the thoracic lymphatic duct (Földi et al., 2012).

List of Clinical Correlates

- Hiatal hernia

- Pernicious anemia

- Peptic ulcers

- Gastroparesis

- Crohn’s disease

- Gastritis

- Viral gastroenteritis

References

Földi, M., Földi, E., Strößenreuther, R. and Kubik, S. (2012) Földi's Textbook of Lymphology: for Physicians and Lymphedema Therapists. Elsevier Health Sciences.