Stomach

The stomach is a muscular organ that lies between the oesophagus and duodenum in the upper abdomen. It lies on the left side of the abdominal cavity caudal to the diaphragm.

Gross anatomy

The stomach ("normal" empty volume 45 mL) is divided into distinct regions:

• cardia: the area that receives the oesophagus (gastro-oesophogeal junction)
• fundus: formed by the upper curvature
• body (corpus): the main central region of the organ
• pylorus (antrum): the lower section of the stomach that facilitates emptying into the small intestine

There are two smooth muscle sphincters, oesophageal and pyloric, that dictate entry into and exit from the stomach. These are under the control of several mechanisms including stimulant (parasympathetic) and inhibitory (orthosympathetic) control from the anterior gastric, posterior, superior and inferior coeliac and myenteric nerve plexuses.

The inner mucosal surface has many rugal folds that act to increase the surface area of the stomach lining and increase its efficiency.

Specific sites

• incisura angularis: small anatomical notch on the stomach located on the lesser curvature of the stomach near the pyloric end
• fornix gastricus: refers to the arch-shaped superior margin of the fundus of the stomach

Relations

• anteriorly: left lobe of liver, anterior abdominal wall, left hemidiaphragm
• posteriorly: lesser sac, stomach bed
• medially: abdominal aorta, coeliac trunk, coeliac lymph nodes

Arterial supply

• lesser curvature: right gastric artery (inferiorly) and left gastric artery (superiorly)
• cardia: left gastric artery
• greater curvature: right gastroepiploic artery (inferiorly) and left gastroepiploic artery and short gastric arteries (superiorly)
• fundus of the stomach: short gastric arteries

Venous drainage³

• left and right gastric veins drain to portal vein
• short gastric vein and left gastroepiploic vein drain to splenic vein
• right gastroepiploic vein drains to superior mesenteric vein³

Lymphatic drainage

Lymphatics drain with arteriesRoutes of the flow of lymph from perigastric nodes to para-aortic lymph nodes include ^4-6: 

• directly to the coeliacleft paracardial lymph nodes
• along the lymph nodes accompanying the splenic artery
• along lymph nodes accompanying the coeliac artery
• along lymph nodes accompanying the superior mesenteric artery
• along the lymph nodes on the posterior surface of the pancreatic head and the nodes accompanying the common hepatic artery

Nomura et al suggested that the most likely route for para-aortic lymph node metastases was from the left gastric artery nodes passing by the coeliac artery ⁴.

Histology

Akin to other areas of the gastrointestinal (GI) tract, the stomach walls are composed of the following layers:

• mucosa: internal layer of epitelium, the lamina propria (loose connective tissue and gastric glandular tissue) and the muscularis mucosae
• submucosa: a fibrous layer of connective tissue under the mucusa
• muscularis externa: this is the muscular layer of the stomach wall, but differs from other GI organs (which have two layers); there are three layers (inner oblique, middle circular and outer longitudinal)
• serosa: the outermost layer of the stomach wall consisting of connective tissue which is continuous with the peritoneum

Cell types

The stomach wall contans several different types of glandular tissue. The cardia, fundus and pylorus all have different types of glands and are composed of a variety of different cells:

• mucous cells: secrete a mucus gell layer and are found throughout the stomach
• parietal (oxyntic) cells: secrete gastric acid and intrinsic factor throughout the stomach
• chief (zymogenic) cells: secrete pepsinogen and rennin in the fundus only
• enteroendocrine (APUD) cells: secrete a variety of products and are found throughout the stomach

Physiology

Control of the stomach relates to the autonomic nervous system and various digestic system hormones:

• gastrin: causes an increase in the secretion of hydrochloric acid (HCl), pepsinogen and intrinsic factor from parietal cells in the stomach; it also causes increased motility in the stomach; released by G-cells in the stomach to distension of the antrum, and digestive products; inhibited by a pH normally <4 (acidic), as well as the hormone somatostatin
• cholecystokinin (CCK): greatest effect on the gall bladder, but it also decreases gastric emptying and increases release of pancreatic juice which is alkaline and neutralizes the chyme
• secretin: has most effects on the pancreas, but will also diminish acid secretion in the stomach
• gastric inhibitory peptide (GIP): decreases both gastric acid and motility
• enteroglucagon: decreases both gastric acid and motility
• glycogen: produced in the brain and stomach, affects the liver and level of glucose in the stomach

Radiographic features

Plain radiograph

The stomach is not usually well visualised on the plain film although a gastric bubble (gas outlining the fundus of the stomach) is often visible on an erect chest or abdominal x-ray.

CT

The stomach wall should be from 2 to 5mm thick, except at the gastro-oesophageal junction.