Anatomy - Gastrectomy

The stomach is – formally speaking – a bulge of the digestive tract that lies between the esophagus and the intestine and has the task of storing and mixing food. This muscular hollow organ forms acidic gastric juice (mucus and HCl) and enzymes that pre-digest some components of the food, in order to then pass the food pulp portionwise into the small intestine.
The stomach is usually located in the left and middle upper abdomen directly under the diaphragm. The position, size, and shape of the stomach vary greatly from person to person and depending on age, filling state, and body position. When moderately filled, the stomach is on average 25-30 cm long and has a storage capacity of 1.5 and in extreme cases even up to 2.5 liters.
The stomach is attached and stabilized in the abdominal cavity by ligaments that, among other things, extend to the liver and spleen. It forms with its convex side the greater curvature of the stomach (greater curvature of the stomach / Curvatura major) and with the concave side the lesser curvature of the stomach (lesser curvature of the stomach / Curvatura minor). Its anterior wall is called Paries anterior, its posterior wall Paries posterior.
The stomach lies intraperitoneally and thus shows a covering of serosa, only the dorsal cardia is free of serosa. The embryonic mesogastria reach through the stomach rotation from their formerly sagittal position into a frontal one: The lesser omentum extends from the lesser curvature to the porta hepatis, the greater omentum spreads from the greater curvature to the transverse colon, the spleen, and the diaphragm.

One can divide the stomach into various sections:

• Stomach entrance / Cardia / Ostium cardiacum:
  The upper stomach opening is an area of 1-2 cm where the esophagus opens into the stomach. Here is the sharp transition from the esophageal mucosa to the gastric mucosa, which can usually be easily recognized with the endoscope.
• Stomach fundus / Fundus gastricus:
  Above the stomach entrance, the fundus bulges upwards, also called "stomach dome" or Fornix gastricus. The fundus is usually filled with air that is involuntarily swallowed during eating. In an upright person, the fundus forms the highest point of the stomach, so that in the X-ray image, the collected air is recognizable as a "gastric bubble". Opposite the stomach entrance, the fundus is delimited by a sharp fold (Incisura cardialis).
• Stomach body / Corpus gastricum:
  The main part of the stomach is formed by the stomach body. Here lie deep longitudinal mucosal folds (Plicae gastricae), which extend from the stomach entrance to the pylorus and are also referred to as the "gastric street".
• Pylorus / Pars pylorica:
  This section begins with the expanded Antrum pyloricum, followed by the pyloric canal (Canalis pyloricus) and ends with the actual pylorus (Pylorus). Here lies the pyloric sphincter (M. sphincter pylori), which is formed by a strong annular muscle layer and closes the lower stomach opening (Ostium pyloricum). The pylorus closes the stomach outlet and periodically allows some food pulp (chyme) to pass into the subsequent duodenum.

Stomach Wall
The stomach wall shows under the microscope from inside to outside a characteristic layered structure:

• Internally, the stomach wall is lined by mucous membrane (Tunica mucosa). The gastric mucosa is divided into three sublayers: The Lamina epithelialis mucosae forms a tough neutral mucus that protects the gastric mucosa from mechanical, thermal, and enzymatic damage. Below it follows the Lamina propria mucosae as a sliding layer, in which the gastric glands (Glandulae gastricae) are embedded. Finally, there is a narrow Lamina muscularis mucosae, which can change the relief of the mucosa.
• The gastric mucosa is followed by a loose sliding layer (Tela submucosa), which consists of connective tissue and in which a dense network of blood and lymph vessels runs, as well as a nerve fiber plexus, the Plexus submucosus (Meissner plexus), which controls gastric secretion. This plexus works independently of the central nervous system (CNS), but can certainly be influenced by it via the autonomic nervous system.
• This is followed by a strong Tunica muscularis, which is divided into three sublayers with fibers running in different directions: an inner layer of small obliquely running muscle fibers (Fibrae obliquae), then a circular muscle layer (Stratum circulare) and outermost an external longitudinal muscle layer (Stratum longitudinale). This musculature is responsible for the peristalsis of the stomach, which is responsible for the constant mixing of the chyme with the gastric juice. Between the circular and longitudinal muscle layers runs a nerve fiber plexus, the Plexus myentericus (Auerbach plexus), which controls the function of the musculature. Just like the Plexus submucosus, this plexus works largely autonomously, but is influenced by the autonomic nervous system.
• This is followed again by another connective tissue sliding layer (Tela subserosa).
• The conclusion is formed by the peritoneum as the abdominal membrane (Tunica serosa).

Gastric Glands
The gastric glands (Glandulae gastricae) are located in the Lamina propria mucosae and can be found in the fundus and corpus of the stomach. Up to 100 glands are located on 1 mm² of the mucosal surface. Various cells are located in the wall of the gland tubule:

• Mucous cells: They produce the same neutral mucus as the epithelial cells.
• Mucous neck cells: These cells lie quite superficially in the gland and secrete alkaline mucus, i.e., the pH value is high due to the hydrogen carbonate ions (OH- ions) contained therein. This property is important for controlling and possibly regulating the pH value of the stomach. The mucus coats the gastric mucosa and thus protects against self-digestion by the aggressive hydrochloric acid (HCl) and enzymes as self-digesting proteins. This cell type is found abundantly in the cardia and in the fundus of the stomach.
• Chief cells: These cells produce the inactive precursor enzyme pepsinogen, which after release is converted by hydrochloric acid (HCl) into the active enzyme pepsin and is responsible for the digestion of food proteins. Since the enzyme only comes into contact with the hydrochloric acid at the surface of the gland, self-digestion of the glands by the enzyme is prevented. This cell form is mainly located in the corpus of the stomach.
• Parietal cells: These cells, which are found in greater numbers in the gastric corpus, produce abundant hydrogen ions (H+ ions), which are needed for the formation of hydrochloric acid (HCl). The hydrochloric acid has a very low pH value of 0.9-1.5. In addition, the parietal cells form the so-called intrinsic factor. This substance forms a complex in the intestine with vitamin B12 from food, which can then pass through the small intestine wall. This vitamin is of particular importance in erythropoiesis (stomach removal can lead to anemia).
• G cells: These cells, which are preferably located in the antrum of the stomach, produce gastrin to increase HCl production in the parietal cells.

The stomach serves as a reservoir for the ingested food. It can store the food for hours and thus ensures that we can cover our daily nutritional needs with a few larger meals. Through peristalsis, the chyme is mixed with the gastric juice, the food is chemically broken down, partially digested, and then passed on in portions to the duodenum.

The arterial supply of the stomach occurs via several blood vessels, all originating from the unpaired celiac trunk, forming numerous anastomoses among themselves and running along the gastric curvatures as vascular arcades for the supply of the organ:

• Arteria gastrica dextra from the A. hepatica propria to the lower part of the lesser curvature,
• Arteria gastrica sinistra to the upper part of the lesser curvature,
• Arteriae gastricae breves from the A. splenica to the fundus,
• Arteria gastroepiploica (-omentalis) dextra from the A. gastroduodenalis to the lower (right) part of the greater curvature,
• Arteria gastroepiploica (-omentalis) sinistra from the A. splenica to the left side of the greater curvature,
• Arteria gastrica posterior from the A. splenica to the posterior wall.

This supplies the stomach through 2 vascular arcades between the A. gastrica sinistra and dextra at the lesser curvature, as well as the A. gastroepiploica sinistra and dextra at the greater curvature.

Parallel to the arterial supply, the 4 large veins of the stomach run along the two curvatures. Overall, collecting veins form from them (V. gastrica sinistra and dextra directly into the V. portae hepatis, V. gastroomentalis sinistra and Vv. gastricae breves to the V. splenica, and V. gastroomentalis dextra to the V. mesenterica sup.), all of which empty into the portal vein.

The neural supply of the stomach is predominantly under the autonomic nervous system, but sensory fibers are also present: The sympathetic nervous system supplies the musculature of the pylorus, the parasympathetic nervous system (N. vagus X) supplies the remaining gastric musculature and the glands of the stomach. The N. vagus runs right and left parallel to the esophagus, passes through the diaphragm via the esophageal hiatus and reaches the anterior surface of the stomach on the left side (Tr. vagalis anterior), and the posterior surface on the right side (Tr. vagalis posterior). Sensory fibers from the stomach, however, run afferent via the N. splanchnicus major to thoracic spinal ganglia.

The efferent lymphatic vessels of the stomach run parallel to the arterio-venous supply of the organ:

• The lymph of the lesser curvature parallel to the Aa. gastricae sinistra / dextra into the Nll. gastrici sinistri / dextri,
• from the gastric fundus parallel to the A. splenica into the Nll. splenici,
• the lymph of the greater curvature parallel along the attachment of the greater omentum to the Nll. gastro-omentales dextri / sinistri,
• from the pyloric region into the Nll. pylorici.
  From the mentioned regional lymph nodes, the lymph subsequently flows into the Nll. coeliaci, the superior mesenteric lymph nodes and the thoracic duct.
  Another drainage pathway for the lymph is provided by the Nll. pancreatici, so that tumors of the stomach can indeed metastasize to the pancreas. A peculiarity of gastric carcinoma is the repeated finding of a noticeable lymph node in the left lateral neck region (Virchow's lymph node), which indicates advanced metastasis.
  For surgical reasons, the lymph node stations are divided into 3 compartments:
• Compartment I (LN group 1-6): all LNs directly at the stomach: paracardial (group 1+2), at the lesser and greater curvature (group 3+4), supra- and infrapyloric (group 5+6).
• Compartment II (LN group 7-11): LNs along the major vessels: A. gastrica sin. (group 7), A. hepatica communis (group 8), Truncus coeliacus (group 9), splenic hilum (group 10), A. lienalis (group 11).
• Compartment III (LN group 12-16): LNs at the hepatoduodenal ligament (group 12), behind the pancreatic head (group 13), at the mesenteric root and the mesentery (group 14+15) as well as along the abdominal aorta (group 16).