Stomach

The stomach is a hollow intraperitoneal organ in the left upper quadrant of the abdomen, between the esophagus and the duodenum in the gastrointestinal tract. It is supplied with arterial blood from the celiac trunk and its branches. The veins of the stomach drain into the portal vein, and the lymphatics eventually drain into the celiac lymph nodes. It is innervated by the sympathetic and parasympathetic nervous system, as well as the myenteric plexus and submucous plexus of the enteric nervous system. The stomach has four histological layers: the mucosa, submucosa, muscularis propria, and serosa. The mucosa is lined with numerous glands containing specialized cells that produce various secretions: e.g., parietal cells, which secrete gastric acid and intrinsic factor, and gastric chief cells, which secrete pepsinogen. Acetylcholine (ACh), gastrin, and histamine are the main stimulators of gastric secretions. Somatostatin, cholecystokinin (CCK), secretin, and gastric inhibitory peptide (GIP) are the main inhibitors.

Overview ^[1]

• Characteristics
  • Hollow, muscular organ
  • First intra-abdominal part of the gastrointestinal tract, situated between the esophagus (proximally) and the duodenum (distally)
  • Divided into the cardia, gastric fundus, body (stomach), and pylorus
• Location
  • LUQ of the abdomen
  • Abdominal regions: epigastric, left hypochondriac, and umbilical
  • Anterior to the stomach
    • Anterior abdominal wall
    • Left lobe of the liver
    • Greater omentum
    • Diaphragm
  • Posterior to the stomach
    • Spleen
    • Tail of the pancreas
    • Left kidney
    • Left adrenal gland
    • Transverse colon
    • Transverse mesocolon and lesser sac
• Function
  • Mechanical digestion via peristalsis
  • Chemical digestion via secretion of gastric acid and digestive enzymes
  • Secretion of intrinsic factor

Anatomical parts

• Sections of the stomach
  • Cardia: the part of the stomach that lies immediately distal to the gastroesophageal sphincter
  • Gastric fundus: the dome-shaped region of the stomach just lateral to the cardia
  • Body (stomach): the main portion of the stomach that lies between the fundus and the pylorus
  • Pylorus: the terminal conical narrowing of the stomach that can be further subdivided into the proximal antrum and the distal pyloric canal
• Curvatures of the stomach
  • Lesser curvature: the medial concave border of the stomach
  • Greater curvature: the lateral convex border of the stomach
• Sphincters of the stomach
  • Gastroesophageal sphincter (lower esophageal sphincter)
    • Circular muscle located at the junction between the gastric cardia and esophagus (Th11)
    • Prevents reflux of gastric contents into the esophagus
  • Pyloric sphincter
    • A muscular ring located in the pyloric canal
    • Controls the movement of gastric contents into the duodenum

The antrum and lower lesser curvature are the most common sites for peptic stomach ulcers.

Peritoneal attachments

The stomach is an intraperitoneal organ.

• Omentum: extends from stomach (and proximal duodenum) to other abdominal organs
  • Greater omentum: from greater curvature and covers intestines
  • Lesser omentum: from lesser curvature to liver
• Peritoneal ligaments of the stomach
  • Gastrohepatic ligament
  • Gastrocolic ligament
  • Gastrosplenic ligament

Vasculature, lymphatics, and innervation of the stomach ^[1]

Arteries

Veins

• Veins of the stomach
  • Right and left gastric veins
  • Right and left gastroepiploic veins
  • Short gastric veins
• Drain into portal vein
• The anastomosis between the left gastric vein and the esophageal vein is a site of portosystemic anastomosis.

Esophageal varices develop in portal hypertension due to the portosystemic shunting of blood from the left gastric vein (portal system) into the esophageal veins (caval system).

Lymphatics

• Perigastric and peripyloric lymph nodes : drain into the celiac lymph nodes

Innervation

The left vagus nerve is anterior to the stomach, and the right vagus is posterior to it. This can be remembered with the mnemonic LARP: Left Anterior, Right Posterior.

• The stomach's four histological layers are the same as the layers of the gastrointestinal tract.
• The mucosa of the stomach is specialized in the following ways:
  • It contains millions of gastric pits that are lined by mucus-secreting cells (foveolar cells) and open into one or more gastric glands.
  • Gastric glands in the lamina propria contain various specialized cells and vary in composition and thickness depending on their location in the stomach.
  • Stem cells located at the necks of the gastric glands proliferate and differentiate to replace gastric cells.
  • Enteroendocrine cells are located throughout the gastric mucosa and secrete various secretory and regulatory products of the gastrointestinal tract.

Types of digestion

• Mechanical digestion: peristalsis of the stomach against a closed pyloric sphincter → breakdown of food into smaller particles
• Chemical digestion: enzymatic breakdown of food into chyme (a semifluid mixture of digested food and digestive enzymes) by gastric acid and enzymes

See “Secretory and regulatory products of the gastrointestinal tract.”

Mechanism of gastric acid secretion

• Gastric acid is secreted by the parietal cells.
• H⁺/K⁺-ATPase pump on the apical cell membrane of parietal cells secretes H⁺ ions into the lumen.
• Carbonic anhydrase in parietal cell cytoplasm converts CO₂ into H⁺ and HCO₃^-.
• Intracellular HCO₃^- is exchanged for Cl^- through the basolateral membrane.
• H⁺ and Cl^- are secreted into the gastric lumen as HCl.

Gastric acid contains high amounts of hydrochloric acid (HCl). Repeated vomiting can therefore cause metabolic alkalosis due to the loss of acid (H⁺).

Phases

Disturbances of gastric secretions

• The stomach is a derivative of the primitive foregut.
• See “Embryology of the gastrointestinal tract.”

• Pathology
  • Peptic ulcer disease (PUD)
  • Autoimmune gastritis, vitamin B12 deficiency (pernicious anemia)
  • Hypertrophic pyloric stenosis
  • Hiatal hernia
  • Congenital diaphragmatic hernias
  • Atrophic gastritis
  • Gastrinoma (Zollinger-Ellison syndrome)
  • Ménétrier disease
  • Gastric cancer
  • MALT lymphoma
• Pharmacology
  • Proton pump inhibitors
  • H2 antihistamines