Stomach

Gaster (ventriculus)

Also known as: gaster

The stomach is the J-shaped, most dilated part of the alimentary canal, between the oesophagus and the duodenum. It stores the meal, churns it with acid and pepsin into chyme, and releases it to the duodenum at a controlled rate.

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Overview

Capacity≈50 mL empty · ≈1–1.5 L after a meal · up to ≈4 L

Gastric pH≈1.5–3.5

Gastric juice≈1.5–2 L/day

Slow-wave frequency≈3/min

Emptying time≈2–4 h (fat ≥6 h)

The stomach lies in the left upper quadrant, in the epigastric, umbilical and left hypochondriac regions. Its shape and position vary with posture, body build and how full it is. It has two orifices (cardial and pyloric), two curvatures and two surfaces. The short, concave lesser curvature faces right and gives attachment to the lesser omentum. The long, convex greater curvature gives attachment to the greater omentum and the gastrosplenic ligament. The angular incisure on the lesser curvature marks the junction of the body with the pyloric part.

The mucosa of the empty stomach is thrown into longitudinal gastric folds (rugae), which flatten as the stomach fills. Millions of gastric pits lead into the gastric glands. The muscularis externa has a third, innermost oblique layer, in addition to the circular and longitudinal layers, which strengthens the churning "antral mill". At the pylorus the circular layer thickens into the true anatomical pyloric sphincter.

The stomach performs receptive relaxation and accommodation through the vagus, so a large meal causes little rise in pressure. Antral peristalsis at about 3 waves per minute, set by pacemaker cells in the greater curvature, grinds food against the closed pylorus. This retropulsion returns larger particles while chyme with particles of about 1–2 mm squirts through. A meal leaves the stomach in about 2–4 hours; fatty meals take longer. Duodenal feedback via the enterogastric reflex, CCK, secretin and GIP keeps delivery matched to how fast the intestine can digest.

Location: Left upper quadrant (epigastrium and left hypochondrium), beneath the left dome of the diaphragm. The pylorus usually lies at the transpyloric plane (L1), just right of the midline.

Parts & subdivisions

Cardia
Region around the cardial orifice, where the oesophagus enters at T11. Contains mucous cardiac glands.
Fundus
Dome-shaped part above the level of the cardial orifice, under the left hemidiaphragm. It usually holds a gas bubble visible on erect radiographs. The cardiac notch separates it from the oesophagus.
Body
Largest part, between the fundus and the angular incisure. Rich in oxyntic glands (parietal and chief cells).
Pyloric antrum and canal
Funnel-shaped antrum leading into the narrow pyloric canal. Its glands contain gastrin-secreting G cells. Site of powerful peristaltic grinding.
Pylorus and pyloric sphincter
Thickened circular muscle surrounding the pyloric orifice. It regulates gastric emptying and limits duodenogastric reflux. The prepyloric vein of Mayo marks it at surgery.
Lesser and greater curvatures
Lesser curvature: lesser omentum and the right and left gastric vessels. Greater curvature: greater omentum, the gastro-omental vessels and the short gastric vessels.
Rugae
Longitudinal mucosal and submucosal folds that allow distension. A "gastric canal" of straighter folds runs along the lesser curvature.
Gastric glands
Glands opening into the gastric pits, containing parietal, chief, mucous neck and enteroendocrine cells.

Anatomy

Innervation: Parasympathetic: anterior vagal trunk (mainly left vagus) and posterior vagal trunk (mainly right vagus), which give the anterior and posterior nerves of Latarjet ending as a "crow's foot" on the antrum. They stimulate secretion and motility. Sympathetic: T6–T9 via the greater splanchnic nerves to the coeliac ganglion; they cause vasoconstriction and inhibit motility. Visceral pain afferents run with the sympathetics and refer pain to the epigastrium.
Arterial supply: All from the coeliac trunk, with rich anastomoses. Lesser curvature: left gastric artery (a direct branch of the coeliac trunk) and right gastric artery (usually from the proper or common hepatic artery). Greater curvature: right gastro-omental artery (from the gastroduodenal artery) and left gastro-omental artery (from the splenic artery). Fundus: short gastric arteries (from the splenic artery). Posterior wall: the inconstant posterior gastric artery (from the splenic artery).
Venous drainage: Veins run with the arteries. The right and left gastric veins drain directly into the hepatic portal vein. The short gastric and left gastro-omental veins drain into the splenic vein. The right gastro-omental vein drains into the superior mesenteric vein.
Lymphatic drainage: Gastric, gastro-omental, pyloric and pancreaticosplenic nodes, all draining to the coeliac nodes and then the cisterna chyli. Spread via the thoracic duct can enlarge the left supraclavicular (Virchow) node, a finding known as Troisier sign.
Relations: Anterior: diaphragm, left lobe of the liver and the anterior abdominal wall. Posterior (the stomach bed), separated by the lesser sac: left crus of the diaphragm, spleen, left suprarenal gland, upper pole of the left kidney, splenic artery, pancreas and transverse mesocolon.
Histology: Simple columnar mucus-secreting surface epithelium lining the gastric pits (foveolae), which lead into glands. Cardiac glands are mucous. Oxyntic (fundic) glands contain parietal, chief and ECL cells. Pyloric glands contain mucous cells, G cells and D cells. The muscularis externa has three layers: oblique, circular and longitudinal.
Development: A fusiform dilatation of the foregut in week 4. It rotates 90° clockwise about its longitudinal axis, so its left side faces forward and the left vagus becomes anterior. The dorsal border grows faster to become the greater curvature. The dorsal mesogastrium forms the greater omentum and the ventral mesogastrium forms the lesser omentum.

Function

Reservoir: stores the meal (receptive relaxation and accommodation) and releases it gradually.
Mechanical digestion: churning and grinding into chyme.
Chemical digestion: pepsin (protein) and gastric lipase (fat).
HCl secretion: kills microbes, denatures proteins, activates pepsinogen and solubilises iron and calcium.
Secretes intrinsic factor, which is essential for vitamin B12 absorption; this is the only indispensable gastric function.
Endocrine and paracrine output: gastrin, ghrelin, somatostatin and histamine.
Absorbs a few lipid-soluble substances, such as alcohol and aspirin.

Physiology: Slow waves at about 3/min. Gastric emptying takes about 2–4 h for a mixed meal and 6 h or more for fatty meals; liquids empty faster than solids. Emptying is slowed by duodenal fat (CCK), acid (secretin), hyperosmolality and distension through the enterogastric reflex. See also gastric acid secretion.

Clinical significance

Peptic ulcer

Gastric ulcers usually lie on the lesser curvature near the angular incisure. Pain is worsened by food. They need biopsy to exclude malignancy and can bleed from the left gastric artery. H. pylori and NSAIDs are the main causes.

Gastric adenocarcinoma

The intestinal type is linked to H. pylori, atrophic gastritis, intestinal metaplasia and dietary nitrosamines. The diffuse type consists of signet-ring cells and produces linitis plastica, a rigid "leather-bottle" stomach; it is associated with CDH1 (E-cadherin) mutations. Spread can reach the Virchow node, the ovaries (Krukenberg tumour) and the umbilicus (Sister Mary Joseph nodule).

Infantile hypertrophic pyloric stenosis

Hypertrophy of the pyloric circular muscle presents at about 3–6 weeks with projectile, non-bilious vomiting after feeds, a palpable "olive" in the epigastrium and visible peristalsis. Loss of gastric HCl produces a hypochloraemic, hypokalaemic metabolic alkalosis. Boys are affected about 4 times as often as girls, and first-borns and early macrolide exposure carry extra risk. Diagnosis is by ultrasound; treatment is fluid and electrolyte correction followed by Ramstedt pyloromyotomy.

Compiled from standard anatomy and physiology references — see the Digestive System sources. For education only; not medical advice.