Explain stomach anatomy

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Stomach Anatomy

The stomach is a J-shaped muscular dilation of the alimentary canal, continuous with the esophagus proximally and the duodenum distally. It serves as the primary food reservoir and begins protein digestion. Capacity ranges from ~30 mL in a neonate to 1.5-2 L in an adult.

Gross Anatomy and Regions

The stomach is divided into 4 anatomic regions:

Anatomic regions of the stomach showing fundus, body, antrum, pylorus, lower esophageal sphincter, and gland mucosa zones

Cardia - A small, ill-defined zone immediately adjacent to the esophagogastric junction. The esophagogastric junction lies at the level of T10, 1-2 cm below the diaphragmatic hiatus.
Fundus - The dome-shaped superior portion projecting upward above the cardia. It contacts the left hemidiaphragm superiorly and the spleen laterally.
Body (Corpus) - The largest region, located below and continuous with the fundus. The incisura angularis (a fixed sharp indentation two-thirds down the lesser curvature) marks the caudal limit of the body.
Antrum and Pylorus - The antrum extends from its indistinct border with the body to the pyloric junction. The pylorus is a tubular structure containing the palpable pyloric sphincter (circular muscle), located ~2 cm to the right of midline at L1. It controls gastric emptying into the duodenum.

Curvatures:

Lesser curvature - right upper border; the incisura angularis is its most notable landmark
Greater curvature - left lower border; may descend below the umbilicus when distended

Relations:

Posterior: pancreas, transverse colon, diaphragm, spleen, left kidney and adrenal gland
Anterior: liver (right lobe overlies the lesser curvature), anterior abdominal wall (left lower aspect)
The posterior stomach wall forms the anterior wall of the omental bursa (lesser peritoneal sac)

Peritoneal Attachments and Ligaments

The stomach is entirely invested in peritoneum (except a small bare area at the esophagogastric junction). This peritoneum forms several named ligaments:

Ligament	From	To
Gastrohepatic (lesser omentum)	Lesser curvature	Liver
Gastrocolic ligament	Greater curvature/fundus	Transverse colon
Gastrosplenic ligament	Greater curvature/fundus	Spleen
Gastrophrenic ligament	Fundus	Diaphragm
Greater omentum	Greater curvature	Hangs down (covers small intestine)

Blood Supply

All gastric arteries derive from the celiac axis:

Lesser curvature arcade:

Left gastric artery (direct celiac branch) - supplies the upper lesser curvature; gives branches toward the cardia
Right gastric artery (from common hepatic artery) - anastomoses with the left gastric artery

Greater curvature arcade:

Left gastroepiploic artery (from splenic artery) - supplies the upper greater curvature
Right gastroepiploic artery (from gastroduodenal artery, itself a branch of common hepatic) - supplies the lower greater curvature; these two often anastomose to complete the arcade (though this arcade is sometimes variably incomplete)

Fundus:

Vasa brevia (short gastric arteries) - multiple small branches arising near the terminal splenic artery; supply the fundus and upper left greater curvature

Venous drainage mirrors the arterial supply and drains into the portal system - lesser curvature veins into the portal vein, greater curvature veins into the splenic vein. The left gastric vein (coronary vein) is clinically important as it dilates markedly in portal hypertension, forming esophageal varices.

Lymphatic Drainage

Lymphatic channels anastomose freely within the gastric wall and ultimately drain to the celiac nodes via four regional pathways:

Inferior gastric region → subpyloric and omental nodes → hepatic nodes → celiac nodes
Splenic/superior greater curvature → pancreaticosplenic nodes → celiac nodes
Superior gastric/lesser curvature → left and right gastric nodes → celiac nodes
Pyloric/hepatic lesser curvature → suprapyloric nodes → hepatic nodes → celiac nodes

This extensive interconnection is why gastric cancer can spread early and widely.

Innervation

Parasympathetic (vagal):

The right and left vagus nerves form the esophageal plexus, then coalesce into the posterior vagal trunk (predominantly right vagus) and anterior vagal trunk (predominantly left vagus) near the gastric cardia
Each trunk gives off hepatic and celiac branches, then continues as the nerve of Latarjet (anterior and posterior) running along the lesser curvature
The nerves of Latarjet supply the gastric body and end as the "crow's foot" at the antrum, stimulating motility and acid secretion

Sympathetic:

Preganglionic fibers arise from T6-T8 spinal nerves, synapse in the bilateral celiac ganglia
Postganglionic fibers travel along gastric vessels
Includes afferent pain fibers and motor fibers to the pyloric sphincter

The embryological rotation of the stomach explains why the right vagus ends up innervating the posterior wall and the left vagus innervates the anterior wall.

Microscopic Anatomy (Histology)

Histology of a gastric gland - mucus-secreting cells at the surface, eosinophilic parietal cells superficially in the glands, and basophilic chief cells in the deepest layer

The gastric wall has the standard 4-layer GI structure (mucosa, submucosa, muscularis, serosa) with stomach-specific features:

Mucosal Layers and Gastric Glands

The mucosa is lined by a simple columnar epithelium that abruptly transitions from squamous esophageal epithelium at the cardia. Surface cells produce a highly viscous neutral mucus protecting the wall from self-digestion.

Glands are classified by region:

Region	Gland Type	Key Cell Types	Secretions
Body & Fundus	Gastric glands proper (oxyntic glands)	Parietal cells, Chief cells, Mucous neck cells	HCl + intrinsic factor (parietal); pepsinogen (chief); mucus (neck)
Cardia	Cardiac glands	Mucous cells only	Mucus, lysozyme
Antrum/Pylorus	Pyloric glands	Mucous columnar cells, G cells	Neutral-to-slightly-acid mucus; gastrin (G cells)

Parietal cells - Large, eosinophilic, triangular cells found in the body; they secrete H⁺ via the H⁺/K⁺-ATPase proton pump (the target of PPIs) against a concentration gradient of 1,000,000:1. They also secrete intrinsic factor, essential for vitamin B12 absorption.

Chief cells - Basophilic columnar cells at the base of body glands; produce pepsinogen I and II, which are activated to pepsin by the acidic environment. The pepsinogen I:II ratio falls with gastric atrophy.

Enteroendocrine cells:

G cells (antrum) - produce gastrin, which stimulates acid secretion
ECL cells (body) - produce histamine, a key local driver of acid secretion
D cells (throughout) - produce somatostatin, which has a negative regulatory role

Muscular Layer

The stomach has 3 muscle layers (unlike the rest of the GI tract which has 2):

Outer longitudinal layer - especially thick; runs along curvatures
Middle circular layer - thickens at the pylorus to form the pyloric sphincter
Inner oblique layer - unique to the stomach; helps with mechanical churning

The incisura angularis functionally separates the stomach into an upper digestive sac (fundus + body) and a lower pyloric canal with emptying function.

Embryology (Brief)

The stomach is recognizable in the 4th week of gestation as a dilation of the distal foregut. The dorsal aspect grows faster than the ventral, forming the greater curvature. The stomach then rotates 90 degrees around its longitudinal axis, placing the greater curvature to the left and lesser curvature to the right - this explains the vagal arrangement described above.

Sources:

Sleisenger and Fordtran's Gastrointestinal and Liver Disease, Chapter 49 (Embryology and Anatomy of the Stomach)
Bailey and Love's Short Practice of Surgery, 28th ed., Chapter 67 (Anatomy of the Stomach and Duodenum; Microscopic Anatomy)
Color Atlas of Human Anatomy Vol. 2, Internal Organs (Microscopic Anatomy of the Stomach)

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