Stomach Histology and Anatomy

Stomach Histology

• The stomach is a mixed exocrine-endocrine organ.
• It's a dilated part of the digestive tract.
• Gross examination reveals four regions: cardia, fundus, body, and pylorus.
• The fundus and body have identical microscopic structures; thus, only three histological regions are recognized.
• The stomach's mucosa and submucosa form folds called rugae when empty.
• These folds flatten when the stomach is filled with food.

Stomach Anatomy

• The stomach has distinct sections as highlighted in the diagram
• The cardia is at the junction of the esophagus, 2-3cm wide.
• The fundus is the dome-shaped upper region on the left of the esophagus, often with gas.
• The body (corpus) is the largest part, responsible for chyme formation.
• The pylorus (pyloric antrum) is funnel-shaped and constricted; it has a pyloric sphincter controlling chyme release into the duodenum.

Stomach Functions

• The stomach continues carbohydrate digestion begun in the mouth.
• It adds acidic fluid to the ingested food.
• Muscular action transforms the food into chyme.
• Initial protein digestion occurs with the enzyme pepsin.
• Gastric lipase aids in triglyceride digestion, aided by lingual lipase.

Gastric Histology

• The stomach's epithelial lining secretes mucus to protect its lining.
• Gastric pits (foveolae) are formed by the epithelial lining's infolding into the mucosa.
• Cardiac region has the shallowest pits, while pyloric region has the deepest.
• Gastric pits increase the gastric lining's surface area.
• 5-7 gastric glands in the lamina propria empty into the bottom of each gastric pit.

Cardia

• A narrow circular band (1.5-3cm wide).
• Its mucosa contains simple or branched tubular cardiac glands.
• Most secretory cells produce mucus and lysozyme (enzyme that attacks bacteria).
• A few parietal cells secrete H⁺ and Cl^-.
• Structure similar to cardiac glands of the terminal esophagus.

Fundus and Body

• The lamina propria of the fundus and body contains branched, tubular gastric (fundic) glands (3-7).
• Each gastric gland has three parts: isthmus, neck, and base.
• The isthmus, near the gastric pit, has differentiating mucous cells, undifferentiated stem cells, and oxyntic (parietal) cells.
• The neck contains stem cells, different mucous neck cells, and parietal cells.
• The base mainly contains parietal and chief (zymogenic) cells; enteroendocrine cells are found in the neck and base.

Pylorus

• Pyloric glands have deep pits with branched tubular structures.
• Pyloric glands produce mucus and the enzyme lysozyme.
• Gastrin (G) cells release gastrin, intercalated between mucous cells.
• Other enteroendocrine cells (D cells) secrete somatostatin, which inhibits gastrin release, stimulated by HCl.

Other Stomach Layers

• The submucosa is dense connective tissue with blood and lymph vessels, including lymphoid cells.
• The muscularis is composed of smooth muscle layers: longitudinal, circular, and oblique, with a thickened circular layer forming the pyloric sphincter.
• The stomach is covered with a thin serosa.

Pyloric-duodenal Junction

• The pyloric-duodenal junction (gastroduodenal) separates the pyloric stomach from the duodenum.
• The pyloric sphincter controls chyme passage.
• Both stomach and duodenum have four layers characteristic of the GI tract.
• Pyloric glands are in the mucosa, while duodenal glands are in the submucosa.
• The mucosa structure changes from long pits and short, coiled glands in the pyloric stomach to broad projections (villi) and crypts in the duodenum.
• The muscularis mucosae is continuous, while the submucosa contains Brunner's glands in the duodenum.
• The muscularis externa expands in the stomach to form the pyloric sphincter.