Gastroesophageal Junction Anatomy

Gastroesophageal Junction

• Muscularis externa has three layers of muscle cells, unlike the two layers found elsewhere in the GI tract.
• The inner oblique layer is unique to the stomach and is found near the boundary with the submucosa.
• The middle circular layer and outer longitudinal layer are also present.

Cardiac Stomach

• The cardiac stomach is the closest to the esophagus and contains mucus-secreting glands.
• It is the narrow region surrounding the opening of the esophagus that contains cardiac glands in the mucosa.
• The epithelium structure abruptly changes from stratified squamous non-keratinized (esophagus) to simple columnar (stomach).

Gastric Pits and Cardiac Glands

• Cross-sections of gastric pits and cardiac glands can be distinguished by their location and cell type.
• Gastric pits are closer to the surface and have smaller, surface mucous cells.
• Cardiac glands are closer to the muscularis mucosae and have larger, mucous-secreting cells.

Fundic Stomach

• The fundic stomach is the largest part of the stomach (body/fundus) and contains fundic (gastric) glands.
• It has folds or ridges called rugae, formed from the mucosa and submucosa.
• The mucosa is composed of the epithelium, lamina propria, and muscularis mucosae.
• Gastric pits are surface invaginations lined with surface mucous cells.

Fundic Glands

• The fundic glands have three major regions: isthmus, neck, and fundus.
• The isthmus is a small region at the apex of the gland adjacent to a gastric pit.
• The neck is the largest part of the gland between the isthmus and the fundus.
• The fundus is the base of the gland adjacent to the muscularis mucosae.
• The glands contain three major cell types: mucous neck cells, parietal cells, and chief cells.

Pyloric Stomach

• The pyloric stomach is closest to the small intestine and contains mucus-secreting glands.
• It forms the distal region of the stomach that opens into the small intestine.
• The mucosa is composed of the epithelium, lamina propria, and muscularis mucosae.
• Pyloric glands appear as cross-sections of the short, coiled tubular glands of only mucous secreting cells.

Small Intestine

• The small intestine does not have villi, but has folds or ridges called plicae circularis (or valves of Kerckring).
• The mucosa is composed of the epithelium, lamina propria, and muscularis mucosae.
• Absorptive cells (or enterocytes) have microvilli (or brush border) to expand the absorptive surface.
• Goblet cells secrete mucus for lubrication.
• Crypts are intestinal glands found at the base of villi.

Recto-Anal Junction

• The anal canal is the site where there is a transition from the simple columnar epithelium of the colon to the stratified squamous epithelium of skin.
• The colorectal zone is on the left side of the specimen.
• Anal glands secrete mucus into the anal canal.
• The internal anal sphincter is an expansion of the inner circular layer of the muscularis externa.
• The pectinate line (anal transition zone) is the junction between the simple columnar epithelium of the colon and the stratified squamous epithelium of the skin.
• The squamous zone of the anal canal is on the right side of the specimen.
• The external sphincter is a skeletal muscle that is part of the pelvic floor.
• Circumanal glands are apocrine glands.