L16: Digestive System I (GI Tract)

Comprehensive vocabulary terms and definitions covering the microanatomy, histology, and clinical specifics of the upper and lower GI tract.

Alimentary canal

Another name for the Gastrointestinal Tract (GIT).

Mucosa

The innermost layer of the GIT consisting of secretory and absorptive epithelium, lamina propria (connective tissue), and a thin muscularis mucosa.

Submucosa

The glandular layer of the GIT containing lymphoid tissue, nerves, blood vessels, and lymphatics.

Muscularis externa

A layer of the GIT generally composed of an outer longitudinal layer and an inner circular layer, though the stomach contains an additional inner oblique layer.

Lower esophageal sphincter

An important barrier at the terminal part of the esophagus that prevents gastroesophageal reflux of gastric contents.

Esophageal glands proper

Small, compound, tubuloalveolar glands located in the submucosa of the esophagus.

Esophageal cardiac glands

Simple tubular or branched tubular glands found in the lamina propria of the esophagus, primarily in its terminal part.

Gastric pits (foveolae)

Numerous openings in the mucosal surface of the stomach that lead into gastric glands.

Mucus-bicarbonate barrier

A pre-epithelial protection mechanism in the stomach that maintains the cell surface at near neutral $pH$ to protect against autodigestion by pepsin and $HCl$.

Chief cells

Small, purple-appearing cells in the body of gastric glands that produce pepsinogen, a precursor to the proteolytic enzyme pepsin.

Parietal cells

Large, pink, sometimes binucleate cells that secrete hydrochloric acid ($HCl$) and intrinsic factor; they feature an extensive intracellular canalicular system.

Mucous neck cells

Cells that secret mucus and are located between parietal cells in the neck of the gastric gland.

Periodic acid-Schiff (PAS)

A staining method used to detect polysaccharides like glycogen and mucosubstances such as glycoproteins and mucins.

Villus

Small finger-like projection ($0.5-1.6\,mm$ in length) of the intestinal wall that protrudes from the epithelial lining to increase surface area.

Brush border

A collective term for the many microvilli projecting from the apical surface of enterocytes in the small intestine.

Goblet cells

Unicellular glands shaped like wine glasses that secrete gel-forming mucins, such as $MUC5AC$, using merocrine or apocrine methods.

Brunner's glands

Tubular submucosal glands found in the duodenum that produce mucus-rich alkaline secretion containing bicarbonate to protect against acidic chyme.

Peyer's patches

Part of the mucosa-associated lymphoid tissue (MALT) found in the ileum, involving specialized microfold (M) cells for antigen entry.

Myenteric (Auerbach's) plexus

Part of the enteric nervous system located between the inner and outer layers of the muscularis externa.

Submucosal (Meissner's) plexus

Part of the enteric nervous system located specifically within the submucosa.

Taniae coli

Three bands of longitudinal smooth muscles (mesocolic, free, and omental) found in the large intestine.

Haustra

Bulges in the large intestine caused by the contraction of the taniae coli.

Appendix

A structure containing lymphoid tissue (GALT) that serves as a haven for useful bacteria when illness flushes them from the rest of the intestines.

VEGF (Vascular Endothelial Growth Factor)

A signaling pathway targeted in molecular therapy for metastatic colon cancer to inhibit disease progression.