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General Histology & Immune Defenses of the GI Tract - Coggle Diagram
General Histology & Immune Defenses of the GI Tract
The 5 Concentric Layers Of The Digestive Tube
Submucosa
Composition
Denser connective tissue harboring major neurovascular networks
Key Components
Submucosal (Meissner's) Plexus: Controls local mucosal secretions and blood flow
Submucosal Glands: Present ONLY in two specific organs: the Esophagus and the Duodenum (Brunner's glands)
Lymphoid elements (abundant in the colon)
Muscularis Externa
Myenteric (Auerbach's) Plexus
Located between the inner circular and outer longitudinal muscle layers (regulates GI motility)
Special Stomach Exception (3 Layers)
Inner Oblique layer
Middle Circular layer
Outer Longitudinal layer
Standard Pattern (2 Layers)
Inner Circular layer
Outer Longitudinal layer
Muscularis Mucosae
Composition
Thin smooth muscle layer arranged into two sub-layers:
Inner Circular layer
Outer Longitudinal layer
Exceptions
Absent at the extreme ends of the tube—specifically the upper 1/3 of the esophagus and the anal canal
External Tunic (Adventitia vs. Serosa)
Adventitia
Loose connective tissue anchoring the organ to adjacent structures; found at the extremities of the tube (esophagus, lower rectum/anal canal)
Serosa
Connective tissue covered externally by a simple squamous mesothelium (visceral peritoneum); lines all intra-peritoneal organs between the two extremities
Mucosa
Surface Epithelium
Simple Columnar (Prismatic)
Throughout most of the GI tract (stomach, small intestine, colon, rectum)
Stratified Squamous
Located at extremities (oral cavity, esophagus, and lower anal canal)
Lamina Propria (Chorion)
Loose connective tissue containing blood vessels, exocrine glands, and a base layer of mucosa-associated lymphoid tissue (MALT)
Immunological Defenses Of The GI Tract
Diffuse Lymphoid Tissue (Primary & Secondary Follicles)
Lymphocytes scattered as isolated cells or aggregated into primary/secondary lymphoid follicles within the lamina propria and submucosa (especially dense in the colon)
Three Well-Defined Lymphoid Formations
Peyer's Patches
Aggregated lymphoid follicles located in the terminal ileum
Appendix
Dense circumferential lymphoid follicles in the wall of the vermiform appendix
Tonsils
Pharyngeal lymphoid tissue at the upper extremity