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The Large Intestine (1.5 m Length / 8 cm Caecum → 4 cm Rectum) - Coggle…
The Large Intestine (1.5 m Length / 8 cm Caecum → 4 cm Rectum)
The Five Concentric Wall Tunics & Enteric Innervation (Flat Surface, Taeniae Coli & Plexuses)
Submucosa (Vascular; Meissner)
Highly vascularized connective tissue containing closed lymphoid follicles and Meissner's Submucosal Plexus (regulates secretions and mucosal blood flow)
Muscularis Externa (Taeniae Coli; Auerbach)
Outer Longitudinal Layer
Condensed into three thick, prominent bands visible in cross-section—the Taeniae Coli
Auerbach's Myenteric Plexus
Situated between muscle layers to regulate intestinal motility and propulsive waves
Inner Circular Layer
Continuous smooth muscle
Muscularis Mucosae (Interrupted)
Inner circular and outer longitudinal smooth muscle layers; frequently pierced/interrupted by lymphoid follicles
Serosa / Adventitia (Adipose Lobules)
Visceral peritoneum rich in subserosal adipose lobules and vessels
Replaced by an adventitia along retroperitoneal segments (ascending and descending colon)
Mucosa (NO Villi; Flat Surface)
Epithelium
Simple columnar epithelium forming a flat surface with NO villi
Cellularity
Surface enterocytes with a striated brush border and abundant goblet cells
Lamina Propria (Chorion)
Loose connective tissue heavily infiltrated with lymphocytes and closed lymphoid follicles
Crypts Of LIEBERKÜHN & Epithelial Renewal Dynamics (LGR5+ Stem Cells & Cell Lineages)
Colonic Crypt Cellularity & Stem Cell Dynamics
LGR5+ Stem Cells (Base of Crypts)
Transit-Amplifying Progenitors (Mitoses in Lower 1/3)
Goblet Cells (Mucus Secretion)
Predominant cell type in the crypts; produce massive quantities of protective mucus
Enterocytes (Absorptive Brush Border)
Absorptive cells equipped with a microvillar brush border
Enteroendocrine Cells (Motility Hormones)
Hormone-producing cells modulating gut motility and secretions
Located at the extreme base of the crypts; drive continuous epithelial regeneration
Morphology : Straight, deep, narrow-lumened tubular glands extending through the full depth of the mucos
Principal Physiological Roles & Gut Microbiota (Water/Electrolyte Axis & Microbiota)
Water Reclamation
Reabsorbs approximately 1 liter of water per day from ileal liquid chyme, concentrating contents into solid feces
Electrolyte Transport
Active absorption of Na⁺, Cl⁻, and K⁺, alongside active secretion of K⁺ into the lumen
Fecal Storage & Propulsive Evacuation
Temporary reservoir function in the sigmoid colon before mass peristaltic propulsion into the rectum
Symbiotic gut microbiota (~5 × 10¹³ anaerobic microorganisms) :
Vitamin Synthesis
Synthesizes Vitamin K and key B-complex vitamins
Immune Protection
Competitive pathogen exclusion and modulation of mucosal immune responses
Fermentation
Breaks down non-digestible dietary fibers (e.g., cellulose)