Large Intestine: Anatomy & Physiology

Anatomy

Layers

  • Mucosa (Columnar Epithelium, Lamina Propria, Muscularis Mucosa)
  • Submucosa
  • Muscularis Propria (Inner Circular, Outer Longitudinal)
  • Serosa

Structure

  • Portions
    • Ascending Colon (Retroperitoneal)
      • Appendix
      • Cecum – Most Common Site of Non-Iatrogenic Perforation
        • Due to Law of LaPlace: ΔP = γ/r
          • Change in Pressure = Surface Tension / Radius
          • *Largest Radius will Have Highest Surface Tension
    • Transverse Colon
    • Descending Colon (Retroperitoneal)
    • Sigmoid Colon
  • Structures
    • Crypts of Lieberkühn (Paneth Cells): Mucin Secreting Goblet Cells of the Small Intestine & Colon
    • Plicae Semiluminares: Transverse Bands/Folds Between Haustra
    • Haustra: Small Pouches Formed by Plicae Semiluminares
    • Taenia Coli: 3 Bands That Run Along the Colon
      • Broaden at Rectosigmoid Junction to Completely Encircle
      • Taenia Libera (Free Taenia Coli)
        • Anterior in Cecum, Ascending, Descending & Sigmoid Colon
        • Inferior in the Transverse Colon
      • Taenia Mesocolica (Mesocolic Taenia Coli)
        • Posteromedial in Cecum, Ascending, Descending & Sigmoid Colon
        • Posterior in Transverse Colon
      • Taenia Omentalis (Omental Taenia Coli)
        • Posterolateral in Cecum, Ascending, Descending & Sigmoid Colon
        • Anterosuperior in Transverse Colon
    • Ileocecal Fold/Veil (Bloodless Fold of Treves) – Peritoneal Fold Between the Ileum & Cecum
    • Mesoappendix – Mesentery of the Appendix

Vascular Supply

  • Arterial Supply
  • Venous Flow
    • IMV into Splenic Vein
    • Splenic Vein & SMV Become the Portal Vein (Behind the Pancreas)
  • Lymphatics
    • Follows Arterial Flow
    • Superior & Inferior Mesenteric Lymph Nodes Drain to the Pre-Aortic Lymph Nodes
    • Pre-Aortic Lymph Nodes Drain to the Cisterna Chyli

Nerves

  • Meissner’s/Submucosal Plexus: Inner Submucosa
  • Auerbach’s/Myenteric Plexus: Outer Muscularis Propria
  • Pelvic Splanchnic Nerves: Parasympathetic Innervation

Colon Anatomy 1

Taenia Coli & Haustra 2

Anatomy of the Cecum & Appendix 3

Physiology

Physiology

  • Colon Secretes K; Reabsorbs NaCl/H2O
    • Active Na/K-ATPase
    • Passive H2O Absorption (Jejunum Absorbs Majority of H2O)
    • Mostly Right Colon
  • Colonocyte Main Nutrient: Short Chain Fatty Acids (SCFA)
    • Produced by Bacterial Fermentation in the Colon
    • Acetate, Butyrate & Propionate
  • Ascending Colon Has the Greatest Absorptive Capacity of Fluid in the Colon

GI Microflora

References

  1. CDC. Wikimedia Commons. (License: CC BY-SA-4.0)
  2. OpenStax College. Wikimedia Commons. (License: CC BY-3.0)
  3. Bakar SM, Shamim M, Alam GM, Sarwar M. Negative correlation between age of subjects and length of the appendix in Bangladeshi males. Arch Med Sci. 2013 Feb 21;9(1):55-67.(License: CC BY-NC-ND-3.0)