KS

Gross Anatomy of Colon (Caecum to Descending Colon) BDS II 2024 (2)

GROSS ANATOMY OF LARGE INTESTINES (COLON)

General Overview

  • Terminal part of the gastrointestinal tract (GIT).

  • Extends from caecum to rectum.

  • Approximately 1.5 meters long.

  • Primary Functions:

    • Absorption of water and electrolytes.

    • Storage of undigested food until defecation is ready.

Major Parts of the Large Intestine

  • Caecum & Appendix

  • Ascending Colon

  • Right Colic (Hepatic) Flexure

  • Transverse Colon

  • Left Colic (Splenic) Flexure

  • Descending Colon

  • Sigmoid Colon

  • Rectum

Anatomical Characteristics

  • Features:

    • Omental appendices: small fat lobules hanging from the surface.

    • Taenia Coli: three flat bands running longitudinally.

      • Converge at the root of the appendix.

      • Shorter than the colon; contribute to sac-like haustrae.

    • Haustra: sac-like pouches between the taeniae coli.

TAENIAE COLI

Function and Variation

  • Remnants of the longitudinal muscle layer.

  • Contraction leads to constrictions, creating haustra.

  • Site of taeniae coli varies:

    • Transverse Colon:

      • Mesocolic Taenia: superior, attached to transverse mesocolon.

      • Omental Taenia: anterior, attached to greater omentum.

      • Free Taenia: inferior, no attachment.

    • Ascending and Descending Colon:

      • Mesocolic Taenia: medial.

      • Omental Taenia: outer (lateral).

      • Free Taenia: anterior.

Internal Surface Structure

  • No villi present; only simple tubular glands in the mucosa.

  • Semi-circular folds known as plica semilunaris observed.

COMPARISON: LARGE INTESTINE VS SMALL INTESTINE

  • Large Intestine Features:

    • Taeniae coli, haustra, omental appendices, semicircular folds/plica semi-lunaris, larger diameter.

  • Small Intestine Features:

    • Lacks taeniae coli, haustra, omental appendices, has circular folds/plica circularis, smaller diameter.

CAECUM

Description and Relations

  • Located in the right iliac fossa; size approximately 6 cm x 8 cm.

  • Upper end transitions to the ascending colon at inter-tubercular plane (L4/L5).

  • Ileum opens into the medial aspect, guarded by the ileocaecal valve to prevent reflux.

  • Appendix opens 2.5 cm below the ileocaecal junction.

Anatomical Relations

  • Anterior: Coils of small intestine, anterior abdominal wall.

  • Posterior:

    • Right gonadal vessels.

    • Lateral cutaneous nerve of the thigh.

    • Genitofemoral nerve, psoas major & iliacus, external iliac artery, femoral nerve, appendix.

Peritoneal Recesses at Ileocaecal Junction

  • Superior ileocaecal recess: Behind fold raised by anterior caecal artery.

  • Inferior ileocaecal recess: Between mesoappendix and inferior ileocaecal fold.

  • Retrocaecal recess: Found behind the caecum.

Blood Supply

  • Arterial Supply:

    • Anterior caecal artery.

    • Posterior caecal artery from ileocolic artery (branch of superior mesenteric artery).

  • Venous Drainage: Corresponds to arterial supply and drains into the superior mesenteric vein.

Nerve Supply

  • Sympathetic Nerves: Via lesser splanchnic nerves (T10-T11) to superior mesenteric plexus.

  • Parasympathetic Nerves: Right and left vagus nerves.

Lymphatic Drainage

  • Accompanies vessels to precaecal nodes, ileocolic nodes, and superior mesenteric nodes.

ASCENDING COLON

Description

  • Measures approximately 13 cm long and is retroperitoneal.

  • Extends from the caecum to the right colic (hepatic) flexure.

Anatomical Relations

  • Anterior: Anterior abdominal wall, liver, greater omentum, coils of small intestine.

  • Posterior: Iliacus, quadratus lumborum, transversus abdominis, lower pole of the right kidney.

Blood Supply

  • Arterial Supply: Ileocolic artery, right colic artery, marginal artery (partially).

  • Venous Drainage: Corresponds to the arterial supply draining into the superior mesenteric vein.

Nerve Supply

  • Sympathetic: Via lesser splanchnic nerves (T10 - T11) to the superior mesenteric ganglion.

  • Parasympathetic: Right & left vagus nerves.

Lymphatic Drainage

  • Accompanies vessels to ileocolic nodes and right colic nodes to superior mesenteric nodes.

TRANSVERSE COLON

Description

  • Extends horizontally across the umbilical region (approximately 45 cm long).

  • Proximal end at the right colic flexure and distal at the left colic flexure.

  • Attached to the greater omentum, mobile and connected to the posterior abdominal wall via transverse mesocolon.

Blood Supply

  • Arterial Supply: Middle colic artery from the superior mesenteric artery (proximal 2/3), left colic artery from inferior mesenteric artery (distal 1/3).

  • Venous Drainage: Corresponds to the arterial supply draining into the superior mesenteric vein.

Nerve Supply

  • Sympathetic: Via lesser splanchnic nerves (T10 - T11) through celiac to mesenteric ganglia.

  • Parasympathetic: Right and left vagus nerves.

Lymphatic Drainage

  • Accompanies vessels to epicolic nodes, paracolic nodes, and middle colic nodes to superior mesenteric nodes.

DESCENDING COLON

Description and Relations

  • Approximately 25 cm long, located in the left upper and lower quadrants.

  • Extends vertically from the left colic flexure to the pelvic brim.

Anatomical Relations

  • Anterior: Coils of small intestines, greater omentum, anterior abdominal wall.

  • Posterior: Lower lateral quadrant of left kidney, transversus abdominis, quadratus lumborum, iliacus, and psoas major.

Blood Supply

  • Arterial Supply: Left colic artery (branch of IMA), sigmoid branches of inferior mesenteric artery.

  • Venous Drainage: Corresponds to the arterial supply draining into the inferior mesenteric vein.

Nerve Supply

  • Sympathetic: Inferior mesenteric plexus via lumbar splanchnic nerves (L1-L2).

  • Parasympathetic: Pelvic splanchnic nerves (S2-S4).

Lymphatic Drainage

  • Accompanies vessels to left colic nodes and inferior mesenteric regional nodes.