The Rectum: Anatomical Overview and Neurovascular Supply

Overview

• The rectum is the most distal segment of the large intestine.
• Functions as a temporary store for feces.
• Continuous with the sigmoid colon proximally and terminates into the anal canal.

Anatomical Structure

• Begins at the level of S3 as a continuation of the sigmoid colon.
• Lacks taenia coli, haustra, and omental appendices distinct from the colon.
• Flexures:
  • Sacral flexure: Anteroposterior curve, concavity anteriorly.
  • Anorectal flexure: Anteroposterior curve, convexity anteriorly, formed by the puborectalis muscle aiding fecal continence.
• Lateral flexures: Superior, intermediate, and inferior, formed by transverse folds of the internal wall.
• Ampulla: Final segment, relaxes to store feces, continuous with the anal canal.

Peritoneal Coverings

• Superior third: Anterior surface and lateral sides are covered by peritoneum.
• Middle third: Only anterior peritoneal covering.
• Lower third: No peritoneal coverings.
• Males: Forms the rectovesical pouch.
• Females: Forms the rectouterine pouch (pouch of Douglas).

Anatomical Relations

• Located in the pelvic cavity, most posterior pelvic viscera.
• Anterior relations:
  • Males: Bladder, prostate, seminal vesicles.
  • Females: Vagina, cervix.
• Posterior relations: Sacrum, coccyx, piriformis, coccygeus, levator ani, sacral plexus.

Neurovascular Supply

• Arterial Supply:
  • Superior rectal artery: Continuation of the inferior mesenteric artery.
  • Middle rectal artery: Branch of the internal iliac artery.
  • Inferior rectal artery: Branch of the internal pudendal artery.
• Venous Drainage:
  • Superior rectal vein to portal venous system.
  • Middle and inferior rectal veins to the systemic venous system.
  • Site of portocaval anastomosis in the anal canal wall.
• Innervation:
  • Sympathetic: Lumbar splanchnic nerves, superior and inferior hypogastric plexuses.
  • Parasympathetic: S2-4 via pelvic splanchnic nerves, inferior hypogastric plexuses.
  • Sensory: Visceral afferent fibers follow parasympathetic supply.

Lymphatic Drainage

• Primary drainage via pararectal lymph nodes to inferior mesenteric nodes.
• Lower rectum lymph drains into internal iliac lymph nodes.

Clinical Relevance: Digital Rectal Examination

• Allows palpation of anterior rectal wall structures.
• Males: Prostate and seminal vesicles can be palpated.
• Females: Cervix can be palpated.
• Bony structures like sacrum and coccyx may also be palpated.