Rectum - Anatomy & Physiology

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Introduction

Structure

  • Exists dorsal to the reproductive organs, bladder and urethra.
  • The cranial portion of the rectum is attached to the dorsal body wall by a short mesorectum which is a continuation of the mesocolon.
  • The mesorectum is reflected to continue with the parietal peritoneum of the pelvic cavity and to cover the urogenital organs ventrally.
    • This forms the rectogenital pouch.
    • Therefore the most distal part of the rectum is retroperitoneal.
      • This distal, retroperitoneal part is directly attached to the vagina in the female and to the urethra in the male.
      • The retroperitoneal space is filled with soft tissue rich in fat.
  • The anal canal joins the bowel to the exterior.
    • This is a short passage derived from the proctodeum (formed by invagination of the surface ectoderm).
    • Before joining the anal canal, the rectum becomes dilated to form the rectal ampulla.
  • At the rectoanal junction, the lumen is constricted by longitudinal folds in the mucosa.
    • These are normally pressed together to occlude the lumen.
  • There are two anal sphincters:
    • Internal anal sphincter, formed by thickening of the circular smooth muscle of the gut and under autonomic control.
    • External anal sphincter, formed from striated skeletal muscle and under voluntary control.

Function

Vasculature

Innervation

Lymphatics

Histology

  • Epithelium is columnar.

Species Differences

Links