Rectum

The rectum is the terminal portion of the large intestine, extending from the pelvic inlet to the anal canal. It is continuous cranially with the descending colon and caudally with the anal canal. It is located within the pelvic cavity, and its anatomical features are as follows:

• Origin: Begins at the pelvic inlet, where the descending colon enters the pelvic cavity and becomes the rectum.

• Termination: Ends at the anocutaneous line, where it becomes the anal canal.

• Course: The rectum follows a dorsocaudal direction, lying dorsal to the reproductive and urinary organs (e.g., prostate in males, vagina and vestibule in females).

• Structure:

  • It is relatively straight but may have a slight dorsal flexure.

  • The mucosa is arranged in longitudinal folds, lacking haustra and taeniae which are present in other parts of the colon.

  • It is surrounded by smooth muscle, with the internal anal sphincter forming as a thickening of the circular muscle layer at the caudal end.

• Peritoneal Relations:

  • The cranial portion is covered by peritoneum, forming a mesorectum.

  • The caudal portion is retroperitoneal, embedded in connective tissue.

• Blood Supply: Primarily from the cranial rectal artery, a continuation of the caudal mesenteric artery, with contributions from the middle and caudal rectal arteries.

• Innervation: Autonomic and somatic fibers via pelvic and pudendal nerves.