anorektalkanalens

The anorektalkanalens, or anorectal canal, refers to the distal portion of the digestive tract that extends from the anorectal junction, where the rectum ends, to the anal opening. It comprises the lower end of the rectum and the anal canal and plays a central role in continence and defecation.

Anatomy and histology

The anorectal canal includes the final rectal segment and the canal leading to the anus. The mucosal lining changes at the pectinate (dentate) line: the region above the line is lined by simple columnar epithelium, while the canal below the line transitions to non-keratinized stratified squamous epithelium. The internal anal sphincter (involuntary smooth muscle) and the external anal sphincter (voluntary skeletal muscle) regulate continence, aided by the surrounding pelvic floor muscles.

Blood supply and innervation

Arterial supply comes from the superior rectal artery (a branch of the inferior mesenteric artery) and, to the lower canal, the middle and inferior rectal arteries (branches of the internal iliac). Venous drainage mirrors the arterial supply, with pathways to both portal and systemic circulations. Innervation includes autonomic fibers from the hypogastric plexus and somatic sensation via the inferior rectal nerves, branches of the pudendal nerve, enabling voluntary control of the external sphincter.

Function and clinical relevance

The anorectal canal stores feces in the rectum and coordinates defecation through sphincter control. Common conditions involve hemorrhoids, anal fissures, and rectal prolapse, as well as malignancies that differ in risk between rectal and anal portions. Evaluation typically includes digital examination and anoscopy, with treatment tailored to the underlying condition.