Anal Canal
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Introduction[edit | edit source]
Rectum is the end part of the large intestine, starts from rectosigmoid colon and end at anorectal junction, it is 12-14 cm in length and its diameter is 4cm. It contains vertical and lateral flexures (bends) they help to control and prevent urgent need to defecate they support and keep feces in rectum.
The anal canal is an extraperitoneal part, it is the final part of the gastrointestinal, starts from anorectal junction, extends posteroinferiorly as a termination of the rectum with 3- 4cm in length, and ends at the anus. Its main function is to maintain fecal continence and evacuate during defecation. In normal conditions it is always collapsed to prevent leakage and just open during defecation. It is surrounded by internal and external anal sphincter. The rectum along with the anal canal are lined with a columnar epithelium and ends at the pectinate line where it becomes a squamous epithelium.
Anatomical Parts[edit | edit source]
Columnar zone: lined with columnar epithelium, the mucous membrane organized in longitudinal folds (anal columns), these longitudinal folds join at their ends and form the anal valves at their end they form the pectinate line, behind anal valves there are anal glands they are at different depths on the anal canal wall, and they are about 4-8 anal gland.
Intermediate zone: lined with non-keratinized columnar epithelium, below the pectinate line and extends to be 1 cm in length.
Cutaneous zone: lined with keratinized columnar epithelium, at the end of the anal canal (anal verge).
Anal Sphincters[edit | edit source]
Internal anal sphincter,
External anal sphincter,
Innervation[edit | edit source]
Nerve supply[edit | edit source]
Parasympathetic innervation (s2-s4) by inferior hypogastric plexus and pelvic splanchnic nerves for the area above the pectinate line, while pudendal nerve (sensory innervation) to the area below the line.
Sympathetic innervation (t12-l2) by inferior mesenteric plexus to the upper part above the line.
Arterial supply[edit | edit source]
Above the pectinate line supplied with a branch from the inferior mesenteric artery, superior rectal artery. Below the pectinate line branches from the internal iliac artery, inferior and middle rectal arteries.
