Yuniarti

The anal canal is the terminal part of the large intestine and of the entire digestive canal. It extends from the superior aspect of the pelvic diaphragm to the anus The canal (2.5-3.5 cm long) begins where the rectal ampulla narrows at the level of the U-shaped sling formed by the puborectalis muscle

The anal canal, surrounded by internal and external anal sphinctersThe internal anal sphincter is an involuntary sphincter surrounding the superior two thirds of the anal canalThe external anal sphincter is a large voluntary sphincter that forms a broad band on each side of the inferior two thirds of the anal canal Internally, the superior half of the mucous membrane of the anal canal is characterized by a series of longitudinal ridges called anal columns. These columns contain the terminal branches of the superior rectal artery and vein. The inferior ends of the anal columns are joined by anal valves. Superior to the valves are small recesses called anal sinuses. The inferior comb-shaped limit of the anal valves forms an irregular line, the pectinate line, that indicates the junction of the superior part of the anal canal

The anal canal superior to the pectinate line differs from the part inferior to the pectinate line in its arterial supply, innervation, and venous and lymphatic drainage The superior rectal artery supplies the anal canal superior to the pectinate.

The middle rectal arteries assist with the blood supply to the anal canal by forming anastomoses with the superior and inferior rectal arteries.The two inferior rectal arteries supply the anal canal inferior to the pectinate line as well as the surrounding muscles and perianal.

The internal rectal venous plexus drains in both directions from the level of the pectinate lineSuperior to the pectinate line, the internal rectal plexus drains chiefly into the superior rectal veinInferior to the pectinate line, the internal rectal plexus drains into the inferior rectal veins (tributaries of the caval venous system) around the margin of the external anal sphincter.The middle rectal veins (tributaries of the internal iliac veins) mainly drain the muscularis externa of the ampulla and form anastomoses with the superior and inferior rectal veins.

Superior to the pectinate line, the lymphatic vessels drain deeply into the internal iliac lymph nodes and through them into the common iliac and lumbar lymph nodes Inferior to the pectinate line, the lymphatic vessels drain superficially into the superficial inguinal lymph nodes,

superior to the pectinate line is visceral innervation from the inferior hypogastric plexus, involving sympathetic, parasympathetic, and visceral afferent fibers inferior to the pectinate line is somatic innervation derived from the inferior anal (rectal) nerves, branches of the pudendal nerve..

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