Anus

 

This structure begins from the rectum and extends to the skin.

Arteries:

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Superior rectal artery, which is a branch of the inferior mesenteric artery. It supplies the rectum and anus up to the anal valves. It is the main arterial supply to the rectum and anus and it anastomoses with other branches.

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Inferior rectal artery, which is a branch of the internal pudendal artery. This gives blood supply mainly to the anus distal to anal valves but anastomoses with the superior rectal branches across the valves.

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Middle rectal artery, which is a branch of the internal iliac artery. Its supply is minimal but supplies muscles of the lower part of rectum (e.g. internal anal sphincter and external anal sphincter). Its anastomoses is poor.

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Median sacral artery supplies posterior wall of anorectal junction. It is derived from the point of bifurcation of aorta. It forms appreciable anastomoses with other rectal veins, especially the inferior rectal vein.

Veins:

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Superior rectal vein, which is a tributary of the inferior mesenteric vein. It drains the rectum and anus up to the anal valves. It anastomoses with other branches.

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inferior rectal vein, which is a tributary of the internal pudendal vein. This gives blood supply, mainly to the anus from distal to anal valves but anastomoses with the superior rectal venous tributaries across the valves.

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Middle rectal vein which is a tributary of the internal iliac vein. It drains the muscles of the lower part of rectum (e.g. the internal and external anal sphincters). Its anastomoses is poor.

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Median sacral vein drains posterior wall of anorectal junction. It does not form any appreciable anastomoses.

Nerves:

Autonomic fibers supply the upper 2/3 of anal canal as follows

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Parasympathetic fibers are through the pelvic splanchnic nerves (or nervi erigentes) from S2-4.

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Sympathetic fibers are from the lumbar splanchnic nerves, which relay in the inferior mesenteric ganglion of the inferior mesenteric plexus and are from the inferior hypogastric plexus.

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Nerve of the anal-pit part of the anal canal are somatic and derived from the inferior rectal nerve

Nerve to the muscles are somatic and are as follows-

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Corrugator cutis ani by the perineal branch of S4

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Subcutaneous external sphincter is by inferior rectal nerve

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Superficial external sphincter by perineal branch of S4perineal branch of S4

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Deep external sphincter by the  inferior rectal nerve

 

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The Human Anatomy Laboratory
Creator: Oluwole Ogunranti