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The perianal, anal and rectal regions lend themselves to early clinical diagnosis without the need to resort to complex investigations.

The anus, anal canal and rectum are a functional unit responsible for the maintenance of continence of feces and flatus plus coordination of defecation*. The basic factors responsible for continence are the internal* sphincter, external* sphincter and the anorectal angle*. There is control by neuromuscular integration.

The presence of a functional sphincter* also helps.

The anorectal region is a junctional* (transitional) zone. The main site of structural and functional transition is the dentate* (pectinate) line. Epithelium, muscle, nerves, vessels and viscera all change at this line. This has many clinical implications such as pain and carcinoma spread.

Proper assessment* and treatment of anorectal conditions requires detailed knowledge of the anatomy of the region.

Human nature* is often a factor here also.

The anal columns (from dentate line to rectum) have a series of (valveless) submucous veins forming a plexus (the internal rectal) that drains into the superior rectal vein. The veins lack support and are subject to pressure effects (hard feces, straining, pregnancy), leading to the formation of internal* hemorrhoids. They can be classified as first, second or third degree*.

The cutaneous part of the anal canal is drained by tributaries of the inferior rectal vein (external anal plexus). These may dilate as external* hemorrhoids. The combination of both types of hemorrhoids is called intero-external*.

Differential diagnosis includes tumors, polyps, skin ...

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