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Anus - Anatomy & Physiology (view source)

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[[Image:Anal Glands.jpg|thumb|right|150px|Anal Glands- Copywright RVC 2008]]

*At the anus, the columnar intestinal epithelium is replaced by the stratified squamous keratinised epithelium of the skin.

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*The '''anal canal''' joins the bowel to the exterior and is the last 2-3cm of the alimentary tract.

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**This is a short passage derived from the proctodeum (formed by invagination of the surface ectoderm).

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*Sebaceous and apocrine sweat glands both occur in this region in association with the anal sphincters.

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**Before joining the anal canal, the rectum becomes dilated to form the ''rectal ampulla''.

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*At the '''rectoanal''' junction, the lumen is constricted by longitudinal folds in the mucosa.

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**These are normally pressed together to occlude the lumen.

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*As the muscosa changes from columnar to cutaneous, three zones are created:

**'''Columnar'''

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***Surrounds the anus.

***Excretory ducts of the '''anal sacs''' open into this region.

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*Sebaceous and apocrine sweat glands both occur in this region in association with the anal sphincters.

−

*The '''anal canal''' joins the bowel to the exterior.

−

**This is a short passage derived from the proctodeum (formed by invagination of the surface ectoderm).

−

**Before joining the anal canal, the rectum becomes dilated to form the ''rectal ampulla''.

−

*At the '''rectoanal''' junction, the lumen is constricted by longitudinal folds in the mucosa.

−

**These are normally pressed together to occlude the lumen.

==Species Differences==

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