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| − | {{toplink
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| − | |backcolour =BCED91
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| − | |linkpage =Alimentary - Anatomy & Physiology
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| − | |linktext =Alimentary System
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| − | |maplink =
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| − | |sublink1=Large Intestine - Anatomy & Physiology
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| − | |subtext1=LARGE INTESTINE
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| − | }}
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| − | <br>
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| | ==Introduction== | | ==Introduction== |
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| | *The anal canal lubricates the passage of faeces. | | *The anal canal lubricates the passage of faeces. |
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| − | ==Histology== | + | ==[[Anus - Histology|Histology]]== |
| − | [[Image:Anal Glands.jpg|thumb|right|150px|Anal Glands- © 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 large 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:
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| − | **'''Columnar'''
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| − | ***Has many longitudinal folds.
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| − | ***Divided from the rectum by the ''anorectal line''.
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| − | ****This is a line where the mucosa is stratified squamous epithelium containing lots of lymphoid tissue.
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| − | **'''Intermediate'''
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| − | ***Divided from the cutaneous zone by the ''anocutaneous line''.
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| − | **'''Cutaneous'''
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| − | ***Skin.
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| − | ***Stratified squamous keratinised epithelium.
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| − | ***Surrounds the anus.
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| − | ***Excretory ducts of the '''anal sacs''' open into this region.
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| | ==Species Differences== | | ==Species Differences== |
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| − | [[Category:Alimentary System - Anatomy & Physiology]] | + | [[Category:Large Intestine - Anatomy & Physiology]] |