Changes

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

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

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

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

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

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

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

**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.

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

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

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

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

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

**'''Columnar'''

**'''Columnar'''