ANAL CANAL
The
anal canal is an ectodermal tube 4 cm in
length continuous
with the rectam.
The distal end is marked by the anal
verge, beyond which lies the
perianal skin.
Proximally, the anal
canal starts at
the
anorectal mucoutaneous junction and shows the pectinate
line or
dentate margin at the junction with the rectum and is
formed at
the
end of five to eight longitudinal folds, the
columns of
Morgagni (Fig. 19.5).
Defecation
This act of evacuation occurs in the rectum and anal
canal.
The rectum and anal canal are empty because of a
week sphincter at the rectosigmoid junction there is also a sharp angle at this
point preventing entry of colonic contents.
The leak form anus is prevented by the
internal anal sphincter a several centimeter
thickening of circular muscle of that anal canal
external and sphincter voluntary muscle around the
anus controlled by the pududat nerve.
Mass movement forces feces into the rectum cause a
sensation of the need to empty the rectum the reflex can be initiated by
sitting or squatting in a convenience holding you breath contraction of
diaphragms and abdominal muscles.
EXAMINATION
Complete examination includes:
*
Visual inspection through
a proctoscope and
a digitial
palpation of the anal canal and rectum
*
Visualisation of the anal canal and distal rectum can also be
obtained by sigmoidoscopy, and should be an integral part of a
routine complete physical examination in all patients
over
forty.
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