hi let's talk about the rectum and anal canal the rectum is a continuation of the sigmoid colon
and the rectosigmoid junction is approximately at the level of s3 so here we can see a ligated uh
sigmoid colon turning into a rectum within the pelvic cavity you can identify the differences
between the rectum and the sigmoid colon by the circulations present on the sigmoid colon as i can
also see teniae coli present there and we know that that outermost layer or that longitudinal layer of
muscle which is condensed into the ribbons of the teniae coli of most of the large intestine
is then decondensed into a robust outer longitudinal layer of muscle in the rectum
so the the rectum will have no circulation so no haustra and no teniae coli we can see the rectum in
a sagittal section here of the pelvis the the rectum here is posterior to the vagina we can see
some transverse folds of the rectum here typically there are three transverse folds and the distal
portion of the rectum tends to be more dilated granted we can't see the the proximal portion
of it here but it it's not as dilated as this and this region we would call the rectal ampulla
and here we can see what would be the rectoanal junction and that's occurring at the level of
the pelvic floor the pelvic diaphragm and it's there that we'll have muscles
in particular the public rectalis muscles that go from the the pubic bones and act as a sling they
meet their counterparts around that rectoanal junction and so the the rectum is a little more
inferior anterior whereas the anal canal has a more posterior orientation to it
with respect to the anal canal there are a lot of interesting things to behold here let's first
continue our earlier discussion of the musculature so coming down here we have an extension of that
longitudinal muscle from the rectum sometimes this is called the conjoint
longitudinal muscle and it's going to separate the anal sphincters so outside or external to that
longitudinal muscle we'll have the external anal sphincter the external anal sphincter
is innervated by the inferior rectal nerves which are branches of the pudendal which are somatic
in origin and we can contrast that with the internal anal sphincter which we can see
right there so that's the internal anal sphincter here we can see that
the counterpart of the internal anal sphincter there and we can see that longitudinal muscle
arising there both the internal anal sphincter and the uh the longitudinal muscle are going to be of
the enteric nervous system and they're going to be extrinsically innervated by
the inferior hypogastric plexus so they will be autonomically innervated we can also see the
the differences in the proximal two-thirds of the anal canal so that's approximately
there so that would be the proximal two-thirds of the canal versus the distal one-third of the canal
the defining line between them is this pectinet or dentate line and we can see
above there are these evaginations of the mucosa which are the anal columns
anal columns tend to be less pronounced in older populations they tend to be
better defined in in younger populations so they they make their way down to that
pectinet line and the spaces between those anal columns are the anal sinuses
so we've discussed the rectum and the anal canal thank you very much for your time