I want to talk about anal sphincters for a
moment and how we can control those sphincters
and also puborectalis. What we have is
a picture of hemisection through
the rectum on this side
and on the other side we have a
transverse section through the pelvis.
What we can see is that here we
have anterior and here we have posterior
in this transverse section. We have
anterior and we have posterior here.
Anterior in the male we have got the
prostrate and then we have the rectum here.
We can see the circular and longitudinal
muscle layers of the rectum here.
What we can also see is that
coming around, if you look at this
transverse image, coming
around from anteriorly
we have this sling like arrangement.
And this sling like arrangement
coming from the pubic bones
on both the left and the
right side is puborectalis
of levator ani. Puborectalis,
it comes from the pubic bone
and it sweeps around the rectum.
It's coming in this direction
in this direction here and
then it's going to sweep around
sweep around the rectum and then
it going to go and attach to the other
pubic bone. So it create
this sling. Now that
is contracted and that
creates this angle.
Creates this angle
called the anorectal
angle which is maintained by puborectalis
and this once again helps
to control defecation.
Relaxation of this muscle
will straighten that angle
and ease defecation. We
also have a number of other
muscles that are involved in
maintaining fecal continent.
And we have external and
internal anal sphincters
and we can see these here. If we
look at the internal anal sphincter
The internal anal sphincter is
going to be a thickening of the
circular and longitudinal
muscles which we have
running around the rectum. So we have
a thickening of these smooth muscles
so we can see these running around
in here. We have a thickening of these
muscles and they form the internal
anal sphincter. These are going to to be controlled
by the autonomic nervous system which
means we are not consciously aware of them.
That is being controlled
unconsciously we are not in
conscious control. We then
have an external anal sphincter
and we are in control
of this sphincter.
The external anal sphincter muscle is a striated
muscle and it's divided into various parts. We have
deep parts. We have superficial
parts and we have subcutaneous parts.
We can also see we have
puborectalis here as well
helping to maintain
Its a ring that goes around
the rectum we can see it
sorry, its a ring that goes around
the rectum we can see around
here. And that surrounds
the opening of the anus
and we can see that
going all the way around.
External anal sphincter, deep part,
superficial and subcutaneous parts.
Importantly this is controlled
by the somatic nervous system.
And when we have the urge to
defecate we can control this
and we can keep this sphincter
shut until an appropriate point.
I have mentioned puborectalis we can
draw that again, a sling like muscle
originating from the pubis. It's formed
as levator ani, the pelvic floor
and it blends with the external
anal sphincter. It passes posterior
to the anorectal junction
creating that anorectal angle.
And this is important in
maintaining the fecal continent.