Today, we’re going to
talk about GI motility.
We’re going to cover a
number of important topics
and the first of which is to try
to explain how GI motility works.
And this will include three important
aspects including peristalsis,
slow waves, and migrating
Then, what we’re going to do is talk about
how swallowing is initiated and controlled.
And finally, we will explain
how gastric emptying works
and how this process is
regulated and controlled.
So let’s go back to
our GI functions and
determine which ones we’re
going to cover today.
And that is excretion, storage,
and most importantly, motility.
To discuss motility, we
need to go through a little
bit deeper on the various
layers of the GI tract.
These layers go from the mucosal
layer, which is the most innermost,
to the serosal layer, which
is the most outermost.
So the nerves are going to be
controlling the muscular activity,
the mucosal cell or layer, then that is the
layer of muscle around the mucosal layer.
Then we have a couple of plexus.
The Meissner plexus and
the submucosal plexus.
The submucosa, and this is important,
this circular layer of muscle.
And finally, the Auerbach complex,
and the longitudinal layer.
So you notice there were three different
layers of muscles in the GI tract.
And this will be important in being
able to squeeze the GI tract together
and to be able to push items
along this particular tube.
And of course, the final
layer is the serosa.
Now, how this process works is through an
intricate process known as persitalsis.
Now, peristalsis is a way of
coordinating muscle contraction
and this is smooth
So you’re going to use acetylcholine
at the site to cause a contraction.
We need to relax the area that
is in front of that contraction.
And that is done via nitric oxide
or vasoactive intestinal peptide.
And these are released
right where you need to
relax that particular
portion of the muscle.
Then, what happens is the
food stuff is pushed along
because you have a contraction
and a relaxation.
And of course, everything is going to
follow to the area of lower pressure.
This whole process is controlled either
by the parasympathetic nervous system
or the enteric nervous
system depending on if it
is centrally driven or
if it is a local reflex.
The central driven is the
parasympathetic nervous system
and the local reflex is the
enteric nervous system.
Now, besides peristalsis, the other
important thing are these sphincters.
Sphincters will be areas that
are constricted during rest
and this prevents movement from one
area of the GI system to another.
And what mediates this
constriction are enkephalins.
Often though, vasoactive intestinal
peptide will be the relaxation agent
for those particular sphincters.
So when you want to open them,
you would give the VIP or nitric oxide some
time to be mediated to cause relaxation.
Now, the other motility issues that need
to be discussed besides peristalsis
and contraction of sphincters
are a lot of the movements
are not to just to move
things through the GI tract,
but rather to mix things up.
Because we have all these
secretions in the GI system.
What you need to do is make
sure they’re well mixed
and so the enzymes can work
in the appropriate spots.