Introduction – Gastrointestinal Motility

00:02 Hello! Today, we’re going to talk about GI motility.

00:06 We’re going to cover a number of important topics and the first of which is to try to explain how GI motility works.

00:12 And this will include three important aspects including peristalsis, slow waves, and migrating motor complexes.

00:21 Then, what we’re going to do is talk about how swallowing is initiated and controlled.

00:26 And finally, we will explain how gastric emptying works and how this process is regulated and controlled.

00:33 So let’s go back to our GI functions and determine which ones we’re going to cover today.

00:39 And that is excretion, storage, and most importantly, motility.

00:46 To discuss motility, we need to go through a little bit deeper on the various layers of the GI tract.

00:53 These layers go from the mucosal layer, which is the most innermost, to the serosal layer, which is the most outermost.

01:01 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.

01:13 Then we have a couple of plexus.

01:15 The Meissner plexus and the submucosal plexus.

01:21 The submucosa, and this is important, this circular layer of muscle.

01:26 And finally, the Auerbach complex, and the longitudinal layer.

01:32 So you notice there were three different layers of muscles in the GI tract.

01:36 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.

01:47 And of course, the final layer is the serosa.

01:52 Now, how this process works is through an intricate process known as persitalsis.

01:57 Now, peristalsis is a way of coordinating muscle contraction and this is smooth muscle contraction.

02:05 So you’re going to use acetylcholine at the site to cause a contraction.

02:11 We need to relax the area that is in front of that contraction.

02:15 And that is done via nitric oxide or vasoactive intestinal peptide.

02:21 And these are released right where you need to relax that particular portion of the muscle.

02:29 Then, what happens is the food stuff is pushed along because you have a contraction and a relaxation.

02:36 And of course, everything is going to follow to the area of lower pressure.

02:40 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.

02:51 The central driven is the parasympathetic nervous system and the local reflex is the enteric nervous system.

02:59 Now, besides peristalsis, the other important thing are these sphincters.

03:04 Sphincters will be areas that are constricted during rest and this prevents movement from one area of the GI system to another.

03:13 And what mediates this constriction are enkephalins.

03:17 Often though, vasoactive intestinal peptide will be the relaxation agent for those particular sphincters.

03:25 So when you want to open them, you would give the VIP or nitric oxide some time to be mediated to cause relaxation.

03:35 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.

03:50 Because we have all these secretions in the GI system.

03:53 What you need to do is make sure they’re well mixed and so the enzymes can work in the appropriate spots.