the four layers of the esophagus are the mucosa submucosa muscularis externa and the adventitia all the way on the outside the mucosa has three sub layers the innermost layers the epithelial layer which is stratified squamous underneath that is the lamina propria which is made of a loose connective tissue and the lamina propria is lying over top the muscularis mucosa which is made of smooth muscle the submucosa is only one layer and it is made of a dense irregular connective tissue there are esophageal glands in the submucosa but we can't see any here all these openings that we're seeing are actually just blood vessels which you can tell more clearly when we're looking closer which we will do in a second the muscularis externa has two layers there's the inner circular layer and the longitudinal layer so the longitudinal layer is running up and down the esophagus so it's going like in the same direction that the food would be going so that's why when you cut it um it looks like bundles it's like you're cutting across a bunch of ropes and the outermost layer the adventitia that's just the anchoring layer that is connecting the esophagus to surrounding structures one more note about the muscularis externa depending on where you are in the esophagus is going to determine what muscle fibers you're seeing if you're just looking at the superior portion you're gonna see a skeletal muscle the middle is gonna be a mix and the most inferior portion will be entirely smooth muscle so that is how i know that i'm looking at an inferior section because this is smooth muscle and once you see what the skeletal muscle looks like in cross section you'll understand how easy it is to tell them apart but before we get to that um these are the top layers a little more closely from this view we can clearly see the little pancake cells stacked on top of each other in the mucosa that's how we know it's stratified squamous underneath will always be the lamina propria and muscularis mucosa so remember the muscularis mucosa is always going to be smooth muscle unlike the muscularis externa there's no transitioning in the types of muscle fibers that you're seeing in the muscularis mucosa now the submucosa now working a little closer we can see that these openings are all just blood vessels because we're not seeing cuboidal tissue there's no little square cells there so we can just assume [Music] that it's lined with simple squamous which would make it a blood vessel and then all the way at the bottom is the muscularis externa so if we're touching the submucosa what layer of the muscularis external must it be it must be the circular layer of the muscularis externa so when you're looking at this it's the same layers that we've been looking at now it's just a slide that has a lighter pigmentation so looking towards the top we see one two three layers which are the stratified squamous lamina propria muscularis mucosa the fourth layer down will be the submucosa laying over top these two layers of the muscularis externa and on this slide we can see much more adventitia than we could on the first one but what i really like about the slide is in the longitudinal layer of the muscularis externa you can clearly see there are two different types of muscle fibers and when you look a little bit closer you can see that these ones are arranged in little bundles those are fascicles and we're only going to see the fascicles in skeletal muscle so this is what the skeletal muscle would look like whereas the smooth muscle is just going to kind of look like an indistinct muscular blob