Hi everyone! In this video we're going to be talking a little bit about membranes. Now in the past we've talked about membranes such as the cell membrane or the basement membrane and those are examples of either cell structures or structures that are closely related to or made by the cell. In this case we're talking about tissue membranes.
So these are membranes that are basically made of membranes. more than one type of tissue and what we've been doing since we've been studying tissues is started we've started putting together various tissue types to show how they work together and membranes are just kind of another example of that a little bit of this will be a review and recap because we've mentioned some of these before but it's also going to be a little bit of a look ahead because some of these are going to come up over and over again in various body systems the first membrane that we want to talk about is the cutaneous membrane And this membrane is basically made of a stratified epithelium and then a couple of layers of connective tissue. Immediately below the epithelium, we have loose connective tissue.
And then below that in the next subsequent layer, we have dense irregular connective tissue. So the cutaneous membrane is better known by the name of skin. So I think once we call it that, it's pretty familiar. And like the other membranes, what we see is that we have a combination of both the epithelium and the connective tissue. And for most of our examples, that will be kind of the theme for this discussion.
So the cutaneous membrane actually gets its own discussion in a later video. But right now, we're just sort of introducing it, especially so that we can use it as an example in tissue injury and repair. The cutaneous membrane is a waterproof covering, so basically, you know, water beads up on our skin when we go outside in the rain, and it doesn't really soak in, and so we have separation from the outside environment. It's also avascular epithelium, which is consistent with epithelium in general, and then we have a bunch of cell types that are present in the connective tissue, such as fibroblasts, white blood cells, etc. So these are some things that...
probably are pretty straightforward, but we're going to bring them up again in the next video, and then also later on we talk about skin separately. The next type of membrane that we want to talk about is the mucous membrane, and the mucous membrane has a couple of key characteristics. So first off, of course, we have an epithelium, and in this particular drawing, I'm drawing the respiratory mucosa.
which is an example of a mucous membrane that we find in the respiratory tract, but this is also sort of meant to serve as a generic example so that we can study mucous membranes in general. So we have in this particular case a single layer of epithelium, this one is pseudostratified, and we see that we have cilia on the surface. And we also have the presence of mucous glands. Now in the respiratory system we call them goblet cells, but In general, a mucus gland is just something that's going to secrete mucus onto the epithelial surface. You'll notice that there's a difference in spelling.
This is kind of a minor distinction, but just for the point of understanding. Mucus, spelled O-U-S, is actually meant to be used as an adjective. And mucus, when described as a noun, so the actual stuff that's being secreted, it's just U-S. So that's why there's two different spellings.
And then, of course, below our basement membrane, our basal lamina, We're going to have connective tissue just like we expect in tissue membranes. And the name of the connective tissue that we find in a mucous membrane is labeled the lamina propria. So we'll see that, I think, first in the respiratory system, but also in the other examples that we will see mucous membranes will identify the name of the connective tissue as lamina propria as well. So mucous membranes function to line passageways and chambers within the body. And basically we're talking about the linings of the digestive tract, the respiratory tract, the urinary tract, and the reproductive tract.
So those are the places where we have mucus membrane and I think the big thing to keep in mind about this is that that's where we're going to have mucus covering the surface of the epithelium in all of those cases and that's one of the key distinguishing features. The purpose of having the mucus is to keep the surface moist and also to reduce friction and facilitate absorption of various particles. In the case of the respiratory system, maybe catching pathogens, but in the digestive tract, maybe protecting the mucus. against some of the acidic environment of the stomach and various things like that.
So there's a lot of variety in the application of the mucus availability on the surface. The next type of membrane that we want to mention is the serous membrane. And this we talked about right in the beginning.
When we talked about body cavities, we described the serous membrane. And we said that we'll have a visceral layer that is basically attached to the outer surface of the organ. and then a parietal layer, which is basically the lining of the inside of the cavity.
And now that we have an understanding of cell types and tissue types, we can actually give a little bit more detail about these membranes. So we have each layer of the serous membrane is made of simple squamous epithelial cells. So it's just a single layer of epithelial cells. And in this case, we refer to these cells as the mesothelium or mesothelial cells.
And it's the only example of mesothelial cells. We did say that in the blood vessels, the inner lining is endothelial cells, right? And that's another example of epithelial cells.
So this is just a specialized term for these specific cells that are found where we have serous membranes. And that's the only place that we're going to find them. And then, of course, we have between the serous membranes, we have the serous fluid. And the serous fluid is actually, there are some blood vessels that are in the connective tissue that's deep.
to the epithelium, to the mesothelium. And most of the source of the fluid for the serous, for the space where the serous fluid is, is actually from those blood vessels, just fluid that leaks out. And it's a little bit regulated by the mesothelial cells.
And basically the purpose of that fluid is to make the lining slide past each other and make it slippery. So in order to really qualify as a membrane, In this discussion, we also said that we're going to have some connective tissue, so deep, so on either side of the mesothelium, we have loose connective tissue. And the composite of the simple squamous epithelial cells and the loose connective tissue is what gives each side of the membrane.
We find serous membranes in the linings of the pleural, pericardial, and peritoneal cavities. And remember that pleural refers to the lungs, so the cavity that contains the lungs, one on either side. The pericardial refers to the cavity containing the heart, and peritoneal refers to where all of the GI organs are, with the exception of the duodenum and the pancreas. So we know that the visceral lining is what covers the organ.
and the parietal lining is what lines the inside of the cavity. And of course, we'll look at these in a little bit more of a detailed manner when we cover each one of those individual organs or structures. And as we mentioned, fluid secreted by the epithelium reduces friction as the organs expanding and contract.
So if we're talking about distension from a large meal, or if we're talking about just the heart beating, the expansion and contraction of the organ causes movement, the linings slide past each other, and we don't have any friction or discomfort associated with it. And the last type of membrane that we want to mention but not really cover is the synovial membrane. So we find synovial membranes lining synovial joints, so basically where bones come together. We want to have a movable surface that doesn't create any discomfort, so we have a little bit of fluid in a membrane.
But the reason that this one doesn't really fit in is because it's not actually epithelium plus connective tissue. It's actually just cartilage. And we're going to push this one off until we cover the skeletal system, and we'll be able to look at it in more detail at that time.
So that basically covers the membrane aspect of our explanation of tissues. And as I mentioned, we just really wanted to take a look at... how the tissues come together to make these types of membranes that we'll see over and over again in the different types of body systems and organs that we'll be studying. So I hope you enjoyed it. Thanks for watching.