Hi everyone, Dr. Mike here. In this video we're going to focus on one of the four tissue types of the body that we call epithelia. Now remember epithelia, its function is there to form boundaries between environments. Now sometimes we want to be able to pass through these boundaries, sometimes we only...
want certain things to pass through these boundaries. Sometimes we don't want anything to pass through at all. Now, other times, these boundaries may facilitate movement across the surface of the boundary. So epithelia, while it does form a boundary between environment It can do this a number of different ways.
So let's have a look at these different ways. First thing is when we look at epithelial tissue, form equals function. That means you can look at the type of epithelia and it tells you what it does.
If it is a single layer or if it is of a particular epithelial cell type in combination, tells you what it can do. Okay, for example, if we look at the most basic type of epithelia, which we call simple squamous. Simple means one layer squamous.
means squished. So here you can see we have simple squamous epithelia located in our lungs. Now I want you to think about it. Form equals function.
It's squished and only one layer because it wants things to move through. Now if it's in the lungs what do you think is going to move through? Gases. So for example simple squamous epithelia located in the lungs is there for gas exchange. Now we can also look at stratified squamous.
This is the squished cells of the epithelia packed on top of each other. Now if it's like that, it's there because one, it's squished, which means it doesn't have many intracellular components. No organelles, no mitochondria, rough or smooth endoplasmic reticulum, Golgi apparatus, anything like that, which is telling you that these cells may likely be dead.
So they're there for protection. It doesn't matter if they're going to be abraised or swiped off due to damage, okay? The term we call is sloughing if those cells disappear over time.
So it's there for protection, okay? So multiple squished cells, which we call stratified, many layers, squamous. We've got stratified squamous cells in the oral cavity, and we've got stratified squamous cells of our skin.
The difference here is that one of them has another layer of stratified epithelia that's keratinized. That means it has a protein inside that's waterproof. Now that's gonna be that of our skin because we want our skin to be waterproof. So both the...
The epithelia with our oral cavity and our skin are stratified squamous, it's just one of them is keratinized. All right, let's move on and look at the tricky one that's sitting in our trachea. So our trachea is our windpipe.
We're bringing air in down our windpipe and we wanna bring air back out. So mainly oxygen in, mainly carbon dioxide out. But we know that the air that we're breathing in isn't pure oxygen or even just pure gas, it's filled with particulates and poly. pollutants and things that we don't want to get down into our lungs.
So what we have is columnar epithelia within our trachea. Now this columnar epithelia looks like it's many layers, but in actual fact, it's one. So we call this pseudostratified.
Pseudo means fake. It looks like it's one thing, but it's not stratified. Pseudostratified epithelia. In actual fact, it's pseudostratified columnar epithelia because they're shaped like columns.
They're long, than they are wider and you can also see that they have these little hairs on the top that we call cilia. So the epithelia we find in our trachea we call pseudostratified columnar ciliated epithelia. Now why do we have this type of epithelia in our trachea?
Well like I was saying before what you'll find is we breathe in a whole bunch of pollutants or particulates and crap that we just don't want to bring into our lungs. So when you've got columnar epithelia that often tells you that there's a lot of intracellular components like rough and smooth endoplasmic reticulum and Golgi apparatus. So they're doing things, they're making stuff.
And so in the columnar epithelia, you should think that they're starting to make something to be secreted. And often it's going to be mucus. So we've got mucus being produced by these pseudostratified columnar epithelia that's going to exude to the surface. And the cilia...
these little hairs they capture and move things across so we've got pseudostratified columnar ciliated epithelia in our trachea because the mucus captures pollutants the cilia takes it and what it does is it throws it up up up up up the trachea so we can cough it out if you're a smoker it actually kills off the cilia which means the mucus may capture the pollutants and particulates but it falls down into their lungs and then what does a smoker I could do everything. Every single morning they will cough and cough and cough to bring up that gunk. Alright, let's move on down to the small intestines.
Now the small intestines have columnar epithelia as well. So straight away you should think if it's columnar it's going to be producing stuff. And it does, it produces mucus and many other different types of... enzymes for example and it also has these little things on top that look like the cilia but in actual fact they look like fingertip like projections this is called villi and micro villi okay fingertip like projections and what they do is they they increase the surface area of the epithelia so that more things can be absorbed.
So the columnar epithelia with microvilli and villi on top is there to produce mucus and secrete it and other enzymes as well and also to absorb the nutrients in the small intestines. All right, let's look at two others. That of the kidneys, the kidneys, specifically the nephron. Now the nephron is going to be these convoluted tubules within the in the kidneys that can selectively absorb or reabsorb, okay, absorb or reabsorb components from what's been filtered in the kidneys and can throw it back into the blood.
It can decide, do I want to pee this out or do I want to throw it back into the blood? And so what we have are cuboidal or simple cuboidal epithelia. So it's one layer, so we want things to be able to go through. It's cuboidal because it wants things to come in and may process it a little bit and throw it back. out or vice versa.
So the nephron of the kidneys contains simple cuboidal epithelia. Now the last one I want to talk about is that of the bladder. Now the bladder needs to distend and snap back into place. Distend, snap back into place.
So it has what we call transitional epithelia. That means it may be cuboidal, it may be columnar, it may be squamous. So that when it stretches, the tissue doesn't get damaged. If there's many different types, it means it can change its shape quite easily.
Stretch it, snap it back into place. So this is a quick run through of the epithelial tissue.