Although we animals are such a bunch of complicated creatures, we are basically made up of just four types of tissue. Epithelial tissue, muscular tissue, connective tissue and nervous tissue. Now, first up is epithelial tissue you can think of them as the thin packing or covering material of pretty much everything in our body so if you look at yourself in the mirror most of what you see is epithelial tissue so what are they they are the covering and and protecting tissues of our body. Epithelium covers most organs and cavities within the body. It also forms a barrier to keep different body systems separate so that they can go about their own function without interfering in other organ system functions.
The skin, the lining of the mouth, the lining of the blood vessels, the lung alveoli, kidney tubules, all of these are made of epithelial tissue. They are again classified based on how many of them are there together, that is how many layers are there and how many layers are there. how they look.
Now, based on how they look, they can be just three of them. Very, very simple. Very, very easy.
They can be like a line. They can be like a cube or they can be like a cylinder. That's it.
Only the one which looks like a line has a funny name, a weird name, actually more than funny. Squamous. Squamous.
You must be wondering what on earth were they thinking? I was also thinking the same thing. But you know, I realized that Squamous has come from a Latin version. Squama which means the scale of a fish or a serpent and true to the name they look like scales just that they aren't that hard in fact they aren't hard at all they are very very very soft the other two have very obvious names cuboidal and columnar now if you just put a single layer It's called simple and if you put many layers, no it's not called complicated, hold on, it's called stratified.
So simple and stratified. Let's do some permutations and combinations and then you have met every kind of epithelial cells there is to meet. Okay quiz time, what's the first one? I'm sure you'll get this, it's simple squamous.
Simply because there is one layer of squamous epithelial cells. And this one, simple columnar. Single layer columnar cells and this one simple cuboidal. You see where I'm getting? I'm sure you are.
Okay, what about this one? There's more than one layer. So it's stratified. What is the type of cells? Cuboidal.
So stratified cuboidal cells. Next, what about this? This one is also simple. Many layers.
So stratified and type of cells squamous. So stratified squamous or squamous stratified. And I've saved the best one for the last.
This one is tricky, so pay attention. This looks neither simple nor stratified. Some cells are wider at the bottom and narrow at the top, while other cells are narrower at the bottom and wider at the top.
It's like they're faking it, right? They're faking stratified epithelium. They're faking stratified epithelium or they're half stratified epithelium. You might have heard the word pseudo before.
It means misleading or deceptive. And that's exactly their name. Pseudo stratified. epithelium and they are found in the lungs and they have some cilia on it.
They have an awesome name for that too. Pseudostratified ciliated columnar epithelial cells. Wow! Okay, now that you know how they look, you need to understand what they do.
They all look their different special ways for a reason, right? So let's understand that. Squamous, for example, is found in cells lining blood vessels or lung alveoli where transportation of substances has to happen through a permeable surface that is in places where you need a very very thin barrier and where else are they found whenever you need a delicate lining the esophagus and the lining of the mouth are also covered with squamous epithelium now the skin which protects the body so nicely is also made up of squamous epithelium but not one layer of squamous epithelium since your body shed skin Yes, it does. You just cannot see it because the particles are way too small.
Epithelial cells are arranged in many, many layers to prevent wear and tear. Around 600,000 particles of skin get shed every hour. You logically cannot keep regenerating a single layer of squamous epithelial cells, right?
So here you will have, yes, you will have stratified squamous epithelial cells. So these multiple layers ensure that the skin can withstand normal wear and tear. You can actually very gently.
Scrape the inner side of his cheek, stain it and observe it under the microscope. You will find stratified squamous epithelial cells. Okay, where would you find cuboidal cells?
In the lining of kidney tubules and ducts of salivary glands, where mechanical support becomes important. Now, epithelial cells can graduate further, earn themselves another degree and specialize themselves to form glands. Sometimes a portion of the epithelial tissue folds inward and a multicellular gland is formed.
This is glandular epithelium. Now a gland is an organ which just gives out stuff. The stuff that it gives out can either be retained inside the body or secreted outside the body. Like salivary glands where saliva goes out and sweat glands where sweat goes out. These are perfect examples of glands which secrete substances outside the body.
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