- [Voiceover] This chapter's looking at how cells
end up making themselves into organs.
These cells that are grouped together have to have
a common function.
So a tissue is groupings of cells with a common function,
they work together.
You cannot just grab a cell from the brain,
a cell from the kidney, one from the leg,
and one from your spleen, doesn't work that way.
The cells must work together to form a common function.
Now we have four primary categories of tissues.
We have the epithelial tissues, connective tissues,
muscle tissue, and nervous tissue.
The nervous tissue is probably the easiest one,
because there's only one type of nervous tissue.
The nervous tissues are what contains neurons.
Makes up your brain, your spinal cord, your nerves.
Now the muscle tissue, there's actually three types.
One type is your cardiac muscle, cardiac, heart.
It's the muscles that make up your heart.
We have smooth muscle.
Smooth muscle is found around organs.
Think your stomach, your intestines, things like that.
And then there's skeletal muscle.
Skeletal muscle is what you typically think of
when you think of muscle.
These are the muscles attached to your bones.
Things like biceps brachii, triceps brachii,
pectoralis major, it's all the main muscles we think of
when you voluntarily move a muscle.
The other two categories, connective and epithelia,
they have quite a few different tissues in each.
So the connective tissues, you can kinda guess what they do,
they're meant to connect one part to another, no problem.
Epithelial, well they're meant to either cover
or line the inside of.
So here's a little schematic showing nervous tissue.
You've got brain, spinal cord, nerves, sure, no problem.
I already mentioned the three types of muscle tissue.
But let's jump down to the epithelial tissue.
The way the book's putting it is boundaries
between different environments.
Well the function is protection, secretion,
absorption, even filtration.
Your skin is going to be a partly epithelial tissue.
Now it says epidermis in parentheses,
that's because your skin actually has multiple layers.
Only the more superficial, the ones you can touch,
towards the surface, are going to be the epidermis.
That's epithelial.
The deeper part of your skin is actually connective tissue.
Connective tissue itself supports, protects,
binds, helps hold things together
or transports from point A to point B.
Bones are a great example.
Your bones give support.
They also give protection of certain organs.
You have your tendons connecting muscle and bone,
fat is gonna be a connective tissue.
Even blood is a connective tissue.
So it's helping it get from point A to point B.
The four different types of tissues.
Let's look a little more specifically
at each type of tissue.
The epithelial tissue, I already said,
lines the body cavities or covers your surface.
So it's the outside of your skin,
it's the inside of your stomach,
the inside of your oral cavity, your mouth.
But you also have epithelial tissues
that are glandular epithelia.
This glandular epithelia is going to be some structure
that can secrete or produce.
These epithelial cells have adapted.
Instead of covering or lining,
they actually make up an entire gland.
We have exocrine glands, for example.
They're secreting right on to the exterior of the body.
So you start looking at this diagram,
you'll see that's an example of your skin.
The glands are secreting right on the skin's surface.
But we also have endocrine glands.
Well, endo is inside, E-N-D-O, inside.
And endocrine glands, they do not secrete onto the exterior
body or the surface, they secrete right into the blood.
Your endocrine glands secrete directly into the blood.
They're secreting their hormones directly into the blood.
So this epithelial tissue can either cover or line a cavity,
but it also can be glandular epithelia.
We start looking at the different types of epithelia.
They're based on number of layers and the shape.
With three primary shapes to look at.
One is referred to a squamous.
Squamous is a flattened, very thin cell.
If you look at that little drawing to the right,
you'll see how one is giving you kind of a
three dimensional perspective,
showing you how flat it can be.
And the other one that is the furthest to the right,
shows how very thin it can be.
That purple is meant to be the nucleus.
You kind of think of the squamous cell
like an easy over egg.
The nucleus, or in the case of an egg, the yolk,
is in the center, with everything else spreading out
around a very flat surface.
Cuboidal, well what's a cube?
A box.
Cuboidal cells are gonna look like a box.
Now they're not the perfect 90 degree corners,
but they're gonna be close.
They're more box-like than they are flat.
Columnar, well what shape is a column?
It's a tall rectangle.
Again, these corners are not a perfect 90 degrees,
but they're more columnar than they are box-like.
And then they are flat, like squamous.
So squamous, cuboidal, columnar, are the three main shapes
to classify your epithelial tissues.
And so the other type of classification was layering.
Well if you have a single layer,
it's referred to as simple.
Now these simple layers are very thin,
it's really easy for different particles
to fuse across them, simply flow across.
For example, the inside lining of your lungs.
You have to have exchange of gases,
oxygen, carbon dioxide.
Well, you have simple squamous tissue here.
Simple one-layer squamous flat makes it
really efficient to have different gases
moving through the membranes of your lungs.
But sometimes you don't want things to pass through.
That's when you have multiple layers.
So you have two ore more layers referred to as stratified.
This stratified is meant to provide protection.
Your skin is a great example of stratified.
If you happen to brush up against something,
more often than not, it does not cut you,
it does not rip your skin off.
Instead, how does skin work?
Well, a few layers of dead cells get rubbed off,
the rest of the skin remains intact.
So we have one layer called simple,
multiple layers called stratified.
So here are some examples of what we're looking at.
We can take the first term, which is how many layers,
and the second term, the shape.
Simple squamous is the top left.
Look at the example of the lungs.
Great for exchange of gases.
Going down, below simple squamous, you have simple cuboidal.
The simple cuboidal, you see the cells, again,
are one layer, but they're more box-like.
Go below that, you get the simple columnar.
Again, one layer of cells, but if you notice,
they're tall, more column-like than they are box-like.
Now, that has a labeling,
of what they call a goblet cell in there.
You can see that more of a reddish-pink color
is actually a goblet cell.
A goblet cell is going to be a glandular epithelial cell.
It's actually going to produce and secrete a mucous.
So the goblet cell's kind of a specialized structure there.
If we go to the right side, you can see,
we start with the right top is stratified squamous.
Stratified means many layers, squamous, flat.
Now if you're looking at this and saying hold on, hold on,
I see the top looks flat, but as you go to the bottom,
those look cube-like.
The trick here is with all stratified tissue,
the name of the cell shape is based on
the most superficial or top layer.
The top layer here are flat cells,
hence, stratified squamous.
Next one down, stratified cuboidal, no problem,
you can tell that one.
Stratified columnar, again, look at the different shapes.
The naming's based on many layers,
but also what's the most superficial,
what's the exposed surface?
These are going to be columnar cells,
hence, stratified columnar.
But some of these cells need to have a little bit
of extra support, ways of holding themselves together.
So what we're seeing right here
are two simple columnar cells.
You can see it's one layer, and they're tall columns,
but they look like they're almost stitched together,
like someone took a sewing machine and just sewed 'em.
What that is is called a tight junction.
The whole purpose of a tight junction
is to hold two epithelial cells very close and very tight.
It prevents things from passing between the cells,
because instead of a very thin space,
there is no space between the cells.
They're basically stitched together to prevent
passage between the cells.
We then have these adhesion junctions.
Look at these adhesion junctions,
doesn't look like they're mostly stitched together,
but we have these little lines that interlock.
With adhesion junctions, you can kinda think of it
as a zipper, those little purple fibers that interlock?
They're interlocking like a zipper would be.
They're gonna hold together and make sure
the cells do not separate.
But you can see there still is some space between the cells.
So their point here is now allowing some flexibility,
but still anchoring the cells to each other.
And the third one here, called gap junctions.
If you look at the blown-up picture,
you can see they're still holding the cells together,
but there's an open channel in the middle.
Gap junctions are meant to allow transfer of ions.
Transfer of water.
They allow different particles to go from one cell
to the adjacent cell next to it.
So the gap junctions are a little, tiny channel.
So gap junctions, adhesion junctions, tight junctions,
they all have their own purpose,
but they all hold something to something else.
They're anchoring cells together,
but tight junction is no space at all.
It's waterproof.
Adhesion junction, you have some space,
therefore, little bit flexibility.
The gap junctions, allow for particles to pass cell to cell.