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- [Voiceover] The category
of connective tissue

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has several general functions.

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Now, there's not one single
tissue that does all these,

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but the category of
connective tissue as a whole

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will cover these.

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So one thing they're doing is

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supports softer organs of the body.

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Well we know bones are connective tissues.

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That's definitely
supporting softer organs.

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Second one, connects parts of body.

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Well, does blood connect
one part to another?

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Sure, it transports
nutrients from one another.

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Stores fat.

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Well, fat itself, adipose,
is a connective tissue.

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Produces blood cells.

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Inside your bones is red bone marrow.

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Red bone marrow is going
to produce blood cells.

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But every single connective tissue

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will contain fibers and cells,

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as well as this thing called
an extracellular matrix.

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Fibers are what gives them flexibility,

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but retains strength.

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Cells, well, that's
what the living part is,

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and this non-living extracellular matrix.

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This is gonna be everything
found in between the cells.

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Could be liquid, could be solid,

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could be minerals, could be whatever.

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Anything non-living in between the cells.

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And some of these tissues
can have a lot of space

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in between the cells.

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The matrix itself can
provide a ton of strength.

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In the case of your bones,

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the matrix is filled with calcium.

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The calcium provides a ton of strength

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in conjunction with the fibers.

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Now we have two general types.

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We either have a fibrous
connective tissue,

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or some special ones.

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The special ones are unique

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and really don't have
their own category per se.

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All right, so first off,

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provides strength and elasticity.

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Well, the strength can
come from the matrix,

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it can also come from the fibers.

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Elasticity, they move.

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Good thing about your nose or your ears.

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Your nose and ears contain cartilage.

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Cartilage is going to be slightly mobile.

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But then think about
tendons and ligaments.

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Well, those tendons and ligaments

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don't really move too much,

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but got a ton of strength,

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they do give just a little bit.

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Some of the cells you'll
find are called fibroblasts.

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The fibroblast is the main cell

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of your fibrous connective tissue.

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We know they're fibroblasts
because the blast at the end

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is what makes the tissue.

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For example, fibrocyte, C-Y-T-E,

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will be the ones that maintain it.

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They just keep it healthy.

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Macrophages.

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Think of these as your garbage disposals.

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They're gonna go around

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destroying whatever shouldn't be there.

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Lymphocytes.

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Well there's that C-Y-T-E,

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so we know that's a
cell that's maintaining,

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it's helping keep alive.

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Lymphocytes and nuetrophils

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are both types of white blood cells.

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It's gonna help to
protect, to keep it safe,

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get rid of any form of particles,

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invaders that shouldn't be there.

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Our three types of fibers,

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collagen, elastic, reticular.

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I'm willing to bet you
can probably figure out

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which one of those three
has the most flexibility.

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And it's sure elastic.

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Elastic is meant to stretch,

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while collagen has a very
high tensile strength.

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It's very strong.

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You can kind of think of collagen

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an equivalent of your steel
girders in a building.

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If you have the same size steel fiber,

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and the same size collagen fiber,

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we're talking microscopic here,

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they'd have almost the
same amount of strength.

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Reticular fibers, well
they're similar to collagen,

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but they're thinner.

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Because they're thinner,

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that means they're not quite as strong.

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So collagen's the strongest,

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elastic are the weakest and most flexible,

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reticular, they fall in
the middle somewhere.

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So here's an artist's
rendition of connective tissue.

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Talk about looking like a mess.

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Can you see those

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kind of almost peach colored or pink color

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or collagen fibers there?

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The thin blue strands,

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those ran through our reticular fibers.

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You're gonna see the kind of
squiggly peach-colored ones

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are elastic fibers.

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You have fat cells in here,

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you have neutrophil cells,

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you've got tons of things.

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All interwoven together.

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And all that space in between,

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everything in between the cells,

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is your matrix, or known
as your ground substance.

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So here's an example of loose
areolar connective tissue.

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Now if you notice, is you
have thick and thin fibers,

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you have a couple of cells
scattered throughout,

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those little purple spheres are cells.

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So we have our cells,

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we have a lot of space between the matrix,

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and there is no order.

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Completely random.

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You can look at tissue upon tissue,

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they will not be the same.

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The similarity is the randomness.

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Dense connective tissue.

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Now can you kind of see that wavy pattern?

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All those waves, all those lines,

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are gonna be collagen fibers.

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That means we've got a
lot of strength in here.

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So all those waves, all
those collagen fibers,

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are running in the same direction.

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That means a lot of strength

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if you pull along the fibers,

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so you pull them left to right.

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But you notice there's no fibers

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running up and down in this picture?

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That's because these are
your tendons and ligaments.

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Tendons and ligaments are only pulled

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or stretched in one direction.

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They don't need the strength
of the fibers running

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in multiple directions.

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Just kind of wavy pattern,
these collagen fibers,

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over and over.

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That's dense connective tissue.

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Then we can move on to some
kind of specialized ones.

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Moving to cartilage here.

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And I mentioned cartilage before,

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with the different types of flexibility,

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but let's look in more
detail what they are.

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Cartilage is produced by the
cells called chondroblasts.

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Now, these chondroblasts
are found in structures

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called lacunae.

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You can kind of think
of lacunae as a house.

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The chondroblasts live inside of lacunae.

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But there's a little catch.

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The chondroblasts are under house arrest.

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They can not leave lacunae.

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So chondroblasts are inside
the structure of lacunae,

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and they cannot leave.

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The unique feature of cartilage,

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is they do not have any blood vessels.

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It's one of the reasons why

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it takes cartilage so long to heal.

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There's no blood in the
tissue to help it heal.

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Plus cartilage has a real
high amount of collagen.

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So a lot of strength,
but still no flexibility.

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So here is cartilage.

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You can kind of see that purple hazy?

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That is going to be the ground substance,

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or the matrix.

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All of those reddish pink spheres you see,

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with almost a white
color circle around it?

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Well that's the chondrocyte,
the reddish pink,

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inside the space which is called lacuna.

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Lacuna is that almost
whitish color around it.

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Think about taking a beach ball
and putting a marble inside,

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or something like that.

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You have two spheres,

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one large, lacuna,

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one smaller, chondrocyte, inside of it.

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Now, this cartilage is great

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for having shock absorption.

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It's great for helping to keep stability,

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but allowing some flexibility.

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Another specialized structure
in connective tissue

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is the bone.

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Now, bone has this inorganic matrix

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with tons of calcium cells.

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Now, it's not just one
type of calcium cell,

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there are many types of calcium cells.

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By mixing all these
calcium cells together,

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the bone can become very, very hard,

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but you also have the fibers.

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Plenty of collagen fiber

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to help keep those cells together.

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This is showing a slide of your bone.

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What you're seeing here

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kinda looks like a tree trunk, almost.

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You see a big black circle in the center,

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and then rings forming around it.

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Those rings are filled with calcium.

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The black dots that look
like they have little

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kind of hairs or roots coming off?

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Those black dots are the cells.

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The cells are embedded in the calcium.

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The big black dot in the middle

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is where you find the blood.

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That's where all the blood
and nerve grid are found.

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So this is your bone.

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A very specialized connective tissue.

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Another specialized is blood.

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Going from complete solid of bone

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to complete liquid of blood.

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It's your only tissue
that is a liquid tissue.

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The matrix is actually fluid,

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it's the plasma of the blood.

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It's the liquid in between
the red blood cells

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and the white blood cells,

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and the platelets.

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You're thinking hold on,
we need to have fibers.

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It still has fibers.

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Blood still contains the fibers.

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But look at the slide,
where are the fibers?

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You can see the platelets,

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you can see a white blood cell,

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you can see a red blood cell,

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but where are the fibers?

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All that whitish color
is going to be matrix,

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but I still don't see the fibers.

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Willing to bet you've
seen the fibers before.

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Any idea where?

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Well, I'm gonna take a guess here

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that you've probably had a cut
at some point in your life.

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When that cut scabs over,

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the scab is made up of many things,

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but one of the main components

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are the fibers from your blood.

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They form this patch

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that is going to cover
and seal up the site.

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Now, it's not just fibers,

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you've got tons of
platelets in there also.

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But those are the fibers.

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You've seen them.

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Any scab is filled with
fibers from the blood.

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And we have adipose tissue.

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Now, adipose tissue is
kind of special because

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the cell itself has very few organelles,

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or very few central components.

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The adipose tissue cell

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is filled with adipose, or fat.

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By filling cell upon
cell with fat, or lipids,

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it's helping to insulate your body.

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It's helping to protect your body.

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It's also great energy storage.

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All right, well insulation,
that makes sense,

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fine, no problem.

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Because if you have a layer of fat,

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it's gonna slow down the heat
from entering or exiting.

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But protection?

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Yeah, those fat cells act as a cushion.

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Energy storage.

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Your body can take the molecules stored

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within these adipose cells

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and break them down into
usable energy for the cells.

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So adipose does more than
just insulate the body.

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It's also protection and energy.

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So here we go looking
at an image of adipose.

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The actual micrograph on the left,

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all those roughly circular,
oval shaped structures,

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with the very thin lines,

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those are going to be the adipose cells.

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That one, almost in the
middle of the picture,

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has a very thick wall, little black dots?

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That's gonna be a blood vessel,

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we don't need to deal with that now.

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So look at the very thin walls,

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kinda that off-white,
almost blueish tinge inside.

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Those are your adipose cells.

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You can see there's no nucleus in there.

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You know, in reality, there is a nucleus.

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The nuclei have pushed all
the way off to the side.

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So we have a nucleus, it's
just pushed off to the side,

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because the fat is filling
the entire inside of the cell.