- [Voiceover] In this chapter,
we're looking at the skeletal system.
So there are three types of connective tissue
that make up your skeletal system.
The most common is gonna be the bones,
which is made of osseous tissue.
It's very hard, very solid.
Now these bones can be held together with ligaments.
Ligaments are a second type of connective tissue.
And the third is cartilage.
Cartilage is a lot of times found between the bones,
providing a cushioning,
and helping to protect the ends of the bones.
So let's start with the functions of the bones themselves.
I'm sure we can all agree that bones are very hard.
Well, why are they hard?
They're hard because of all the calcium, all the minerals
that's found within the bone.
So what are these bones doing?
Well, one, support.
Support, as in providing a framework for your body.
Support, as in supporting your various muscles,
making sure the muscles have something to attach to.
Protection.
Can you think of any organs that are encased in bone,
and nicely protected?
Well, the brain's one.
The brain's inside the skull,
nice and protected.
The spinal cord.
Again, within bone,
nice and protected.
Your heart, lungs are encased by the rib cage.
Again, nice and protected.
So bones can provide a nice amount of protection
for various organs.
Movement.
Well, the muscles that move your body
have to have something to pull against.
If you took all the bones out of your body,
what would you be?
A puddle of blob on the floor.
Because the muscles and bones work together.
Not only for structure,
to give you your support,
but they also allow for a lever system
where the muscles can pull against the bones,
creating a movement.
This one might sound a little odd,
but blood cell formation.
Inside quite a few bones in your body,
the actual inside workings of these bones
are hollow cavities.
It's these hollow cavities
that are going to allow
the production of blood.
And then we have our mineral storage.
Mentioned before that the mineral storage
is primarily calcium,
but there are other minerals stored as well.
But calcium really is that nice, hard, solid structure
that provides the strength behind your bones.
But there's also a second mineral, phosphate.
Now, phosphate might not be as prevalent as calcium,
but it still plays a major roll
in the functionality of the bones.
Now, this calcium inside your bones
is actually located inside what's called the matrix.
It's just a grouping of all these inorganic things.
You have minerals in there,
you have some fibers in there,
but there are no living materials inside that matrix.
One of the types is called compact bone.
Now, compact bone is primarily what you think of
when you see a bone.
It's gonna be solid, it's gonna be relatively smooth,
you're not gonna see holes in it.
It's what covers the entire outside of the bone,
and forms the majority of the shaft of the bone,
or the middle.
Spongy bone, well that's usually inside of another bone.
Very rarely, you can actually see the spongy bone
because the spongy bone is encased by compact bone.
Now, I have this term up there called trabeculae.
Really, what that is are tiny little lines
in the spongy bone.
Those tiny lines are give support
and give structure to the spongy bone.
Just think of a sponge,
like a kitchen sponge or a sponge out of the ocean.
Does it look like there's any real pattern there?
Probably not.
The spongy bone also looks very haphazard.
We're to have a total of three primary cell types
in the bone.
Ostoeblast, oteocytes, and osteoclasts.
The osteoblast cell
is going to be a cell that will start to create
and make the osseous tissue,
or make the bone,
while the osteocytes,
they get trapped sometimes.
Once they get trapped in that solid matrix of calcium,
they can't get out.
So they stay there
and monitor the health of the bone.
Now this third one might sound a little bit off,
because the purpose of an osteoclast
is to break the bone down,
remove calcium,
and try and pull the calcium into the blood.
If you're wondering,
why would you want to break down the bone?
Well, sometimes your body needs to
shift around a little bit.
Sometimes your body needs to remove it
because you have too much.
All depends on what signals
are received in your body.
The bones themselves,
we have long bones.
Think about your upper arm and your lower arm.
You have flat bones.
Things like your skull,
they're very thin, but long and wide.
Then you have these irregular bones,
the ones that don't really match up.
They have all these unusual, different shapes.
Inside your compact bone,
you have these building blocks,
these kind of basic structures.
These are called osteons.
Now, an osteon, sometimes is referred to
as the haversian system.
Osteon's a lot easier and a lot shorter,
so just stick with that.
Pretty much what the osteon is
is a rough, ring shape
of the cellular arrangement.
That means that you're seeing all the cells
in roughly a ring shape.
And the very outside,
periosteum.
Periosteum is a connective tissue
meant to cover the outside of the bone,
helping to protect it
and keep everything in proper balance.
So if you look at the very top of this image,
you're gonna see a micrograph, a photograph,
of an osteon.
If you notice, it kinda looks almost like rings there.
You can see the little dots inside of the rings
going around and around that central canal.
So that is your compact bone.
While the spongy bone,
if you look in the middle diagram on the bottom,
you can see the spongy bone
has all these openings and holes,
just lines and lines and lines
all interconnected.
There are two more types of connective tissue
from the skeleton.
We have our cartilage.
Main purpose, support.
Helps to cushion the joints so they come together.
And there are three different types,
called fibrocartilage, hyaline cartilage,
and elastic cartilage.
Well, hyaline cartilage is the most common.
That's the one you'll usually hear.
Elastic cartilage,
well the name kinda gives it away.
It's going to stretch.
But what's nice is it'll stretch,
but then it comes back to it's original shape.
Ligaments.
Ligaments are bone to bone connection.
You have many, many, many,
parallel fibers of collagen.
So you have all these parallel fibers
giving a ton of strength
across that ligament.