- [Voiceover] As the bones are growing,
there's various different hormones
that are gonna help control the bone growth.
In preadolescence, you're starting off with growth hormone,
causing stimulation of bone lengthening.
The growth hormone is produced by the pituitary gland
up near the brain,
but as you continue on into early adolescence,
estrogen and testosterone are taking over.
Estrogen, female; testosterone, male.
They're to stimulate the bone lengthening again,
but as you continue into the late adolescence,
these same two hormones, estrogen and testosterone,
instead of causing more bone lengthening,
they now are causing the cartilage,
found in the growth plates, to be replaced with bone.
Once the cartilage in the growth plates is gone,
that's it, the bone cannot lengthen.
The same hormones that can cause lengthening
in early adolescence will then cause the cessation,
or stopping, of bone lengthening in late adolescence.
So if you look at these chondroblast cells,
we mentioned chondroblast before,
the ones that make cartilage.
Well, the chondoblasts make the cartilage,
but eventually the osteoblasts will come in
replacing the chondoblasts.
As the osteoblast cells start to grow,
they're gonna start to form bone.
Once they mature, they kind of stay in place,
they get stuck; they're called osteocytes.
These are the mature bone cells, the ones that maintain,
the ones that monitor, the ones that keep the bone healthy.
So blast is immature, it's making something.
C-Y-T-E cyte is mature, it's just maintaining something
and then we have these osteoclast cells.
The osteoclast cells are the ones
that will break down the bone.
They're gonna take the calcium out, take the minerals out,
basically they're just dissolving the bone.
So you can take a look table 5.1,
get a little more information on these cells,
and also have (mumbles) animation.
So check back in learning module,
take a peek at that animation.
But as you age, even after those growth plates are closing,
the bone can still change shape.
It can't get longer, but it can get thicker,
it can get wider, it could add strength, can lose strength.
These are all dependent on numerous factors.
What's your dietary intake?
How much exercise do you have?
What age are you?
Even gender, male versus female, comes into play
and all this regulation throughout the rest of life
after the growth plates are closed,
it's all regulated by two hormones,
or primarily regulated by two hormones,
parathyroid hormone, or PTH, and calcitonin.
Parathyroid hormone is meant
to remove calcium from the bone.
Well if you're thinking, "Why would you want to do that?"
Well, you might want to remove calcium
because your bones might be too dense or too heavy.
You don't need that much density.
Or maybe you need calcium someplace else in your body,
so you pull it out of the bones to send it someplace else.
The flip side, or the antagonist, is calcitonin.
It's going to actually add calcium to the bone,
so it cause calcium to be deposit in the bones,
making the bones denser, stronger, thicker.
So parathyroid hormone and calcitonin.
But sometimes a simple maintenance isn't good enough.
Sometimes the bones become damaged.
So bone repair usually starts
with the formation of a hematoma.
A hematoma is going to be a large, kind of swollen area
filled up with fluid.
Now, odds are the fluid's gonna be blood, in this case,
but the hematoma's gonna serve several purposes.
One function, it's gonna allow for the callus formation.
A callus is going to be initial stages
of recreating the bone to go back into the damaged location.
So what you have here is gonna have a callus forming
for more of a kind of cartilage material
that will slowly get stronger and stronger
until it turns into a solid bone material.
So here's an example.
This is the femur, for instance.
If you take compressive force
and push down on the top of the femur,
all right, and you see how the bone's
kind of bent a little bit in the middle there.
So it has more pressure to one side
as the bone tries to buckle a little bit.
So what happens is, you're body's going to say,
"Okay fine, no problem, I'll take bone off the one side,
"put it on the other side."
The result is you end up with
a relatively straight bone coming down.
That bone now matches the force.
Both sides have about the same amount
of force being exerted.
So your body is constantly trying to match up
and moderate the force on your bones.