00:01
So now let's switch gears
and talk about the bones role
in maintaining homeostasis
in the body.
00:08
Specifically,
the bones store 99% of the
body's calcium.
00:14
The parathyroid gland,
which is located on the
posterior portion of the thyroid,
secretes a hormone,
the parathyroid hormone.
00:24
And this allows osteoclast
to be stimulated,
which are going to reabsorb
the calcium from the bones
and release it into the blood.
00:35
Parathyroid hormone also stimulates
the production of another chemical
calcitriol
by the kidneys,
and this also causes the body
to retain
or hold on to any calcium
instead of getting rid of it
through waste.
00:54
So if we look at
the feedback loop associated
with bone's role in
Calcium homeostasis,
what happens is
the stimulus would be a decrease in
the amount of blood calcium.
01:09
As the blood calcium levels decrease
or are lowered,
the parathyroid glands receive
this message.
01:17
They then send this message
to the parathyroid
where it secretes
the parathyroid hormone
and the parathyroid hormone
is going to activate
the parathyroid hormone
gene.
01:29
This gene then activates
both the kidneys
with calcitriol
and the osteoclast
in the bone
to both retain calcium
in the blood
as well as
to release calcium
from the bones
so that we may increase the levels
of blood calcium in the body.
01:47
We do this until we return
to the homeostatic level
of blood calcium
that we need
in order for our body to perform
functions.
01:57
As you will find in later chapters,
the level of calcium in the blood is
extremely important
for us to carry out a lot
of our everyday activities.