- [Voiceover] Red blood cell functionality
really is dependent on the amount
of oxygen and carbon dioxide.
One of the main functions of the red blood cell
is to transport your oxygen from your lungs
to your body's tissues.
But then on the return trip, the red blood cells
can take up some carbon dioxide.
Allowing the carbon dioxide, which is a waste product
to be taken from your tissues and transported
to your lungs where it can exhale it.
So here's a picture of your red blood cells.
You can see they're kind of looking
like this biconcave disc, almost like,
a donut that the center wasn't punched out of.
But these are tiny, tiny, tiny things.
What's more interesting is what's inside.
Even though they're called a red blood cell,
there's no nucleus.
The nucleus was removed before
the red blood cell made it to maturation.
So, what's inside instead?
Tons and tons of hemoglobin.
This molecule used on the right-hand side of the screen
is a hemoglobin molecule.
Don't worry about trying to figure out
what all the lines mean and everything.
The important parts is, notice how
there are four of those heme groups that contain iron.
This iron is what allows oxygen to bind,
or for that matter, carbon dioxide.
So since each hemoglobin molecule
has four heme groups with four irons,
each hemoglobin molecule can bind
a total of four oxygen molecules.
We can have four oxygen molecules per hemoglobin.
Each red blood cell will have
hundreds and hundreds of hemoglobin.
In one cubic millimeter, you can get
about five million red blood cells.
If you're wondering what five million
red blood cells looks like,
or how big a cubic millimeter is,
take your thumb and index finger and put them together.
Now take your other finger and put across the top
so you form a little tiny triangle at the very tip
of your thumb and index finger.
That tiny triangle is roughly a cubic millimeter.
It'll have about five million red blood cells
in that little space.
So how do they start off?
Your red bone marrow, which is found
in the ends of your big bones, your long bones,
or it's found in your bones like
the skull and the vertebrae.
This red bone marrow has stem cells inside of it.
Stem cells are special because they
can become pretty much anything.
Now. this particular stem cell can become
any type of formed element in the blood.
As you can see, this stem cell can become
erythrocyte or a red blood cell,
it can become leukocytes or white blood cells,
or it can become the platelets at the very bottom.
That means this one stem cell can end up
making a total of seven different particles.
It's not important to know all the in-between
names of everything, what's important for us
is knowing that the stem cell is found
in the red bone marrow at the end of long bones,
and that stem cell can make all
the white blood cells, the red blood cells
and the platelets from the same original stem cell.
So we have the erythrocyte red blood cell.
We have the five different white blood cells:
the neutrophil, the eosinophil,
basophil, monocyte, lymphocyte.
All five of those white blood cells
have their own functionality, but they
are all made from the same stem cell.
Platelets, they come from the megakaryocyte.
That megakaryocyte just breaks pieces off
to create these little platelets that float in your blood.
Life span comes up about 120 days in humans,
so give or take, three to four months.
It's controlled by a hormone.
The hormone erythropoietin is produced from the kidneys.
This erythropoeitin goes to the red bone marrow
causing it to produce blood cells.
So it's all based on O2 availability.
If you have a low amount of oxygen
available in your blood, the kidney senses it
saying "Hey, we got a problem here."
The kidneys initiate erythropoietin
which goes to your red bone marrow
the red bone marrow increases red blood cells
then red blood cells increase in number
meaning there's more hemoglobin to carry oxygen,
oxygen levels go back up, and just like that,
you're back to that set point,
that normal level of O2 availability.
It's kind of weird to think about,
but your kidneys are really the ones
that control your blood production.
They're the ones that can tell if there is
a low amount or a high amount of O2 availability.