Voiceover: The kidneys are pretty crazy.
They can hold about 22 percent of your
entire blood supply at any time.
I've heard somewhere that you can have about
1.1 liters per minute of your blood flow through.
And in a normal person, that's got about
5 liters of blood, that means that within
5 minutes all of your blood will
pass through your kidneys, that's crazy.
So, I think we should investigate further
into how our kidneys work, and we'll start in
this video with a brief overview before going
into the specific parts of what are involved.
So, with these two kidneys right here,
we're going to take in some blood,
that will come in through our renal artery
and come out at the end through our
ureters right there to produce urine.
So, that's sort of the overview look
of what we're going to be doing here,
and the reason why we do this is because
there are cells in our body produce waste products
or change up the acidity or the osmolality
of our blood. We've heard these terms before.
And it's very important for us to regulate
what is the pH of our blood or how acidic it is
or how many osmoles we have or things that
dictate where ions or water flows.
And our kidneys make sure that that's at a set level.
So going into the details, when blood
comes into our kidneys, they enter through
the renal artery, so I've got two renal
arteries right here, one right there,
one right there, and as you can see,
it's going to go branch off and have a
whole bunch of other networks that are
going to be disseminated from here, and
I'll talk a little more about that
in a separate video. But what happens is that
we're going to have filtration of our blood,
and from that filtrate that comes out, we're
going to process it and reabsorb some ions and water.
And as we reabsorb the things that are important,
we are going to collect it into our renal vein.
So here are two blue renal veins right here
for each of our kidneys. Our renal veins
are going to take the returned or
reabsorbed nutrients back into our blood
and send it on its way. All right, very cool.
So now we know sort of how the blood
enters and leaves. Now, let's talk about
the two main functions our kidneys are responsible.
What are the two main functions that they
need to carry out in order for us to filter our blood?
So, the first function you probably guessed
is filtration. We take our blood and we
filter it out, so we have all our waste
products and some important molecules
like ions or amino acids or glucose that
end up in a filtrate that then passes
through the kidneys. So somethings in that filtrate,
we want to get rid off, all the wasty stuff
that we don't need, and so another or the
second very important function of our kidneys
is collection, and between these two jobs,
the kidney will take our blood and put out
some urine. Now, at this point, I should
also mention that there is a single functional
unit, and so when we talk about our functions,
there is a unit that we can talk about.
The single smallest functional unit of a
kidney is called the nephron, the nephron,
and the nephron is responsible for filtration
and collection. We'll talk about some
other structures in a minute that are
only responsible for collection,
but the nephron is charged with filtration
and collection, so it's got two hats on.
And the nephron is sort of situated in
two parts of the kidney. The first part
is sort of this outside area right here.
You can kind of see that it's the shell
of the kidney right, and as a shell, we
call it the renal cortex. Cortex is a term
you probably heard of before right.
Cerebral cortex, adrenal cortex. Cortex just means
the shell, so that's this light tan
part on the outside. These darker parts
inside right here, there is a couple of them
that you can see. This is sort of in the middle
and so we call that the renal medulla,
the renal medulla, and medulla you might have
heard of like the adrenal medulla or
the medulla oblongata, it just means the middle,
okay the middle, so it's inside the cortex.
So, our nephron is situated between the
cortex and the medulla, it sort of starts
up here and squiggles around and then it
dips into your medulla and then it jumps
back out over here and then it dips in again.
And so I'll draw that in a separate video,
sort of all the separate parts of the nephron,
but just understand that it
dances between your cortex and your medulla.
And where it's dancing determines whether
it wants to reabsorb important things or
allow some stuff to be collected into the urine.
Now, for the collection process, we have
these little tips that are kind of kissing
our renal medulla, right, so these little
tips right here that collect the urine in the first place,
the first point that urine sort of presents itself.
This is called the renal calyx, the renal calyx.
And if we've got a whole bunch of these,
we call them the renal calyces, the renal calyces.
And so that's the first part you're going
to have urine be present. There is a whole
bunch of these guys that meet together
and then you've got this central area right there.
That central area is called the renal pelvis,
the renal pelvis, and that's just where all your
calyces collect together, and once you've got
urine in your renal pelvis, it's going to go
out this tube right here, and that's where
urine is going to exit our kidneys.
This tube right there is just called the ureter,
the ureter, and we've got two ureters right here.
That's going to send urine away from the kidneys,
and as we'll talk about in a separate video,
into the bladder. And now that we've talked
about the ureter, this is a pretty good time
to mention what these three guys make together.
Whatever you've got in organ like our
kidney right here, I'll sort of highlight that.
That's your kidney, and then there are some
things that are coming out of your kidney,
these three guys right there. We call the place
where we've got tubes or vessels coming out, the hilum,
the hilum, and if we've got more than one of them,
we can call them the hila, but we've got a
renal artery, a renal vein, and a ureter
coming out of the renal hilum over here.
All right, and so that's the anatomical
structure of our kidneys. Now, why don't
we take a step back and let me make a
philosophical note if I may. What's the
point of the kidney even doing this?
Why should we even filter and collect urine?
What's the whole purpose of this altogether?
Well, the kidneys are actually a very
important organ for maintaining something
that's called homeostasis, and you've probably
heard of this term before. It's a big buzz
word in biology. Homeostasis just means the
way things are, the status quo, which can
mean things like what the pH in your blood is.
So your kidneys maintain the pH in your blood
by regulating the amount of hydrogen ions
that are there. It could also mean blood pressure
because when you've a lot of salt ... And you've
probably heard this from doctors.
If you've a lot of salt intake, you're going
to have high blood pressure, so your kidneys
make sure you excrete the right amount of
sodium and chloride ions to make sure that
you don't have high blood pressure, but there are
other things here that the kidney also maintains
homeostasis of. And that could be things
like osmolality, and of course the main thing
that we're going to talk about in an
upcoming video, is just the excretion of
waste products of getting rid of the extra
materials that we have, and one of the main
waste products that the kidney gets rid off
is something that's called urea.
And we'll touch on urea in a little bit, but
this just goes to show you how important
your kidneys really are. There is a lot at
stake here, and so it's very important to have
these guys filtering your blood to produce
urine to maintain homeostasis.