Voiceover: All right, so I think we have a pretty good
appreciation of how we have some smaller ions, amino acids,
glucose and even water than can leak through these
fenestrations and get into this space right here.
Remember, this is just Bowman's space.
They can get into Bowman's space where we can then
process them into the rest of the nephron.
This is Bowman's space, and we have these
podocytes that hug the arterioles right here
by holding on to the endothelial cells.
We also have this basement membrane that
prevents giant proteins in our red and
white blood cells from leaking through.
And we have these tubule cells that help line
the other side, and they're epithelial cells,
they're in the class of epithelial cells. Excellent.
Now the last thing I want to cover is what's
happening here from having an arterial go into
a structure and then give off another arterial.
That's a little weird, right,
because we usually like thinking about arterioles
going into capillaries and then giving out a venule.
Well one way to think about this is sort of like a
marathon where there are a lot of people running on the
same street from point A to point B, and they're either
running in a narrow street or a wide street.
Let's make a table to think about this.
What would happen if we look at our
afferent and our efferent arterioles,
and we change the diameter of the vessel.
What does that do to the rate of filtration?
We'll write filtration right here.
How does the diameter of our vessels
change the rate of filtration?
If we increase the diameter of the afferent arterial,
or if we have a very wide path that allows a lot of marathon
runners to run into the glomerulus, that means there's going
to be a lot of blood here that includes all of the ions,
and the amino acids and glucose, in addition to
our blood cells and giant proteins we talked about.
There's going to be a lot of stuff over here.
So if there's a lot of stuff running over these
fenestrations you're going to have a lot of leakage,
and so there's going to be a lot of filtration.
More filtration occurs if there are more
people or more marathon runners running into
this space right here, so more filtration.
What about if we did that with the efferent arteriole?
Let's say we increase the diameter of the efferent
arteriole so there's space for more marathon runners
to run away from this very narrow street,
or this place where a lot of people can run off the
pavement and get into these holes and go elsewhere.
If we increase the diameter of our efferent arterial
and allow people to leave, they're not going to be
able to stay around here for a long period of time,
they're not going to be near these fenestrations.
That means that our filtration rate will
decrease, because the blood is moving away
from the place that it would be filtered.
The same thing goes if we decrease
the diameter of our afferent arteriole.
If we decrease the amount of runners or blood that can
come into the glomerulus, that means there's going to
be less fluid filtered out, so a lower filtration rate.
This is actually what happens with renal artery stenosis.
If we have a very narrow or stenosed vessel -
that's what stenosis means, it's just narrow -
renal artery, that means there's going to be less blood
that branches off and goes to our afferent arteriole.
There's going to be less blood that runs across
our fenestrations and is filtered away.
On the flip side, if we decrease the diameter of our
efferent arterial that makes it difficult for our runners
to leave this fenestrated vessel, so there's going to be
some backup, there's going to be a lot of ions and amino
acids and glucose hanging around here near these holes.
If blood backs up that means so do these guys,
so then they're going to be filtered through these holes
and collected into Bowman's space, so our filtration
rate will increase, it will increase because there's
a lot of backup that allows more time for filtration.
Maybe if you're interested in learning about kidney diseases
later on there's a lot of stuff that tweaks this system,
that messes around with the afferent arterial
or the efferent arterial, sort of like what
I talked about for renal artery stenosis.
I encourage you to think about what can go wrong
with this process and how things can change,
that's kind of the best way to learn about it.
That's how our glomerulus works.
Let's move on to the next part of our nephron.