- [Instructor] The nephrons are the main functional
unit of the kidney.
There are usually about a million nephrons per kidney.
That's why you can technically have one kidney
and still function perfectly normally.
Now the nephron is meant to take the blood and filter it,
making sure that the proper concentration of ions,
things like sodium or potassium or calcium,
making sure they're in the proper concentration
leaving the body.
Now each one of these nephrons,
each one of these roughly million nephrons,
is one long, thin, hollow tube.
It just turns and curves and twists back on itself.
It's just one consistently long, thin tube.
These nephrons, they pull roughly about
180 liters of fluid from the body every day.
Now, I'm not sure about you guys,
but I don't drink 180 liters of fluid.
That's why the nephrons are so important.
The majority of this 180 liters is returned to the body.
The only things that aren't returned to the blood
will be the waste products, or anything that's in excess,
or you have too much of.
So, it's filtering over and over and over,
but thankfully, most of it is just simply returned
back to the body.
So what is the nephron made up from?
We have this structure called the glomerular capsule.
Now, the glomerular capsule, if you think of a capsule,
it's kind of like a covering,
something that goes over something.
It's the very end or the start of the nephron tubule.
It's the end where the actual filtration occurs.
It's where the blood comes in and gets filtered out.
From this glomerular capsule,
you go to to proximal tubule.
Well the term proximal means close.
The proximal tubule is close to the glomerular capsule.
What ends up happening in the proximal tubule
is it will carry the filtered fluid,
so the stuff the glomerular capsule filters out,
it will carry that down into the medulla of the kidney.
So down toward the center of the kidney.
It will pass that fluid through the Loop of Henle.
The Loop of Henle can be long or can be short.
It might only dip into the medulla a little bit,
or go all the way to the very center of medulla.
Then we have this distal tubule.
While the proximal tubule is the one that's close
to the glomerular capsule, distal means far away.
The distal tubule is at the far end of the actual nephron.
Once the fluid leaves the distal tubule,
it's out of the nephron.
Because it's out of the nephron
and goes into a collecting duct.
Now each individual collecting duct can have several
or even dozens of nephrons attached.
All this fluid, all this fluid that's going to become urine,
is being dumped into these collecting ducts,
then traveling down towards the renal pelvis.
The renal pelvis is basically a collecting area.
It's where all these collecting ducts
can empty the urine into.
Now it is still within the kidney.
So here we go, you can see the kidney's the bottom left.
Now look at that little black box,
that's what's being blown up.
You can see how the cortex is the top portion.
Well that cortex being the top portion,
that means that's the outside edge.
Medulla's a little bit darker brown shading.
Well you can see here is the glomerulus.
The glomerulus is going to be a capillary.
It's where the blood is brought into the nephron.
It's brought in on these afferent arteriole,
and leaves on the efferent arteriole.
You can kind of think of efferent as exit,
e for efferent, e for exit.
So blood comes in, gets filtered,
and some blood leaves.
It's filtered out into the glomerular capsule.
That glomerular capsule will collect all the filtrate,
or all the fluid, that's left the glomerulus,
the capillary.
It then heads into that proximal tubular,
you can see how it comes
right off of the glomerular capsule,
kinds of twists and turns and curves.
Eventually it will lead down to the Loop of Henle.
The Loop of Henle goes down either shallow or deep
into the medulla, then come back up again.
So it descends down, and it ascends up
Which eventually gets to the distal tubule.
Well distal is further away,
it's further away from the glomerular capsule.
That connects to the collecting duct,
and carries the urine down.
Carries all the way down into the renal pelvis.
The renal pelvis is what is collecting
and going to, momentarily, store the urine.
So what brings blood into the kidney?
Well we have our renal artery.
The renal artery is what brings blood
right from your main aorta,
major blood vessel in your body.
The renal artery comes off of there,
and flows blood right into the kidneys.
It gets smaller and smaller into arterioles eventually,
mentioned afferent entering, efferent leaving.
And then capillaries.
Capillaries are meant for exchange of fluid.
Exchange of small particles.
So the glomerular capillary,
that's found within the glomerular capsule.
That's where filtration occurs.
The other two capillaries,
the peritubular and the vasa recta,
are going to be capillaries found out around
the rest of the nephron.
The peritubular capillary is found
around the proximal and distal tubules.
That means the peritubular capillary is going
to be found out in the outer surfaces, or outer edges.
So it's found in the cortex.
The vasa recta is around the Loop of Henle.
So it's found around the Loop of Henle,
that means it's more toward the internal,
it's around the medulla.
So looking at this figure,
we can see that the renal artery heads
into the kidney on the left there.
And it branches and branches and branches,
it gets smaller and smaller,
until eventually you get down
to these little arterioles, afferent goes in,
efferent will come out of the glomerulus.
But then here are the other capillaries.
The peritubular capillaries,
you can see on the left-hand side of the large image,
are all around the proximal and distal tubule.
They're up in the cortex.
While on the right side of this figure,
you see the vasa recta
are looping around the Loop of Henle.
Now the way this is drawn,
technically you would have peritubular capillaries
around both nephrons.
The one on the left and the one on the right.
You'd have the vasa recta around both nephrons.
The one on the right, the one on the left.
Just for simplicity purposes,
they only put the peritubular capillaries
on one nephron, and the vasa recta on one.
But in reality, you'll have both sets of capillaries
on each nephron.