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- [Instructor] The nephrons
are the main functional

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unit of the kidney.

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There are usually about a
million nephrons per kidney.

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That's why you can
technically have one kidney

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and still function perfectly normally.

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Now the nephron is meant to
take the blood and filter it,

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making sure that the proper
concentration of ions,

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things like sodium or
potassium or calcium,

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making sure they're in
the proper concentration

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leaving the body.

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Now each one of these nephrons,

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each one of these
roughly million nephrons,

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is one long, thin, hollow tube.

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It just turns and curves
and twists back on itself.

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It's just one consistently
long, thin tube.

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These nephrons, they pull roughly about

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180 liters of fluid
from the body every day.

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Now, I'm not sure about you guys,

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but I don't drink 180 liters of fluid.

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That's why the nephrons are so important.

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The majority of this 180
liters is returned to the body.

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The only things that aren't
returned to the blood

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will be the waste products,
or anything that's in excess,

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or you have too much of.

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So, it's filtering over and over and over,

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but thankfully, most of
it is just simply returned

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back to the body.

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So what is the nephron made up from?

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We have this structure called
the glomerular capsule.

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Now, the glomerular capsule,
if you think of a capsule,

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it's kind of like a covering,

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something that goes over something.

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It's the very end or the
start of the nephron tubule.

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It's the end where the
actual filtration occurs.

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It's where the blood comes
in and gets filtered out.

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From this glomerular capsule,

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you go to to proximal tubule.

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Well the term proximal means close.

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The proximal tubule is close
to the glomerular capsule.

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What ends up happening
in the proximal tubule

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is it will carry the filtered fluid,

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so the stuff the glomerular
capsule filters out,

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it will carry that down into
the medulla of the kidney.

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So down toward the center of the kidney.

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It will pass that fluid
through the Loop of Henle.

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The Loop of Henle can
be long or can be short.

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It might only dip into
the medulla a little bit,

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or go all the way to the
very center of medulla.

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Then we have this distal tubule.

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While the proximal tubule
is the one that's close

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to the glomerular capsule,
distal means far away.

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The distal tubule is at the
far end of the actual nephron.

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Once the fluid leaves the distal tubule,

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it's out of the nephron.

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Because it's out of the nephron

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and goes into a collecting duct.

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Now each individual collecting
duct can have several

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or even dozens of nephrons attached.

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All this fluid, all this fluid
that's going to become urine,

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is being dumped into
these collecting ducts,

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then traveling down
towards the renal pelvis.

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The renal pelvis is
basically a collecting area.

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It's where all these collecting ducts

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can empty the urine into.

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Now it is still within the kidney.

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So here we go, you can see
the kidney's the bottom left.

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Now look at that little black box,

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that's what's being blown up.

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You can see how the
cortex is the top portion.

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Well that cortex being the top portion,

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that means that's the outside edge.

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Medulla's a little bit
darker brown shading.

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Well you can see here is the glomerulus.

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The glomerulus is going to be a capillary.

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It's where the blood is
brought into the nephron.

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It's brought in on these
afferent arteriole,

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and leaves on the efferent arteriole.

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You can kind of think of efferent as exit,

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e for efferent, e for exit.

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So blood comes in, gets filtered,

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and some blood leaves.

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It's filtered out into
the glomerular capsule.

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That glomerular capsule will
collect all the filtrate,

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or all the fluid, that's
left the glomerulus,

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the capillary.

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It then heads into that proximal tubular,

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you can see how it comes

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right off of the glomerular capsule,

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kinds of twists and turns and curves.

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Eventually it will lead
down to the Loop of Henle.

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The Loop of Henle goes
down either shallow or deep

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into the medulla, then come back up again.

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So it descends down, and it ascends up

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Which eventually gets
to the distal tubule.

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Well distal is further away,

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it's further away from
the glomerular capsule.

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That connects to the collecting duct,

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and carries the urine down.

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Carries all the way down
into the renal pelvis.

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The renal pelvis is what is collecting

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and going to, momentarily,
store the urine.

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So what brings blood into the kidney?

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Well we have our renal artery.

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The renal artery is what brings blood

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right from your main aorta,

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major blood vessel in your body.

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The renal artery comes off of there,

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and flows blood right into the kidneys.

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It gets smaller and smaller
into arterioles eventually,

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mentioned afferent
entering, efferent leaving.

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And then capillaries.

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Capillaries are meant
for exchange of fluid.

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Exchange of small particles.

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So the glomerular capillary,

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that's found within
the glomerular capsule.

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That's where filtration occurs.

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The other two capillaries,

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the peritubular and the vasa recta,

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are going to be capillaries
found out around

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the rest of the nephron.

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The peritubular capillary is found

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around the proximal and distal tubules.

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That means the peritubular
capillary is going

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to be found out in the outer
surfaces, or outer edges.

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So it's found in the cortex.

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The vasa recta is around
the Loop of Henle.

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So it's found around the Loop of Henle,

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that means it's more toward the internal,

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it's around the medulla.

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So looking at this figure,

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we can see that the renal artery heads

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into the kidney on the left there.

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And it branches and branches and branches,

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it gets smaller and smaller,

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until eventually you get down

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to these little arterioles,
afferent goes in,

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efferent will come out of the glomerulus.

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But then here are the other capillaries.

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The peritubular capillaries,

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you can see on the left-hand
side of the large image,

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are all around the
proximal and distal tubule.

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They're up in the cortex.

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While on the right side of this figure,

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you see the vasa recta

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are looping around the Loop of Henle.

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Now the way this is drawn,

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technically you would have
peritubular capillaries

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around both nephrons.

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The one on the left and
the one on the right.

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You'd have the vasa recta
around both nephrons.

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The one on the right, the one on the left.

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Just for simplicity purposes,

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they only put the peritubular capillaries

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on one nephron, and the vasa recta on one.

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But in reality, you'll have
both sets of capillaries

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on each nephron.