00:00:00
i'm about to draw this diagram of a
00:00:02
nephron it's the functional unit of
00:00:04
filtration in the kidney but before we
00:00:06
jump to the white board and do that
00:00:07
let's take a look at the kidney model
00:00:08
and see where these things are located
00:00:13
so here on my model is one of the
00:00:14
nephrons you'll see
00:00:16
this loop that comes down and you notice
00:00:18
that loop is also in the diagram
00:00:20
there's going to be this capsule that
00:00:21
surrounds some blood vessels that's
00:00:22
going to be
00:00:23
right in there you can kind of see those
00:00:24
yellow dots and there's going to be a
00:00:25
collecting duct which we see on the
00:00:27
right side of our
00:00:28
diagram that i drew and that collecting
00:00:30
duct is going to take the urine that
00:00:32
gets filtered out
00:00:33
of the blood it's going to take it down
00:00:35
to the bottom it's going to enter into
00:00:36
the calyx
00:00:38
then to the major calyx and it'll travel
00:00:40
down here through the ureters to get
00:00:41
down to the bladder
00:00:42
these nephrons which include the capsule
00:00:45
the tube that loops down the collecting
00:00:46
duct
00:00:47
there's millions of those throughout the
00:00:48
kidney they're located in the renal
00:00:51
pyramids
00:00:52
including the renal medulla and then
00:00:53
part of them is in the renal cortex
00:00:55
those tubes of the nephron are also
00:00:58
surrounded with blood vessels that come
00:01:00
into the kidneys so we see those blood
00:01:01
vessels right there we also see those in
00:01:03
the diagram that i've drawn so now that
00:01:04
we know where those nephrons are located
00:01:06
within the kidney
00:01:08
let's jump to whiteboard and get started
00:01:09
so there's two main regions in our
00:01:11
diagram here
00:01:12
here at this top half above the dotted
00:01:14
line is the renal cortex
00:01:16
and everything below the dotted line is
00:01:18
the renal medulla
00:01:19
also being drawn right now we've got
00:01:21
something that's called the bowman's
00:01:22
capsule
00:01:23
this bowman's capsule is going to be the
00:01:24
beginning of the nephron where
00:01:26
filtration first happens but before we
00:01:28
get into that we have to deliver some
00:01:29
blood
00:01:30
to the nephron and so we're going to
00:01:31
have a renal artery coming in or really
00:01:34
a branch of the renal artery
00:01:35
that's going to be bringing blood in and
00:01:37
if you notice here once that renal
00:01:39
artery gets to the bowman's capsule
00:01:40
it's going to kind of split into a
00:01:42
couple sections and sort of form this
00:01:44
thin coiled section of artery here that
00:01:46
kind of bunches up in a ball like this
00:01:48
inside of the bowman's capsule now that
00:01:51
bunch of artery is called the glomerulus
00:01:54
so blood will come in through this
00:01:56
branch of the renal artery
00:01:57
into the glomerulus now if you notice
00:01:59
the branches of the glomerulus are a lot
00:02:01
thinner than the artery coming in and so
00:02:03
imagine if you try to take a bunch of
00:02:05
fluid that's in a vessel like this and
00:02:07
then suddenly force it into a thinner or
00:02:09
smaller vessel
00:02:10
well that's going to greatly increase
00:02:12
the pressure that increased pressure
00:02:14
from trying to force a lot of fluid into
00:02:16
tiny little vessels is going to cause a
00:02:18
lot of that fluid to leak
00:02:19
out of the glomerulus into the bowman's
00:02:22
capsule and that's the whole point of
00:02:23
this is to get fluid from the glomerulus
00:02:25
into the bowman's capsule we call that
00:02:27
process filtration
00:02:28
and basically that's going to mean that
00:02:30
the blood plasma and it's going to be
00:02:31
about 20
00:02:32
of the blood plasma that comes through
00:02:34
here is going to exit the glomerulus
00:02:36
and go into the bowman's capsule now
00:02:38
once that blood plasma or that fluid is
00:02:40
in the bowman's capsule
00:02:41
we call it the filtrate so if you hear
00:02:43
me refer to the filtrate throughout the
00:02:44
rest of the video
00:02:45
i'm talking about fluid from the blood
00:02:47
that was blood plasma
00:02:49
that once it's in the bowman's capsule
00:02:51
and then the rest of the nephron
00:02:52
we stop calling it blood plasma we start
00:02:54
calling it filtrate
00:02:55
so in a period of 24 hours we're going
00:02:58
to filter about 180 liters
00:03:00
of our blood plasma through the bowman's
00:03:02
capsule
00:03:03
to become filtrate now if we urinated
00:03:05
out 180 liters per day we would get
00:03:08
dehydrated super quick and we would not
00:03:09
have enough fluid for our bodies to
00:03:11
survive
00:03:11
so luckily filtration is not the only
00:03:13
thing that's going to occur we also have
00:03:15
the process of
00:03:16
reabsorption so we're going to take a
00:03:19
lot of fluid out of our blood
00:03:20
but we're going to put most of it back
00:03:22
and we're just going to keep out stuff
00:03:23
that we want to get rid of
00:03:24
that could be water if we have too much
00:03:26
water in the body it's going to be other
00:03:28
wastes that we're trying to get rid of
00:03:30
it's going to be salt so if we have too
00:03:31
much salt
00:03:32
in the body and it's really kind of a
00:03:33
weird inefficient system because
00:03:36
why not just take out the stuff we want
00:03:37
to get rid of but that's not how our
00:03:38
kidneys work we're going to filter out
00:03:40
lots of things even stuff that we want
00:03:42
to keep and then we'll selectively
00:03:43
determine what do we put back into the
00:03:45
bloodstream to keep in the body and
00:03:46
that's how we'll regulate what we
00:03:48
urinate out
00:03:49
and what we keep inside filtration is
00:03:50
going to take place in the bowman's
00:03:52
capsule and glomerulus
00:03:53
and then reabsorption is going to take
00:03:54
place through the whole rest of the
00:03:56
nephron that we're about to draw on our
00:03:58
diagram
00:03:58
okay so where does that filtrate go next
00:04:00
well first it's going to go through
00:04:01
something called the proximal
00:04:03
convoluted tubule proximal because it's
00:04:05
right after the bowman's capsule it's
00:04:07
going to be proximal to it we'll have a
00:04:09
distal
00:04:09
convoluted tubule that's farther away
00:04:11
but proximal because it's close to the
00:04:13
beginning
00:04:13
convoluted just means that it sort of
00:04:15
meanders like it doesn't just go
00:04:16
straight to where it's going it's going
00:04:17
to kind of take some turns and stuff
00:04:19
like that
00:04:19
once it reaches the end of the proximal
00:04:21
convoluted tubule it's going to descend
00:04:23
down into the medulla in what we call
00:04:26
the nephron loop or sometimes called the
00:04:28
loop of henle
00:04:29
so far everything we've done has been in
00:04:30
the renal cortex or the outer layer of
00:04:32
the kidney
00:04:33
but now this loop is going to dip down
00:04:35
into the medulla and we'll talk about
00:04:37
why that's important in a minute but
00:04:38
just know for now that dips down into
00:04:40
the medulla
00:04:40
and then it comes back out of the
00:04:42
medulla into the renal cortex
00:04:44
there the nephron loop is going to
00:04:45
connect to the distal convoluted tubule
00:04:48
notice it's
00:04:49
kind of windy and convoluted just like
00:04:51
the proximal one was
00:04:52
once it gets to the end of the distal
00:04:54
convoluted tubule it's going to connect
00:04:56
with something called the collecting
00:04:57
duct
00:04:58
if you notice in the collecting duct
00:04:59
there's lots of branches coming out of
00:05:01
it that's because there's lots of
00:05:02
nephrons
00:05:03
that all connect to the same collecting
00:05:05
duct but the big idea here is that all
00:05:06
of the urine that we're filtering out
00:05:08
is collecting together into collecting
00:05:10
ducts which then joined together to form
00:05:12
the calyx
00:05:13
which is going to connect to the ureter
00:05:15
so we can bring that down to the bladder
00:05:17
so our end of the collecting duct there
00:05:18
will connect down to the ureter but we
00:05:20
haven't talked about that reabsorption
00:05:22
component yet
00:05:23
let's go ahead and add in the other
00:05:24
blood vessels here so we said that we
00:05:26
have blood coming
00:05:27
in about 20 percent of our blood plasma
00:05:29
is going to filter out
00:05:31
into the bowman's capsule from the
00:05:32
glomerulus but 80
00:05:34
of the plasma is going to stay in these
00:05:36
blood vessels as well as all the red
00:05:38
blood cells and white blood cells those
00:05:40
are going to stay in the blood vessel
00:05:41
they're too big to really go through
00:05:43
filtration here and end up there also a
00:05:45
lot of our bigger proteins in our blood
00:05:47
plasma
00:05:47
are too big to actually get filtered out
00:05:49
so most of those will stay
00:05:50
in the blood vessel here that blood
00:05:52
vessel is going to take that blood
00:05:54
over here to where the nephron loop is
00:05:57
so that reabsorption
00:05:58
can occur let's start in the proximal
00:06:00
convoluted tubule and see what happens
00:06:01
here so we filtered out a bunch of the
00:06:03
fluid and then h2o and nutrients are
00:06:05
going to get
00:06:06
reabsorbed back into the bloodstream
00:06:07
like i said it's kind of inefficient we
00:06:09
filtered a bunch out but we're going to
00:06:10
put most of that back into the
00:06:12
bloodstream
00:06:12
about two-thirds of the water that we
00:06:14
filtered out is going to reabsorb back
00:06:16
into the bloodstream from the proximal
00:06:18
convoluted tubule and a lot of the
00:06:20
important nutrients that we need such as
00:06:21
sugars and vitamins and stuff
00:06:23
are going to diffuse out of the proximal
00:06:24
convoluted tubule into
00:06:26
the blood vessels again so that we don't
00:06:28
urinate out all of that good stuff that
00:06:30
we need
00:06:30
in our bloodstream okay so about
00:06:32
two-thirds of the water and most of the
00:06:33
nutrients
00:06:34
have been reabsorbed back into our
00:06:36
artery here
00:06:37
and then as this nephron loop descends
00:06:40
down into the medulla
00:06:41
it's gonna get increasingly salty in
00:06:44
other words it's gonna have a lot more
00:06:45
sodium it's gonna have a lot more
00:06:46
chloride and other ions in that area
00:06:48
we're going to talk about how the
00:06:50
medulla got so salty in just a minute
00:06:52
but for now know
00:06:53
that this is very salty it's a lot more
00:06:54
salty as we descend down into the
00:06:56
medulla and what salt does
00:06:58
is it essentially attracts water so as
00:07:00
the nephron loop descends
00:07:02
water is going to be diffusing out of
00:07:04
that nephron loop back into our blood
00:07:06
vessels
00:07:06
and that process of water diffusion
00:07:08
because of a highly salty area
00:07:11
is osmosis so the big idea there water
00:07:14
is leaving the descending nephron loop
00:07:16
and it's being attracted essentially to
00:07:17
the saltiness of the medulla
00:07:20
and that water is going to enter back
00:07:21
into our bloodstream here from there the
00:07:23
filtrate is going to wrap around the
00:07:25
nephron loop
00:07:26
and enter the ascending nephron loop now
00:07:28
in the ascending nephron loop we
00:07:29
suddenly
00:07:30
have an area that's impermeable to water
00:07:32
water can't
00:07:33
leave or enter in this ascending part of
00:07:36
the loop so it's different
00:07:37
physiologically than the descending part
00:07:39
in the descending part water was leaving
00:07:40
due to osmosis in the ascending part
00:07:43
water can't diffuse
00:07:44
back and forth into or out of the
00:07:46
nephron loop what is happening though
00:07:48
is sodium and chloride ions are being
00:07:50
actively transported out
00:07:52
they're being pumped out and that's
00:07:54
what's actually making the medulla salty
00:07:55
in the first place
00:07:56
is that we have pumps for sodium and
00:07:59
chloride to pump out those ions
00:08:01
which is going to make this medulla
00:08:02
salty and just because it's happening
00:08:04
here on the diagram it's really
00:08:06
happening all throughout this whole
00:08:08
medulla area right here this active
00:08:10
transport of the salt ions
00:08:12
is really what makes this osmosis part
00:08:14
earlier on in the nephron loop possible
00:08:16
but of course it's active transport so
00:08:18
it takes a lot of energy so we need a
00:08:20
lot of energy for our kidneys to
00:08:21
function
00:08:22
like i said it's a little bit
00:08:23
inefficient okay great from there the
00:08:24
filtrate is going to travel
00:08:26
through the distal convoluted tubule and
00:08:29
at the distal convoluted tubule
00:08:31
water can diffuse out note that i said
00:08:34
it can diffuse out i didn't say that it
00:08:36
will that depends on something
00:08:37
the water can also diffuse out from the
00:08:40
collecting duct
00:08:41
but again that's going to depend this is
00:08:43
where the true regulation happens
00:08:45
where our body is going to decide do we
00:08:46
want to try to conserve as much water as
00:08:48
possible
00:08:49
or do we want to try to urinate out a
00:08:51
lot of water so basically if you're
00:08:53
dehydrated
00:08:54
we're going to reabsorb as much water as
00:08:56
we can the distal convoluted tubule will
00:08:58
become very leaky to water so that water
00:09:00
is going to be leaving
00:09:01
and so will the collecting duct the
00:09:02
collecting duct will become very
00:09:03
permeable to water
00:09:04
so the water can leak out into the salty
00:09:06
medulla area and again that's if we're
00:09:09
dehydrated we're trying to conserve
00:09:11
water we don't want any water leaving
00:09:13
through the collecting duct to the
00:09:14
ureter because then we're going to lose
00:09:16
that water whenever we urinate
00:09:17
instead if we're dehydrated we want to
00:09:19
get any water that we can that's still
00:09:21
left over in our filtrate we want to get
00:09:22
that water back into the bloodstream
00:09:24
so we're going to let it leak out of
00:09:25
here and diffuse back into our
00:09:27
bloodstream
00:09:28
so we can keep it in circulation and
00:09:29
keep all the water in our body but
00:09:31
how does our body regulate that well
00:09:33
there's a special hormone that's
00:09:34
involved and so this
00:09:36
process of reabsorption of water in the
00:09:38
distal convoluted tubule
00:09:40
and collecting duct is only going to
00:09:42
happen if adh is present adh stands for
00:09:45
anti-diuretic hormone
00:09:47
it's a hormone released by the pituitary
00:09:49
gland that's little gland hanging off
00:09:50
the front of your brain
00:09:52
it's also known as vasopressin but i
00:09:54
like the term adh because it describes
00:09:56
what it does
00:09:56
a diuretic is anything that makes you
00:09:58
pee more and an
00:10:00
antidiuretic is something that would
00:10:02
make you pee less
00:10:03
so anti-diuretic hormone makes you pee
00:10:06
less how does it make you urinate less
00:10:08
well it's going to cause the distal
00:10:09
convoluted tubule
00:10:10
and the collecting duct to leak more
00:10:12
water so water leaves there
00:10:14
and enters back into the bloodstream the
00:10:16
plus in my diagram just means that it
00:10:18
stimulates
00:10:18
water getting reabsorbed back into the
00:10:20
bloodstream but what if we're not
00:10:22
dehydrated what if we've been drinking
00:10:23
plenty of water and our body actually
00:10:25
has more water than it needs and it
00:10:26
wants to get rid of some of that water
00:10:27
well then our brain our pituitary is
00:10:30
going to stop releasing adh
00:10:32
antidiuretic hormone if antidiuretic
00:10:34
hormone is not present
00:10:35
well then the distal convoluted tubule
00:10:37
and the collecting duct will not be
00:10:39
permeable to water
00:10:40
so in other words all of the filtrate
00:10:42
that enters in the distal convoluted
00:10:43
tubule
00:10:44
is going to stay there as it travels
00:10:45
through and down the collecting duct
00:10:47
all that water will stay in the
00:10:49
collecting duct and then into the ureter
00:10:50
so we can urinate out a lot of water
00:10:52
that would make our urine a lot lighter
00:10:54
because it has so much water present in
00:10:55
other words it's very dilute
00:10:57
to contrast that if we had a lot of adh
00:10:59
well then
00:11:00
we're going to be reabsorbing most of
00:11:01
that water and so that's going to make
00:11:02
the urine a lot darker
00:11:04
because it has less water compared to
00:11:06
the amount of solute or
00:11:07
other waste that we're getting rid of so
00:11:09
to summarize one more time
00:11:10
if we're dehydrated and our brain is
00:11:12
releasing a lot of adh that's going to
00:11:14
cause the distal convoluted tubule
00:11:16
and the collecting duct to become
00:11:17
permeable to water or leaky to water
00:11:20
water is going to get reabsorbed back
00:11:21
into the bloodstream at a greater amount
00:11:23
so that we're not producing a lot of
00:11:25
urine
00:11:25
because we're trying to keep water in
00:11:26
the body however if we've got plenty of
00:11:28
water in the body
00:11:29
our brain won't be releasing adh and so
00:11:31
if there's no adh then the distal
00:11:33
convoluted tubule
00:11:34
and the collecting duct will not be
00:11:35
permeable to water that water is going
00:11:37
to stay
00:11:37
in the urine as it goes down the
00:11:39
collecting duct and will produce a lot
00:11:41
more urine now
00:11:42
filtration and reabsorption the kidneys
00:11:44
is a lot more complex than what i've
00:11:46
presented in this diagram
00:11:47
there's lots of other ions involved
00:11:49
there's other hormones involved like
00:11:51
angiotensin one and two and aldosterone
00:11:53
and a bunch of other things but this is
00:11:55
a pretty good overview of how the system
00:11:57
works
00:11:57
all right that was a lot of information
00:11:59
let's do a quick recap here blood is
00:12:00
going to enter into the glomerulus from
00:12:02
a renal artery
00:12:03
about 20 of that blood plasma is going
00:12:05
to get filtered out into the bowman's
00:12:07
capsule
00:12:08
that filtrate will travel through the
00:12:09
proximal convoluted tubule
00:12:11
about two-thirds of the water that got
00:12:13
filtered out will get reabsorbed back in
00:12:14
the bloodstream just here in the
00:12:16
proximal convoluted tubule
00:12:18
nutrients also get reabsorbed so we make
00:12:19
sure we keep all those important
00:12:21
nutrients in the bloodstream
00:12:23
the filtrate will travel down the
00:12:25
descending nephron loop
00:12:26
where more water is going to diffuse out
00:12:29
in the process of osmosis
00:12:30
because this medulla is very salty so
00:12:33
water is going to diffuse out back into
00:12:34
the bloodstream here
00:12:35
as the filtrate goes up the ascending
00:12:37
nephron loop
00:12:38
sodium and chloride ions are going to
00:12:40
get actively transported or
00:12:42
pumped out of the nephron loop which is
00:12:44
what caused this medulla to be salty in
00:12:46
the first place
00:12:47
which is driving the osmosis which is
00:12:49
happening in the descending loop
00:12:51
as that filtrate passes up into the
00:12:52
distal convoluted tubule
00:12:54
more water can be reabsorbed into the
00:12:57
bloodstream
00:12:57
in the distal convoluted tubule as well
00:12:59
as the collecting duct
00:13:01
but that's only going to happen in the
00:13:02
presence of adh
00:13:04
our pituitary gland is going to release
00:13:06
more or less adh in order to regulate
00:13:08
how much of this fluid gets reabsorbed
00:13:10
and that's how we'll regulate whether we
00:13:12
produce a lot of urine
00:13:13
or just a little bit of urine any fluid
00:13:15
or waste that doesn't get reabsorbed
00:13:16
will travel down the collecting duct to
00:13:18
the ureter
00:13:19
and then to the bladder we can expel it
00:13:21
in the process of urination speaking of
00:13:22
which
00:13:23
i need to go use the bathroom but before
00:13:25
i do that take a moment
00:13:27
pause the video and see if you can
00:13:29
explain all of the stuff that i just
00:13:30
explained
00:13:31
talk about the process of filtration
00:13:33
what happens in the different tubules
00:13:35
and loops
00:13:36
and then how this is regulated by adh at
00:13:39
the end
00:13:43
and if you can use the diagram here to
00:13:45
explain that whole process
00:13:46
then you know this process pretty well
00:13:50
hey uh mortimer can you believe this is
00:13:51
the last anatomy and physiology video of
00:13:53
the year
00:13:55
what are we gonna do all summer
