00:01
The intrinsic controls
include renal autoregulation.
00:06
Again, these are going to
maintain our nearly constant GFR
when the mean
arterial pressure(MAP)
is in the reign of 80 to 180.
00:17
If we get out of this range,
then autoregulation
is not going to work.
00:23
There are two types of
renal autoregulation.
00:27
We have myogenic mechanisms
of autoregulation
and tubuloglomerular
feedback mechanisms
of autoregulation.
00:37
First let's take a closer look
at the myogenic mechanisms
of autoregulation.
00:43
Local smooth muscles
are going to contract
when they are stretch.
00:47
And increased blood pressure
causes those smooth
muscles to stretch
and this leads to constriction
of the afferent arterioles.
00:57
This constriction of the afferent
arterioles then restricts blood flow
into the glomerulus.
01:05
This protects our glomeruli
from damage that would be
due to a high blood pressure.
01:13
A decrease in our blood pressure
would cause dilation
of our afferent arterioles.
01:20
Both of these are going to
help maintain our normal GFR
despite the normal fluctuations
in our blood pressure and
other parts of the body.
01:32
With tubuloglomerular
feedback mechanisms
of autoregulation.
01:37
There's going to be a
flow dependent mechanism
that is directed by cells known
as the macula densa cells.
01:46
The macula densa
cells are a part
of the a sending limb
of the nephron loop
that makes contact with
the afferent arteriole
of the glomerulus.
01:58
These are going to respond
to the filtrate sodium
chloride concentrations.
02:05
If the glomerular
filtration rate is high,
then the filtrate flow
rate is also high.
02:12
This will then
lead to a decrease
in reabsorption time,
which means that there's salt
concentrations will be higher
than normal or higher than
what they're supposed to be
in the filtrate.
02:26
A feedback mechanism will
then cause the constriction
of the afferent arteriole,
which will then lower the
net filtration pressure
which will then lower the
glomerular filtration rate.
02:39
And this will allow more time
for the salt or sodium
chloride to be reabsorbed.
02:46
The opposite mechanism occurs
when you have a decrease
in the glomerular
filtration rate,
which will lead to a lower
sodium chloride concentration
than what is expected
in the ascending limb
of the nephron loop.
03:02
So along with our
intrinsic controls,
we also have extrinsic controls.
03:07
The purpose of these
extrinsic controls
is to regulate the
glomerular filtration rate
in order to maintain
systemic blood pressure.
03:19
These extrinsic controls
will override the
intrinsic controls
if our blood volume needs to
be increased for any reason.
03:30
Under normal conditions at rest
are renal blood vessels
are nice and dilated.
03:36
And this is due to the renal
auto regulation mechanisms
that are taking place
at this point are
intrinsic controls.
03:45
However,
under abnormal conditions
such as an extremely low
extracellular fluid volume,
which leads to a
low blood pressure
are sympathetic nervous
system takes over.
03:58
Norepinephrine it's
going to be released
by the sympathetic
nervous system
and epinephrine will
be released by cells
and the adrenal medulla.
04:08
This will cause a
systemic vasoconstriction
which will then
lead to an increase
in our systemic blood pressure.
04:17
This will also
cause a constriction
of the afferent arterioles
which will decrease our
glomerular filtration rate.
04:26
These effects will then
cause the blood volume
and subsequently the blood
pressure to increase.
04:34
Another extrinsic control,
is the renin-angiotensin-aldosterone
mechanism.
04:41
This is actually
the main mechanism
for increasing blood pressure.
04:46
This involves the release of
renin from granular cells.
04:51
Granular cells are cells
found in the kidney
next and also referred to
as juxtaglomerular cells
because of their proximity
next to the glomerulus.
05:03
These are modified
smooth muscle fibers
that are going to
make up the wall
of the afferent arteriole
of the glomerulus.
05:12
There are three pathways
that leads to the release
of renin by the cells.
05:18
Either direct stimulation
of the granular cells
by the sympathetic
nervous system
stimulation by activated
macula densa cells
when the filtrate sodium
chloride concentrations
are lower than normal,
or by reduce stretch of
these granular cells.
05:40
So the first intrinsic control
is our myogenic autoregulation.
05:46
Let's see how this
response to a decrease
in our systemic blood pressure.
05:52
If the systemic blood
pressure goes down
then the blood pressure
and the afferent arteriole
also is going to go down
and also the glomerular
filtration rate
will be lower than normal.
06:07
Also the stretch of
the smooth muscles
in the walls of the
afferent arteriole
also will be decreased.
06:15
We respond to this
with vasodilation of
the afferent arteriole,
which will then increase the
glomerular filtration rate.
06:26
The second intrinsic control
is are tubuloglomerular
autoregulation.
06:33
In response to a decrease in
our systemic blood pressure.
06:37
This is going to
lead to a decrease
in our glomerular
filtration rate.
06:43
The filtrate flow
and a sodium chloride
in the ascending loop will
then be lower than normal.
06:51
From there,
the macula densa cells
of the juxtaglomerular
complex of the kidneys
will release
vasoactive chemicals,
which are going to
lead to vasodilation
of the afferent arteriole.
07:06
This will subsequently caused
the glomerular filtration
rate to go back up.
07:14
The first extrinsic control
is our hormonal control
through our
renin-angiotensin-aldosterone mechanism.
07:25
In this case,
if the systemic blood
pressure is lowered
then the granulocells
of the juxtaglomerular complex
are going to release renin.
07:34
This then causes the
activation of angiotensin II.
07:40
Angiotensin II can then either
cause vasoconstriction and
our systemic arterioles,
which will then increase
our systemic blood pressure
or Angiotensin II can also cause
this secretion of aldosterone
by the adrenal cortex.
07:59
Aldosterone leads to an increase
in our sodium reabsorption
by the kidney tubules.
08:06
Because of osmosis,
water will follow the salt
and also be reabsorbed.
08:12
This causes an increase
in our blood volume.
08:16
And that increase
in our blood volume
also causes the systemic
blood pressure to go back up.
08:24
The second extrinsic control
is our neural controls.
08:28
So in this case
when our systemic
blood pressure is low.
08:32
This is going to
inhibit baroreceptors
found in our blood vessels
of our systemic circulation.
08:40
This causes the activation
of the sympathetic
nervous system.
08:45
And from there we
get vasoconstriction
of the systemic arterioles,
which is going to increase
peripheral resistance
and increase the
systemic blood pressure.