what we're looking at here is a Reno cor
pusle we can see Bowman capture around
the
outside and the gulus
inside and in essence it's fairly
straightforward blood goes in via the
afferent
arterial labeled six
here from here the blood goes into the
capillary
Network or the ball of capillaries which
is the
glus as the blood goes through the glus
the process of ultra filtration takes
place and gular filtrate is formed the
gular filtrate moving from the gular
capillaries into the space this gular
space then the blood goes out again via
the epin
material labeled
seven in this
model and the filtration is on grounds
of molecular size so large molecules
like proteins or large structures like
blood cells will not be filtered out
because it's an ultra
filtration but smaller molecules like
water amino acids glucose and atomic
scale structures such as ion
will be freely filtered into the
glomular
filtrate so let's look at this in a
little more
detail now if we take this out actually
we can see the
capture what we're looking at there is
Bowman's
capsule still called Bowman's
capsu and this is the parietal
epithelium the outside layer the
parietal epi helium and all this area in
here is Bowman's
space The Bowman space and it's into
Bowman space that the gular
filtrate will be filtered out
into and then we notice once the
glomular filtrate is formed it goes down
into the first part of the renal
tubule that is the proximal renal tu U
and as we can
see this has got a brush
border this is composed of
microvilli and this increases greatly
the internal surface area for the
reabsorption processes that need to take
place the brush border made of micro
vill I'm going to try and put my uh glus
back in
now there we have the glus back
in more or
less and now we can see that the ultra
filtration takes place between the
capillaries of the glus and Bowman
space once the gular filtrate is formed
we can see it can go from the space down
into the proximal part of the nefron for
the processes of reabsorption to start
to take
place so the
apperent
arterial is bringing blood in from a
branch of the renal
artery and we can see there's a swollen
bit
here that's part of the juxa glomular
apparatus
which we'll be thinking about later on
but for now we notice that these
cells these granular cells that form the
juter glomular apparatus are in close
proximity to this
structure perched on top
here now what this structure is is this
is actually the distal convoluted tubule
or the start of the dist or convoluted
jubu of the very
same
nephron that started there at the bottom
so this goes down the descending loop
around the loop of Henley back
up and it finds its own glus
again and the juter gular apparatus jua
means
beside so you can see that this is
beside the glus
and this part here where the cells are
closest together is called the macular
denser and the J apparatus is that bit
and the cells in the wall of the aparant
arterial as well so that's the distal
tubule with a macular
denser and then we can see that the
efferent
arterial is leaving there and the
afferent and the an arterial aligned
with vascular endothelial
cells so the capsular are epithelial
cells but the blood vessels aligned with
endothelial
cells now it's fairly obvious when we
look at this glus that it's in two
colors we've got a white bit on one side
and a red bit on the other side what's
that
about well this does not represent a
hystological change it's just this model
trying to explain things to us so if we
look at the left part
first what we're actually seeing
there labeled nine on this model what
we're actually seeing there if we looked
at it from the outside we would see that
the capillary the gular capillary is
covered with these cells called
pites and these pod aites pod means feet
they are cells with feet as we'll see
this forms the viseral
epithelium so Bowman's capsu is the
parietal epithelium and the pites are
the viseral
epithelium of the glomular
capsule and we notice that there are
very fine red lines
here these fine red lines
there and they represent the filtration
slits between the individual
pyes so the pites have these feet like
structures that wrap around the GLA
capillaries and those red lines that we
see there are actually filtration slits
the gular filtrate is physically
filtered through those slits from
the Lumin of the capillary into Bowman
space and they're actually covered with
something called a slit membrane as well
which is also
dialing as it generates glomular
filtrate
now when we look at
the other side of the capillary here
labeled C capillar is labeled eight what
we're actually seeing there is these are
exactly the same cells but they're well
exactly the same structure it's still
the glomular capillaries but it's
modeled without the
pites so if you like in the red
capillaris the pites have been dissected
off
to reveal the vascular endothelial
cells and we notice in the vascular
endothelial
cells that there are dark
areas representing the nuclei of the
cells and if we look at greater detail
we can probably see that there's lots of
smaller dots all
over these are actual little physical
pores called
fenestrations so this means that the
blood is exposed sometimes to the
capillary membrane and sometimes to
these
fenestrations little holes and in
life
these
endothelial capillary cells where we see
the fenestrations are actually covered
with a basement membrane that goes round
like that like this piece of
film they're completely surrounded by
that basement membrane and it's this
basement membrane surrounding the
vascular
endothelium and the fenestrations of the
glomular capillaries that is the dialing
membrane so in order to be dialed in
order for ultra filtration to take place
material goes through the
fenestrations through the dialing
membrane through the slip filters in the
podici
sites and through these filtration slits
in the podici
sites before it can get out
into Bowman space where it is then
glomular
filtrate after this dialing process of
ultra filtration has taken
place and it's interesting that when you
take into account the various forces
involved the positive pressure inside
the capillaries is only around 10 mm of
mercury overall when we account for the
osmotic pressures and the reverse
pressures so the dialing process is
taking place under a pressure of 10 mm
of
mercury any material left in the
capillaries that is not subject to ultra
filtration will
leave via the efferent arterial so the
process through is afferent
arterial glomular capillary cells where
the blood is subject to this physical
filtration
process out through the efferent
arterial and exiting the
glus from the ephrine arterial
now I want to spend a little bit of time
on this fascinating structure here the
juter gular
apparatus now these
cells in
the wall and extending out from the
wall of the aferin
arterial are modified smooth muscle
cells and these are the juer gular cells
they're sometimes called granular cells
because they appear granular and the
reason that they appear granular is they
contain VES of
renin so this is the place where the
renin is uh produced and
secreted and these cells are sometimes
described as myo Endocrine
cells because they have the
characteristics of muscle cells they're
part of the smooth muscle wall of the
apperant
arterial but they're also secretory they
secrete the
renin now the renin as you probably
know acts on the renin angot tensing
mechanism and that will cause Vaso
constriction raising blood vessels
raising blood pressure by constricting
blood vessels throughout the body and it
will also increase the amount of
Alder sterone present in the blood which
will increase sodium
reabsorption and this happens in two
basic
ways first of all if the blood pressure
passing through the apent arterial is
reduced that's detected in the afer
arterial and if the blood pressure is
low these cells will respond by
producing renin
and renin will stimulate the Angiotensin
mechanism and that will raise blood
pressure by increasing the amount of
sodium in the blood therefore increasing
intravascular
volume and
also via the mechanism of peripheral
Vaso
constriction so that will increase blood
pressure but there's a second mechanism
here and it's related to these macular
densa
cells now these macular densa
cells are cells which appear closer
together the nuclei are closer
together and they're different from the
cells in other areas of the distal
convoluted tubu and indeed other parts
of the
Nephron and these macular denser cells
are able to respond to sodium levels in
the
filtrate so if the sodium levels in the
filtrate are
low these cells will produce
messages chemical based messages which
will go to
the granular
cells stimulating them to produce renin
so the renin can be produced directly it
can be stimulated by low blood pressure
in the afferent
arterial but renin can also be
stimulated when these macular denser
cells detect low levels of sodium in the
filtrate and the point about low levels
of sodium in the filtrate is that that
indicates A reduced Glam filtration
rate so if the gular filtration rate is
reduced that can be detected in this
distal
tubule and the distal tubule can
release chemicals locally here cytokine
type chemicals that can cause renin to
be released and can also alter the Vaso
tone of this apparent
arterial so if there's a reduced
glomular
filtration that can be regulated by by
dilation of the afren
arterial allowing more blood to go into
the
glus thereby increasing the gular
filtration rate so it's very clever that
the disto tubule there with the macular
denser is actually
controlling the formation of the gular
filtrate which will shortly be in that
tubu so each nephron
is auto regulating
itself and this is called tubog glomular
feedback feedback between the
tube the nefron and the glus tubulo
gular
feedback and that controls and
regulates GFR
glomular filtration
rate so the nefron is
via this jular apparatus is controlling
its own activity but it's also relating
or controlling whole body blood pressure
and in fact the most common cause of
essential
hypertension is that the kidney for some
reason is
producing too much renin stimulating the
Angiotensin mechanism
excessively so that's a brief
introduction to
the
glus and the renal cor
pusle and the jxa glomular apparatus