Comes here of this bend. This is the end of, this is the beginning of distal congulated
tubule and end of the thick part of ascending limb of loop of henle. Here nature has put
a very beautiful system. There are some cells here which are very very slightly modified
structure, this group of cells here the nephron cells are somewhat modified. These are tall,
these are dark looking and these cells love to taste the fluid here, these cells are sensitive
to, they are sensitive to sodium they are sodium sensors. What is the function of these
cells? These are sodium sensing cells. Right? Now, actually this is pressure sensing system
and this is sodium sensing system. This system together makes a whole appratus. Now look,
afferent arteriole with polkesin and this specialized group of cells from distal congulated
tubule and its junction with the proximal part. Is that right? This group of cell and
this group of cell they make one specialized apparatus. These acting as a baroreceptors
and these acting as chemoreceptors. These are the baroreceptors, these are the chemo
receptors. They measure the blood pressure, they measure the sodium concentration. Is
that right? and they are held together by some connective tissue cells. They are held
together by some yes? connective tissue cells. Now! I told you this blood pressure measuring
device, baroreceptor group it is called "Polkesin" and this sodium sensing device it is present
in every nephron, it has a special name. You know what is the name of these special group
of cells? Which measure the sodium. Thank God the researcher who found it he did not
put his name on this. Actually in the beginning when researchers looked at the nephron structure
they found this area was little bit more dark as compared to the rest of the nephron. These
group of cells were darker. So they just called it "Macula Densa". That there is some macule,
macule means patch, patch of cells which is looking very dense. So this is called, what
is name of this thing? "Macula Densa". Now Polkesin is from afferent arteriole and Macula
Densa is from distal congulated tubule, this is vascular component and this is nephron
component. This is pressure measuring device and this is sodium measuring device and they
are held together through connective tissue cells which are called "Lacis cells". All
this apparatus as a group is present in every neprhon. It means every nephron has blood
pressure measuring device as well as sodium measuring system and as a group polkesin +
macula densa they are given a very special name and all of you know that name. What is
the name of this apparatus? Yeah! "Juxtaglomerular apparatus". Have you heard of it? So this
is juxtaglomerular apparatus. Just they call it a special apparatus. Right? juxta posed
to glomerulous. juxtaglomerulous with the glomerulous there is a very special apparatus.
Thank God they did not put a very complex name for it. They just say there is special
apparatus, they never knew in the beginning what is its function. Now they know, Now!
Lets go back to our analogy. We were saying that the person is bleeding blood pressure
is going down, blood flow is going yes? down! So when blood flow is less baroreceptors are
activated in juxtaglomerular
apparatus and they release "Renin". Meanwhile when your blood flow is less then glomerular
filtration is more or less? Less of course! If there is less blood coming. Right? Then
filtration is also less. Now you think really with your own cortex. That, if filtration
is very less, listen listen :D if filtration is very less the fluid will move through this
lumen rapidly or slowly. Sure? So whenever GFR is less luminal flow becomes slow. When
movement of the fluid from the lumen becomes slow then what happens? These cells which
are working on this luminal fluid. They have more chance to work or less chance to work?
More my friend... Of course, Look! If there are many mangoes going here attention Mr.
Hadayat lets suppose there is water going and lot of mangoes going here and you are
sitting here to catch the mangoes. If flow is very fast you will miss the mangoes but
if it very very slowly coming you will catch every mango. Did you get it? These cells work
like you! They are not catching mangoes there, they are catching sodium there. So when blood
pressure becomes less, glomerular filtrate becomes less. Luminal flow becomes less. These
cells extract extra-ordinary amount of sodium and by the time the little fluid reaches here
it is more than normal amount of sodium or less than normal amount of sodium? Less than
normal amount of sodium. Then macula densa, it loves to taste sodium so whenever GFR is
less the proximal part of nephron works on the slowly moving fluid, extract too much
sodium so less sodium reaches the sodium sensing device and whenever macula densa feels there
is less sodium coming it becomes super active. It is activated when there is less sodium
reaching here and it releases some nitric oxide is released by it and prostaglandins
are released by it and they activate these polkesin cells. Macula Densa requests this
that "Please" listen to us! There is very little sodium coming here. There is something
wrong with GFR. Probably blood is not coming well. So please release more "Renin". So renin
release becomes further augmented. So now renin has been released under two influences.
Under "Pressure change" and under "Sodium change". So every glomerulous has juxtaglomerular
apparatus. Apparatus consists of blood pressure measuring device and apparatus consists of
sodium sensing device. Blood pressure measuring device is derived from the afferent arteriole
smooth muscle, sodium measuring device is a derivative of nephron cells. Together they
make "juxtaglomerular apparatus". Whenever blood flow is less to the kidney. Right? This
apparatus releases excessive renin in the blood. Now what this renin should do? Renin
should "Correct" the balance. Bring the patient out of tragedy. What was the tragedy? Blood
pressure was going down and blood volume was going down. Now function of renin is to bring
the blood pressure back as well as blood volume up. So that patient does not die. For example,
patient has lost 1 liter of blood than somehow blood pressure should be maintained and somehow
blood volume should be maintained. We will talk about how renin does it but before that
we will talk about one more factor. What is that? That is, that whenever your blood pressure
goes down, lets suppose here is your heart. So what really happens? What is it? What is
this? Carotid system has carotid body. What is the function of..."SORRY" Carotid Sinus
not carotid body. This what I am saying is "Carotid Sinus". Carotid sinus is another
"Blood pressure measuring device". It also has baroreceptors. When patient is bleeding,
the blood flow to the kidney is more or less? Less! So whenever blood flow becomes less,
this carotid system is also activated and special neurons they report to the central
nervous system that blood pressure is falling. They report to the central nervous system
that blood pressure is falling. In the central nervous system, Right? Ok, Lets forget about
this part of the diagram :) and concentrate only on this. This is going into peritubular
capillaries and than it collects back as venous blood. Ok connect it here. This was renal
arterial flow and this is renal venous flow. Venous blood going back. Right? and arterial
blood.