Today we are going to talk about the renin angiotensin adlosterone axis or the system
right it is one of the very important physiological system which is doing lot of function but
most important function is blood pressure regulation. That how this system regulates
your blood pressure. So lets start first to understand its physiology. Right and to understand
its physiology lets take an example that due to some reason my blood pressure is going
down for example i develop some hemmorrage or bleeding I am loosing the blood out of
my body. Than how this system is activated. Because the duty of this system is duty of
renin angiotensin aldosterone system is to maintain my blood volume and to maintain my
blood pressure. Volume and pressure in the vascular system should be regulated by this
system. It plays one of the very important role. Lets disturb the volume and pressure
and see what happens to this system. Example we take that there is a patient and he got
on road side accident and he is loosing blood. Right? Ofcourse. Now we will discuss that
how this system is activated. Lets suppose that this is the circulatory system of that
patient. Right? The organs which are going to play a role in this whole game is No 1
central nervous system which is responsible for sympathetic outflow. We will talk about
the kidney. Is that right? Rather drawing the full kidney we will draw a nephron here
Right? We will draw a small kidney here. Right? Then there is a role played by the liver.
We will talk about that what is that role and than very important role is played by
pulmonary circulatory system and ofcourse we will not forget the role that is played
by adrenal cortex. Now lets start one by one. What really happens that when your patient
is bleeding lets suppose patient is loosing the blood here naturally blood pressure is
going down and blood volume is going down. Is that right? Many things will happen in
that body, one of the thing which will happen that if patient is bleeding and blood pressure
goes down the blood flow to kidney will increase or decrease? Decrease! So the first thing
we will say there is reduced renal perfusion. Now! Whenever there is reduced renal perfusion,
right? Then veins from the kidney, the veins from the kidney start bringing an enzyme in
the blood. This enzyme is released in blood from the kidney. This enzyme is called "Renin".
What I have said that whenever blood pressure goes down kidney's start producing more renin
and more renin comes into blood. But first of all we must study the kidney thoroughly
that by reducing the blood pressure how kidney start producing renin. Right? For this purpose
I will bring one nephron out and show on the nephron the appratus which is suppose to release
"Renin". One kidney has how many nephrons? You know, kidneys have very specialized tubes,
you are millionaire as far as nephrons are concerned! :D In one kidney there are out
1.2 Million nephrons but i will just bring out of this kidney one nephron out right?
Lets suppose this is the nephron here and this nephron I am going to drawn outside to
explain that how really this system works. This is one epithelial tube of nephron from
the kidney. Right? and we will see how normally this nephron works in relationship to blood
supply. Lets suppose this is afferent arteriole which is bringing the blood to the nephron.
These are glomerular cappiliaries and here is efferent arterioles. What is this? This
is afferent arterioles. Here it is efferent arteriole. Right? and here is your nephron.
Now what really happens? That we say that blood is patient is bleeding, naturally blood
coming to kidney is less so ofcourse the blood flow to this nephron is also less. So afferent
arteriole has poor blood flow. Now there is very interesting thing. Nature has put blood
pressure measuring devices with every nephron. What a master system in the nature that nature
has put blood pressure measuring device with every nephron, so every nephron knows how
much blood is coming to it. Is it enough or not. So Mr. Hadayat will you tell me? What
is the blood pressure measuring device with every nephron? Anyone has idea about? You
have any idea. Every nephron has blood pressure measuring device. If you have 2.5 million
nehphrons right now in your 2 kidneys there are 2.5 million blood pressure measuring devices
with every nephron. Let me tell you one thing. You see what is this? This is afferent arteriole.
These are the normal smooth muscle of afferent arteriole. As afferent arteriole approaches
that, what is this? "Glomerulous". Right? Its smooth muscles become altered. They are
no more normal smooth muscles. These are very specialized smooth muscles. Right? and this
group of very specialized smooth muscle which is present in the wall of afferent nephron,
sorry afferent arteriole. This is blood pressure measuring device. These are the baroreceptors.
It means nature considers blood flow to nephron extremely important that is why nature measures
the blood flow to every nephron. Right? and this whole group, it has been given a special
name. The name is called "Polkesin". So what is polkesin? Polkesin is made of special appratus
which is made of what? Modified afferent arteriolar smooth muscle which are able to measure the
blood flow to nephron and whenever blood flow to nephron becomes less, whenever the blood
flow to nephron becomes less then they start releasing "Renin" into blood. So it means
they have double action. One action is to measure the blood flow and second action is
to release the renin. It means they are acting like an "Endocrine Gland", because one group
of cell releases the hormone into the blood and acting into some distant area so every
nephron has some small endocrine system with it. Am I clear? This is the blood pressure
measuring device. Whenever your blood flow is coming less and there is less pressure
on this apparatus as soon as this apparatus sense that blood flow is less or blood pressure
is less it will start releasing which substance? "Renin". Ok write it like this :) It is the
renin. So this is one way how renin is released by the special apparatus by the nephron. Now
another mechanism is also there. First understand normal. Normally what happens that when blood
is moving through the glomerular capillaries, there is some filtration done, there is glomerular
filtrate. Am i clear? Now! This glomerular filtrate normally has lot of sodium and many
other substances. Ofcourse what are these? These are the cells in the walls of the nephron.
Right? Now listen! Nephron has lots of cells in its wall. Now you see. Normally, when there
is normal blood flow then there is normal filtration and filtration is about 120 ml
per minute in the all nephron. This filtered material starts going down but because it
has lots of sodium nephron cells take the sodium back to the body. Is that right? About
70% of the sodium or 60 - 70% of the sodium which is filtered as it is moving throught
he proximal congulated tubule it is reabsorbed back to the body. We don't want to loose the
sodium. Then sodium keeps on moving forward and about 25% of the sodium is reabsorbed
here. If 65% sodium if 100 untis of sodium go down 65% is reabsorbed here and 25% is
reabsorbed here. How much is left?