Lets come back!
I was saying as soon as blood pressure goes down, carotid sinus through the sinus nerve,
right?
This is through the vagus?
9th nerve glossopharyngeal nerve.
Right?
This message is given to the central nervous system that blood pressure is going down.
As soon as central nervous system senses that blood pressure is going down it will stimulate
the sympathetic outflow through the vasomotor center in the medulla.
So from the medulla fibers will come down, neuronal connections will come down and stimulate
what thing out?
Stimulate sympathetic outflow.
This sympathetic outflow which is going out, suppose these are preganglionic sympathetic
neurons, and here are postganglionic sympathetic neurons.
I will not go to detail of all sympathetic fibers, right now we are concerned only with
those sympathetic fibers which are coming to juxtaglomerular apparatus.
These are sympathetic neurons which are coming to juxtraglomerular apparatus.
Actually as soon as blood pressure starts going down, vasomotor center is stimulated,
lots of sympathetic outflow come.
Some of the sympathetic fibers come to juxtaglomerular apparatus, and what they will release there?
They will release....neurons will release....neurons will release norepinephrine.
Right? and these cells have receptors for norepinephrine.
These are Beta-1 adrenergic receptors.
What are these receptors?
Beta-1 adrenergic receptor.
You must know there are beta-1 adrenergic receptors present on juxtraglomerular apparatus
beause beta blocker block them also and help us in hypertension management.
So there are beta-1 adrenergic receptors present over here.
So sympathetic outflow stimulates these beta-1 receptors and when beta-1 receptors are stimulated
here, more release of renin, according to Mr. Hadayat speculations.
More release of "Renin".
So how many mechanism are there to release the renin from here?
Two local and one systemic.
Intra renal mechanism is, low blood pressure in the afferent arteriole and low sodium concentration
to the macula densa.
Both of them release renin, these two are intrarenal mechanism of release of renin.
Extrarenal mechanism of release of renin is, most important sympathetic fibers connected
with that.
Is that right?
So we see this juxtaglomerular apparatus can measure the pressure directly, can measure
the sodium concentration directly and in every emergency whenever sympathetic nervous system
will fire renin will come.
Now what this renin will do?
Lets see what this renin is going to do.
This renin is going to the general circulation, the renin will go to the general circulation.
Now renin has come to the systemic circulation.
Right?
through the renal veins.
Now what renin will do here?
I told you renin is an enzyme.
Right? and every enzyme works on special type of substrate.
It will also work on some special type of substrate.
Before we go for that...
You know liver has lots of hepatocytes.
Hepatocytes produce lots of protein, Normally, you know they produce albumins than globulins
and alpha globulins, beta globulins but not gamma globulins because gamma globulins are
immuno globulins, antibodies which come from plasma cells, B cells.
Most of the proteins other than the gamma globulins, most not all, but most of the proteins
are produced by liver cells.
Liver cells produce one very special type of protein normally, and this protein is called
"Angiotensinogen".
Angiotensinogen.
Right?
Angiotensinogen, ok i will write it in small way, this is angiotensinogen.
Right?
From where it is coming?
It is coming from Liver and it is not coming only during crisis it is produced by the liver
all the time.
Right now all of you have in your blood angiotensinogen.
As soon as renin comes it will work on angiotensinogen, it will work on, angiotensinogen and convert
the angiotensinogen into angiotensin I. It is angiotensin I.
So what is the function of renin?
Renin is an enzyme which can convert angiotensinogen into angiotensin I.
Is that right?
Now all of you know it, that when angiotensin I passes through the lungs, it converts into
angiotensin II.
That is the crust of understanding.
That angiotensin I when it is passing through the lungs it converts into angiotensin II.
It means in the lungs there should be some enzyme which converts angiotensin 1 into angiotensin
II and that enzyme is called angiotensin converting enzyme.
Again, when angiotensin I passes through the lungs it converts into angiotensin II.
Angiotensin II.
Right?
When angiotensin passes through the lungs it converts into angiotensin II.
This is large protein molecule.
It is decapeptide, I mean 10 amino acid then there is enzyme in the lungs which breaks
down two more amino acids and this product is octapeptide only 8 amino acids.
I want to know one thing, angiotensin converting enzyme, on which so many drugs work, angiotensin
converting enzyme are present in which part of the lungs?
Are they present in bronchioles?
Are they present in alveoli?
Are they present in capillaries?
Are they present "where" ? :D
Where in the lungs angiotensin converting enzyme is present?
All of you know there are many drugs that inhibit that enzyme, we must know where is
that enzyme.
Yes, we talk to abbas.
No idea? :O
Jamie?
Same? :O
Yes hadayat ullah? :D
You are with the majority or you will try to guess something?
In the lungs everyone has heard, there is enzyme called angiotensin converting enzyme.
Have you heard of it or not?
Mashallah you have heart of it :D.
Where exactly is it present?
No idea?
Jamie?
Just guess it.
WILD GUESS!
You don't want to even guess? :D
Maybe it is present on the plura.
Yes?
Any "Wild Guess"?
Alveoli.
What do you think?
Pneumocytes.
Ok!
Right it down on the book and put a "VERY BIG" Cross on it :D.
You know why?
If it is present in alveoli then tell me one thing it means your blood has to pass through
alveoli :D
Alveoli are blood flow system or air flow system?
They are air pockets or blood pockets?
Yes?
No!
Alveoli are air pockets and pulmonary capillaries are attached with them but pulmonary capillaries
are not alveoli themselves.
Right?
So, one thing is sure alveoli should not have the enzyme otherwise there will be tragedy.
Blood has to jump into alveoli so that angiotensin I should convert into angiotensin II.
Ok let me explain.
Actually here is alveoli.
Lets suppose this is air way, and these are suppose alveolar system, these are air pockets,
of course blood should not enter there.
Is that right?