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#1
10-03-2009
 USMLE Forums Newbie Steps History: Step 1 Only Posts: 2 Threads: 1 Thanked 1 Time in 1 Post Reputation: 11
Arteriolar Constriction in Hypertension

Ok, as far as I understand is that when you have high pressure in a tube you have to decrease the resistance in order to maintain the flow.
The equation is
Pressure = Flow / Resistance

Then how come we have increased resistance (vaso constriction) in hypertension ?
 The above post was thanked by: wahaha007 (01-10-2010)

#2
10-03-2009
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 3,316 Threads: 170 Thanked 5,039 Times in 1,820 Posts Reputation: 5092

First off,
the equation you put is wrong
the correct one is this
Flow = pressure / resistance, Pressure = Flow X resistance that's why Mean Arterial Pressure is the product of cardiac output and peripheral vascular resistance.

So when Q = P/R then if you increase P then you must increase R to maintain the same blood flow.

Furthermore, in hypertension there's a phenomenon called "Arteriolar Rarefaction" which is the progressive constriction of arterioles ultimately leading to their complete shut down and they gradually disappear and decrease in number, this is thought to be an attempt to decrease flow to the organs when vasoconstriction is no longer enough to offset the high blood pressure and it's thought that the mechanism is a "flush away" of vascular endothelial vasodilators (such NO) by the jetting hypertensive flow.

Losing arterioles, will further exaggerate the increase in peripheral vascular resistance (loss of parallel resistances) and is a factor in increasing the afterload in hypertensive patients who end up hypertrophying their left ventricle to overcome the pressure volume.

 The above post was thanked by: wahaha007 (01-10-2010)
#3
10-03-2009
 USMLE Forums Newbie Steps History: Step 1 Only Posts: 2 Threads: 1 Thanked 1 Time in 1 Post Reputation: 11

Wooooow,

Are you a physiologist?

 Tags Cardiovascular-, Physiology-

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