Question 48

[vpteruna3172]

Since Mitral Valve Stenosis causes a decreased blood flow in both left atrium and ventricle, then there is a decreased blood flow in aorta as well.
I thought that decreased blood flow is inversely proportional to pressure.
My answer was pulmonary artery. Because it delivers the deoxygenated blood from the right ventricle to the lung. So, I thought there wouldn't be an elevated pressure in the pulmonary artery

Can somebody please explain it to me?

Thanks..

[vpteruna3172]

What I meant was blood flow is inversely proportional to pressure. Decreased blood flow --> increased pressure.

[admin]

Imagine a hose that had no flow of water at all. What would be the pressure? Zero. If the flow is great, then the pressure is high. It is the same with blood vessels.

[dnpgr16513]

Hi,

I'm still confused. I also said the pulmonary artery because the pulmonary artery is taking blood AWAY from the heart. This blood has not been in contact yet with the mitral valve stenosis. However, after blood passes through the left atrium and left ventricle, blood flow is reduced, causing higher pressure in locations following the stenosis. Thus, I assumed since the aorta is after the left atrium, the aorta will also exhibit effects of elevated blood pressure. Is this logic wrong?

thanks so much!

[mcat_premed3832]

Yes, the logic is incorrect.

Again, consider the example of water flowing inside of a hose. No water, no pressure; a little water, will cause a little pressure and so forth.

Now back to the hose: if there is water flowing through a hose and then you step on the hose, you just caused a narrowing (obstruction or stenosis). Does the flow of water after the narrowing increase or decrease? Of course it decreases. In fact kids playing with hoses know that if you obstruct it, water backs up and pressure increases to every part of the hose before the obstruction, so much so, that sometimes water starts spurting out or leaking from where the hose screws into the tap.

Not to mention: the question gives it away! It says that there is decreased blood flow when you cross the mitral valve. So if the question is telling you that on one side of the mitral valve there is reduced flow, and, there is only one part of the circulatory system among the answer choices which is on that side of the mitral valve (the aorta), that is pretty much giving the answer away.

The following is clearly not necessary but just underlines the above . . . Don't forget from physics (fluids) that Flow = Volume per unit time (PHY 6.1.3). Clearly after the obstruction, flow is reduced (again, this is said in the question) and so less volume per minute is delivered to the right ventricle. Thus less volume per minute will be delivered to the aorta.

Everything before the obstruction backs up just like what happens after an accident on the highway.

Beyond this question and the MCAT: "This left atrial pressure is transmitted to the pulmonary vasculature and causes pulmonary hypertension." http://en.wikipedia.org/wiki/Mitral_stenosis

Of course, hypertension means high blood pressure which happens to the entire pulmonary circulatory systems as a result of mitral stenosis.

[dnpgr16513]

Thanks so much! Definitely makes more sense

[jsfkt78927]

This question is repeated a couple times. Its on test 7 and 8. Fix that please gold standard, we paid for 10 tests. Not 10 tests with intentional repeats.

[mcat_premed3832]

1500 questions, less than 20 repeats.

Nonetheless, thanks (sincerely) for pointing them out because we will change them and within one week.

[enolia852008]