Welcome Guest Search | Active Topics |

Tag as favorite
Depth and circulatory question
Options
Previous Topic Next Topic
cathy4208
#1 Posted : Wednesday, July 01, 2015 12:22:48 AM
Rank: Newbie

Groups: Registered
Joined: 6/29/2015
Posts: 8

Thanks: 0 times
Was thanked: 0 time(s) in 0 post(s)
Why does the body induce fainting when circulation to the brain is insufficient?

A) The CNS ischemic response increases the pressure of blood travelling to the brain
B) Brain response to this insufficiency cause brain BP to exceed ventricular BP
C) An active brain results in reduced metabolic need, allowing circulation to catch up
D) Fainting reduces the effect of gravity which reduces the blood pressure as blood flows from the heart to the brain

I was debating between A and D, and wasn't sure why A is wrong or why D is correct. The answer mentions that pressure is proportional to height and inversely proportional to depth, and fainting prevents blood pressure from dropping. Where should I assume the zero point in this scenario and why?
Back to top
Report?
heatherjudd
#2 Posted : Tuesday, July 07, 2015 5:58:02 PM
Rank: Instructor

Groups: Registered
Joined: 5/25/2012
Posts: 0

Thanks: 0 times
Was thanked: 0 time(s) in 0 post(s)
Blood is a non-ideal fluid, and if we are talking about lack of blood in the brain we are really talking about the heart having trouble getting it there. If we could just increase the pressure (as in A) we wouldn't need to fall down, increasing pressure just helps push blood up. If you lower the head relative to the heart (and to everything) the heart doesn't need to work quite so hard to 'defy' gravity and pull the blood from your feet to your head. This means even as the heart does less work, more blood with naturally flow to the brain. And since no part of your head it very high above your heart when lying down, the heart need to excerpt much less pressure to get it there.

This question forces you to step a little outside physics and consider how the body works to move blood - a true MCAT style question.
Back to top
Report?
robinluo
#3 Posted : Sunday, June 12, 2016 4:29:44 PM
Rank: Instructor

Groups: Registered
Joined: 6/9/2016
Posts: 2

Thanks: 0 times
Was thanked: 0 time(s) in 0 post(s)
The question stem is asking for a reason to explain why fainting is the "natural/right/beneficial" response to low brain circulation.

While A) may be a valid reason, it does not address fainting.

D) is the answer because it explains how fainting helps the brain recover from low brain circulation.

-Robin
Back to top
Report?
Users browsing this topic
Guest
Tag as favorite
You cannot post new topics in this forum.
You cannot reply to topics in this forum.
You cannot delete your posts in this forum.
You cannot edit your posts in this forum.
You cannot create polls in this forum.
You cannot vote in polls in this forum.

Clean Slate theme by Jaben Cargman (Tiny Gecko)
Powered by YAF | YAF © 2003-2009, Yet Another Forum.NET
This page was generated in 0.117 seconds.