Lowest Blood Pressure

[Chunkle]

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I know that capillaries have a rather low BP because of the overall total area, but are BP in the veins even lower? And how about the atrium of the heart.. I remember reading in TPR Hyperlearning that BP is even lower in the right atrium.

So where is BP the lowest? And if someone could give me a method to reason it out, that would be great.

 

[cartersam]

BP in right atrium < BP in veins < BP in capillaries.

Think about it this way:

Fluid only flows from high to low pressure. If for any reason, blood pressure were higher in the veins than in the capillaries, blood would flow backward, which obviously cannot happen.

It is similar in concept to current, wherein direction always goes from maximum electric potential to minimum potential.

 

[Chunkle]

Thanks! Another question: how about velocity?

Capillaries have the lowest velocity of blood correct? Since its area is the greatest.

 

[argama]

Although BP in R. Atrium is lowest, for the purpose of the MCAT, if the answer choice did not say R. Atrium but rather just "Heart", then should the answer be "Veins"?

 

[Chunkle]

Although BP in R. Atrium is lowest, for the purpose of the MCAT, if the answer choice did not say R. Atrium but rather just "Heart", then should the answer be "Veins"?

This is in aamc #7. the choices are the heart and capillaries, no veins. Capillaries is the correct answer, although if veins was on there, I would put that. I think its because the heart also includes the ventricles, especially the left one, would have a very high pressure.

 

[richkaj]

It is dealing with the surface area of the capillaries. There are more capillaries/routes with less resistance than both arteries and veins...

 

[sciencebooks]

Thanks! Another question: how about velocity?

Capillaries have the lowest velocity of blood correct? Since its area is the greatest.

Yep, using "continuity equation." There's an awesome thread on here showing the pressure/velocity/area difference relationships with the cardiac system. I can try to dig it up if you want, but it seems like you've got it, 🙂.