Pressure question; pascals.

[pfaction]

Artery has a gauge pressure of 10^4 Pa. Why would this be more than atmospheric pressure, which I thought was 10^5 Pa? TBR GChem 2, fluids, passage 3 on pg 96.

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[kasho11]

So you think 10^4 is more than 10^5?

Edit - Or are you saying that TBR says artery pressure is higher?

 

[hellocubed]

awwww sheeeiiittt.

I remember this question and was freaking out about it too.
The passage actually says "gauge pressure" for the arterial pressure.

That actually means relative to atmospheric pressure (so 10^4 on top of atm).

 

[kasho11]

Total pressure = atmospheric pressure + gauge pressure

 

[MedPR]

Gauge pressure can get confusing, but it's simple if you remember that you cannot have negative pressure.

 

[hellocubed]

Edit - Or are you saying that TBR says artery pressure is higher?

TBR has several associated passage problems where the answer is "artery pressure is higher."
But it's difficult to figure out if you don't know that

Total P= Atm+Gauge

 

[kasho11]

Gauge pressure can get confusing, but it's simple if you remember that you cannot have negative pressure.

Except in the pleural space by the lungs?

 

[pfaction]

Yeah what some other people said. It was like, "the gauge pressure is 10^4". I'm like, okay, so it's less than ATM pressure, which is 10^5.

I remember this question and was freaking out about it too.
The passage actually says "gauge pressure" for the arterial pressure.

That actually means relative to atmospheric pressure (so 10^4 on top of atm).

Yeah, I figured it out--WHEN I GOT THE QUESTION WRONG.

I mean if it says gauge, how are we supposed to assume it means Patm+pgH?

 

[MrNeuro]

Except in the pleural space by the lungs?

its not negative its lower than atmospheric

dP = rho*g*dh

it can get confusing when you have to subtract or add the gauge pressure but i think the MCAT would be clear on that

 

[pfaction]

it can get confusing when you have to subtract or add the gauge pressure but i think the MCAT would be clear on that


Okay, I just wanted to make sure I wasn't ****ing up the definition. Pgauge is NOT Ptotal, which is Psurface+Patm. Pgauge is proportional to depth, whereas Ptotal is Psurface at the y intercept. I was so thoroughly confused when I got that wrong. "But...10^5 Pa is atmospheric, and this is 10^4 and 10^3....what?!)

 

[MrNeuro]

it can get confusing when you have to subtract or add the gauge pressure but i think the MCAT would be clear on that


Okay, I just wanted to make sure I wasn't ****ing up the definition. Pgauge is NOT Ptotal, which is Psurface+Patm. Pgauge is proportional to depth, whereas Ptotal is Psurface at the y intercept. I was so thoroughly confused when I got that wrong. "But...10^5 Pa is atmospheric, and this is 10^4 and 10^3....what?!)

Pgauge is literally = rho*g*h think of it as the OVER pressure or UNDER pressure

Ptotal = Patm + pgh or Ptotal = Patm + (+/-Pgauge)

Pgauge = rho*g*dh