Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

Atmospherical pressure is around 760 mmHg, while blood pressure is on average 100 mmHg. Then why do you bleed from cuts, and why does a cut aorta spray blood? The atmosphere should press the blood back in, or at least stop it from spraying.

share|improve this question
13  
Correct answer: because those 100 mmHg are measured relative to atmospheric pressure. The absolute arterial pressures would be 860 mmHg if atmospheric is 760 mmHg. –  Georg Sep 23 '11 at 19:37
    
The distinction the Georg is (correctly) making is that between "gauge" (measured with respect to something (usually the surrounding atmosphere)) and "absolute" pressure (measured with respect to vacuum). –  dmckee Sep 23 '11 at 20:36
    
Thanks, @georg! –  Karin Sep 24 '11 at 8:09
1  
@georg: This is an answer-- can you place it in the answers so this question can be removed from the "unanswered" list? –  Ron Maimon Oct 10 '11 at 5:37
add comment

1 Answer

When they say blood pressure is 100 mmHg, that really means 100 mmHg higher than atmospheric pressure. It's a gauge pressure, not an absolute pressure. The corresponding absolute pressure would be about (760 + 100) mmHg.

Originally posted by Georg in a comment

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.