blood pressure and atmospheric pressure

ananthu

The normal atmospheric pressure is 760 mm of Hg. But the normal human blood pressure is around 120/80 mm only. In that case how equilibrium of our body is achieved? For any vessel to retain its original shape its inside pressure and outside pressure should remain equal. If the outside pressure exceeds the vessel will be crushed inward and if the inside one exceeds it will blow up. In the case of our body, assuming it as vessel, how the pressure of atmosphere which is nearly six times higher than the blood pressure inside, could not crush the body inward?
Are there any other inward forces make up for the rest in order to counteract the atmospheric pressure? Also why do we not feel the atmospheric pressure acting on our body surface at all?

uart

The blood pressure measurments are "relative pressure", meaning the figures that you state are above atmospheric pressure.

ananthu

Thank you for your reply. But I couldn't follow what you exactly mean. Will you please elaborate?

russ_watters

760+120=880

Think about it: the measurement is taken with a pressure measuring device open to atmosphere.

ananthu

Does it mean that the actual blood pressure is 880 mm of Hg? In that case it means the actual blood pressure is 120 mm higher than that of the outside pressure.If so how balance is achieved? If there is no balancing mechanism, I should feel as if my blood is pushing my body from inside!

xxChrisxx

Mechanical strength of blood vessels.

Not everything gets crushed because of a pressure difference. Think of, a can of fizzy drink, a high pressure hose pipe, gas/water pipes, an aeroplane. All are pressure containers.

So just like a waterpipe with high pressure water rushing through it doesn't explode (usually) neither do blood vessels. Note that if blood pressure get's too high, your blood vessels can break.

russ_watters

120 mm is not a lot of pressure for a hose like your blood vessels to hold.

Andy Resnick

That may seem true, but recall that hypertension starts around 140 mmHg: that's an increase of only 2% absolute pressure. (16% increase in gauge pressure, tho).

ananthu

Thank you for all the replies. I am happy that my doubts and the chain of answers have led to a new realm of interesting details and facts which are seldom found in text books.

juzlam

ok, i guess its really2 fair explaination. but, if thts the case, when 1 person die, we must observe tht the body would shrink with 880 mmHg pressure. 880 is a huge pressure difference. if the difference is maintain to 120-80, meaning, our heart is just the elevation (pumpung power of only 120)...dont u guys think so?

I still damn impressed with the design of the heart to sustain pumping on average of 100000 times a day even with that 120 pressure ramp.

russ_watters

Welcome to PF!

Pressurized and compressed are two different things. Our blood is pressurized, but is not noticeably compressed.

juzlam

ok, get the point. (correct me if its not allign with what u try to explain)..basically, after someone die, there is no more pressure generated from inside, that would definately damage the body as pressure inside is not in equilibrium with pressure outside. however, due to the physical properties of human body which built from very minimal compressible substances, so tht, our body could still maintain its original state even without internal pressure generated from the blood circulation.is tht the point?