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.
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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
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$\begingroup$ I am quite sure here but let me say. does this mean the space suit pressure for an astronaut is 860 mmHg or close to it? If an astronaut is out in space without any suite, does he explode? $\endgroup$– Flow.NKCommented Sep 26, 2023 at 11:18
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Because liquids and gases exerts same pressure and the density of liquids is more than gases. So,blood is also a liquid that is why blood flow when we get cut .
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3$\begingroup$ This is incorrect. See the other answer, for example. Liquids and gasses do not necessarily exert the same pressure. They can be at a wide range of pressures depending on other factors. They also weren't asking why blood flows; but why it is able to spray, which does partially relate to it's pressure. $\endgroup$– JMacCommented Apr 24, 2019 at 14:49