ELI5, if you get an injury underwater (say in the ocean) that opens the skin and bleeds, what stops your body from intaking water?

Question

ELI5, if you get an injury underwater (say in the ocean) that opens the skin and bleeds, what stops your body from intaking water?

In: 1476

Answer 1

Your circulatory system is pressurized; everything you hear about blood pressure is literally referring to the pressure of blood in your blood vessels. So an open wound won’t suck in seawater.

However, the blood pressure away from major veins and arteries isn’t that high, so the blood isn’t spraying out (think about how slowly blood comes out of a paper cut). That means that contaminants in the water like parasites or bacteria can get into your body if the water mixes with your blood or if they can “swim” into your body faster than blood flows out.