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Swim Bladder

Submitted by eodonovan on Fri, 12/15/2017 - 09:59

The partial pressure (tension) of O2 in water and fish blood is the same (0.2 atm), however, the partial pressure of O2 in the swim bladder is much greater (at 500 m, 40 atm). Fish can secrete O2 in the swim bladder against a pressure gradient and keep it by a rete mirabile (“miracle net”). The tension of O2 in the venous capillaries leaving the bladder is equal  to the one in the bladder (high). O2 starts go away, but the arterial capillaries surrounding the venous capillaries catch the leaving O2 (arterial capillaries contain blood with a lower O2 tension going in the opposite direction; countercurrent exchange occurs). The arterial blood carries the O2 back to the swim bladder.



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