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Open versus Closed Circulatory Systems

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An open circulatory system releases blood into open body cavities where it bathes tissue directly; a closed system keeps blood confined within vessels throughout its circuit.

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An insect's hemolymph pools around organs; a vertebrate's blood stays inside arteries, veins, and capillaries.

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An open system moves blood at lower pressure, limiting how quickly it delivers oxygen to active tissue.

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