Overview of Chapter

Open circulations supply many invertebrates: from crabs, lobsters, insects and spiders to starfish, sea urchins and some mol-lusks. More animal species employ open circulations than the closed 'pump-tube' circulations of vertebrates. In open circulations, movements of the body assist open pumps to propel blood or hemolymph over and around organs inside an open cavity or hemocoel. From the pump or heart, blood traverses tubes passing direct to gills or brain, but ultimately blood leaves the tubes to percolate through the open cavity. Because open circulations lack capillaries, tissues and organs surrounding the cavity must take up nutrients and discharge wastes into the slowly moving blood direct. In some forms, the 'blood' of the open circulation transports oxygen in addition to foodstuffs and wastes, but in insects, oxygen distributes via a separate tubular system of tracheae. Open cavity circulations, unlike closed circulations, continue to function when shrunk to spider or gnat size making cavity circulations ideal models for supplying miniaturized microfluidic devices. We begin with a thought experiment.

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