Anatomy: Animals Inside

Circulatory System

What are the differences between an open and a closed circulatory system?

In an open circulatory system, found in many invertebrates (for example, spiders, cray-fish, and grasshoppers), the blood is not always contained within the blood vessels. Periodically, the blood leaves the blood vessels to bathe the tissues with blood and then returns to the heart; thus, no interstitial body fluid is separate from the blood. A closed circulatory system, also called a cardiovascular system, is found in all vertebrate animals and many invertebrates; in a closed system, the blood never leaves the blood vessels.


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