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Chapter 23: The Circulatory, Respiratory, Digestive, and Excretory Systems

Difficulty Level: At Grade Created by: CK-12
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What do you think this picture represents? Does it show a network of tree branches? Interconnected pipes of a plumbing system? Actually, it is a microscopic image of tiny human blood vessels.

Blood vessels are part of the circulatory system, the “highway” system of the human body that transports materials to all of its cells. Red blood cells carry some of these materials, so they are a little like trucks on a highway. In this chapter, you will learn more about blood vessels, red blood cells, and other structures of the circulatory system.

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