Biology 2010 Student Edition

Published by Prentice Hall
ISBN 10: 9780133669510
ISBN 13: 978-0-13366-951-0

Chapter 33, Circulatory and Respiratory Systems - Assessment - 33.1 The Circulatory System - Understand Key Concepts/Think Critically - Page 972: 12

Answer

The arteries do not need valves because blood is pushed through them with powerful contractions from the heart. This powerful pressure keeps blood flowing in one direction from the heart to parts of the body.

Work Step by Step

The arteries do not need valves because blood is pushed through them with powerful contractions from the heart. This powerful pressure keeps blood flowing in one direction from the heart to parts of the body. This pressure is almost absent in the veins.
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