That's why some of them — especially veins in the arms and legs that have to work against gravity — have venous valves that help keep the blood from flowing backward.
这就是为什么它们中的一些——尤其是胳膊和腿上的静脉，必须对抗重力——有静脉瓣膜来帮助防止血液倒流。
Venous valve
原声例句
Crash Course 解剖生理学篇
英语百科
Vein
Veins are blood vessels that carry blood toward the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart. In contrast to veins, arteries carry blood away from the heart.
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