a: Circulatory system ~
b: a network of one-way streets

What: "The circulatory system is like a network of one-way streets. If blood started flowing the wrong way, the blood gases (oxygen and carbon dioxide) might mix, causing a serious threat to your body. In the lungs, capillaries on the outside of the alveoli exchange carbon dioxide and oxygen. Fresh, oxygen-rich blood enters the pulmonary veins and then returns to the heart, re-entering through the left atrium. "

Writer: stevewest
Where: Reference Link Has Evaporated
Date: Jun 11 2014 5:30 PM

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