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The human body must be supplied continuously with
oxygen and nutrients so as to be able to maintain its vital functions. At
the same time, the cells of the body have to be freed of carbon dioxide
and metabolic products. It is the blood circulation which fulfils both
these functions. The transporting channels are the vessels which form a
closed system of elastic tubes in which the blood circulates. The energy
for blood flow is provided by the pumping action of the heart. The blood
circulation is organised into two circular processes connected in series:
the systemic circulation and the pulmonary circulation. |
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