| Popis: |
None of these definitions are correct, since it is impossible for the heart to pump blood through the entire circulatory system. Ventricular contraction forces blood into the aorta and pulmonary artery, but these vessels become progressively smaller and end in 25,000 miles of capillaries. Some of these have a diameter not much larger than a red blood cell, and if laid end to end, the capillary system would cover the area of three football fields. The heart could never pump air through this complicated network, much less a viscous fluid like blood, since this would require a force or pressure capable of lifting a 100-pound weight 1 mile high. |
