The human body is truly a fascinating and complex creation of our Maker. Because of the complexity and variability, many of its workings were little known until recent years. Some of the more amazing facts of the circulatory system follow. If the individual blood vessels of a single adult, i.e., artery, arteriole capillary, venule and vein, were laid end to end, they would extend more than 60,000 miles. For the average adult, the heart beats 70 times per minute; for the well-conditioned athlete, 50-60 beats per minute; and for the extraordinary athlete, as few as 37 times per minute. The volume of blood pumped per beat is approximately 80ml, which is equivalent to 5-6 liters quarts) of fluid per minute. During heavy exercise, it may increase to over 30 quarts per minute. The volume of blood pumped is approximately 5000-6000 quarts per day during more than 1000 cycles of the total blood supply of approximately 10 pints in the average human. Another point of interest is the ability of the arterioles to constrict, thereby decreasing the flow of blood to the skin to as little as 1 per cent of its normal value. This is done to preserve blood temperature at 37° Centigrade and is called vasoconstriction. Within the venous system, the body's blood gathering network, there is a tremendous redundancy of paths all leading back to the heart because of a system of valving that allows blood flow in one direction only. Should one path become closed or impaired, there is always another to be taken. The venous system will be explained in more detail in later paragraphs. The above information is summarized from the writings of Langely (1) and Nourse (2).



College and Department

Ira A. Fulton College of Engineering and Technology; Mechanical Engineering



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Veins, Electronics in biology