One might think that a completely closed system would facilitate the work of the heart, but this is not so. A great deal of force is required to pump the blood through the capillaries and tiniest arterioles. As the arteries become more and more ramified, their total cross-section increases and finally becomes 800 times that of the aorta along which the blood flows from the heart, and this leads to an increase in resistance. The thing is that we have from 100 to 160 thousand million capillaries with a total length of 60 to 80 thousand kilometres. I. F. Cyon, a well-known Russian physiologist, calculated that the work performed by the heart in a man’s lifetime is equal to the effort which would be required to move a goods train to the top of the highest mountain in Europe. Mont Blanc, 4810 metres high.

Even in man in a resting state the heart pumps 6 litres of blood per minute, i. e. not less than 6 to 10 tons a day. During a lifetime our hearts pump 150 to 250 thousand tons of blood. But, in spite of all this, a man cannot boast of the work done by his heart.

Since it is difficult directly to compare the work done by the hearts of large and small animals, scientists usually calculate how much blood the heart pumps per minute per 100 grams of body weight. Even in a slow-moving snail the heart works under about the same strain as in man, while the hearts of most animals work more intensively. A dog’s heart, for instance, pumps about twice as much blood as a man’s, and a cat’s ten times that of a man’s heart.

While the heart is working, quite high pressure is maintained in the arteries. Even in such a small animal as the larva of a dragon-fly or in a frog, the pressure reaches 30 and even 38 millimetres of mercury. In most cases the pressure is even higher: in an octopus it is 60, in a rat 75, in a man 160-180 and in a horse it is as high as 200 milĀ­limetres of mercury.

April 22, 2010 at 10:10 pm by admin
Category: Action of Heart
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