Pumping Blood with Pressure - April 22, 2010 by admin

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 mil­limetres of mercury.

Heart Beat Dependant on Body Weight - April 20, 2010 by admin

On the eighteenth day after conception the human embryo is but a tiny bundle of cells. It is at that time that the heart starts beating regularly and continues to do so without stopping until death. The heart is probably the only organ which does not shirk its work and keeps func­tioning at a good rate, even if it belongs to the most inveterate lazybones. In a tiny three-week-old human embryo, that has no real blood as yet, the heart beats once every second. Later on, when the child is born, the pulse becomes more rapid, approaching 140 beats a minute.

Fortunately, this is the peak and the pulse rate then gradually drops. In an adult the heart beats at a rate of some 76 times a minute while a person is resting, but may increase by as much as 150 per cent during hard work. This means that in a hundred-year lifetime a man’s heart beats about five thousand mil­lion times.

When one considers this figure, it is surprising that the heart never grows tired and, as long as it is healthy, copes easily with its task, literally without stopping for a second.

Man’s metabolism is far from perfect and considerably inferior to that of small warm-blooded animals. The thing is that the smaller the size of a body, the less the area in which it decreases. For this reason smaller organisms have to produce much more warmth per gram of body weight than larger ones. Their metabolism is more intensive and thus the heart has to beat more energetically than in man. Indeed, the smaller the animal, the quicker is its heart beat. For instance, the heart of a whale whose body weighs 150 tons beats seven times per minute, that of an elephant weighing three tons 46 times, that of a cat weighing 1.3 kilograms 240 times, while the heart of a coal tit weighing as little as eight grams beats 1200 times per minute.