A Heart was Beating… - April 24, 2010 by admin

Owing to the automatism of the heart of the vertebrate, it can continue working even when removed from the body. The latest cardiac drugs were first tested on a heart taken from a frog which, under proper experimental conditions, goes on beating for many hours.

It is a popular misconception that when death occurs the heart automatically stops beating. In reality, this is not always the case. The Russian physician Andreev succeeded in making the heart of a newborn baby beat again four days after its death.

Several centuries ago people did not even suspect that this was possible. The famous physician Andreas Vesalius, who treated the Emperor Charles V, was among the few scientists granted the right to dissect bodies. He was sentenced to death by the Holy Inquisition on a charge of dissecting the body of a woman who was still alive. It was only thanks to the kindness of Philip II, the heir to the throne, that this dreadful and unjust death penalty was commuted to a penitent pilgrimage to the holy places on Mount Sinai and in Jerusalem. Vesalius did, incidentally, perish during this pilgrimage.

This accusation against the extremely popular scientist and famous physician of that epoch was motivated by the fact that the cardiac muscle of the woman who had been undoubtedly dead continued to contract. The reason why her heart continued to function for many hours after death cannot be established. None of the many astonished spectators who witnessed this dramatic event had a shadow of a doubt that the woman was alive. As for Vesalius, he was sure that accident was due to his own negligence and thought that the sentence proclaimed was just.

High Blood Pressure - April 23, 2010 by admin

Normally, the larger the animal, the higher is its blood pressure. This can clearly be seen in eels, sharks and other fish whose sizes vary considerably. The longer the eel or shark, the higher is its blood pressure. There are, however, many exceptions to this rule, one of which is a cock whose blood pressure is the same as that of a horse.

There is no doubt that the heart of a great blue whale weighing 600 to 700 kilograms, even if it does not function normally, will do much more work than the heart of a coal tit weighing about 5 thousand million times less, i. e. only 0.15 gram. For a correct estimation, a comparison is made between the work done by one gram of cardiac muscle. In this case man also has nothing to boast about. Each gram of our heart does work equal to 4000 gram-centimetres per minute, about the same as the heart of a snail. A frog’s heart works three times as hard, a rabbit’s five times as hard, whilst that of a white mouse works twelve times as hard.

Most of the earth-dwelling animals are horizontal. Their brain and heart, the two most important organs, are on the same level. This is very convenient since no additional effort is required on the part of the animal’s heart to supply the brain with blood. It is quite different for man whose brain is on a much higher level than-his heart. The same applies to a six-metre giraffe whose heart is situated 2 to 3 metres lower than his brain. All the creatures, following the same general plan (man, the cock, the giraffe), have high blood pressure.

The heart of typically horizontal animals is unable to supply the brain with blood when they take up an unnatural position. If a rabbit or a snake is placed in a vertical position, they will soon ‘faint’ because of brain anaemia. Nor are such animals very comfortable when placed with their head much lower than the heart since the supply of blood to the brain is confused owing to a disrupted outflow. However, the animal kingdom abounds with virtuosi acrobats. An obvious example are bats who do not care very much in what position their body is.

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.

Pulsating Vessels & Blood Amount - April 22, 2010 by admin

It’s not a secret that the smaller the aquarium, the more intensively it is used and the more rapid the currents in it have to be so that the same liquid can be used over and over again. It is small wonder that insects can afford the luxury of having very slow currents in their aquaria, taking 30-35 minutes to make one complete cycle. Man cannot afford this. The blood in our internal aquarium completes a cycle in as little as 23 seconds and performs over 3700 cycles per day. This is, however, not the maximum. In a dog a complete cycle takes 16 seconds, in a rabbit only 7.5 seconds, and in the smaller animals even less.

In vertebrates the matter is complicated since the aquarium itself is very large, but has little water in it. Not can it be filled up. The total length of all man’s blood vessels is about 100 thousand kilometres. Most of them are usually empty since 7-10 litres of blood are far from enough to till them and only the most hard-working organs are supplied intensively. For this reason heavy-duty functions cannot be performed by many systems simultaneously. After a good meal the digestive organs are the most energetic. They receive a considerable amount of blood, while the brain is not adequately supplied to function normally. Hence, we experience drowsiness.

To set the waters of the internal aquarium in motion, it was necessary to have devices very different from the cilia of sponges. Muscle pumps proved much more dependable. The earliest pumps were nothing more than a pulsating vessel, i. e. a very simple heart, which drove hemolymph into the smaller vessels and thence into the interstitial and intercel­lular spaces. Having watered them, the hemolymph returned to the pulsating vessel. Such an open system could not provide proper circulation, and this is why insects, the highest representatives of the invertebrates, developed pumps which not only force out, but also suck in. For this purpose their hearts are freely attached to special muscles, known as the pterygoid muscles, that stretch the heart, thus creating a negative pressure that sucks in the liquid passing through the tissues.

A pulsating vessel is a low-capacity unit, and lower animals usually have many pumping devices. In the earthworm the main pulsating vessel, that extends throughout its entire body, drives the blood from the rear to the front end. On its way, the blood flows into side vessels which themselves act as hearts pushing the blood into even finer arteries. All these numerous hearts function independently, co-ordinating, at best, their work with the partner in the segment. And this is the extent of the organization.

Supplying Heart with Blood - April 21, 2010 by admin

Lower animals have sought their own means of supplying the heart with blood. Nature proved to be thousands of millions of years ahead of Napoleon when he said that the way to a soldier’s heart is through his stomach. In creating lamellibranch (bivalve) mollusks nature decided to pierce their heart through.

However, it did not use Cupid’s arrow for the purpose but merely the end-gut. No one knows why an intestine should go through the heart ventricles of a mollusk. This is, no doubt, the simplest way to supply the blood with nutrients, and perhaps the supply of nutrients to the cardiac muscle itself is most improved.

The main function of the cardiovascular system is to transport all the necessary materials to all parts of the body. Some substances move in the blood by themselves, but others, mainly gases, travel on the back of the red blood corpuscles (erythrocytes). Every cubic millimetre of blood contains 4.5-5 million carriers, making a total of 35000000000000, the world’s largest caravan.

The size of the erythrocytes is negligible, only eight microns each, but if arranged in a chain, like camels in a caravan, they would encircle the Earth seven times around the equator. The red corpuscles of a whale, the largest living creature on the Earth, would form several caravans and each would stretch as far as the Sun.

About Heart Cycle - April 21, 2010 by admin

Why is the heart able to work at such a high rate? First of all, it is not absolutely correct to think that the heart works without rest. The cardiac muscle quite often rests, but the periods of rest are very brief. A heart beat lasts for about-0.49 of a second and, if a man is resting, a 0.31 second interval follows each beat. The period of rest is actually longer since not all parts of the heart work simultaneously.

The heart cycle starts with the contraction of the auricles, whilst the ventricles rest, and the ventricles contract while the auricles relax. The auricles take about 0.11-0.14 of a second to contract and this is followed by a 0.66 second rest. In other words, every day they work for no more than 3.5-4 hours and rest for about 20 hours. The ventricles take somewhat longer to contract, about 0.27-0.35 second, and rest for 0.45-0.53 second. Consequently, every twenty-four hours the heart’s ventricles work for 8.5-10.5 hours and rest for 13.5-15.5 hours.

In little birds the heart also rests, but their hearts contract and rest more frequently. The heart of a willow tit contracts 1000 times per minute; a single contraction of the auricles lasts 0.014 second with an ensuing rest of 0.046 second. The ventricles contract for 0.024 and rest for 0.036 second. Thus, the auricles work for only 5 hours 40 minutes and rest for 18 hours 20 minutes, whilst the ventricles work for 9 hours 36 minutes and rest for 14 hours 24 minutes. This differs very little from man’s.

Nevertheless, man is quite able to considerably improve the way in which his heart works by prolonging the period of its rest. According to medical research, in a well-trained sportsman the heart, when at rest, contracts less frequently than the heart of other people, the frequency being as low as 40 and even 28 beats per minute.

To cope with such a tremendous task as is the lot of the heart, rest alone is not enough. The heart must also be well nourished and have a good supply of oxygen. This explains why the heart in higher animals has its own, very powerful circulation system.

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.