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.

Facts About Blood Pressure - April 22, 2010 by admin

Higher animals found it expedient to separate themselves not only from the external but also from the internal ocean by providing themselves with a closed circulatory system. However, this problem has as yet not been completely solved. The main channel of the internal river, i. e. the cardiovascular system in mammals, is a closed one, but it takes in many streamlets, lymphatic vessels, through which the fluids from the interstitial and intercellular spaces flow.

This means that the tissues and organs completely blocked themselves off from the waters of the internal ocean, but reserved the right to pour their waters into this mobile reservoir. Of course, the isolation of this internal ocean is only relative. In the arterial part of the capillaries, the walls of which are fairly thin, but the blood pressure is still high, a certain amount of liquid seeps into the intercellular spaces. This leakage would be still greater since the banks cannot withhold it sufficiently, if it were not the high oncotic pressure of the blood (caused by the proteins dissolved in it), which prevents the water from leaving the dissolved proteins.

In a resting state a small amount of water percolates into the tissues, but it all returns to the venous section of the capillary where the blood pressure is lower than the oncotic pressure of the plasma; the liquid starts to be actively attracted into the plasma by the proteins dissolved in it. The force which acts inside the venous section of the capil­lary and makes the liquid return to the blood stream is about twice that in the arterial section which forces the liquid into the interstitial spaces. This is why it is all returned.

However, during periods of work it is quite another mat­ter. In this case the blood pressure in the arterial section of the capillary will be so high that its walls will be able to retain neither water nor proteins. In the venous section of the capillary the blood pressure will remain fairly high, while the oncotic pressure will drop owing to loss of proteins; the liquid will have neither the stimulus nor the opportunity to return to the blood stream. The only alternative left to it will be to enter the lymphatic system. Thus, in the body the lymphatic system acts in a way similar to the system of drains in towns which prevents the streets and squares from becoming flooded during heavy rainfall.

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.

Animal System of Transportation - April 22, 2010 by admin

The system of transportation in animals developed grad­ually. When the particles of a live matter first joined together to form an independent unicellular organism and separated themselves from the ocean by means of an envelope, nature had to think of a way of organizing transportation within a unicellular body. A solution was soon found, and nature built the cell in the form of a microscopic ocean and provided it with its own currents. Thus, the simplest intracellular transportation system has been retained in multicellular animals and in man. The protoplasm of any cell in our body is mobile and protoplasmatic currents exist even in the nerve cells.

Multicellular animals had to develop a more complex system. The most primitive of them, for instance sponges, use the water where they live for this purpose. The ocean currents proved to be unreliable, so instead they use cilia to make the sea water flow through the ducts and pores of their body, thus supplying all parts with nutrients and oxygen.

Higher animals separated themselves completely from the ocean and provided themselves with their own ‘aquaria’ for transportation purposes. Nowadays the largest aquaria belong to the gastropod (univalve) mollusks, whose blood occupies 90 per cent of their body volume. This is evidently too excessive and the larvae of insects have an aquarium not exceeding 40 per cent of the weight of their body, whilst that of adult insects takes up 25 per cent. Birds and mammals have even smaller aquaria, only 7-10 per cent of their body weight, the tiniest reservoir being found in fishes where it is only 1.5-3 per cent of the body weight.