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.

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.