The more multicellular the organism of a living being, the more complicated is its blood circulation or cardiovascular system. In primitive multicellular organisms, a simple system of ducts that is both intestinal and circulatory is sufficient. But already the earthworm has a primitively developed circulatory system. From developmental stage to developmental stage it became more complicated and reaches its highest form in the highly developed mammals, as man is one.
Evolution of the metabolic cycle
The heart muscle also requires a particularly abundant blood supply, since it must keep the blood moving day and night without interruption. It is supplied by the coronary arteries. As is well known, life is bound to metabolic processes in the cells. No living being – whether composed of one or a multitude of cells – can exist without the uptake of nutrients and the release of metabolic products. They represent the essential part of the unity between the organism and the environment. Unicellular organisms existing in water absorb their “food” directly from the environment, from the water, and release their metabolic degradation products into the water. Both only need to pass the cell membrane in both directions. But also every single cell of a cell association or of a complicatedly built multicellular organism is subject to the same laws as the unicellular organism with regard to its metabolism. It, too, receives nourishment from its environment, the extracellular space, and releases its degradation products back there. But the fluid from which such a cell receives its nourishment is not water like lake or sea water, but the body fluid, which, formed over millions of years, is very precisely adapted to the respective living being and its living conditions and must be constantly renewed. This necessity gave rise to the so-called circulatory system, which is the indispensable prerequisite for the metabolism of every single cell of a higher organized living being. It transports vital substances – oxygen and other nutritive substances – to each individual cell and brings their metabolic products to where they are processed or excreted.
Structure and function of the circulatory system
To what basic processes is the circulatory system related? To answer this question, we must start from lower animal species. If we imagine that multicellular organisms arose from the division of single cells, which, however, did not completely separate from each other, then we understand that in primitive multicellular organisms all that is needed is a system of channels into which the fluid enters from the outside and brings the nutrients it contains into direct contact with the cells. Thus, in such creatures, the intestine and the circulatory system are identical; the primitive swallowing reflex always carries new water containing nutrients into the canal system. In the course of evolution, the gastrovascular (gastrum – stomach, vasculum – vessel) system developed, in which channels emanate from the stomach into which the “swallowed” water flows and reaches the cells. Thus, the nutrients present in the water enter the interior of the organism through a swallowing reflex and from there they are delivered to the individual cells through a system of channels. We all know that combustion is a main element of metabolism inside the cells and that without oxygen there is no combustion. The larger and more multicellular the organism became, the higher the demand for oxygen became. As a result, near the upper opening of the body, where the swallowing reflex pumped water into the intestine, special cells developed that took up oxygen from the water and passed it on to the body. At about the same time as this process of differentiation, the canal system formerly associated with the intestine developed into an independent system. Only nutrients filtered through intestinal wall cells could now enter the special body juice present here – the so-called hemolymph. Thus arose:
1. the external metabolism with its two parts, the absorption of oxygen and the absorption of food with its processing, which takes place within the intestine, into water-soluble substance compounds that can be absorbed by the intestinal cells,
2. the internal metabolism, which has its prerequisite in the supply of oxygen and other nutritive substances, which are transported to each individual cell with the help of the hemolymph.The vascular system through which such specific fluids reach the cells is an open system at lower stages of development and merges into fluid spaces from which the cells are supplied with nutrients. Only at higher levels of development has it evolved into a closed system. The circular movement of the body fluid in such animal species is still triggered by the swallowing reflex of the upper body orifice, which, with the rhythm with which it pumps the water into the intestine, also rhythmically keeps the fluid in motion in all other canal systems. This rhythmic became the cause of a stronger reorganization of cells particularly sensitive to stimuli, which first transferred the movement initiated in the pharyngeal part with the act of swallowing to deeper sections of the intestinal tube and vascular systems, and later found their own rhythmic coordinated by nerve connections among themselves. (This explains that the intestine and vascular system are kept in function by the same portion of the nervous system, called the autonomic nervous system).
Function and development of blood in the cardiovascular system.
Now it is not difficult to understand why fish – even if they are not taking food, always move their mouth and at the same time their gills, because in the gills have concentrated the cells that take oxygen from the water and pass it to the blood. Here we have to mention the word “blood” for the first time, because where previously only hemolymph saturated with nutrients circulated, at this stage of development the blood composed of numerous individual cells, water, dissolved protein and salt substances is already moving. The step up to this point is relatively easy to comprehend when one considers that even the cell assemblies that were far from the gills had to be supplied with oxygen. This necessitated the development of cells whose sole function is oxygen transport. These cells circulate in the blood fluid, filling with oxygen each time they pass the gills and carrying it to the most distant parts of the body. In the course of further development, the rhythm transmitted by the swallowing reflex to the vascular system was no longer sufficient to guarantee the organism’s need for nutrients and oxygen. Thus, a central “blood pumping station” gradually emerged, the heart, in the middle of the circulatory system, where the blood movement brought the strongest stress to the vascular walls, and where the constant rhythmicity finally gave rise to cells “qualified” for rhythmicity. As is well known, all these stages of development arose in animals that lived in water. This would not have been possible on land. But after the intestine and the vascular system were separated, after the gill system, the cell-containing blood and the heart had developed, the gills “only” had to reorganize themselves into lungs by getting used to taking oxygen from the air instead of from the water, and already a necessary condition for the existence of living beings on land was given: the external metabolism. Thereby for the second part of the external metabolism still the possibility had to be present to take up occasionally liquid into the intestine. In addition, certain glands (salivary glands) were needed to mix solid food with liquid so that nutrients dissolved in water could continue to pass through the intestinal wall and from there enter the blood. Everyone knows from school that the heart is divided into certain chambers, one of which (right) pumps the deoxygenated blood from the body to the lungs, the other (left) pumps the blood newly oxygenated in the lungs to the periphery of the body. From the intestines, partly with the portal vein via the liver, partly via a special lymphatic system, the actual nutrients enter the blood before the heart. Thus, the cardiovascular system has an important auxiliary function in maintaining life. The absorbed oxygen or the nutrients that enter the blood through the intestinal tract reach the periphery, the smallest blood vessels, from where the supply of each cell of the body takes place after the aforementioned substances have left the bloodstream and complicated exchange processes have taken place.
Importance of oxygen in the cardiovascular system
Thus, from our overview of the evolutionary history of cardiovascular function, it can be deduced that the circulatory system in the multicellular organism arose from the need of each cell for metabolism.If we have understood this, then we will also understand the measures that are necessary to keep the cycle – as far as possible – in order. Before that, however, a few facts must be mentioned. We have already mentioned rhythmicity, which is mutually coordinated and maintained by nerve cells and their connections with each other and by the power of muscle cells. However, like the performance of each cell, it is dependent on metabolism – thus requires the supply of oxygen and other nutrients. Accordingly, all organs with their individual cells must be supplied with blood to maintain their vital activity, including the brain. The brain in particular reacts very sensitively to a lack of oxygen: so-called fainting or unconsciousness is usually due to this. The lack of oxygen in the coordinating centers of the brain can also disrupt the coordination of the functions of individual organs. Such regulations also concern the system of glands with internal secretion, on whose products (hormones) a regulated activity of other organ functions depends. The heart muscle also needs a particularly abundant blood supply, as it must keep the blood moving day and night without interruption. It is supplied by the coronary vessels. Their occlusion by calcification foci and blood clots, or their constriction by prolonged vascular spasms, are therefore of great importance to human life and provide the organic basis for a number of heart ailments. We see that the maintenance of the healthy process of life requires the regularity of a vast sum of interdependent processes.
Prevention of cardiovascular diseases.
Even if we do not know all of these processes, how can we nevertheless help ourselves to keep our circulatory system in order? Animals, for example, know nothing about their circulatory systems, and yet they do not – assuming they live in the wild – die prematurely from heart or circulatory disorders. Their search for food and water, their activity conditioned by the environment, protect them from such diseases. Their muscles have to move; their metabolism is thus put under greater strain, and at the same time the blood is driven to the herd. But they will never – if they are not seduced by man – eat more than their sense of hunger allows. The people, however, have facilitated their life process to a large extent. The driving possibilities spare them the running. They eat gladly, often much too much, and feel the rest afterwards as pleasant. At the same time, however, the human circulatory system requires muscular movement just as much as that of the animal. For example, if physical work is done that causes increased muscular activity, various processes interlock to bring more blood to the active organs. An active organ is always supplied with more blood than an inactive one. If the workload is lighter, a shift in the amount of circulating blood is then sufficient. But if heavy muscular work is performed, involving large muscular areas, the blood supply is increased by emptying the so-called blood stores. The heart thereby works harder to “pump” the larger circulating blood volume through the body. This enables it to meet the increased demands. But also from the central nervous system, simultaneously with the changed motor activity, the muscle work, the blood vessels that supply the muscles are influenced. This facilitates the blood supply to this highly stressed area. In addition, the metabolic products produced by the increased muscle activity have a regulating effect on the cardiovascular system. Breathing is also significantly increased, as it must also adapt to the new conditions. In other words:
Physical work or sports and exercise also train the human circulatory system. But other factors can also change cardiovascular activity, such as positive or negative emotions via the central nervous system. Joy and anticipation make the heart beat faster; anger, fear, and constant conflict can negatively affect cardiac activity. General physical training, as we can achieve by playing several sports, has a positive effect on the overall organism and thus on cardiovascular activity. Education to enjoy sports and exercise and everything beautiful makes the individual’s life richer in positive emotions. Good knowledge, successful work, trust in each other and mutual respect make it poorer in fear, anger and conflicts.Thus, in our time and our social order, which gives him sufficient opportunity for education and sports practice as well as for professional success, man has numerous opportunities to protect his circulation from damage with his life, his habits and the demands he makes on his organism in physical and mental terms. The great adaptability of the human organism permits even one who has previously suffered circulatory damage through illness or harmful lifestyle habits to recover if the individual gradually makes greater and greater demands on his circulation by changing his lifestyle.
