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The circulatory system of animals as a result of the evolutionary development of the world

The circulatory system of animals has come a long way of forming during the evolutionary development of the world. It was formed on the site of the rudimentary parts of the primary body cavity, which in the higher animals was displaced by the cellum, or by the secondary body cavity. In the process of ontogenesis, the circulatory system of animals began to fulfill a universal role, namely the transfer of nutrients, oxygen, metabolic products, hormones and other biologically significant elements. Thus, it is the most important integrating system of a living organism, which ensures its integrity.

Scientists-zoologists distinguish a complete blood system from such primitive representatives of fauna as nemerty, ringed worms, echinoderms, mollusks and insects, that is, those classes that belong to the type of invertebrates. In their common ancestor, the structure of the circulatory system was very primitive - a small system of lacunae, representing cavities without epithelial cells, in which the direction of blood flow was not established. In modern invertebrates, the principle of the structure of the circulatory system is also very primitive: the two main longitudinal vessels - the ventral and dorsal vessels lie under and above the intestine, respectively. And they are connected with each other by transverse blood vessels that span the intestine into the ring and have numerous branches to the internal organs and veils of the body. In this case, the peculiarity of the functioning of the system lies in the fact that the blood moves back along the abdominal vessel, and forward along the dorsal vessel. The function of the movement of blood is provided by rhythmic contraction of the site of the spinal vessel.

In the process of evolution, the circulatory system of animals was perfected differently in all classes. Its development does not originate from the highly organized circulatory system of invertebrates. This explains its main functional feature: the presence of a muscular pulsating organ, called the heart, which appears in primitively organized representatives of chordates - in the cyclostomes. Also, the movement of blood occurs along the abdominal vessel forward, and along the dorsal vessel - back.

The circulatory system of vertebrates has a single plan of structure, the complication and improvement of which occurred gradually with the evolutionary process. But not all evolutionary changes were aromorphoses, that is, progressive morpho-physiological changes. The complication of the organization or structure can not be considered a progressive feature of the changes that will make the animal, its acquired, more highly developed. In the evolutionary transformations of the circulatory system of chordates, the development of the present heart from the most ancient representatives, as well as the intensification of its activity and the formation of a closed circulatory system in the class of the maxillofacus, was the undoubted aromorphosis. Also, the most important aromorphoses are the transformation of the main vessels and heart in the separation of venous and arterial blood streams in reptiles, birds and animals.

The circulatory system of animals is formed by the heart and blood vessels. The heart is a hollow muscular organ that provides movement of blood through the vessels, pumping it. From it to all organs blood moves through the arteries, and from the organs to the heart - through the veins. The heart of different classes of vertebrates can be both single-chambered (in Cyclostomes), and two-chamber (fish), three-chamber (amphibians, reptiles) and four-chamber (birds, mammals). Thus, the anatomy of the heart can determine the degree of basic metabolism of the organism and allows to divide the animals into cold-blooded and warm-blooded animals. In primitive chordates, constantly living in water, the simplest principle of the organization of the circulatory system is that it has one circulatory system. The output of animals on land presupposes a more intensive metabolism, is characterized by the appearance of pulmonary respiration, and, as a consequence, the appearance of a second circle of blood circulation, which is responsible for gas exchange of blood in the lungs. The circulatory system of animals is difficult to organize, together with a complete separation of the circulation circles, it is characterized by a four-chambered heart, as well as the presence of additional circles such as the placental, cardiac and Willis circulatory system.

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