The circulatory system (open and closed) is the mechanism by which the coordinated movement of blood (hemolymph) through the body is possible, which ensures its full life activity. Its very movement in the system occurs in connection with the pulsation of the heart muscle, or contractions of the thickened walls of the aorta and arteries, or of the organs of movement and muscles of the body. It is with the help of blood circulation that substances and heat are transported for metabolic processes, which also affect the metabolic rate. Closed and open circulatory system: how do they differ and for whom are they characteristic? The answers to these questions will be presented in the article.
An open circulatory system is found in almost all invertebrates, as well as in the lower chordates (in the lancelet). The blood flow in these organisms is caused by the contraction of the heart or “hearts”, as well as, to some extent, the contraction of the muscles of the body. A characteristic feature is a large volume of blood at a low speed of its movement.
A closed circulatory system can consist of one circle of blood circulation (fish and cyclostomes) and two - small and large (reptiles, amphibians, birds, mammals). Flowing along the small and large circle, the blood periodically changes its composition, and is either venous or arterial. And in cold-blooded animals, even the venous and arterial in the aorta or heart are mixed, while the speed of blood flow is low. The metabolism between body tissues and blood is carried out through the thin walls of the capillaries. Filtration of decay products occurs mainly in the kidneys, or in other excretory organs.
The open circulatory system is very imperfect, but among the owners of a closed circulatory system the most ideal option for birds and mammals. In representatives of these classes, it consists of a four-chamber heart and two circles of blood circulation. Normally, arterial blood here never mixes with venous. Characteristic enough high pressure. Another advantage is the considerable speed of blood flow through the vessels (for comparison: the time of one circulation of blood in insects is approximately 22 minutes, in a dog it is already 16 seconds, and in a rabbit - 7.5 seconds). Thanks to these features, the warmth of higher species of animals is possible, which allows you to have a constant body temperature, regardless of environmental conditions. Inherent in birds and mammals and high metabolic efficiency.
Blood circulation in the human body is ensured by the contractions of the heart, which works like a pump. Among other factors contributing to the movement of blood are respiratory movements, skeletal muscle contractions, and blood pressure differences. One of the characteristics of cardiac activity is the pulse rate. Pulse is a periodic expansion of the arteries that coincides with contractions of the heart muscle. Its frequency depends on many reasons, including body weight, temperature and body condition, physical and emotional stress, and so on. Normally, the pulse rate in an adult is 60-80 beats per minute. The speed of blood flow in the vessels is different: from less than 1 mm / s in capillaries to 50 cm / s in large arteries. The time of the entire blood circulation in the body is about 20-25 seconds. Blood moves toward a decrease in pressure, which is greatest in the aorta and large arteries and the smallest, even negative, in the vena cava. The backward movement of blood is prevented by valves that close the atrioventricular openings, the mouth of the pulmonary artery and aorta, and the valves located on the walls of large veins. With sufficient contractile function of the heart, blood circulation is not impaired.
As you can see, the circulatory system open and closed have very characteristic features that every erudite, and not only, person needs to know.