The circulatory system is unclosed and closed

The circulatory system (unclosed and closed) is the mechanism by which it is possible to carry out a coordinated movement of blood (hemolymph) through the body, which ensures its full vital activity. Its movement in the system arises in connection with the pulsation of the heart muscle, or contractions of the thickened walls of the aorta and arteries, or organs of movement and muscles of the trunk. It is through the circulation of blood that substances and heat are transported for metabolic processes that affect the rate of metabolism. A closed and unclosed circulatory system: how do they differ and for whom are they characteristic? The answers to these questions will be set forth in the article.

The circulatory system unclosed is found in practically 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", and also, to some extent, by contraction of the musculature 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 circulation (fish and cyclostomes) and two - small and large (reptiles, amphibians, birds, mammals). Flowing through a small and large circle, the blood periodically changes its composition, and is then venous, then arterial. And cold-blooded animals even mix venous and arterial in the aorta or heart, while the blood flow velocity is small. The exchange of substances between the tissues of the body and blood is carried out through the thin walls of the capillaries. Filtration of decay products occurs mainly in the kidneys, or in other organs of excretion.

The circulatory system unclosed is very imperfect, but among the holders of the closed circulatory system the most ideal variant in birds and mammals. In representatives of these classes it consists of a four-chambered heart and two circles of blood circulation. Normally, arterial blood is never mixed with venous blood . A fairly high pressure is typical. Another advantage is the considerable speed of blood flow through the vessels (for comparison: the time of one blood turnover in insects is about 22 minutes, the dog is already 16 seconds, and the rabbit has 7.5 seconds). It is thanks to these features that the warm-bloodedness of higher species of animals is possible, which allows to have a constant body temperature, regardless of environmental conditions. The high metabolic efficiency is characteristic of birds and mammals.

Blood circulation in the human body is provided by contractions of the heart, which works like a pump. Among other factors contributing to the movement of blood are respiratory movements, contractions of skeletal muscles, a difference in pressure in the vessels. One of the characteristics of cardiac activity is the pulse rate. Pulse is a periodic expansion of the arteries, which coincides with contractions of the heart muscle. Its frequency depends on a variety of causes, 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 rate of blood flow in the vessels varies from less than 1 mm / s in capillaries to 50 cm / s in large arteries. The time of the whole circulation of blood on 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 hollow veins. The reverse movement of the blood is prevented also by the valves that close the atrioventricular orifice, the mouth of the pulmonary artery and the aorta, and the valves located on the walls of large veins. With sufficient contractile function of the heart, blood circulation is not disturbed.

As you can see, the circulatory system, which is not closed and closed, has very characteristic features, which must be known to every erudite person, and not only, to man.