Large and small circles of circulation: scheme

In mammals and humans, the circulatory system is the most complex. It is a closed system consisting of two circles of blood circulation. Providing warm-bloodedness, it is more energy-efficient and allows a person to occupy that niche of habitat in which he is now.

The circulatory system is a group of hollow muscular organs responsible for the circulation of blood through the vessels of the body. It is represented by the heart and vessels of different calibers. These are the muscular organs that form circulatory circles. Their scheme is proposed in all textbooks on anatomy and is described in this publication.

The concept of circulatory circles

The circulatory system consists of two circles - the corporal (large) and pulmonary (small). Circle of blood circulation is a system of arterial, capillary, lymphatic and venous vessels that carries blood from the heart into the vessels and its movement in the opposite direction. The central organ of blood circulation is the heart, since in it, without mixing arterial and venous blood, two circles of blood circulation cross.

Great Circle Circulation

A large circle of blood circulation is the system of providing peripheral tissues with arterial blood and its return to the heart. It starts from the left ventricle, from where the blood enters the aorta through the aortic aperture with the tricuspid valve. From the aorta, the blood is directed to the smaller corporal arteries and reaches the capillaries. This is a set of organs that forms the leading link.

Here, oxygen enters the tissue, and carbon dioxide is captured from them by red blood cells. Also in the blood, the blood carries amino acids, lipoproteins, glucose, the metabolic products of which are carried from the capillaries to the venules and then to the larger veins. They flow into the hollow veins, which return blood directly to the heart in the right atrium.

The right atrium ends with a large circle of blood circulation. The scheme looks like this (along the course of blood circulation): the left ventricle, the aorta, the elastic arteries, the muscular-elastic arteries, the muscular arteries, the arterioles, the capillaries, the venules, the veins and the hollow veins that return the blood to the heart in the right atrium. From the big circle of blood circulation the brain, all skin, bones feed. In general, all human tissues are fed from blood vessels of the great circle of blood circulation, and small is only a place of oxygenation of blood.

Small Circle Circulation

The pulmonary (small) circle of blood circulation, the scheme of which is presented below, originates from the right ventricle. In it, the blood flows from the right atrium through the atrioventricular orifice. From the cavity of the right ventricle, oxygen depleted (venous) blood through the output (pulmonary) tract enters the pulmonary trunk. This artery is thinner than the aorta. It is divided into two branches, which are sent to both lungs.

Lungs are the central organ that forms a small circle of blood circulation. The scheme of a person, described in the textbooks on anatomy, explains that pulmonary blood flow is needed for oxygenation of the blood. Here it gives carbon dioxide and absorbs oxygen. In the sinusoidal capillaries of the lungs with an atypical diameter of about 30 μm and gas exchange occurs.

Subsequently, blood, saturated with oxygen, is guided through the system of intrapulmonary veins and is collected in 4 pulmonary veins. All of them are attached to the left atrium and carry there oxygen-rich blood. This ends the circles of blood circulation. The scheme of the small pulmonary circle looks like this (in the course of blood flow): right ventricle, pulmonary artery, intrapulmonary arteries, pulmonary arterioles, pulmonary sinusoids, venules, pulmonary veins, left atrium.

Features of the circulatory system

A key feature of the circulatory system, which consists of two circles, is the need for a heart with two or more chambers. In fish, the circle of circulation is one, because they have no lungs, and all gas exchange takes place in the vessels of the gills. As a result, the fish's heart is single-chambered - it is a pump that pushes blood in only one direction.

Amphibians and reptiles have respiratory organs and, accordingly, circulatory circles. The scheme of their work is simple: from the ventricle, the blood is sent to the vessels of a large circle, from the arteries to the capillaries and veins. Venous return to the heart is also realized, however, from the right atrium, the blood enters the common ventricle for two circles of circulation. Since the heart of these animals is three-chambered, the blood from both circles (venous and arterial) is mixed.

In humans (and mammals) the heart has a 4-chamber structure. In it two ventricles and two auricles are divided by partitions. The absence of mixing of the two types of blood (arterial and venous) became a giant evolutionary invention that provided the warmth of mammals.

Blood supply of the lungs and heart

In the circulatory system, which consists of two circles, light and heart nutrition is of particular importance. These are the most important organs ensuring the closure of the bloodstream and the integrity of the respiratory and circulatory systems. So, the lungs have in their thickness two circles of blood circulation. But their tissue is fed by vessels of a large circle: bronchial and pulmonary vessels branching from the aorta and from the intrathoracic arteries, carrying blood to the lung parenchyma. And from the right divisions the body can not eat, although some oxygen diffuses from there. Hence, the large and small circles of circulation, the scheme of which is described above, perform different functions (one enriches the blood with oxygen, and the second sends it to the organs, taking deoxygenated blood from them).

The heart also feeds on the vessels of a large circle, but the blood in its cavities is capable of providing oxygen to the endocardium. At the same time, a part of the myocardium veins, mostly small ones, flows directly into the chambers of the heart. It is noteworthy that the pulse wave on the coronary arteries spreads into the cardiac diastole. Therefore, the body is only supplied with blood when it "rests."

It is interesting

Circles of blood circulation, the scheme of which is presented above in the relevant sections, provide both warm-bloodedness and high endurance. Let a person not be an animal that often uses its power to survive, but it allowed other mammals to populate certain habitats. Previously, they were inaccessible to amphibians and reptiles, let alone fish.

In phylogenesis, a large circle appeared earlier and was characteristic of fish. A small circle was supplemented only by those animals that completely or completely came to the land and settled it. Since its introduction, the system of respiration and circulation has been considered together. They are connected functionally and structurally.

This is an important and already indestructible evolutionary mechanism for leaving the aquatic habitat and settling the land. Therefore, the continuing complication of mammalian organisms will now go not in the way of complicating the respiratory and circulatory system, but in the direction of strengthening the oxygen-binding function of the blood and increasing the lung area.