Mammals have the most complex circulatory system. It is a closed system that includes two circles of blood circulation. Energetically, this is more profitable, as it provides warm-bloodedness and allows a person to occupy exactly the niche in which he is at the moment.
Circulatory system
This system includes a group of muscle organs that have a hollow structure. They are responsible for the process of blood circulation through the vessels located in the body. It is represented, in particular, by the heart and blood vessels of different sizes. These muscular organs form a small and large circle of blood circulation. The scheme given in the article helps to visualize the mechanism of work.
The concept of blood circulation
The system consists of two circles. One of them is called large, or bodily, and the second - small, or pulmonary. The blood circulation includes arterial, capillary, lymphatic and venous vessels. This system provides blood supply to blood vessels from the heart, as well as its reverse movement. The heart is a central organ. It is in it that the small and large circles of blood circulation cross (the scheme is presented below), and without mixing venous and arterial blood.
Large or corporal circle
The large circle is a system that provides peripheral tissue with arterial blood , and then returns it back. It starts from the left ventricle. From it through the aortic orifice, which has a tricuspid valve, blood flows into the aorta. Then it goes to other, smaller arteries, reaches the capillaries. These bodies together constitute the leading link.
It is here that oxygen enters the tissues, from which red blood cells then capture carbon dioxide. In addition, blood transports glucose, lipoproteins, amino acids and metabolic products into the tissues into the venules, and then into the veins from the capillaries. The veins, in turn, flow into the vena cava, returning blood to the right atrium of the heart.
Small, large and heart circles of blood circulation have a unique structure.
The body circle ends precisely with the atrium. The blood circulation scheme is as follows, if we consider it in the direction of blood flow: it starts from the left ventricle, then comes the aorta, elastic arteries, then muscle-elastic and muscle arteries, then arterioles, capillaries. They connect with venules, veins and vena cava, which return blood to the right atrium of the heart. A large circle nourishes the brain, the entire skin and bones with blood. Thus, all tissues of the human body are fed from a large circle. The small circle, in turn, represents a place of blood oxygenation.
Schemes of small and large circles of blood circulation can also be found on the Web.
Pulmonary or pulmonary circulation
The second circle, called pulmonary, starts from the right ventricle. Blood enters it from the right atrium through the atrioventricular opening. Oxygen-depleted blood, called venous, from the cavity of the right ventricle enters the pulmonary trunk through the pulmonary (exit) tract. This artery is much thinner than the aorta. It is divided into two branches directed to both lungs.
The central organ that forms the small circle are the lungs. Pulmonary blood flow is required for blood oxygenation. It is here that the return of carbon dioxide and oxygen intake occurs. Gas exchange is carried out in sinusoidal pulmonary capillaries, which have an atypical diameter for the body - about 30 microns. This can be seen in the diagram of the small and large circles of blood circulation.
After oxygen saturation, blood is sent to the pulmonary veins through the system of intrapulmonary veins. There are four of them, all of them are attached to the left atrium, transferring oxygen-enriched blood into it. Circles of blood circulation on this and end. The scheme of the pulmonary circle can be described as follows: the right ventricle begins, followed by the pulmonary artery and intrapulmonary arteries, after - the pulmonary arterioles, as well as pulmonary sinusoids, then venules and pulmonary veins. It ends with the left atrium.
What else reflects the scheme of small and large circles of blood circulation?
Characteristic 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. For example, in fish, there is only one circulatory circle, since they have no lungs, and gas exchange is carried out in the gill vessels. Thus, the heart of fish is single-chamber and plays the role of a pump that pushes blood moving in one direction.
Amphibians and reptiles have lungs, so they have circulatory circles. They work according to a simple scheme: blood from the ventricle is sent to the vessels forming a large circle, from the arteries directly to the capillaries and veins. In addition, venous return has been realized, but from the right atrium, blood enters the ventricle, which is common to both circles. In connection with the fact that in such animals the heart is three-chambered, blood mixes from both circles. A very different picture reflects the scheme of the large and small circle of blood circulation of a person.
Mammals and humans have a four-chamber heart. The presence of partitions in it provides a separation into two atria and two ventricles. It is the lack of mixing of venous and arterial that provides mammals with warm-bloodedness.
Blood supply to the heart and lungs
A special role in the system, consisting of two circles, is played by the nutrition of the heart and lungs. They are the most important organs that ensure the integrity of the circulatory and respiratory systems, as well as the isolation of the bloodstream. Thus, in the thickness of the lungs there are two circles of blood circulation, nevertheless, their tissue feeds on the vessels of the large circle: the aorta and the intrathoracic arteries have branches in the form of bronchial and pulmonary vessels that carry blood to the lung and its parenchyma. The pattern of blood movement in the small and large circles of blood circulation is very interesting.
The lungs cannot feed from the right, despite the fact that part of the oxygen diffuses from them. Thus, we can conclude that two circles of blood circulation perform different functions: the first enriches the blood with oxygen, and the second transfers it to all organs, and the oxygenated blood is taken from them.
The heart feeds directly from the vessels of a large circle. The blood that is in its cavities nourishes the endocardium with oxygen. At the same time, some myocardial veins, mainly small ones, enter the cardiac chambers.
We examined the scheme of small and large circles of blood circulation.