How many circles of blood circulation are there in the human body? Circulation circles - large, small, coronary and their features

What is the pulmonary circulation?

From the right ventricle, blood is pumped into the capillaries of the lungs. Here it “gives” carbon dioxide and “takes” oxygen, after which it goes back to the heart, namely the left atrium.

moves along a closed circuit which consists of the large and small circles of blood circulation. The path in the pulmonary circulation is from the heart to the lungs and back. In the pulmonary circulation, venous blood from the right ventricle of the heart enters pulmonary lungs, where it gets rid of carbon dioxide and is saturated with oxygen and flows through the pulmonary veins into the left atrium. After this, the blood is pumped into the systemic circulation and flows to all organs of the body.

Why is the pulmonary circulation needed?

Division circulatory system human blood circulation has one significant advantage: oxygen-enriched blood is separated from “used” blood saturated with carbon dioxide. Thus, it is subjected to significantly less load than if, in general, it pumped both oxygen-saturated and carbon dioxide-saturated. This structure of the pulmonary circulation is due to the presence of a closed arterial and venous system connecting the heart and lungs. In addition, precisely due to the presence of the pulmonary circulation, it consists of four chambers: two atria and two ventricles.

How does the pulmonary circulation function?

Blood enters the right atrium through two venous trunks: the superior vena cava, which brings blood from upper parts body, and the inferior vena cava, which brings blood from its lower parts. From the right atrium, blood enters the right ventricle, from where it is pumped through the pulmonary artery into the lungs.

Heart valves:

In the heart there are: one between the atria and the ventricles, the second between the ventricles and the arteries emerging from them. prevent backflow of blood and provide direction of blood flow.

Positive and negative pressure:

Alveoli are located on branches of the bronchial tree (bronchioles).

Under high pressure, blood is pumped into the lungs; under negative pressure, it enters the left atrium. Therefore, blood moves through the capillaries of the lungs at the same speed all the time. Thanks to the slow flow of blood in the capillaries, oxygen has time to penetrate the cells and carbon dioxide enters the blood. When oxygen demand increases, for example during intense or severe physical activity, the pressure created by the heart increases and blood flow accelerates. Due to the fact that blood enters the lungs at a lower pressure than into the systemic circulation, the pulmonary circulation is also called the low-pressure system. : Its left half, which does the heavier work, is usually somewhat thicker than the right.

How is blood flow regulated in the pulmonary circulation?

Nerve cells, acting as a kind of sensors, constantly monitor various indicators, for example, acidity (pH), concentration of liquids, oxygen and carbon dioxide, content, etc. All information is processed in the brain. From it, corresponding impulses are sent to the heart and blood vessels. In addition, each artery has its own internal lumen, ensuring a constant blood flow rate. When the heartbeat speeds up, the arteries widen; when the heartbeat slows down, they narrow.

What is the systemic circulation?

Circulatory system: through the arteries, oxygenated blood is carried from the heart and supplied to the organs; Through the veins, blood saturated with carbon dioxide returns to the heart.

Oxygenated blood travels through the blood vessels of the systemic circulation to all human organs. The diameter of the largest artery, the aorta, is 2.5 cm. The diameter of the smallest blood vessels, capillaries, is 0.008 mm. The systemic circulation begins from, from here arterial blood enters the arteries, arterioles and capillaries. Through the walls of the capillaries, the blood releases nutrients and oxygen to tissue fluid. And the waste products of cells enter the blood. From the capillaries, blood flows into small veins, which form more large veins and drain into the superior and inferior vena cava. The veins bring venous blood to the right atrium, where the systemic circulation ends.

100,000 km of blood vessels:

If we take all the arteries and veins of an adult of average height and connect them into one, then its length would be 100,000 km, and its area would be 6000-7000 m2. Such a large amount in the human body is necessary for the normal implementation of metabolic processes.

How does the systemic circulation work?

From the lungs, oxygenated blood flows into the left atrium and then into the left ventricle. When the left ventricle contracts, blood is ejected into the aorta. The aorta divides into two large iliac arteries, which run down and supply blood to the limbs. Blood vessels branch off from the aorta and its arch, supplying blood to the head, chest wall, arms and torso.

Where are the blood vessels located?

Blood vessels of the extremities are visible in the folds, for example, veins can be seen in the elbow bends. The arteries are located somewhat deeper, so they are not visible. Some blood vessels are quite elastic, so when you bend an arm or leg they are not pinched.

Main blood vessels:

The heart is supplied with blood by the coronary vessels belonging to the systemic circulation. The aorta branches into a large number of arteries, and as a result, the blood flow is distributed over several parallel vascular networks, each of which supplies blood to a separate organ. The aorta, rushing down, enters the abdominal cavity. Arteries that supply the digestive tract and spleen depart from the aorta. Thus, organs actively involved in metabolism are directly “connected” to the circulatory system. In the area of ​​the lumbar spine, just above the pelvis, the aorta branches: one of its branches supplies blood to the genitals, and the other to the lower extremities. Veins carry oxygen-depleted blood to the heart. From lower limbs venous blood collects in the femoral veins, which unite to form the iliac vein, which gives rise to the inferior vena cava. Venous blood flows from the head through the jugular veins, one on each side, and from upper limbs- along the subclavian veins; the latter, merging with the jugular veins, form the innominate veins on each side, which unite to form the superior vena cava.

Portal vein:

System portal vein is the circulatory system into which blood vessels The digestive tract receives blood depleted of oxygen. Before entering the inferior vena cava and the heart, this blood passes through the capillary network

Connections:

In the fingers and toes, intestines and anus there are anastomoses - connections between the afferent and efferent vessels. Rapid heat transfer is possible through such connections.

Air embolism:

If at intravenous administration When taking medications, air enters the bloodstream, which can cause an air embolism and lead to death. Air bubbles clog the capillaries of the lungs.

ON A NOTE:

The opinion that arteries carry only oxygenated blood, and veins carry blood containing carbon dioxide, is not entirely correct. The fact is that in the pulmonary circulation the opposite is true - used blood is carried by arteries, and fresh blood is carried by veins.

The cardiovascular system includes two systems: the circulatory system (circulatory system) and the lymphatic system (lymph circulation system). The circulatory system combines the heart and blood vessels - tubular organs in which blood circulates throughout the body. The lymphatic system includes lymphatic capillaries, lymphatic vessels, lymphatic trunks and lymphatic ducts branched in organs and tissues, through which lymph flows towards large venous vessels.

Along the route lymphatic vessels from organs and parts of the body to trunks and ducts lie numerous The lymph nodes related to the organs of the immune system. The study of the cardiovascular system is called angiocardiology. The circulatory system is one of the main systems of the body. It ensures the delivery of nutrients, regulatory, protective substances, oxygen to tissues, removal of metabolic products, and heat exchange. It is a closed vascular network that penetrates all organs and tissues, and has a centrally located pumping device - the heart.

The circulatory system is connected by numerous neurohumoral connections with the activities of other body systems, serves as an important link in homeostasis and provides blood supply adequate to current local needs. For the first time, an accurate description of the mechanism of blood circulation and the importance of the heart was given by the founder of experimental physiology, the English physician W. Harvey (1578-1657). In 1628, he published the famous work “An Anatomical Study of the Movement of the Heart and Blood in Animals,” in which he provided evidence of the movement of blood through the vessels of the systemic circulation.

The founder of scientific anatomy A. Vesalius (1514-1564) in his work “On the structure human body"gave a correct description of the structure of the heart. The Spanish physician M. Servetus (1509-1553) in the book “The Restoration of Christianity” correctly presented the pulmonary circulation, describing the path of blood movement from the right ventricle to the left atrium.

The blood vessels of the body are combined into the systemic and pulmonary circulation. In addition, the coronary circulation is additionally distinguished.

1)Systemic circulation - bodily , starts from the left ventricle of the heart. It includes the aorta, arteries of various sizes, arterioles, capillaries, venules and veins. The large circle ends with two vena cavae flowing into the right atrium. Through the walls of the body's capillaries, the exchange of substances between blood and tissues occurs. Arterial blood gives oxygen to tissues and, saturated with carbon dioxide, turns into venous blood. Usually a vessel is suitable for the capillary network arterial type(arteriole), and a venule comes out of it.

For some organs (kidney, liver) there is a deviation from this rule. So, an artery - an afferent vessel - approaches the glomerulus of the renal corpuscle. An artery, an efferent vessel, also emerges from the glomerulus. A capillary network inserted between two vessels of the same type (arteries) is called arterial miraculous network. The capillary network is built like a miraculous network, located between the afferent (interlobular) and efferent (central) veins in the liver lobule - venous miraculous network.

2)Pulmonary circulation - pulmonary , starts from the right ventricle. It includes the pulmonary trunk, which branches into two pulmonary arteries, smaller arteries, arterioles, capillaries, venules and veins. It ends with four pulmonary veins flowing into the left atrium. In the capillaries of the lungs, venous blood, enriched with oxygen and freed from carbon dioxide, turns into arterial blood.

3)Coronary circle of blood circulation - cordial , includes the vessels of the heart itself to supply blood to the heart muscle. It begins with the left and right coronary arteries, which arise from the initial part of the aorta - the aortic bulb. Flowing through the capillaries, the blood delivers oxygen and nutrients to the heart muscle, receives metabolic products, including carbon dioxide, and turns into venous blood. Almost all veins of the heart flow into the common venous vessel- coronary sinus, which opens into the right atrium.

Only a small number of the so-called smallest veins of the heart flow independently, bypassing the coronary sinus, into all chambers of the heart. It should be noted that the heart muscle needs a constant supply of large amounts of oxygen and nutrients, which is ensured by a rich blood supply to the heart. With a heart weight of only 1/125-1/250 of body weight, in coronary arteries 5-10% of all blood ejected into the aorta arrives.

The work of all body systems does not stop even during a person’s rest and sleep. Cell regeneration, metabolism, brain activity at normal indicators continue regardless of human activity.

The most active organ in this process is the heart. Its constant and trouble-free operation provides blood circulation sufficient to maintain all human cells, organs, and systems.

Muscular work, the structure of the heart, as well as the mechanism of blood movement throughout the body, its distribution throughout various departments The human body is a fairly broad and complex topic in medicine. As a rule, such articles are filled with terminology that is incomprehensible to a person without a medical education.

This edition describes the blood circulation briefly and clearly, which will allow many readers to expand their knowledge in health matters.

Note. This topic interesting not only for general development, knowledge of the principles of blood circulation, the mechanisms of the heart can be useful if it is necessary to provide first aid for bleeding, injuries, heart attacks and other incidents before the arrival of doctors.

Many of us underestimate the significance, complexity, high accuracy, coordination of the heart and blood vessels, as well as human organs and tissues. Day and night without stopping, all elements of the system communicate with each other in one way or another, providing the human body with nutrition and oxygen. A number of factors can upset the balance of blood circulation, after which, in a chain reaction, all areas of the body that are directly and indirectly dependent on it will be affected.

Studying the circulatory system is impossible without basic knowledge of the structure of the heart and human anatomy. Considering the complexity of the terminology and the vastness of the topic, upon first acquaintance with it, for many it becomes a discovery that a person’s blood circulation goes through two whole circles.

Complete blood circulation in the body is based on the synchronization of the work of the muscular tissues of the heart, the difference in blood pressure created by its work, as well as the elasticity and patency of arteries and veins. Pathological manifestations, affecting each of the above factors, worsen the distribution of blood throughout the body.

It is its circulation that is responsible for the delivery of oxygen, useful substances into organs, as well as the removal of harmful carbon dioxide, metabolic products harmful to their functioning.

The heart is a muscular organ of the human body, divided into four parts by partitions that form cavities. Through contraction of the heart muscle, various things are created inside these cavities. blood pressure ensuring the operation of valves that prevent accidental reflux of blood back into the vein, as well as the outflow of blood from the artery into the ventricular cavity.

At the top of the heart there are two atria, named according to their location:

1. Right atrium. Dark blood comes from the superior vena cava after which due to contraction muscle tissue under pressure it splashes into the right ventricle. Contraction begins at the point where the vein connects to the atrium, which provides protection against blood flowing back into the vein.
2. Left atrium. The cavity is filled with blood through the pulmonary veins. By analogy with the mechanism of myocardium described above, the blood squeezed out by contraction of the atrium muscle enters the ventricle.

The valve between the atrium and the ventricle opens under blood pressure and allows it to freely pass into the cavity, after which it closes, limiting its ability to return back.

The ventricles are located at the bottom of the heart:

1. Right ventricle. The blood pushed out from the atrium enters the ventricle. Next, it contracts, closes the three leaflet valves and opens the pulmonary valve under blood pressure.
2. Left ventricle. The muscle tissue of this ventricle is significantly thicker than the right one; therefore, during contraction, it can create more strong pressure. This is necessary to ensure the force of blood release into the systemic circulation. As in the first case, the pressure force closes the atrium valve (mitral) and opens the aortic valve.

Important. The full functioning of the heart depends on the synchronicity and rhythm of contractions. Dividing the heart into four separate cavities, the entrances and exits of which are separated by valves, ensures the movement of blood from the veins to the arteries without the risk of mixing. Anomalies in the development of the structure of the heart and its components disrupt the mechanics of the heart, and therefore the blood circulation itself.

The structure of the circulatory system of the human body

In addition to the rather complex structure of the heart, the structure of the circulatory system itself has its own characteristics. Blood is distributed throughout the body through a system of hollow interconnected vessels of various sizes, wall structure, and purpose.

Structure vascular system human body includes the following types of vessels:

1. Arteries. The vessels, which do not contain smooth muscles in their structure, have a durable shell with elastic properties. When additional blood is released from the heart, the walls of the artery expand, which allows you to control the blood pressure in the system. During the pause, the walls stretch and narrow, reducing the lumen of the inner part. This prevents the pressure from falling to critical levels. The function of arteries is to transport blood from the heart to the organs and tissues of the human body.
2. Vienna. The flow of venous blood is ensured by its contractions, the pressure of the skeletal muscles on its membrane, and the pressure difference at the pulmonary vena cava during lung function. A feature of its functioning is the return of waste blood to the heart for further gas exchange.
3. Capillaries. The structure of the wall of the thinnest vessels consists of only one layer of cells. This makes them vulnerable, but at the same time highly permeable, which determines their function. The exchange between tissue cells and plasma that they provide saturates the body with oxygen, nutrition, and cleanses it of metabolic products through filtration in the network of capillaries of the relevant organs.

Each type of vessel forms its own so-called system, which can be examined in more detail in the presented diagram.

Capillaries are the thinnest of vessels; they dot all parts of the body so densely that they form so-called networks.

The pressure in the vessels created by the muscle tissue of the ventricles varies, depending on their diameter and distance from the heart.

Types of blood circulation, functions, characteristics

The circulatory system is divided into two closed systems that communicate thanks to the heart, but perform different tasks. We are talking about the presence of two circles of blood circulation. Medical experts call them circles because of the closedness of the system, distinguishing two main types: large and small.

These circles have fundamental differences in both structure, size, number of vessels involved, and functionality. The table below will help you learn more about their main functional differences.

Table No. 1. Functional characteristics, other features of the systemic and pulmonary circulation:

As can be seen from the table, circles perform completely different functions, but have the same importance for blood circulation. While the blood cycles through the large circle once, inside the small circle it completes 5 cycles in the same period of time.

In medical terminology, the term “additional circulation” is sometimes also encountered:

• cardiac - passes from the coronary arteries of the aorta, returns through the veins to the right atrium;
• placental – circulates in the fetus developing in the uterus;
• Willis - located at the base of the human brain, acts as a reserve blood supply in case of blockage of blood vessels.

One way or another, all additional circles are part of the larger one or are directly dependent on it.

Important. Both circles of blood circulation maintain balance in work of cardio-vascular system. Poor circulation due to the occurrence of various pathologies in one of them leads to an inevitable impact on the other.

Big circle

From the name itself you can understand that this circle differs in size and, accordingly, in the number of vessels involved. All circles begin with the contraction of the corresponding ventricle and end with the return of blood to the atrium.

The large circle originates when the strongest left ventricle contracts, pushing blood into the aorta. Passing along its arc, thoracic, abdominal segment, it is redistributed along the network of vessels through arterioles and capillaries to the corresponding organs and parts of the body.

It is through the capillaries that oxygen, nutrients, and hormones are released. When it flows into the venules, it takes carbon dioxide with it, harmful substances formed by metabolic processes in the body.

Then, through the two largest veins (superior and inferior hollow veins), the blood returns to the right atrium, completing the cycle. You can visually see the pattern of blood circulating in a large circle in the figure below.

As can be seen in the diagram, the outflow of venous blood from the unpaired organs of the human body does not occur directly to the inferior vena cava, but bypass. Saturating the organs with oxygen and nutrition abdominal cavity, the spleen rushes to the liver, where it is cleansed through capillaries. Only after this the filtered blood enters the inferior vena cava.

The kidneys also have filtering properties; the double capillary network allows venous blood to directly enter the vena cava.

Despite the relatively short cycle, coronary circulation is of great importance. The coronary arteries leaving the aorta branch into smaller ones and go around the heart.

Entering its muscle tissue, they are divided into capillaries that feed the heart, and the outflow of blood is provided by three cardiac veins: small, middle, large, as well as the thymus and anterior cardiac veins.

Important. The constant work of heart tissue cells requires a large amount of energy. About 20% of the total amount of blood pushed out of the organ, enriched with oxygen and nutrients into the body, passes through the coronary circle.

Small circle

The structure of the small circle includes much fewer involved vessels and organs. In the medical literature it is more often called pulmonary and for good reason. This organ is the main one in this chain.

Within our means blood capillaries, entwining the pulmonary vesicles, gas exchange has essential values for the body. It is the small circle that subsequently makes it possible for the large circle to saturate the entire human body with enriched blood.

Blood flow through the small circle is carried out in the following order:

1. By contraction of the right atrium, venous blood, darkened due to excess carbon dioxide in it, is pushed into the cavity of the right ventricle of the heart. The atriogastric septum is closed at this moment to prevent blood from returning into it.
2. Under pressure from the muscle tissue of the ventricle, it is pushed into the pulmonary trunk, while the tricuspid valve separating the cavity from the atrium is closed.
3. After blood enters the pulmonary artery, its valve closes, which eliminates the possibility of its return to the ventricular cavity.
4. Passing through a large artery, the blood enters the area where it branches into capillaries, where carbon dioxide is removed and oxygenated.
5. Scarlet, purified, enriched blood through the pulmonary veins ends its cycle at the left atrium.

As you can see when comparing two blood flow patterns, in a large circle dark venous blood flows through the veins to the heart, and in a small circle purified scarlet blood flows and vice versa. The arteries of the pulmonary circle are filled with venous blood, while the arteries of the large circle carry enriched scarlet blood.

Circulatory disorders

In 24 hours, the heart pumps more than 7,000 liters through human vessels. blood. However, this figure is relevant only if the entire cardiovascular system is stable.

Only a few can boast of excellent health. Under conditions real life Due to many factors, almost 60% of the population has health problems, the cardiovascular system is no exception.

Its work is characterized by the following indicators:

• efficiency of the heart;
• vascular tone;
• condition, properties, blood mass.

The presence of deviations in even one of the indicators leads to disruption of the blood flow of two circulatory circles, not to mention the detection of their entire complex. Specialists in the field of cardiology distinguish between general and local disorders that impede the movement of blood through the circulation; a table with a list of them is presented below.

Table No. 2. List of disorders of the circulatory system:

The above-described disorders are also divided into types depending on the circulatory system which it affects:

1. Disorders of the central circulation. This system includes the heart, aorta, vena cava, pulmonary trunk and veins. Pathologies of these elements of the system affect its other components, which threatens a lack of oxygen in the tissues and intoxication of the body.
2. Peripheral circulation disorders. It implies a pathology of microcirculation, manifested by problems with blood supply (arterial/venous anemia), rheological characteristics of blood (thrombosis, stasis, embolism, disseminated intravascular coagulation), and vascular permeability (blood loss, plasmorrhagia).

The main risk group for the manifestation of such disorders is primarily genetically predisposed people. If parents have problems with blood circulation or heart function, there is always a chance to pass on a similar diagnosis by inheritance.

However, even without genetics, many people expose their body to the risk of developing pathologies in both the systemic and pulmonary circulation:

• bad habits;
• passive lifestyle;
• harmful working conditions;
• constant stress;
• predominance of junk food in the diet;
• uncontrolled use of medications.

All this gradually affects not only the condition of the heart, blood vessels, blood, but also the entire body. The result is a decrease protective functions body, the immune system weakens, which provides opportunities for the development of various diseases.

Important. Changes in the structure of the walls of blood vessels, muscle tissue of the heart, and other pathologies can be caused infectious diseases, some of them are sexually transmitted.

The most common diseases of the cardiovascular system worldwide medical practice considers atherosclerosis, hypertension, ischemia.

Atherosclerosis usually has chronic form and progresses quite quickly. Violation of protein-fat metabolism leads to structural changes, mainly large and medium arteries. Sprawl connective tissue provoke lipid-protein deposits on the walls of blood vessels. Atherosclerotic plaque closes the lumen of the artery, preventing blood flow.

Hypertension is dangerous due to constant stress on blood vessels, accompanied by oxygen starvation. As a result, dystrophic changes occur in the walls of the vessel, and the permeability of their walls increases. Plasma leaks through the structurally altered wall, forming edema.

Coronary heart disease (ischemic) is caused by a violation of the cardiac circulation. Occurs when there is a deficiency of oxygen sufficient for the full functioning of the myocardium or a complete stop of blood flow. Characterized by dystrophy of the heart muscle.

Prevention of circulatory problems, treatment

The best option for preventing diseases and maintaining proper blood circulation in the systemic and pulmonary circles is prevention. Compliance with simple but sufficient effective rules will help a person not only strengthen the heart and blood vessels, but also prolong the youth of the body.

Basic steps to prevent cardiovascular diseases:

• quitting smoking, alcohol;
• maintaining a balanced diet;
• playing sports, hardening;
• compliance with the work and rest regime;
• healthy sleep;
• regular preventive examinations.

Annual examination medical specialist will help with early detection signs of blood circulation problems. If a disease is detected initial stage development experts recommend drug treatment, drugs of the corresponding groups. Following your doctor's instructions increases your chances of a positive outcome.

Important. Quite often the disease is asymptomatic for a long time, which gives him the opportunity to progress. In such cases, surgery may be necessary.

Quite often, for the prevention and treatment of the pathologies described by the editors, patients use traditional methods treatments and prescriptions. Such methods require prior consultation with your doctor. Based on the patient's medical history, individual characteristics a specialist will give detailed recommendations regarding his condition.

In the human body, blood moves through two closed systems of vessels connected to the heart - small And big circles of blood circulation.

Pulmonary circulation - This is the path of blood from the right ventricle to the left atrium.

Venous, low-oxygen blood enters the right side hearts. Shrinking right ventricle throws it into pulmonary artery. Through the two branches into which the pulmonary artery is divided, this blood flows to light. There, the branches of the pulmonary artery, dividing into smaller and smaller arteries, pass into capillaries, which densely entwine numerous pulmonary vesicles containing air. Passing through the capillaries, the blood is enriched with oxygen. At the same time, carbon dioxide passes from the blood into the air, which fills the lungs. Thus, in the capillaries of the lungs, venous blood is converted to arterial blood. It enters the veins, which, connecting with each other, form four pulmonary veins, which flow into left atrium(Fig. 57, 58).

The blood circulation time in the pulmonary circulation is 7-11 seconds.

Systemic circulation - this is the path of blood from the left ventricle through arteries, capillaries and veins to the right atrium.Material from the site

The left ventricle contracts and pushes arterial blood into aorta- the largest human artery. Arteries branch off from it, which supply blood to all organs, in particular to the heart. The arteries in each organ gradually branch out, forming a dense network of smaller arteries and capillaries. From the capillaries of the systemic circulation, oxygen and nutrients flow to all tissues of the body, and carbon dioxide passes from the cells to the capillaries. In this case, the blood turns from arterial to venous. The capillaries merge into veins, first into small ones and then into larger ones. Of these, all the blood collects in two large vena cava. Superior vena cava carries blood to the heart from the head, neck, arms, and inferior vena cava- from all other parts of the body. Both vena cava flow into the right atrium (Fig. 57, 58).

The blood circulation time in the systemic circulation is 20-25 seconds.

Venous blood from the right atrium enters the right ventricle, from which it flows through the pulmonary circulation. At the exit of the aorta and pulmonary artery from the ventricles of the heart, semilunar valves(Fig. 58). They look like pockets located on the inner walls of blood vessels. When blood is pushed into the aorta and pulmonary artery, the semilunar valves are pressed against the walls of the vessels. When the ventricles relax, blood cannot return to the heart due to the fact that, flowing into the pockets, it stretches them and they close tightly. Consequently, semilunar valves ensure the movement of blood in one direction - from the ventricles to the arteries.

In mammals and humans, the circulatory system is the most complex. This is a closed system consisting of two circles of blood circulation. Providing warm-bloodedness, it is more energetically beneficial and allows a person to occupy the habitat niche in which he is currently located.

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

The concept of blood circulation

The circulatory system consists of two circles - the bodily (large) and pulmonary (small). The circulatory system is a system of blood vessels of the arterial, capillary, lymphatic and venous type, which supplies blood from the heart to the vessels and its movement in the opposite direction. The heart is central, since two circles of blood circulation intersect in it without mixing arterial and venous blood.

Systemic circulation

The systemic supply of peripheral tissues is called the systemic circulation arterial blood and its return to the heart. It starts from where the blood comes out into the aorta through the aortic opening from the aorta, the blood goes to the smaller bodily arteries and reaches the capillaries. This is a set of organs that forms the adductor link.

Here oxygen enters the tissues, and from them carbon dioxide is captured by red blood cells. Blood also transports amino acids, lipoproteins, and glucose into tissues, the metabolic products of which are carried out from capillaries into venules and further into larger veins. They drain into the vena cava, which returns blood directly to the heart into the right atrium.

The right atrium ends the systemic circulation. The diagram looks like this (along the blood circulation): left ventricle, aorta, elastic arteries, muscular elastic arteries, muscular arteries, arterioles, capillaries, venules, veins and vena cava, returning blood to the heart into the right atrium. The brain, all skin, and bones are nourished from the systemic circulation. In general, all human tissues are nourished by the vessels of the systemic circulation, and the small one is only a place of blood oxygenation.

Pulmonary circulation

The pulmonary (lesser) circulation, the diagram of which is presented below, originates from the right ventricle. Blood enters it from the right atrium through the atrioventricular opening. From the cavity of the right ventricle, oxygen-depleted (venous) blood flows through the outlet (pulmonary) tract into the pulmonary trunk. This artery is thinner than the aorta. It divides into two branches that go to both lungs.

Lungs are central authority, which forms the pulmonary circulation. The human diagram described in anatomy textbooks explains that pulmonary blood flow is necessary for oxygenation of the blood. Here it gives off carbon dioxide and takes in oxygen. In the sinusoidal capillaries of the lungs, with a diameter atypical for the body of about 30 microns, gas exchange occurs.

Subsequently, oxygenated blood is sent through the intrapulmonary venous system and collected in the 4 pulmonary veins. All of them are attached to the left atrium and carry oxygen-rich blood there. This is where the blood circulation ends. The diagram of the small pulmonary circle looks like this (in the direction of blood flow): right ventricle, pulmonary artery, intrapulmonary arteries, pulmonary arterioles, pulmonary sinusoids, venules, 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. Fish have only one blood circulation, because they do not have lungs, and all gas exchange takes place in the vessels of the gills. As a result, the fish heart is single-chambered - it is a pump that pushes blood in only one direction.

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

In humans (and mammals), the heart has a 4-chamber structure. It contains two ventricles and two atria separated by septa. The absence of mixing of two types of blood (arterial and venous) became a gigantic evolutionary invention that ensured the warm-bloodedness of mammals.

and hearts

In the circulatory system, which consists of two circles, it is of particular importance lung nutrition and hearts. These are the most important organs that ensure the closure of the bloodstream and the integrity of the respiratory and circulatory systems. So, the lungs have two circles of blood circulation in their thickness. But their tissue is nourished by the vessels of the systemic circle: bronchial and pulmonary vessels branch off from the aorta and intrathoracic arteries, carrying blood to the lung parenchyma. And the organ cannot receive nutrition from the right sections, although some of the oxygen diffuses from there. This means that the large and small circles of blood circulation, the diagram 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 is also fed by the vessels of the systemic circle, but the blood in its cavities is capable of providing oxygen to the endocardium. In this case, part of the myocardial veins, mainly small ones, flow directly into the It is noteworthy that the pulse wave to the coronary arteries propagates into cardiac diastole. Therefore, the organ is supplied with blood only when it is “resting”.

The human blood circulation, the diagram of which is presented above in the relevant sections, provides both warm-bloodedness and high endurance. Even though humans are not an animal that often uses their strength to survive, this has allowed other mammals to populate certain habitats. Previously, they were inaccessible to amphibians and reptiles, and even more so to fish.

In phylogeny, the large circle appeared earlier and was characteristic of fish. And the small circle supplemented it only in those animals that entirely or completely came to land and populated it. Since its inception, the respiratory and circulatory systems have been considered together. They are connected functionally and structurally.

This is an important and already indestructible evolutionary mechanism for exiting aquatic environment habitats and settlement of land. Therefore, the ongoing complication of mammalian organisms will now be directed not along the path of complication of the respiratory and circulatory system, but in the direction of strengthening the oxygen-binding system and increasing the area of ​​the lungs.