What kind of blood flows in the left ventricle. Circles of blood circulation in humans: who discovered and what types exist
Question 1. What kind of blood flows through the arteries of the large circle, and what - through the arteries of the small?
Arterial blood flows through the arteries of the large circle, and venous blood flows through the arteries of the small circle.
Question 2. Where does the systemic circulation begin and where does it end, and where does the small one?
All vessels form two circles of blood circulation: large and small. A large circle begins in the left ventricle. The aorta departs from it, which forms an arc. Arteries branch off from the aortic arch. From the initial part of the aorta coronary vessels that supply blood to the myocardium. The part of the aorta that is in chest, is called thoracic aorta, and the part that is in abdominal cavity, - abdominal aorta. The aorta branches into arteries, arteries into arterioles, and arterioles into capillaries. From the capillaries of the large circle, oxygen and nutrients come to all organs and tissues, and carbon dioxide and metabolic products come from the cells into the capillaries. The blood changes from arterial to venous.
Purification of blood from toxic decay products occurs in the vessels of the liver and kidneys. Blood from the digestive tract, pancreas, and spleen enters the portal vein of the liver. In the liver, the portal vein branches into capillaries, which then recombine into a common trunk of the hepatic vein. This vein flows into the inferior vena cava. Thus, all blood from the abdominal organs, before entering the large circle, passes through two capillary networks: through the capillaries of these organs themselves and through the capillaries of the liver. The portal system of the liver ensures the neutralization of toxic substances that are formed in the large intestine. The kidneys also have two capillary networks: a network of renal glomeruli, through which blood plasma containing harmful metabolic products (urea, uric acid), passes into the cavity of the nephron capsule, and a capillary network that braids the convoluted tubules.
Capillaries merge into venules, then into veins. Then, all the blood enters the superior and inferior vena cava, which flow into the right atrium.
The pulmonary circulation begins in the right ventricle and ends in the left atrium. Venous blood from the right ventricle enters the pulmonary artery, then to the lungs. In the lungs, gas exchange occurs, venous blood turns into arterial. Through four pulmonary veins, arterial blood enters the left atrium.
Question 3. To a closed or open system refers to the lymphatic system?
The lymphatic system should be classified as open. It blindly begins in the tissues with lymphatic capillaries, which then combine to form lymphatic vessels, and those, in turn, form the lymphatic ducts that flow into the venous system.
After all, it is a shame for future doctors not to know the basis of the basics - circles of blood circulation. Without this information and understanding of how blood moves through the body, it is impossible to understand the mechanism of development of vascular and heart diseases, to explain the pathological processes that occur in the heart with a particular lesion. Without knowing the circles of blood circulation it is impossible to work as a doctor. This information will not interfere with a simple layman, because knowledge about one's own body is never superfluous.
1 Big trip
To better imagine how a large circle of blood circulation works, let's fantasize a little? Imagine that all the vessels of the body are rivers, and the heart is a bay, into the bay of which all the channels of the rivers fall. We set off on a journey: our ship begins a great voyage. From the left ventricle we swim into the aorta - the main vessel human body. This is where the systemic circulation begins.
Oxygenated blood flows in the aorta, because aortic blood is distributed throughout the human body. The aorta gives off branches, like a river, tributaries that supply blood to the brain, all organs. Arteries branch to arterioles, which in turn give off capillaries. Bright, arterial blood gives the cells oxygen, nutrients, and takes the metabolic products of cellular life.
Capillaries are organized into venules that carry dark, cherry-colored blood, because it has given oxygen to the cells. The venules converge into larger veins. Our ship completes its journey along the two largest "rivers" - the superior and inferior vena cava - enters the right atrium. The path is over. You can schematically represent a large circle as follows: the beginning is the left ventricle and aorta, the end is the vena cava and the right atrium.
2 Small Journey
What is the pulmonary circulation? Let's go on our second trip! Our ship originates from the right ventricle, from which the pulmonary trunk departs. Remember that completing the systemic circulation, we moored in the right atrium? From it, venous blood flows into the right ventricle, and then, with heart contraction, is pushed into the vessel, departing from it - the pulmonary trunk. This vessel travels to the lungs, where it bifurcates into the pulmonary arteries and then into the capillaries.
Capillaries envelop the bronchi and alveoli of the lungs, give off carbon dioxide and metabolic products and are enriched with life-giving oxygen. Capillaries organize into venules, leaving the lungs, and then into larger ones. pulmonary veins. We are accustomed to the fact that venous blood flows in the veins. Just not in the lungs! These veins are rich in arterial, bright scarlet, O2 rich blood. Through the pulmonary veins, our ship sails to the bay, where its journey ends - to the left atrium.
So, the beginning of the small circle is the right ventricle and the pulmonary trunk, the end is the pulmonary veins and the left atrium. A more detailed description is as follows: the pulmonary trunk is divided into two pulmonary arteries, which in turn branch into a network of capillaries, like a cobweb enveloping the alveoli, where gas exchange occurs, then the capillaries gather into venules and pulmonary veins that flow into the left upper cardiac chamber of the heart.
3 Historical facts
Having dealt with the departments of blood circulation, it seems that there is nothing complicated in their structure. Everything is simple, logical, understandable. Blood leaves the heart, collects metabolic products and CO2 from the cells of the whole body, saturates them with oxygen, returns to the heart again already venous blood, which, passing through the natural "filters" of the body - the lungs, becomes arterial again. But it took many centuries to study and understand the movement of blood flow in the body. Galen mistakenly assumed that the arteries do not contain blood, but air.
This position today can be explained by the fact that in those days the vessels were studied only on corpses, and in a dead body the arteries are bled, and the veins, on the contrary, are full-blooded. It was believed that blood is produced in the liver, and it is consumed in the organs. Miguel Servet in the 16th century suggested that “the spirit of life originates in the left heart ventricle, the lungs contribute to this, where the air and blood coming from the right heart ventricle are mixed”, thus, the scientist recognized and described for the first time a small circle.
But little attention was paid to the discovery of Servetus. The father of the circulatory system is considered to be Harvey, who already in 1616 wrote in his writings that the blood "circulates through the body." For many years he studied the movement of blood, and in 1628 he published a work that became a classic, and crossed out all ideas about the blood circulation of Galen, in this work the circles of blood circulation were outlined.
Harvey did not discover only the capillaries discovered later by the scientist Malpighi, who supplemented the knowledge of the "circles of life" with a connecting capillary link between arterioles and venules. The microscope helped the scientist to open the capillaries, which gave an increase of up to 180 times. Harvey's discovery was met with criticism and challenge by the great minds of those times, many scientists did not agree with Harvey's discovery.
But even today, reading his works, one is surprised at how accurately and in detail for that time the scientist described the work of the heart and the movement of blood through the vessels: “The heart, doing work, first makes a movement, and then rests in all animals while they are still alive. At the moment of contraction, it squeezes out blood from itself, the heart is emptied at the moment of contraction. The circulatory circles were also described in detail, with the exception that Harvey could not observe the capillaries, but he accurately described that the blood is collected from the organs and flows back to the heart?
But how does the transition from arteries to veins take place? This question haunted Harvey. Malpighi revealed this secret of the human body by discovering capillary circulation. It's a shame that Harvey did not live several years before this discovery, because the discovery of capillaries with 100% certainty confirmed the veracity of Harvey's teachings. The great scientist did not have a chance to feel the fullness of the triumph of his discovery, but we remember him and his huge contribution to the development of anatomy and knowledge of nature. human body.
4 Largest to smallest
I would like to dwell on the main elements of the circles of blood circulation, which are their framework, along which the blood moves - the vessels. Arteries are vessels that carry blood away from the heart. The aorta is the most important and important artery of the body, it is the largest - about 25 mm in diameter, it is through it that blood enters other vessels that depart from it and is delivered to organs, tissues, cells.
Exception: the pulmonary arteries carry not O2-rich blood, but CO2-rich blood to the lungs.
Veins are vessels that carry blood to the heart, their walls are easily extensible, the diameter of the vena cava is about 30 mm, and the small ones are 4-5 mm. The blood in them is dark, the color of ripe cherries, saturated with metabolic products.
Exception: the pulmonary veins are the only ones in the body through which arterial blood flows.
Capillaries are the thinnest vessels, consisting of only one layer of cells. The single-layer structure allows gas exchange, the exchange of useful and harmful products between cells and directly capillaries.
The diameter of these vessels is only 0.006 mm on average, and the length is not more than 1 mm. That's how small they are! However, if we sum up the length of all the capillaries together, we will get a very significant figure - 100 thousand km ... Our body inside is shrouded in them like a cobweb. And no wonder - after all, every cell of the body needs oxygen and nutrients, and capillaries can ensure the supply of these substances. All vessels, both the largest and smallest capillaries, form a closed system, or rather two systems - the aforementioned circles of blood circulation.
5 Important features
What are circulatory circles for? Their role cannot be overestimated. Just as life on Earth is impossible without water resources, so human life is impossible without the circulatory system. The main role of the great circle is:
- Providing oxygen to every cell of the human body;
- The flow of nutrients from the digestive system into the blood;
- Filtration from blood to excretory organs life products.
The role of the small circle is no less important than those described above: the removal of CO2 from the body and metabolic products.
Knowledge about the structure of one's own body is never superfluous, knowledge about how the circulatory departments function leads to a better understanding of the body's work, and also forms an idea of the unity and integrity of organs and systems, the connecting link of which is undoubtedly the bloodstream, organized into circulatory circles.
Vessels in the human body form two closed circulatory systems. Allocate large and small circles of blood circulation. The vessels of the large circle supply blood to the organs, the vessels of the small circle provide gas exchange in the lungs.
Systemic circulation: arterial (oxygenated) blood flows from the left ventricle of the heart through the aorta, then through the arteries, arterial capillaries to all organs; from the organs, venous blood (saturated with carbon dioxide) flows through the venous capillaries into the veins, from there through the superior vena cava (from the head, neck and arms) and the inferior vena cava (from the trunk and legs) to the right atrium.
Small circle of blood circulation: venous blood flows from the right ventricle of the heart through the pulmonary artery into a dense network of capillaries braiding the pulmonary vesicles, where the blood is saturated with oxygen, then arterial blood flows through the pulmonary veins into the left atrium. In the pulmonary circulation, arterial blood flows through the veins, venous blood through the arteries. It starts in the right ventricle and ends in the left atrium. The pulmonary trunk emerges from the right ventricle, carrying venous blood to the lungs. Here, the pulmonary arteries break up into vessels of smaller diameter, passing into the capillaries. Oxygenated blood flows through the four pulmonary veins into the left atrium.
Blood moves through the vessels due to the rhythmic work of the heart. During ventricular contraction, blood is pumped under pressure into the aorta and pulmonary trunk. Here the highest pressure develops - 150 mm Hg. Art. As blood moves through the arteries, the pressure drops to 120 mm Hg. Art., and in the capillaries - up to 22 mm. The lowest pressure in the veins; in large veins it is below atmospheric.
Blood from the ventricles is ejected in portions, and the continuity of its flow is ensured by the elasticity of the walls of the arteries. At the moment of contraction of the ventricles of the heart, the walls of the arteries are stretched, and then, due to elastic elasticity, they return to their original state even before the next blood flow from the ventricles. Thanks to this, the blood moves forward. Rhythmic fluctuations in the diameter of arterial vessels caused by the work of the heart are called pulse. It is easily palpable in places where the arteries lie on the bone (radial, dorsal artery of the foot). By counting the pulse, you can determine the heart rate and their strength. In an adult healthy person at rest, the pulse rate is 60-70 beats per minute. With various diseases of the heart, arrhythmia is possible - interruptions in the pulse.
With the highest speed, blood flows in the aorta - about 0.5 m / s. In the future, the speed of movement decreases and in the arteries reaches 0.25 m / s, and in the capillaries - approximately 0.5 mm / s. The slow flow of blood in the capillaries and the large length of the latter favor metabolism (the total length of capillaries in the human body reaches 100 thousand km, and the total surface of all body capillaries is 6300 m 2). The big difference in the speed of blood flow in the aorta, capillaries and veins is due to the unequal width of the total cross section of the bloodstream in its various parts. The narrowest such area is the aorta, and the total lumen of the capillaries is 600-800 times greater than the lumen of the aorta. This explains the slowing down of blood flow in the capillaries.
The movement of blood through the vessels is regulated by neurohumoral factors. Impulses sent along the nerve endings can cause either narrowing or expansion of the lumen of the vessels. Two types of vasomotor nerves approach the smooth muscles of the walls of blood vessels: vasodilators and vasoconstrictors.
The impulses going through these nerve fibers, arise in the vasomotor center of the medulla oblongata. In the normal state of the body, the walls of the arteries are somewhat tense and their lumen is narrowed. Impulses continuously flow from the vasomotor center along the vasomotor nerves, which cause a constant tone. Nerve endings in the walls of blood vessels react to changes in blood pressure and chemical composition, causing excitement in them. This excitation enters the central nervous system, resulting in a reflex change in the activity of the cardiovascular system. Thus, the increase and decrease in the diameters of the vessels occurs in a reflex way, but the same effect can also occur under the influence of humoral factors - chemicals that are in the blood and come here with food and from various internal organs. Among them, vasodilators and vasoconstrictors are important. For example, the pituitary hormone - vasopressin, the thyroid hormone - thyroxine, the adrenal hormone - adrenaline constrict blood vessels, enhance all the functions of the heart, and histamine, which is formed in the walls of the digestive tract and in any working organ, acts in the opposite way: it expands capillaries without affecting other vessels . A significant effect on the work of the heart has a change in the content of potassium and calcium in the blood. Increasing the calcium content increases the frequency and strength of contractions, increases excitability and conduction of the heart. Potassium causes the exact opposite effect.
Expansion and narrowing of blood vessels in various organs significantly affects the redistribution of blood in the body. More blood is sent to a working organ, where the vessels are dilated, to a non-working organ - \ less. The depositing organs are the spleen, liver, subcutaneous fatty tissue.
The pulmonary circulation enriches the blood in the lungs with oxygen. It starts from the right ventricle (from where the blood feeds the pulmonary trunk, which divides into two branches that supply blood to the left and right lungs) and ends with the left atrium. The pulmonary circulation supplies oxygen to the blood supplying the lungs. It begins in the right ventricle of the heart, from where venous blood is supplied to the common pulmonary artery (trunk), which divides into two branches leading to the left and right lungs. The end point of the pulmonary circulation is the left atrium.
Anatomical features of the pulmonary circulation
Blood in the body flows through a closed circulatory system that connects the heart and lungs, which consists of small and large circles of blood circulation. In the second of them, her path runs from the heart to the lungs and then in the opposite direction. Blood from the veins of the right heart ventricle, entering the artery of the lungs and its branches - capillaries, gets rid of excess carbon dioxide, and is also saturated with a new supply of oxygen (respiration) received in return, after which it flows through the veins of the lungs into the left atrium.
Pulmonary networks of capillaries braid the alveoli, the so-called "pulmonary vesicles". Each tiny alveolus has a blood vessel attached to it. Only the thinnest porous wall of the capillary and lung separates blood from atmospheric air, so that oxygen and other gases can freely penetrate through it, entering the vessels and alveoli. This is how gas exchange occurs. Its principle is the transition from a higher concentration to a lower one. For example, if there is a lack of oxygen in the venous blood, its entry into the capillaries is carried out from atmospheric air. As for carbon dioxide, here, on the contrary, it enters the pulmonary alveoli, because there its concentration is lower.
Venous blood, which is saturated with oxygen and got rid of excess carbon dioxide, acquires a scarlet color, becomes arterial and from the capillary system again enters four veins of the lungs (two on the left and on the right), after which it flows into the left atrium. It contains the end of the pulmonary circulation. The blood that has entered the atrium flows into the left ventricle, in which the systemic circulation takes its source, supplying it to all organs.
Divided into two circles circulatory system The body gains a significant advantage, because due to this, the oxygen-rich blood is separated from the waste, which is saturated with carbon dioxide, and as a result, the heart is significantly less stressed. It is precisely because of the existence of a small circle of blood circulation that the human heart consists of four chambers in the form of two ventricles and two atria.
The functioning of the pulmonary circulation
Blood is supplied to the right atrium through two pulmonary veins - the upper vena cava, which pumps it from the upper half of the body and the lower empty vein, through which blood flows from the lower part of it. Then it flows into the right ventricle, after which it is transferred to the lungs through pulmonary artery.
The heart is equipped with two pairs of valves: one is located between the ventricles and the atria, and the second is between the ventricles and the arteries extending from them. The valves do not allow the reverse flow of blood to be carried out, giving it a direction.
Any kind of liquid flows from where the pressure is higher to a place where it is lower, and the more the pressure differs, the faster the flow. Blood in the veins of both circulations also flows due to the difference in pressure created by heart contractions. Blood pressure in the left ventricle and in the aorta is higher than in the right atrium and in the vena cava. This pressure difference moves blood in the systemic circulation. In the lesser circle, its movement is provided by high pressure in the pulmonary artery and right cardiac ventricle, combined with low pressure in the left atrium and pulmonary veins. The aorta and large arteries are subject to the highest pressure (hence the name - “ arterial pressure"). It is not a constant value.
Blood is pumped into the lungs through high pressure, and under the influence of negative pressure flows into the left atrium. Thus, it constantly moves through the pulmonary vessels at the same speed. Due to the fact that the blood flow is slow, oxygen has time to get into the cells, while carbon dioxide enters the blood. When the need for oxygen is increased (for example, with severe physical activity and intense sports), heart pressure rises, accelerating blood flow. Due to the fact that in the pulmonary circulation, blood enters the lungs under less pressure than in the large circle, its other name is the system low pressure. The human heart lacks symmetry: its left side, which performs the most difficult work, is usually thicker than the right.
Regulation of the pulmonary circulation
A variety of blood indicators, such as: acidity, hormone levels, the degree of concentration of fluids, carbon dioxide, oxygen, etc. controlled nerve cells playing the role of sensors. All available information is processed by the brain, sending certain impulses to the heart and veins. Each artery has its own internal lumen, providing a continuous rate of blood flow. The vessels of the pulmonary circulation expand during the acceleration of the heartbeat and narrow when it slows down.
To avoid problems with blood circulation, fraught with dangerous complications You need to lead a healthy, active lifestyle and eat well regularly. After all, it is easier to prevent any disease than to cure it later.
The human body provides for the movement of blood through the systemic and pulmonary circulation in order for the liquid tissue to successfully cope with its duties: it transports the substances necessary for their development to the cells and carries away the decay products. Despite the fact that such concepts as “large and small circle” are rather arbitrary, since they are not completely closed systems (the first goes into the second and vice versa), each of them has its own task and purpose in the work of the cardiovascular system.
The human body contains from three to five liters of blood (less for women, more for men), which constantly moves through the vessels. It is a liquid tissue, which contains a huge number of different substances: hormones, proteins, enzymes, amino acids, blood cells and other components (their number is in the billions). Such a large content in plasma is necessary for the development, growth and successful life of cells.
Blood transfers nutrients and oxygen to tissues through capillary walls.. Then it takes carbon dioxide and decay products from the cells and takes them to the liver, kidneys, lungs, which neutralize them and bring them out. If, for some reason, the blood flow is stopped, a person will die within the first ten minutes: this time is enough for the brain cells deprived of nutrition to die, and the body to be poisoned by toxins.
The substance moves through the vessels, which is a vicious circle consisting of two loops, each of which originates in one of the ventricles of the heart, ends in the atrium. In each circle there are veins and arteries, and one of the differences in the circles of blood circulation consists of the composition of the substance that is in them.
The arteries of the greater loop contain oxygen-enriched tissue, while the veins contain carbon dioxide-rich tissue. In the small loop, the opposite is observed: the blood that needs to be cleaned is in the arteries, while the fresh blood is in the veins.
Small and large circles perform two different tasks in the work of the cardiovascular system. In a large loop, human plasma flows through the vessels, transfers the necessary elements to the cells and picks up waste. In the small circle, the substance is cleared of carbon dioxide and saturated with oxygen. In this case, the plasma flows only forward through the vessels: valves prevent the reverse movement of the liquid tissue. Such a system, consisting of two loops, allows different types blood does not mix with each other, which greatly facilitates the task of the lungs and heart.
How is the blood cleansed?
The functioning of the cardiovascular system depends on the work of the heart: rhythmically contracting, it forces the blood to move through the vessels. It consists of four hollow chambers arranged one after the other according to the following scheme:
- right atrium;
- right ventricle;
- left atrium;
- left ventricle.
Both ventricles are much larger than the atria. This is due to the fact that the atria simply collect and send the substance that has entered them into the ventricles, and therefore perform less work (the right one collects blood with carbon dioxide, the left one is saturated with oxygen).
According to the scheme, the right side of the heart muscle does not touch the left side. A small circle originates inside the right ventricle. From here, blood with carbon dioxide is sent to the pulmonary trunk, which later diverges in two: one artery goes to the right, the second to the left lung. Here the vessels are divided into a huge number of capillaries that lead to the pulmonary vesicles (alveoli).
Further, gas exchange takes place through the thin walls of the capillaries: red blood cells, which are responsible for transporting gas through the plasma, detach carbon dioxide molecules from themselves and combine with oxygen (blood is transformed into arterial blood). Then the substance leaves the lungs through four veins and ends up in the left atrium, where the pulmonary circulation ends.
It takes four to five seconds for the blood to complete the small circle. If the body is at rest, this time is enough to provide it with the right amount of oxygen. With physical or emotional stress, the pressure on the human cardiovascular system increases, which causes an acceleration of blood circulation.
Features of blood flow in a large circle
Purified blood enters from the lungs into the left atrium, then goes into the cavity of the left ventricle (the systemic circulation originates here). This chamber has the thickest walls, due to which, when contracted, it is able to eject blood with a force sufficient for it to reach the farthest parts of the body in a few seconds.
The ventricle during contraction ejects liquid tissue into the aorta (this vessel is the largest in the body). Then the aorta diverges into smaller branches (arteries). Some of them go up to the brain, neck, upper limbs, part - down, and serves the organs that are below the heart.
In the systemic circulation, the purified substance moves through the arteries. Them distinctive feature are elastic, but thick walls. Then the substance flows into smaller vessels - arterioles, from them - into capillaries, whose walls are so thin that gases and nutrients easily pass through them.
When the exchange ends, the blood, due to the added carbon dioxide and decay products, becomes more dark color, is transformed into venous blood and sent through the veins to the heart muscle. The walls of the veins are thinner than arterial ones, but they are characterized by a large lumen, so much more blood is placed in them: about 70% of the liquid tissue is in the veins.
If on the move arterial blood the heart has the main influence, then the venous moves forward due to the contraction of the skeletal muscles, which pushes it forward, as well as breathing. Since most of the plasma that is in the veins moves up to prevent it from flowing into reverse side, valves are provided in the vessels to hold it. At the same time, the blood that flows to the heart muscle from the brain moves through the veins that do not have valves: this is necessary to avoid blood stasis.
Approaching the heart muscle, the veins gradually converge with each other. Therefore, only two large vessels enter the right atrium: the superior and inferior vena cava. In this chamber, a large circle is completed: from here, the liquid tissue flows into the cavity of the right ventricle, then gets rid of carbon dioxide.
The average speed of blood flow in big circle when a person is in a calm state, a little less than thirty seconds. At exercise, stress, other factors that excite the body, the movement of blood can accelerate, since the need for cells in oxygen and nutrients during this period increases significantly.
Any diseases of the cardiovascular system negatively affect blood circulation, blocking blood flow, destroying the vascular walls, which leads to starvation and cell death. Therefore, you need to be very careful about your health. If you experience pain in the heart, tumors in the extremities, arrhythmia and other health problems, be sure to consult a doctor to determine the cause of circulatory disorders, malfunctions cardiovascular system and prescribed a treatment plan.
