Of course not. Like any liquid, blood simply transmits the pressure exerted on it. During systole, it transmits increased pressure in all directions, and a wave of pulse expansion runs from the aorta along the elastic walls of the arteries. She runs at an average speed of about 9 meters per second. With damage to the vessels by atherosclerosis, this rate increases, and its study is one of the important diagnostic measurements in modern medicine.

The blood itself moves much more slowly, and this speed is completely different in different parts of the vascular system. What determines the different speed of blood movement in arteries, capillaries and veins? At first glance, it may seem that it should depend on the level of pressure in the corresponding vessels. However, this is not true.

Imagine a river that narrows and widens. We know perfectly well that in narrow places its flow will be faster, and in wide places it will be slower. This is understandable: after all, the same amount of water flows past each point of the coast in the same time. Therefore, where the river is narrower, the water flows faster, and in wide places the flow slows down. The same applies to the circulatory system. The speed of blood flow in its different sections is determined by the total width of the channel of these sections.

In fact, in a second, the same amount of blood passes through the right ventricle as through the left one; the same amount of blood passes on average through any point of the vascular system. If we say that an athlete's heart during one systole can eject more than 150 cm 3 of blood into the aorta, this means that the same amount is ejected from the right ventricle into the pulmonary artery during the same systole. This also means that during the atrial systole, which precedes the ventricular systole by 0.1 seconds, the indicated amount of blood also passed from the atria into the ventricles “in one go”. In other words, if 150 cm 3 of blood can be ejected into the aorta at once, it follows that not only the left ventricle, but also each of the three other chambers of the heart can contain and eject about a glass of blood at once.

If the same volume of blood passes through each point of the vascular system per unit time, then due to the different total lumen of the channel of arteries, capillaries and veins, the speed of movement of individual blood particles, its linear velocity will be completely different. Blood flows fastest in the aorta. Here the speed of blood flow is 0.5 meters per second. Although the aorta is the largest vessel in the body, it represents the narrowest point in the vascular system. Each of the arteries into which the aorta splits is ten times smaller than it. However, the number of arteries is measured in hundreds, and therefore, in total, their lumen is much wider than the lumen of the aorta. When the blood reaches the capillaries, it completely slows down its flow. The capillary is many million times smaller than the aorta, but the number of capillaries is measured in many billions. Therefore, the blood in them flows a thousand times slower than in the aorta. Its speed in the capillaries is about 0.5 mm per second. This is of tremendous importance, because if the blood quickly rushed through the capillaries, it would not have time to give oxygen to the tissues. Since it flows slowly, and the erythrocytes move in one row, "in single file", this creates the best conditions for blood contact with tissues.

A complete revolution through both circles of blood circulation in humans and mammals takes an average of 27 systoles, for humans it is 21-22 seconds.

How long does it take for blood to circulate throughout the body?

How long does it take blood to make a circle throughout the body?

Good day!

The average heartbeat time is 0.3 seconds. During this period of time, the heart pushes out 60 ml of blood.

Thus, the rate of blood moving through the heart is 0.06 l/0.3 s = 0.2 l/s.

In the human body (adult) is, on average, about 5 liters of blood.

Then, 5 liters will push through in 5 l / (0.2 l / s) = 25 s.

Large and small circles of blood circulation. Anatomical structure and main functions

The large and small circles of blood circulation were discovered by Harvey in 1628. Later, scientists from many countries made important discoveries regarding the anatomical structure and functioning of the circulatory system. To this day, medicine is moving forward, studying methods of treatment and restoration of blood vessels. Anatomy is enriched with new data. They reveal to us the mechanisms of general and regional blood supply to tissues and organs. A person has a four-chambered heart, which makes blood circulate through the systemic and pulmonary circulation. This process is continuous, thanks to it absolutely all cells of the body receive oxygen and important nutrients.

Meaning of blood

Large and small circles of blood circulation deliver blood to all tissues, thanks to which our body functions properly. Blood is a connecting element that ensures the vital activity of every cell and every organ. Oxygen and nutrients, including enzymes and hormones, enter the tissues, and metabolic products are removed from the intercellular space. In addition, it is the blood that provides a constant temperature of the human body, protecting the body from pathogenic microbes.

From the digestive organs, nutrients continuously enter the blood plasma and are carried to all tissues. Despite the fact that a person constantly consumes food containing a large amount of salts and water, a constant balance of mineral compounds is maintained in the blood. This is achieved by removing excess salts through the kidneys, lungs and sweat glands.

Heart

Large and small circles of blood circulation depart from the heart. This hollow organ consists of two atria and ventricles. The heart is located on the left side of the chest. Its weight in an adult, on average, is 300 g. This organ is responsible for pumping blood. There are three main phases in the work of the heart. Contraction of the atria, ventricles and a pause between them. This takes less than one second. In one minute, the human heart beats at least 70 times. Blood moves through the vessels in a continuous stream, constantly flows through the heart from a small circle to a large one, carrying oxygen to organs and tissues and bringing carbon dioxide into the alveoli of the lungs.

Systemic (large) circulation

Both large and small circles of blood circulation perform the function of gas exchange in the body. When the blood returns from the lungs, it is already enriched with oxygen. Further, it must be delivered to all tissues and organs. This function is performed by a large circle of blood circulation. It originates in the left ventricle, bringing blood vessels to the tissues, which branch into small capillaries and carry out gas exchange. The systemic circle ends in the right atrium.

Anatomical structure of the systemic circulation

The systemic circulation originates in the left ventricle. Oxygenated blood comes out of it into large arteries. Getting into the aorta and the brachiocephalic trunk, it rushes to the tissues with great speed. One large artery carries blood to the upper part of the body, and the other to the lower part.

The brachiocephalic trunk is a large artery separated from the aorta. It carries oxygen-rich blood up to the head and arms. The second large artery - the aorta - delivers blood to the lower body, to the legs and tissues of the body. These two main blood vessels, as mentioned above, are repeatedly divided into smaller capillaries, which penetrate organs and tissues like a mesh. These tiny vessels deliver oxygen and nutrients to the intercellular space. From it, carbon dioxide and other metabolic products necessary for the body enter the bloodstream. On the way back to the heart, the capillaries reconnect to form larger vessels called veins. The blood in them flows more slowly and has a dark tint. Ultimately, all the vessels coming from the lower body are combined into the inferior vena cava. And those that go from the upper body and head - into the superior vena cava. Both of these vessels enter the right atrium.

Small (pulmonary) circulation

The pulmonary circulation originates in the right ventricle. Further, having made a complete revolution, the blood passes into the left atrium. The main function of the small circle is gas exchange. Carbon dioxide is removed from the blood, which saturates the body with oxygen. The process of gas exchange is carried out in the alveoli of the lungs. Small and large circles of blood circulation perform several functions, but their main significance is to conduct blood throughout the body, covering all organs and tissues, while maintaining heat exchange and metabolic processes.

Lesser circle anatomical device

From the right ventricle of the heart comes venous, oxygen-poor blood. It enters the largest artery of the small circle - the pulmonary trunk. It divides into two separate vessels (right and left arteries). This is a very important feature of the pulmonary circulation. The right artery brings blood to the right lung, and the left, respectively, to the left. Approaching the main organ of the respiratory system, the vessels begin to divide into smaller ones. They branch until they reach the size of thin capillaries. They cover the entire lung, increasing thousands of times the area on which gas exchange occurs.

Each tiny alveolus has a blood vessel. Only the thinnest wall of the capillary and the lung separates blood from atmospheric air. It is so delicate and porous that oxygen and other gases can freely circulate through this wall into the vessels and alveoli. This is how gas exchange takes place. The gas moves according to the principle from a higher concentration to a lower one. For example, if there is very little oxygen in the dark venous blood, then it begins to enter the capillaries from atmospheric air. But with carbon dioxide, the opposite happens, it passes into the alveoli of the lung, since its concentration is lower there. Further, the vessels are again combined into larger ones. Ultimately, only four large pulmonary veins remain. They carry oxygenated, bright red arterial blood to the heart, which flows into the left atrium.

Circulation time

The period of time during which the blood has time to pass through the small and large circle is called the time of the complete circulation of blood. This indicator is strictly individual, but on average it takes from 20 to 23 seconds at rest. With muscle activity, for example, while running or jumping, the blood flow speed increases several times, then a complete blood circulation in both circles can take place in just 10 seconds, but the body cannot withstand such a pace for a long time.

Cardiac circulation

The large and small circles of blood circulation provide gas exchange processes in the human body, but blood also circulates in the heart, and along a strict route. This path is called the “cardiac circulation”. It begins with two large coronary cardiac arteries from the aorta. Through them, blood enters all parts and layers of the heart, and then through small veins is collected in the venous coronary sinus. This large vessel opens into the right heart atrium with its wide mouth. But some of the small veins directly exit into the cavity of the right ventricle and atrium of the heart. This is how the circulatory system of our body is arranged.

full circle circulation time

In the Beauty and Health section, to the question How many times a day does the blood rotate through the body? And how long does one complete circulation of blood take? given by the author Ўliya Konchakovskaya, the best answer is The time of a complete blood circulation in a person is on average 27 systoles of the heart. With a heart rate of 70-80 beats per minute, the circulation of blood occurs in approximately 20-23 seconds, however, the speed of blood movement along the axis of the vessel is greater than at its walls. Therefore, not all blood makes a complete circuit so quickly and the time indicated is minimal.

Studies on dogs have shown that 1/5 of the time of the complete circulation of blood falls on the passage of blood through the pulmonary circulation and 4/5 - through the large.

So in 1 minute about 3 times. For the whole day we consider: 3*60*24 = 4320 times.

We have two circles of blood circulation, one full circle rotates 4-5 seconds. count here!

Large and small circles of blood circulation

Large and small circles of human circulation

Blood circulation is the movement of blood through the vascular system, which provides gas exchange between the body and the external environment, the metabolism between organs and tissues, and the humoral regulation of various body functions.

The circulatory system includes the heart and blood vessels - the aorta, arteries, arterioles, capillaries, venules, veins, and lymphatic vessels. Blood moves through the vessels due to the contraction of the heart muscle.

Blood circulation takes place in a closed system consisting of small and large circles:

• A large circle of blood circulation provides all organs and tissues with blood with nutrients contained in it.
• The small, or pulmonary, circle of blood circulation is designed to enrich the blood with oxygen.

Circulatory circles were first described by the English scientist William Harvey in 1628 in his work Anatomical Studies on the Movement of the Heart and Vessels.

The pulmonary circulation begins from the right ventricle, during the contraction of which venous blood enters the pulmonary trunk and, flowing through the lungs, gives off carbon dioxide and is saturated with oxygen. Oxygen-enriched blood from the lungs through the pulmonary veins enters the left atrium, where the small circle ends.

A large circle of blood circulation begins from the left ventricle, during the contraction of which blood enriched with oxygen is pumped into the aorta, arteries, arterioles and capillaries of all organs and tissues, and from there it flows through the venules and veins into the right atrium, where the large circle ends.

The largest vessel in the systemic circulation is the aorta, which emerges from the left ventricle of the heart. The aorta forms an arc from which arteries branch off, carrying blood to the head (carotid arteries) and to the upper limbs (vertebral arteries). The aorta runs down along the spine, where branches depart from it, carrying blood to the abdominal organs, to the muscles of the trunk and lower extremities.

Arterial blood, rich in oxygen, passes throughout the body, delivering nutrients and oxygen to the cells of organs and tissues necessary for their activity, and in the capillary system it turns into venous blood. Venous blood, saturated with carbon dioxide and cellular metabolic products, returns to the heart and from it enters the lungs for gas exchange. The largest veins of the systemic circulation are the superior and inferior vena cava, which flow into the right atrium.

Rice. Scheme of small and large circles of blood circulation

It should be noted how the circulatory systems of the liver and kidneys are included in the systemic circulation. All blood from the capillaries and veins of the stomach, intestines, pancreas, and spleen enters the portal vein and passes through the liver. In the liver, the portal vein branches into small veins and capillaries, which then reconnect into a common trunk of the hepatic vein, which flows into the inferior vena cava. All the blood of the abdominal organs before entering the systemic circulation flows through two capillary networks: the capillaries of these organs and the capillaries of the liver. The portal system of the liver plays an important role. It ensures the neutralization of toxic substances that are formed in the large intestine during the breakdown of amino acids that are not absorbed in the small intestine and are absorbed by the colon mucosa into the blood. The liver, like all other organs, also receives arterial blood through the hepatic artery, which branches off from the abdominal artery.

There are also two capillary networks in the kidneys: there is a capillary network in each Malpighian glomerulus, then these capillaries are connected into an arterial vessel, which again breaks up into capillaries braiding the convoluted tubules.

Rice. Scheme of blood circulation

A feature of blood circulation in the liver and kidneys is the slowing down of blood flow, which is determined by the function of these organs.

Table 1. The difference between blood flow in the systemic and pulmonary circulation

Systemic circulation

Small circle of blood circulation

In what part of the heart does the circle begin?

In the left ventricle

In the right ventricle

In what part of the heart does the circle end?

In the right atrium

In the left atrium

Where does gas exchange take place?

In the capillaries located in the organs of the chest and abdominal cavities, the brain, upper and lower extremities

in the capillaries in the alveoli of the lungs

What kind of blood moves through the arteries?

What kind of blood moves through the veins?

Time of blood circulation in a circle

Supply of organs and tissues with oxygen and transport of carbon dioxide

Saturation of blood with oxygen and removal of carbon dioxide from the body

The blood circulation time is the time of a single passage of a blood particle through the large and small circles of the vascular system. More details in the next section of the article.

Patterns of the movement of blood through the vessels

Basic principles of hemodynamics

Hemodynamics is a branch of physiology that studies the patterns and mechanisms of blood movement through the vessels of the human body. When studying it, terminology is used and the laws of hydrodynamics, the science of the movement of fluids, are taken into account.

The speed at which blood moves through the vessels depends on two factors:

• from the difference in blood pressure at the beginning and end of the vessel;
• from the resistance that the fluid encounters along its path.

The pressure difference contributes to the movement of the fluid: the greater it is, the more intense this movement. Resistance in the vascular system, which reduces the speed of blood flow, depends on a number of factors:

• the length of the vessel and its radius (the longer the length and the smaller the radius, the greater the resistance);
• blood viscosity (it is 5 times the viscosity of water);
• friction of blood particles against the walls of blood vessels and among themselves.

Hemodynamic parameters

The speed of blood flow in the vessels is carried out according to the laws of hemodynamics, common with the laws of hydrodynamics. Blood flow velocity is characterized by three indicators: volumetric blood flow velocity, linear blood flow velocity and blood circulation time.

Volumetric blood flow velocity - the amount of blood flowing through the cross section of all vessels of a given caliber per unit of time.

The linear velocity of blood flow is the speed of movement of an individual blood particle along the vessel per unit of time. In the center of the vessel, the linear velocity is maximum, and near the vessel wall it is minimum due to increased friction.

Blood circulation time - the time during which blood passes through the large and small circles of blood circulation. Passing through a small circle takes about 1/5, and passing through a large circle - 4/5 of this time

The driving force of blood flow in the vascular system of each of the circles of blood circulation is the difference in blood pressure (ΔР) in the initial section of the arterial bed (aorta for a large circle) and the final section of the venous bed (vena cava and right atrium). The difference in blood pressure (ΔP) at the beginning of the vessel (P1) and at the end of it (P2) is the driving force for blood flow through any vessel of the circulatory system. The force of the blood pressure gradient is used to overcome the resistance to blood flow (R) in the vascular system and in each individual vessel. The higher the blood pressure gradient in the circulation or in a separate vessel, the greater the volumetric blood flow in them.

The most important indicator of the movement of blood through the vessels is the volumetric blood flow rate, or volumetric blood flow (Q), which is understood as the volume of blood flowing through the total cross section of the vascular bed or the section of an individual vessel per unit time. The volumetric flow rate is expressed in liters per minute (L/min) or milliliters per minute (mL/min). To assess volumetric blood flow through the aorta or the total cross section of any other level of the vessels of the systemic circulation, the concept of volumetric systemic blood flow is used. Since the entire volume of blood ejected by the left ventricle during this time flows through the aorta and other vessels of the systemic circulation per unit of time (minute), the concept of systemic volumetric blood flow is synonymous with the concept of minute volume of blood flow (MOV). The IOC of an adult at rest is 4-5 l / min.

Distinguish also volumetric blood flow in the body. In this case, they mean the total blood flow flowing per unit of time through all the afferent arterial or efferent venous vessels of the organ.

Thus, volumetric blood flow Q = (P1 - P2) / R.

This formula expresses the essence of the basic law of hemodynamics, which states that the amount of blood flowing through the total cross section of the vascular system or an individual vessel per unit time is directly proportional to the difference in blood pressure at the beginning and end of the vascular system (or vessel) and inversely proportional to the current resistance blood.

The total (systemic) minute blood flow in a large circle is calculated taking into account the values ​​of the average hydrodynamic blood pressure at the beginning of the aorta P1, and at the mouth of the vena cava P2. Since the blood pressure in this section of the veins is close to 0, then the value P equal to the average hydrodynamic arterial blood pressure at the beginning of the aorta is substituted into the expression for calculating Q or IOC: Q (IOC) = P / R.

One of the consequences of the basic law of hemodynamics - the driving force of blood flow in the vascular system - is due to the blood pressure created by the work of the heart. Confirmation of the decisive importance of blood pressure for blood flow is the pulsating nature of blood flow throughout the cardiac cycle. During heart systole, when blood pressure reaches its maximum level, blood flow increases, and during diastole, when blood pressure is at its lowest, blood flow decreases.

As blood moves through the vessels from the aorta to the veins, blood pressure decreases and the rate of its decrease is proportional to the resistance to blood flow in the vessels. The pressure in arterioles and capillaries decreases especially rapidly, since they have a large resistance to blood flow, having a small radius, a large total length and numerous branches, creating an additional obstacle to blood flow.

The resistance to blood flow created in the entire vascular bed of the systemic circulation is called total peripheral resistance (OPS). Therefore, in the formula for calculating volumetric blood flow, the symbol R can be replaced by its analogue - OPS:

From this expression, a number of important consequences are derived that are necessary for understanding the processes of blood circulation in the body, evaluating the results of measuring blood pressure and its deviations. The factors affecting the resistance of the vessel, for the fluid flow, are described by Poiseuille's law, according to which

From the above expression it follows that since the numbers 8 and Π are constant, L in an adult changes little, then the value of peripheral resistance to blood flow is determined by the changing values ​​of the vessel radius r and blood viscosity η).

It has already been mentioned that the radius of muscle-type vessels can change rapidly and have a significant impact on the amount of resistance to blood flow (hence their name - resistive vessels) and the amount of blood flow through organs and tissues. Since the resistance depends on the value of the radius to the 4th power, even small fluctuations in the radius of the vessels greatly affect the values ​​of resistance to blood flow and blood flow. So, for example, if the radius of the vessel decreases from 2 to 1 mm, then its resistance will increase by 16 times, and with a constant pressure gradient, the blood flow in this vessel will also decrease by 16 times. Reverse changes in resistance will be observed when the radius of the vessel is doubled. With a constant average hemodynamic pressure, blood flow in one organ can increase, in another - decrease, depending on the contraction or relaxation of the smooth muscles of the afferent arterial vessels and veins of this organ.

The viscosity of the blood depends on the content in the blood of the number of red blood cells (hematocrit), protein, lipoproteins in the blood plasma, as well as on the aggregate state of the blood. Under normal conditions, the viscosity of the blood does not change as quickly as the lumen of the vessels. After blood loss, with erythropenia, hypoproteinemia, blood viscosity decreases. With significant erythrocytosis, leukemia, increased aggregation of erythrocytes and hypercoagulability, blood viscosity can increase significantly, which leads to an increase in resistance to blood flow, an increase in the load on the myocardium and may be accompanied by impaired blood flow in the vessels of the microvasculature.

In the established circulation regime, the volume of blood expelled by the left ventricle and flowing through the cross section of the aorta is equal to the volume of blood flowing through the total cross section of the vessels of any other part of the systemic circulation. This volume of blood returns to the right atrium and enters the right ventricle. Blood is expelled from it into the pulmonary circulation and then returned through the pulmonary veins to the left heart. Since the IOCs of the left and right ventricles are the same, and the systemic and pulmonary circulations are connected in series, the volumetric blood flow velocity in the vascular system remains the same.

However, during changes in blood flow conditions, such as when moving from a horizontal to a vertical position, when gravity causes a temporary accumulation of blood in the veins of the lower trunk and legs, for a short time, the left and right ventricular cardiac output may become different. Soon, intracardiac and extracardiac mechanisms of regulation of the work of the heart equalize the volume of blood flow through the small and large circles of blood circulation.

With a sharp decrease in venous return of blood to the heart, causing a decrease in stroke volume, arterial blood pressure may decrease. With a pronounced decrease in it, blood flow to the brain can decrease. This explains the feeling of dizziness that can occur with a sharp transition of a person from a horizontal to a vertical position.

Volume and linear velocity of blood flow in the vessels

The total volume of blood in the vascular system is an important homeostatic indicator. Its average value is 6-7% for women, 7-8% of body weight for men and is in the range of 4-6 liters; 80-85% of the blood from this volume is in the vessels of the systemic circulation, about 10% - in the vessels of the pulmonary circulation, and about 7% - in the cavities of the heart.

Most of the blood is contained in the veins (about 75%) - this indicates their role in the deposition of blood in both the systemic and pulmonary circulation.

The movement of blood in the vessels is characterized not only by volume, but also by the linear velocity of blood flow. It is understood as the distance over which a particle of blood moves per unit of time.

There is a relationship between the volumetric and linear blood flow velocity, which is described by the following expression:

where V is the linear velocity of blood flow, mm/s, cm/s; Q - volumetric blood flow velocity; P is a number equal to 3.14; r is the radius of the vessel. The value Pr 2 reflects the cross-sectional area of ​​the vessel.

Rice. 1. Changes in blood pressure, linear blood flow velocity and cross-sectional area in different parts of the vascular system

Rice. 2. Hydrodynamic characteristics of the vascular bed

From the expression of the dependence of the linear velocity on the volumetric velocity in the vessels of the circulatory system, it can be seen that the linear velocity of blood flow (Fig. 1.) is proportional to the volumetric blood flow through the vessel (s) and inversely proportional to the cross-sectional area of ​​this vessel (s). For example, in the aorta, which has the smallest cross-sectional area in the systemic circulation (3-4 cm 2), the linear velocity of blood movement is the highest and is at rest approx. cm / s. With physical activity, it can increase by 4-5 times.

In the direction of the capillaries, the total transverse lumen of the vessels increases and, consequently, the linear velocity of blood flow in the arteries and arterioles decreases. In capillary vessels, the total cross-sectional area of ​​which is greater than in any other part of the vessels of the great circle (much larger than the cross-section of the aorta), the linear velocity of blood flow becomes minimal (less than 1 mm/s). Slow blood flow in the capillaries creates the best conditions for the flow of metabolic processes between blood and tissues. In veins, the linear velocity of blood flow increases due to a decrease in their total cross-sectional area as they approach the heart. At the mouth of the vena cava, it is cm / s, and with loads it increases to 50 cm / s.

The linear velocity of plasma and blood cells depends not only on the type of vessel, but also on their location in the blood stream. There is a laminar type of blood flow, in which the blood flow can be conditionally divided into layers. In this case, the linear velocity of the movement of blood layers (mainly plasma), close to or adjacent to the vessel wall, is the smallest, and the layers in the center of the flow are the largest. Friction forces arise between the vascular endothelium and the parietal layers of blood, creating shear stresses on the vascular endothelium. These stresses play a role in the production of vasoactive factors by the endothelium, which regulate the lumen of the vessels and the rate of blood flow.

Erythrocytes in vessels (with the exception of capillaries) are located mainly in the central part of the blood stream and move in it at a relatively high speed. Leukocytes, on the contrary, are located mainly in the parietal layers of the blood flow and perform rolling movements at a low speed. This allows them to bind to adhesion receptors at sites of mechanical or inflammatory damage to the endothelium, adhere to the vessel wall, and migrate into tissues to perform protective functions.

With a significant increase in the linear velocity of blood movement in the narrowed part of the vessels, in the places where its branches depart from the vessel, the laminar nature of blood movement can change to turbulent. In this case, the layering of the movement of its particles in the blood flow may be disturbed, and between the wall of the vessel and the blood, greater friction forces and shear stresses may occur than with laminar movement. Vortex blood flows develop, the likelihood of damage to the endothelium and the deposition of cholesterol and other substances in the intima of the vessel wall increases. This can lead to mechanical disruption of the structure of the vascular wall and initiation of the development of parietal thrombi.

The time of a complete blood circulation, i.e. the return of a blood particle to the left ventricle after its ejection and passage through the large and small circles of blood circulation, is in postcos, or after about 27 systoles of the ventricles of the heart. Approximately a quarter of this time is spent on moving blood through the vessels of the small circle and three quarters - through the vessels of the systemic circulation.

Large and small circles of blood circulation. Blood flow rate

How long does it take for the blood to make a full circle?

and adolescent gynecology

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Circulation is the continuous movement of blood through a closed cardiovascular system, which ensures the exchange of gases in the lungs and body tissues.

In addition to providing tissues and organs with oxygen and removing carbon dioxide from them, blood circulation delivers nutrients, water, salts, vitamins, hormones to cells and removes metabolic end products, and also maintains a constant body temperature, ensures humoral regulation and the interconnection of organs and organ systems in body.

The circulatory system consists of the heart and blood vessels that permeate all organs and tissues of the body.

Blood circulation begins in the tissues, where metabolism takes place through the walls of the capillaries. The blood that has given oxygen to organs and tissues enters the right half of the heart and is sent to the pulmonary (pulmonary) circulation, where the blood is saturated with oxygen, returns to the heart, entering its left half, and again spreads throughout the body (large circulation) .

The heart is the main organ of the circulatory system. It is a hollow muscular organ consisting of four chambers: two atria (right and left), separated by an interatrial septum, and two ventricles (right and left), separated by an interventricular septum. The right atrium communicates with the right ventricle through the tricuspid valve, and the left atrium communicates with the left ventricle through the bicuspid valve. The mass of the heart of an adult is on average about 250 g in women and about 330 g in men. The length of the heart is cm, the transverse size is 8-11 cm and the anteroposterior is 6-8.5 cm. The volume of the heart in men is on average cm 3, and in women cm 3.

The outer walls of the heart are formed by the cardiac muscle, which is similar in structure to the striated muscles. However, the heart muscle is distinguished by the ability to automatically contract rhythmically due to impulses that occur in the heart itself, regardless of external influences (cardiac automaticity).

The function of the heart is to rhythmically pump blood into the arteries, which comes to it through the veins. The heart contracts about once per minute at rest (1 time per 0.8 s). More than half of this time it rests - relaxes. The continuous activity of the heart consists of cycles, each of which consists of contraction (systole) and relaxation (diastole).

There are three phases of cardiac activity:

• atrial contraction - atrial systole - takes 0.1 s
• ventricular contraction - ventricular systole - takes 0.3 s
• total pause - diastole (simultaneous relaxation of the atria and ventricles) - takes 0.4 s

Thus, during the entire cycle, the atria work 0.1 s and rest 0.7 s, the ventricles work 0.3 s and rest 0.5 s. This explains the ability of the heart muscle to work without fatigue throughout life. The high efficiency of the heart muscle is due to the increased blood supply to the heart. Approximately 10% of the blood ejected from the left ventricle into the aorta enters the arteries departing from it, which feed the heart.

Arteries are blood vessels that carry oxygenated blood from the heart to organs and tissues (only the pulmonary artery carries venous blood).

The wall of the artery is represented by three layers: the outer connective tissue membrane; middle, consisting of elastic fibers and smooth muscles; internal, formed by the endothelium and connective tissue.

In humans, the diameter of the arteries ranges from 0.4 to 2.5 cm. The total volume of blood in the arterial system averages 950 ml. Arteries gradually branch into smaller and smaller vessels - arterioles, which pass into capillaries.

Capillaries (from the Latin “capillus” - hair) are the smallest vessels (the average diameter does not exceed 0.005 mm, or 5 microns), penetrating the organs and tissues of animals and humans that have a closed circulatory system. They connect small arteries - arterioles with small veins - venules. Through the walls of the capillaries, consisting of endothelial cells, there is an exchange of gases and other substances between the blood and various tissues.

Veins are blood vessels that carry blood saturated with carbon dioxide, metabolic products, hormones and other substances from tissues and organs to the heart (with the exception of pulmonary veins that carry arterial blood). The wall of the vein is much thinner and more elastic than the wall of the artery. Small and medium-sized veins are equipped with valves that prevent the reverse flow of blood in these vessels. In humans, the volume of blood in the venous system averages 3200 ml.

The movement of blood through the vessels was first described in 1628 by the English physician W. Harvey.

Harvey William () - English physician and naturalist. He created and introduced into the practice of scientific research the first experimental method - vivisection (live cutting).

In 1628 he published the book "Anatomical Studies on the Movement of the Heart and Blood in Animals", in which he described the large and small circles of blood circulation, formulated the basic principles of blood movement. The date of publication of this work is considered the year of the birth of physiology as an independent science.

In humans and mammals, blood moves through a closed cardiovascular system, consisting of a large and small circles of blood circulation (Fig.).

The large circle starts from the left ventricle, carries blood throughout the body through the aorta, gives oxygen to the tissues in the capillaries, takes carbon dioxide, turns from arterial to venous and returns to the right atrium through the superior and inferior vena cava.

The pulmonary circulation starts from the right ventricle, carries blood through the pulmonary artery to the pulmonary capillaries. Here the blood gives off carbon dioxide, is saturated with oxygen and flows through the pulmonary veins to the left atrium. From the left atrium through the left ventricle, blood again enters the systemic circulation.

Small circle of blood circulation- pulmonary circle - serves to enrich the blood with oxygen in the lungs. It starts from the right ventricle and ends at the left atrium.

From the right ventricle of the heart, venous blood enters the pulmonary trunk (common pulmonary artery), which soon divides into two branches that carry blood to the right and left lungs.

In the lungs, arteries branch into capillaries. In the capillary networks braiding the pulmonary vesicles, the blood gives off carbon dioxide and receives a new supply of oxygen in return (pulmonary respiration). Oxygenated blood acquires a scarlet color, becomes arterial and flows from the capillaries into the veins, which, having merged into four pulmonary veins (two on each side), flow into the left atrium of the heart. In the left atrium, the small (pulmonary) circle of blood circulation ends, and the arterial blood that enters the atrium passes through the left atrioventricular opening into the left ventricle, where the systemic circulation begins. Consequently, venous blood flows in the arteries of the pulmonary circulation, and arterial blood flows in its veins.

Systemic circulation- bodily - collects venous blood from the upper and lower half of the body and similarly distributes arterial blood; starts from the left ventricle and ends with the right atrium.

From the left ventricle of the heart, blood enters the largest arterial vessel - the aorta. Arterial blood contains nutrients and oxygen necessary for the life of the body and has a bright scarlet color.

The aorta branches into arteries that go to all organs and tissues of the body and pass in their thickness into arterioles and further into capillaries. Capillaries, in turn, are collected in venules and further into veins. Through the wall of the capillaries there is a metabolism and gas exchange between the blood and body tissues. Arterial blood flowing in the capillaries gives off nutrients and oxygen and in return receives metabolic products and carbon dioxide (tissue respiration). As a result, the blood entering the venous bed is poor in oxygen and rich in carbon dioxide and therefore has a dark color - venous blood; when bleeding, the color of the blood can determine which vessel is damaged - an artery or a vein. The veins merge into two large trunks - the superior and inferior vena cava, which flow into the right atrium of the heart. This part of the heart ends with a large (corporeal) circle of blood circulation.

In the systemic circulation, arterial blood flows through the arteries, and venous blood flows through the veins.

In a small circle, on the contrary, venous blood flows from the heart through the arteries, and arterial blood returns to the heart through the veins.

The addition to the great circle is third (cardiac) circulation serving the heart itself. It begins with the coronary arteries of the heart emerging from the aorta and ends with the veins of the heart. The latter merge into the coronary sinus, which flows into the right atrium, and the remaining veins open directly into the atrial cavity.

The movement of blood through the vessels

Any fluid flows from a place where the pressure is higher to where it is lower. The greater the pressure difference, the higher the flow rate. The blood in the vessels of the systemic and pulmonary circulation also moves due to the pressure difference that the heart creates with its contractions.

In the left ventricle and aorta, blood pressure is higher than in the vena cava (negative pressure) and in the right atrium. The pressure difference in these areas ensures the movement of blood in the systemic circulation. High pressure in the right ventricle and pulmonary artery and low pressure in the pulmonary veins and left atrium ensure the movement of blood in the pulmonary circulation.

The highest pressure is in the aorta and large arteries (blood pressure). Arterial blood pressure is not a constant value [show]

Blood pressure- this is the blood pressure on the walls of the blood vessels and chambers of the heart, resulting from the contraction of the heart, which pumps blood into the vascular system, and the resistance of the vessels. The most important medical and physiological indicator of the state of the circulatory system is the pressure in the aorta and large arteries - blood pressure.

Arterial blood pressure is not a constant value. In healthy people at rest, the maximum, or systolic, blood pressure is distinguished - the pressure level in the arteries during the systole of the heart is about 120 mm Hg, and the minimum, or diastolic - the pressure level in the arteries during the diastole of the heart is about 80 mm Hg. Those. arterial blood pressure pulsates in time with the contractions of the heart: at the time of systole, it rises to damm Hg. Art., and during diastole decreases domm Hg. Art. These pulse pressure oscillations occur simultaneously with the pulse oscillations of the arterial wall.

Pulse- periodic jerky expansion of the walls of the arteries, synchronous with the contraction of the heart. The pulse is used to determine the number of heartbeats per minute. In an adult, the average heart rate is beats per minute. During physical exertion, the heart rate may increase up to beats. In places where the arteries are located on the bone and lie directly under the skin (radial, temporal), the pulse is easily felt. The propagation speed of the pulse wave is about 10 m/s.

Blood pressure is affected by:

1. work of the heart and force of cardiac contraction;
2. the size of the lumen of the vessels and the tone of their walls;
3. the amount of blood circulating in the vessels;
4. blood viscosity.

A person's blood pressure is measured in the brachial artery, comparing it with atmospheric pressure. For this, a rubber cuff connected to a pressure gauge is put on the shoulder. The cuff is inflated with air until the pulse at the wrist disappears. This means that the brachial artery is compressed by a lot of pressure, and blood does not flow through it. Then, gradually releasing air from the cuff, monitor the appearance of a pulse. At this moment, the pressure in the artery becomes slightly higher than the pressure in the cuff, and the blood, and with it the pulse wave, begins to reach the wrist. The readings of the pressure gauge at this time characterize the blood pressure in the brachial artery.

A persistent increase in blood pressure above the indicated figures at rest is called hypertension, and its decrease is called hypotension.

The level of blood pressure is regulated by nervous and humoral factors (see table).

(diastolic)

The speed of blood movement depends not only on the pressure difference, but also on the width of the bloodstream. Although the aorta is the widest vessel, it is the only one in the body and all the blood flows through it, which is pushed out by the left ventricle. Therefore, the speed here is maximum mm/s (see Table 1). As the arteries branch out, their diameter decreases, but the total cross-sectional area of ​​all arteries increases and the blood velocity decreases, reaching 0.5 mm/s in the capillaries. Due to such a low rate of blood flow in the capillaries, the blood has time to give oxygen and nutrients to the tissues and take their waste products.

The slowing down of blood flow in the capillaries is explained by their huge number (about 40 billion) and the large total lumen (800 times the lumen of the aorta). The movement of blood in the capillaries is carried out by changing the lumen of the supply small arteries: their expansion increases the blood flow in the capillaries, and their narrowing decreases it.

The veins on the way from the capillaries, as they approach the heart, enlarge, merge, their number and the total lumen of the bloodstream decrease, and the speed of blood movement increases compared to the capillaries. From Table. 1 also shows that 3/4 of all blood is in the veins. This is due to the fact that the thin walls of the veins can easily stretch, so they can contain much more blood than the corresponding arteries.

The main reason for the movement of blood through the veins is the pressure difference at the beginning and end of the venous system, so the movement of blood through the veins occurs in the direction of the heart. This is facilitated by the suction action of the chest ("respiratory pump") and the contraction of skeletal muscles ("muscle pump"). During inhalation, the pressure in the chest decreases. In this case, the pressure difference at the beginning and at the end of the venous system increases, and the blood through the veins is sent to the heart. Skeletal muscles, contracting, compress the veins, which also contributes to the movement of blood to the heart.

The relationship between the speed of blood flow, the width of the bloodstream and blood pressure is illustrated in Fig. 3. The amount of blood flowing per unit of time through the vessels is equal to the product of the speed of blood movement by the cross-sectional area of ​​the vessels. This value is the same for all parts of the circulatory system: how much blood pushes the heart into the aorta, how much it flows through the arteries, capillaries and veins, and the same amount returns back to the heart, and is equal to the minute volume of blood.

Redistribution of blood in the body

If the artery extending from the aorta to any organ, due to the relaxation of its smooth muscles, expands, then the organ will receive more blood. At the same time, other organs will receive less blood due to this. This is how blood is redistributed in the body. As a result of redistribution, more blood flows to the working organs at the expense of the organs that are currently at rest.

The redistribution of blood is regulated by the nervous system: simultaneously with the expansion of blood vessels in the working organs, the blood vessels of the non-working organs narrow and blood pressure remains unchanged. But if all the arteries dilate, this will lead to a drop in blood pressure and to a decrease in the speed of blood movement in the vessels.

Blood circulation time

Circulation time is the time it takes for blood to travel through the entire circulation. A number of methods are used to measure blood circulation time. [show]

The principle of measuring the time of the blood circulation is that some substance that is not usually found in the body is injected into the vein, and it is determined after what period of time it appears in the vein of the same name on the other side or causes an action characteristic of it. For example, a solution of the alkaloid lobeline, which acts through the blood on the respiratory center of the medulla oblongata, is injected into the cubital vein, and the time is determined from the moment the substance is injected until the moment when a short-term breath holding or cough occurs. This happens when the lobelin molecules, having made a circuit in the circulatory system, act on the respiratory center and cause a change in breathing or coughing.

In recent years, the rate of blood circulation in both circles of blood circulation (or only in a small, or only in a large circle) is determined using a radioactive isotope of sodium and an electron counter. To do this, several of these counters are placed on different parts of the body near large vessels and in the region of the heart. After the introduction of a radioactive isotope of sodium into the cubital vein, the time of appearance of radioactive radiation in the region of the heart and the studied vessels is determined.

The circulation time of the blood in humans is on average about 27 systoles of the heart. With heartbeats per minute, the complete circulation of blood occurs in about a second. We must not forget, however, that the speed of blood flow along the axis of the vessel is greater than that of its walls, and also that not all vascular regions have the same length. Therefore, not all blood circulates so quickly, and the time indicated above is the shortest.

Studies on dogs have shown that 1/5 of the time of a complete blood circulation occurs in the pulmonary circulation and 4/5 in the systemic circulation.

Innervation of the heart. The heart, like other internal organs, is innervated by the autonomic nervous system and receives dual innervation. Sympathetic nerves approach the heart, which strengthen and accelerate its contractions. The second group of nerves - parasympathetic - acts on the heart in the opposite way: it slows down and weakens heart contractions. These nerves regulate the heart.

In addition, the work of the heart is affected by the hormone of the adrenal glands - adrenaline, which enters the heart with blood and increases its contractions. The regulation of the work of organs with the help of substances carried by the blood is called humoral.

Nervous and humoral regulation of the heart in the body act in concert and provide an accurate adaptation of the activity of the cardiovascular system to the needs of the body and environmental conditions.

Innervation of blood vessels. Blood vessels are innervated by sympathetic nerves. Excitation propagating through them causes contraction of smooth muscles in the walls of blood vessels and constricts blood vessels. If you cut the sympathetic nerves going to a certain part of the body, the corresponding vessels will expand. Consequently, through the sympathetic nerves to the blood vessels, excitation is constantly supplied, which keeps these vessels in a state of some narrowing - vascular tone. When excitation increases, the frequency of nerve impulses increases and the vessels narrow more strongly - vascular tone increases. On the contrary, with a decrease in the frequency of nerve impulses due to inhibition of sympathetic neurons, vascular tone decreases and blood vessels dilate. To the vessels of some organs (skeletal muscles, salivary glands), in addition to vasoconstrictor, vasodilating nerves are also suitable. These nerves become excited and dilate the blood vessels of the organs as they work. Substances that are carried by the blood also affect the lumen of the vessels. Adrenaline constricts blood vessels. Another substance - acetylcholine - secreted by the endings of some nerves, expands them.

Regulation of the activity of the cardiovascular system. The blood supply of the organs varies depending on their needs due to the described redistribution of blood. But this redistribution can only be effective if the pressure in the arteries does not change. One of the main functions of the nervous regulation of blood circulation is to maintain a constant blood pressure. This function is carried out reflexively.

There are receptors in the wall of the aorta and carotid arteries that are more irritated if blood pressure exceeds normal levels. Excitation from these receptors goes to the vasomotor center located in the medulla oblongata and inhibits its work. From the center along the sympathetic nerves to the vessels and the heart, a weaker excitation begins to flow than before, and the blood vessels dilate, and the heart weakens its work. As a result of these changes, blood pressure decreases. And if for some reason the pressure falls below the norm, then the irritation of the receptors stops completely and the vasomotor center, without receiving inhibitory influences from the receptors, intensifies its activity: it sends more nerve impulses per second to the heart and blood vessels, the vessels constrict, the heart contracts, more often and stronger, blood pressure rises.

Hygiene of cardiac activity

The normal activity of the human body is possible only in the presence of a well-developed cardiovascular system. The rate of blood flow will determine the degree of blood supply to organs and tissues and the rate of removal of waste products. During physical work, the need of organs for oxygen increases simultaneously with the increase and increase in heart rate. Only a strong heart muscle can provide such work. To be enduring for a variety of work activities, it is important to train the heart, increase the strength of its muscles.

Physical labor, physical education develop the heart muscle. To ensure the normal function of the cardiovascular system, a person should start his day with morning exercises, especially people whose professions are not related to physical labor. To enrich the blood with oxygen, physical exercises are best done in the fresh air.

It must be remembered that excessive physical and mental stress can cause disruption of the normal functioning of the heart, its diseases. Alcohol, nicotine, drugs have a particularly harmful effect on the cardiovascular system. Alcohol and nicotine poison the heart muscle and nervous system, causing sharp disturbances in the regulation of vascular tone and heart activity. They lead to the development of severe diseases of the cardiovascular system and can cause sudden death. Young people who smoke and drink alcohol are more likely than others to develop spasms of the heart vessels, causing severe heart attacks and sometimes death.

First aid for wounds and bleeding

Injuries are often accompanied by bleeding. There are capillary, venous and arterial bleeding.

Capillary bleeding occurs even with a minor injury and is accompanied by a slow flow of blood from the wound. Such a wound should be treated with a solution of brilliant green (brilliant green) for disinfection and a clean gauze bandage should be applied. The bandage stops bleeding, promotes the formation of a blood clot and prevents microbes from entering the wound.

Venous bleeding is characterized by a significantly higher rate of blood flow. The escaping blood is dark in color. To stop bleeding, it is necessary to apply a tight bandage below the wound, that is, further from the heart. After stopping the bleeding, the wound is treated with a disinfectant (3% solution of hydrogen peroxide, vodka), bandaged with a sterile pressure bandage.

With arterial bleeding, scarlet blood gushes from the wound. This is the most dangerous bleeding. If the artery of the limb is damaged, it is necessary to raise the limb as high as possible, bend it and press the wounded artery with your finger in the place where it comes close to the surface of the body. It is also necessary to apply a rubber tourniquet above the wound site, i.e. closer to the heart (you can use a bandage, a rope for this) and tighten it tightly to completely stop the bleeding. The tourniquet must not be kept tightened for more than 2 hours. When it is applied, a note must be attached in which the time of applying the tourniquet should be indicated.

It should be remembered that venous, and even more arterial bleeding can lead to significant blood loss and even death. Therefore, when injured, it is necessary to stop the bleeding as soon as possible, and then take the victim to the hospital. Severe pain or fright can cause the person to lose consciousness. Loss of consciousness (fainting) is a consequence of inhibition of the vasomotor center, a drop in blood pressure and insufficient supply of blood to the brain. The unconscious person should be allowed to sniff some non-toxic substance with a strong odor (for example, ammonia), moisten his face with cold water, or lightly pat his cheeks. When olfactory or skin receptors are stimulated, excitation from them enters the brain and relieves inhibition of the vasomotor center. Blood pressure rises, the brain receives sufficient nutrition, and consciousness returns.

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Everything about everything. Volume 5 Likum Arkady

How fast does blood flow in us?

Blood flows through blood vessels differently than water flows through plumbing pipes. The vessels that carry blood from the heart to all parts of the body are called arteries. But their system is built in such a way that the main artery already branches at some distance from the heart, and the branches, in turn, continue to branch until they turn into thin vessels called capillaries, through which blood flows much more slowly than through the arteries.

Capillaries are fifty times thinner than a human hair, and therefore blood cells can only move through them one after the other. It takes them about a second to pass through the capillary. Blood is pumped from one part of the body to another by the heart, and it takes about 1.5 seconds for the blood cells to pass through the heart itself. And from the heart they are chasing to the lungs and back, which takes from 5 to 7 seconds. It takes about 8 seconds for blood to travel from the heart to the vessels of the brain and back.

The longest way - from the heart down the torso through the lower limbs to the very toes and back - takes up to 18 seconds. Thus, the entire path that blood makes through the body - from the heart to the lungs and back, from the heart to different parts of the body and back - takes about 23 seconds.

The general condition of the body affects the speed at which blood flows through the vessels of the body. For example, increased temperature or physical work increases the heart rate and makes the blood circulate twice as fast. During the day, a blood cell makes about 3,000 trips through the body to the heart and back.