The movement of blood in a small circle. Small circle of blood circulation

Heart is the central organ of blood circulation. It is a hollow muscular organ, consisting of two halves: left - arterial and right - venous. Each half consists of interconnected atria and ventricle of the heart.

Venous blood through the veins enters the right atrium and then to the right ventricle of the heart, from the latter to the pulmonary trunk, from where it follows the pulmonary arteries to the right and left lungs. Here the branches of the pulmonary arteries branch to the smallest vessels - capillaries.

In the lungs deoxygenated blood saturated with oxygen, becomes arterial and is sent to the four pulmonary veins left atrium then enters the left ventricle of the heart. From the left ventricle of the heart, blood enters the largest arterial highway - the aorta, and along its branches, which decay in the tissues of the body to the capillaries, it spreads throughout the body. Having given oxygen to the tissues and taking carbon dioxide from them, the blood becomes venous. Capillaries, reconnecting with each other, form veins.

All veins of the body are connected into two large trunks - the superior vena cava and the inferior vena cava. AT superior vena cava blood is collected from areas and organs of the head and neck, upper limbs and some parts of the walls of the body. The inferior vena cava fills with blood from lower extremities, walls and organs of the pelvic and abdominal cavity.

Both vena cava bring blood to the right atrium, which also receives venous blood from the heart itself. This closes the circle of blood circulation. This blood path is divided into small and big circle circulation.

Small circle of blood circulation(pulmonary) starts from the right ventricle of the heart with the pulmonary trunk, includes branches of the pulmonary trunk to the capillary network of the lungs and pulmonary veins that flow into the left atrium.

Systemic circulation(bodily) starts from the left ventricle of the heart by the aorta, includes all its branches, the capillary network and veins of the organs and tissues of the whole body and ends in the right atrium. Consequently, blood circulation takes place in two interconnected circles of blood circulation.

2. The structure of the heart. Cameras. Walls. Functions of the heart.

Heart(cor) - hollow four-chamber muscular organ which pumps oxygenated blood into the arteries and receives venous blood.

The heart consists of two atria that receive blood from the veins and push it into the ventricles (right and left). The right ventricle supplies blood to the pulmonary arteries through the pulmonary trunk, and the left ventricle supplies blood to the aorta.

In the heart, there are: three surfaces - pulmonary (facies pulmonalis), sternocostal (facies sternocostalis) and diaphragmatic (facies diaphragmatica); apex (apex cordis) and base (basis cordis).

The boundary between the atria and ventricles is the coronary sulcus (sulcus coronarius).

Right atrium (atrium dextrum) is separated from the left by an atrial septum (septum interatriale) and has a right ear (auricula dextra). There is a recess in the septum - an oval fossa, formed after the fusion of the foramen ovale.

The right atrium has openings of the superior and inferior vena cava (ostium venae cavae superioris et inferioris), delimited by an intervenous tubercle (tuberculum intervenosum) and an opening of the coronary sinus (ostium sinus coronarii). On the inner wall of the right ear there are pectinate muscles (mm pectinati), ending in a border crest that separates the venous sinus from the cavity of the right atrium.

The right atrium communicates with the ventricle through the right atrioventricular orifice (ostium atrioventriculare dextrum).

Right ventricle (ventriculus dexter) is separated from the left interventricular septum (septum interventriculare), in which the muscular and membranous parts are distinguished; has an opening of the pulmonary trunk (ostium trunci pulmonalis) in front and a right atrioventricular opening (ostium atrioventriculare dextrum) in the back. The latter is covered by a tricuspid valve (valva tricuspidalis), which has an anterior, posterior and septal cusps. The leaflets are held by tendinous chords, due to which the leaflets do not turn out into the atrium.

On the inner surface the ventricle has fleshy trabeculae (trabeculae carneae) and papillary muscles (mm. papillares), from which tendon chords begin. The opening of the pulmonary trunk is covered by the valve of the same name, consisting of three semilunar valves: anterior, right and left (valvulae semilunares anterior, dextra et sinistra).

Left atrium (atrium sinistrum) has a cone-shaped extension facing anteriorly - the left ear (auricular sinistra) - and five openings: four openings of the pulmonary veins (ostia venarum pulmonalium) and the left atrioventricular opening (ostium atrioventriculare sinistrum).

left ventricle (ventriculus sinister) has a left atrioventricular opening behind, covered mitral valve(valva mitralis), consisting of the anterior and posterior cusps, and the aortic opening, covered by the valve of the same name, consisting of three semilunar valves: posterior, right and left (valvulae semilunares posterior, dextra et sinistra). On the inner surface of the ventricle there are fleshy trabeculae (trabeculae carneae), anterior and posterior papillary muscles (mm. papillares anterior et posterior).

Heart, cor, is an almost cone-shaped hollow organ with well-developed muscular walls. It is located at the bottom anterior mediastinum on the tendon center of the diaphragm, between the right and left pleural sacs, enclosed in the pericardium, pericardium, and fixed by large blood vessels.

The heart has a shorter rounded, sometimes more elongated sharp shape; in the filled state, in size it approximately corresponds to the fist of the person under study. The size of the heart of an adult is individual. So, its length reaches 12-15 cm, the width (transverse size) is 8-11 cm, and the anteroposterior size (thickness) is 6-8 cm.

Mass of the heart ranges from 220 to 300 g. In men, the size and mass of the heart is larger than in women, and its walls are somewhat thicker. The posterior superior expanded part of the heart is called the base of the heart, basis cordis, large veins open into it and large arteries emerge from it. The anterior and lower free-lying part of the heart is called apex of the heart, apes cordis.

Of the two surfaces of the heart, the lower, flattened, diaphragmatic surface, facies diaphragmatica (inferior), adjacent to the diaphragm. Anterior, more convex sternocostal surface, facies sternocostalis (anterior), facing the sternum and costal cartilages. The surfaces merge into each other with rounded edges, while the right edge (surface), margo dexter, is longer and sharper, the left pulmonary(lateral) surface, facies pulmonalis, is shorter and rounded.

On the surface of the heart three furrows. Crown groove, sulcus coronarius, is located on the border between the atria and ventricles. Front and rear interventricular grooves, sulci interventriculares anterior et posterior, separate one ventricle from the other. On the sternocostal surface, the coronal groove reaches the edges of the pulmonary trunk. The place of transition of the anterior interventricular sulcus to the posterior one corresponds to a small depression - cut of the apex of the heart, incisura apicis cordis. They lie in the furrows vessels of the heart.

Heart function- rhythmic injection of blood from the veins into the arteries, that is, the creation of a pressure gradient, due to which its constant movement occurs. This means that the main function of the heart is to provide blood circulation by communicating blood with kinetic energy. The heart is therefore often associated with a pump. It is distinguished by exceptionally high performance, speed and smoothness of transients, margin of safety and constant tissue renewal.

. STRUCTURE OF THE HEART WALL. CONDUCTION SYSTEM OF THE HEART. STRUCTURE OF THE PERICARD

Wall of the heart It consists of the inner layer - the endocardium (endocardium), the middle layer - the myocardium (myocardium) and the outer layer - the epicardium (epicardium).

The endocardium lines the entire inner surface of the heart with all its formations.

The myocardium is formed by cardiac striated muscle tissue and consists of cardiac cardiomyocytes, which ensures complete and rhythmic contraction of all chambers of the heart.

The muscle fibers of the atria and ventricles start from the right and left (anuli fibrosi dexter et sinister) fibrous rings. Fibrous rings surround the corresponding atrioventricular orifices, forming a support for their valves.

The myocardium consists of 3 layers. The outer oblique layer at the apex of the heart passes into the curl of the heart (vortex cordis) and continues into the deep layer. The middle layer is formed by circular fibers.

The epicardium is built on the principle of serous membranes and is a visceral sheet of the serous pericardium.

The contractile function of the heart is provided by its conducting system, which consists of:

1) sinoatrial node (nodus sinuatrialis), or Keyes-Fleck node;

2) the atrioventricular ATV node (nodus atrioventricularis), passing downwards into the atrioventricular bundle (fasciculus atrioventricularis), or the His bundle, which is divided into the right and left legs (cruris dextrum et sinistrum).

Pericardium (pericardium) is a fibrous-serous sac in which the heart is located. The pericardium is formed by two layers: the outer (fibrous pericardium) and the inner (serous pericardium). The fibrous pericardium passes into the adventitia of the large vessels of the heart, and the serous one has two plates - parietal and visceral, which pass into each other. Between the plates is the pericardial cavity (cavitas pericardialis), it contains serous fluid.

Innervation: branches of the right and left sympathetic trunks, branches of the phrenic and vagus nerves.

Circulation- this is a continuous flow of blood in the vessels of a person, giving all the tissues of the body all the substances necessary for normal functioning. The migration of blood elements helps to remove salts and toxins from the organs.

Purpose of blood circulation is to ensure the flow of metabolism ( metabolic processes in the body).

Circulatory organs

The organs that provide blood circulation include such anatomical formations as the heart along with the pericardium covering it and all the vessels passing through the tissues of the body:

Vessels of the circulatory system

All vessels in the circulatory system are divided into groups:

1. Arterial vessels;
2. Arterioles;
3. capillaries;
4. Venous vessels.

arteries

Arteries are those vessels that carry blood from the heart to internal organs. A common misconception among the general public is that the blood in the arteries always contains a high concentration of oxygen. However, this is not the case, for example, venous blood circulates in the pulmonary artery.

Arteries have a characteristic structure.

Their vascular wall consists of three main layers:

1. endothelium;
2. Muscle cells located under it;
3. A shell made up of connective tissue(adventitia).

The diameter of the arteries varies widely - from 0.4-0.5 cm to 2.5-3 cm. The entire volume of blood contained in the vessels of this type, usually is 950-1000 ml.

When moving away from the heart, the arteries divide into smaller vessels, the last of which are arterioles.

capillaries

Capillaries are the smallest component of the vascular bed. The diameter of these vessels is 5 µm. They permeate all tissues of the body, providing gas exchange. It is in the capillaries that oxygen leaves the bloodstream, and carbon dioxide migrates into the blood. This is where the exchange of nutrients takes place.

Vienna

Passing through the organs, the capillaries merge into larger vessels, forming first venules, and then veins. These vessels carry blood from the organs towards the heart. The structure of their walls differs from the structure of the arteries, they are thinner, but much more elastic.

A feature of the structure of the veins is the presence of valves - connective tissue formations that block the vessel after the passage of blood and prevent its reverse flow. AT venous system contains much more blood than in the arterial - about 3.2 liters.

The structure of the systemic circulation

1. Blood is expelled from the left ventricle where the systemic circulation begins. Blood from here is ejected into the aorta - the largest artery human body.
2. Immediately after leaving the heart the vessel forms an arc, at the level of which the common carotid artery departs from it, supplying the organs of the head and neck, as well as subclavian artery, which nourishes the tissues of the shoulder, forearm and hand.
3. The aorta itself goes down. From its upper, thoracic, section, arteries depart to the lungs, esophagus, trachea and other organs contained in the chest cavity.
4. Below Aperture the other part of the aorta is located - the abdominal. It gives branches to the intestines, stomach, liver, pancreas, etc. Then the aorta is divided into its own terminal branches- the right and left iliac arteries that supply blood to the pelvis and legs.
5. Arterial vessels, dividing into branches, are converted into capillaries, where the blood, previously rich in oxygen, organic matter and glucose, gives these substances to the tissues and becomes venous.
6. Great circle sequence blood circulation is such that the capillaries are connected to each other in several pieces, initially merging into venules. They, in turn, also gradually connect, forming first small and then large veins.
7. In the end, two main vessels are formed- superior and inferior vena cava. Blood from them flows directly to the heart. The trunk of the vena cava empties into right half organ (namely, right atrium) and the circle closes.

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The main purpose of blood circulation are the following physiological processes:

1. Gas exchange in the tissues and in the alveoli of the lungs;
2. Delivery of nutrients to the organs;
3. Receipt of special means of protection against pathological influences - immunity cells, proteins of the coagulation system, etc.;
4. Removal of toxins, toxins, metabolic products from tissues;
5. Delivery to the organs of hormones that regulate metabolism;
6. Providing thermoregulation of the body.

Such a multitude of functions confirms the importance of the circulatory system in the human body.

Features of blood circulation in the fetus

The fetus, being in the mother's body, is directly connected with her by its circulatory system.

It has several main features:

1. in interventricular septum connecting the sides of the heart;
2. ductus arteriosus passing between the aorta and the pulmonary artery;
3. The ductus venosus that connects the placenta and the fetal liver.

Such specific features of the anatomy are based on the fact that the child has pulmonary circulation due to the fact that the work of this organ is impossible.

Blood for the fetus, coming from the body of the carrying mother, comes from vascular formations included in the anatomical composition of the placenta. From here, blood flows to the liver. From it, through the vena cava, it enters the heart, namely, into the right atrium. Through oval window blood flows from the right to the left side of the heart. Mixed blood is distributed in the arteries of the systemic circulation.

The circulation system is one of critical components organism. Thanks to its functioning in the body, the flow of all physiological processes, which are the key to normal and active life.

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Circles of human circulation

Diagram of the human circulation

Human circulation- a closed vascular pathway that provides a continuous flow of blood, carrying oxygen and nutrition to the cells, carrying away carbon dioxide and metabolic products. It consists of two successively connected circles (loops), starting with the ventricles of the heart and flowing into the atria:

• systemic circulation begins in the left ventricle and ends in the right atrium;
• pulmonary circulation begins in the right ventricle and ends in the left atrium.

Large (systemic) circulation

Structure

Functions

The main task of the small circle is gas exchange in the pulmonary alveoli and heat transfer.

"Additional" circles of blood circulation

Depending on the physiological state organism, as well as practical expediency, sometimes they distinguish extra circles circulation:

• placental
• cordial

Placental circulation

Fetal circulation.

The mother's blood enters the placenta, where it gives oxygen and nutrients to the capillaries of the umbilical vein of the fetus, which passes along with two arteries into umbilical cord. The umbilical vein has two branches: most of the blood flows through the venous duct directly into the inferior vena cava, mixing with deoxygenated blood from the lower body. Smaller part blood enters the left branch of the portal vein, passes through the liver and hepatic veins, and then also enters the inferior vena cava.

After birth, the umbilical vein becomes empty and turns into a round ligament of the liver (ligamentum teres hepatis). The venous duct also turns into a cicatricial cord. In premature babies, the venous duct may function for some time (usually scarring after a while. If not, there is a danger of development hepatic encephalopathy). At portal hypertension, the umbilical vein, and the duct of Arantia can recanalize and serve as pathways for bypass blood flow (porto-caval shunts).

Mixed (arterial-venous) blood flows through the inferior vena cava, the saturation of which with oxygen is about 60%; venous blood flows through the superior vena cava. Almost all blood from the right atrium oval hole enters the left atrium and then the left ventricle. From the left ventricle, blood is ejected into the systemic circulation.

A smaller portion of blood flows from the right atrium to the right ventricle and pulmonary trunk. Since the lungs are in a collapsed state, the pressure in the pulmonary arteries is greater than in the aorta, and almost all the blood passes through the arterial (Botallov) duct into the aorta. The arterial duct flows into the aorta after the arteries of the head and upper limbs leave it, which provides them with more enriched blood. AT

Heart is the central organ of blood circulation. It is a hollow muscular organ, consisting of two halves: left - arterial and right - venous. Each half consists of interconnected atria and ventricle of the heart.
The central organ of blood circulation is heart. It is a hollow muscular organ, consisting of two halves: left - arterial and right - venous. Each half consists of interconnected atria and ventricle of the heart.

• Arteries, moving away from the heart, carry blood circulation. Arterioles perform a similar function.
• Veins, like venules, help return blood to the heart.

Arteries are tubes through which the systemic circulation moves. They have a fairly large diameter. Able to withstand high pressure due to the thickness and ductility. They have three shells: inner, middle and outer. Due to their elasticity, they are independently regulated depending on the physiology and anatomy of each organ, its needs and the temperature of the external environment.

The system of arteries can be represented as a bushy bundle, which becomes smaller the farther from the heart. As a result, in the limbs they look like capillaries. Their diameter is not more than a hair, but they are connected by arterioles and venules. Capillaries have thin walls and have one epithelial layer. This is where the exchange of nutrients takes place.

Therefore, the value of each element should not be underestimated. Violation of the functions of one, leads to diseases of the entire system. Therefore, in order to maintain the functionality of the body, you should lead a healthy lifestyle.

Heart third circle

As we found out - a small circle of blood circulation and a large one, these are not all components of the cardiovascular system. There is also a third way in which the movement of blood flow occurs and it is called - heart circle circulation.

This circle originates from the aorta, or rather from the point where it is divided into two coronary arteries. Blood through them penetrates through the layers of the organ, then through small veins passes into the coronary sinus, which opens into the atrium of the chamber of the right section. And some of the veins are directed to the ventricle. The path of blood flow through the coronary arteries is called the coronary circulation. Collectively, these circles are the system that produces the blood supply and nutrient saturation of the organs.

Coronary circulation has the following properties:

• blood circulation in enhanced mode;
• supply occurs in the diastolic state of the ventricles;
• there are few arteries here, so the dysfunction of one gives rise to myocardial diseases;
• excitability of the CNS increases blood flow.

Diagram 2 shows how the coronary circulation functions.

The circulatory system includes the little-known circle of Willis. Its anatomy is such that it is presented in the form of a system of vessels that are located at the base of the brain. Its value is difficult to overestimate, because. its main function is to compensate for the blood that it transfers from other "pools". The vascular system of the circle of Willis is closed.

The normal development of the Willis tract occurs only in 55%. A common pathology is an aneurysm and underdevelopment of the arteries connecting it.

At the same time, underdevelopment does not affect the human condition in any way, provided that there are no disturbances in other basins. May be detected by MRI. Aneurysm of the arteries of the Willis circulation is performed as surgical intervention in the form of a bandage. If the aneurysm has opened, the doctor prescribes conservative methods of treatment.

The Willisian vascular system is intended not only to supply the brain with blood flow, but also as a compensation for thrombosis. In view of this, the treatment of the Willis tract is practically not carried out, because. dangerous value not for health.

Blood supply in the human fetus

The fetal circulation is the following system. Blood flow with high levels of carbon dioxide upper area enters the right atrium through the vena cava. Through the hole, blood enters the ventricle, and then into the pulmonary trunk. Unlike the human blood supply, the pulmonary circulation of the fetus does not go to the lungs. Airways, and into the duct of the arteries, and only then into the aorta.

Diagram 3 shows how the blood moves in the fetus.

Features of the fetal circulation:

1. Blood moves due to the contractile function of the organ.
2. Starting from the 11th week, the blood supply is affected by breathing.
3. Great importance is given to the placenta.
4. The small circle of the fetal circulation is not functioning.
5. Mixed blood flow enters the organs.
6. Identical pressure in arteries and aorta.

Summing up the article, it should be emphasized how many circles are involved in the blood supply of the whole organism. Information on how each of them works allows the reader to independently understand the intricacies of anatomy and functionality. human body. Don't forget that you can ask a question in online mode and get a response from competent medical professionals.

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Tests

27-01. In what chamber of the heart does the pulmonary circulation conditionally begin?
A) in the right ventricle
B) in the left atrium
B) in the left ventricle
D) in the right atrium

27-02. Which statement correctly describes the movement of blood in the pulmonary circulation?
A) begins in the right ventricle and ends in the right atrium
B) begins in the left ventricle and ends in the right atrium
B) begins in the right ventricle and ends in the left atrium
D) begins in the left ventricle and ends in the left atrium

27-03. Which chamber of the heart receives blood from the veins of the systemic circulation?
A) left atrium
B) left ventricle
B) right atrium
D) right ventricle

27-04. Which letter in the figure indicates the chamber of the heart, in which the pulmonary circulation ends?

27-05. The figure shows the human heart and large blood vessels. What letter indicates the inferior vena cava?

27-06. What numbers indicate the vessels through which venous blood flows?

A) 2.3
B) 3.4
B) 1.2
D) 1.4

27-07. Which of the following statements correctly describes the movement of blood in the systemic circulation?
A) begins in the left ventricle and ends in the right atrium
B) begins in the right ventricle and ends in the left atrium
B) begins in the left ventricle and ends in the left atrium
D) begins in the right ventricle and ends in the right atrium

Circulation- this is the movement of blood through the vascular system, providing gas exchange between the body and external environment, metabolism between organs and tissues and humoral regulation various functions organism.

circulatory system includes the heart and - the aorta, arteries, arterioles, capillaries, venules, and veins. 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:

• The systemic circulation provides all organs and tissues with blood and its nutrients.
• 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.

Small circle of blood circulation It 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.

Systemic 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 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 the arteries branch off, carrying blood to the head () and to 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 portal vein branches into small veins and capillaries, which then reconnect into the 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. Gate system the liver plays an important role. It ensures the neutralization of toxic substances that are formed in the large intestine during the breakdown of unabsorbed in small intestine amino acids 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

Blood circulation time 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- This 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 vascular system, which reduces the speed of blood movement, 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.

Linear blood flow velocity - the speed of movement of an individual blood particle along a 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. Normally, it is 17-25 s. 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 the great circle) and the final section of the venous bed (vena cava and right atrium). blood pressure difference ( ΔР) at the beginning of the vessel ( P1) and at the end of it ( R2) is driving force 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 volumetric blood flow velocity, 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 the volumetric blood flow through the aorta or the total cross section of any other level of the vessels of the systemic circulation, the concept is used volumetric systemic circulation. 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 (MOC). 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, the volume 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 R2. Since in this section of the veins the blood pressure is close to 0 , then into the expression for calculation Q or IOC value is substituted R equal to the mean hydrodynamic blood pressure at the beginning of the aorta: 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 value of blood pressure for blood flow is the pulsating nature of the blood flow throughout 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 you can replace it with an analogue - OPS:

Q = P/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

where R- resistance; L- vessel length; η - blood viscosity; Π - number 3.14; r is the radius of the vessel.

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

It has already been mentioned that the radius of the vessels muscular type can quickly change 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 contraction or relaxation. smooth muscle 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. AT normal conditions blood viscosity does not change as rapidly as the lumen of blood vessels. After blood loss, with erythropenia, hypoproteinemia, blood viscosity decreases. With significant erythrocytosis, leukemia, increased erythrocyte aggregation and hypercoagulability, blood viscosity can increase significantly, which leads to an increase in blood flow resistance, an increase in the load on the myocardium and may be accompanied by a violation of blood flow in the vessels of the microvasculature.

In the established regime of blood circulation, 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. From it, blood is expelled into the pulmonary circulation and then through the pulmonary veins returns to 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 torso and legs, for a short time, the cardiac output of the left and right ventricles 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. average value it is for women 6-7%, for men 7-8% of body weight 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 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:

V \u003d Q / Pr 2

where V- linear velocity of blood flow, mm/s, cm/s; Q- volumetric blood flow velocity; P- number equal to 3.14; r is the radius of the vessel. 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 magnitude of the linear velocity on the volume 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 largest and is at rest about 20- 30 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 (500-600 times the cross-section of the aorta), the linear velocity of blood flow becomes minimal (less than 1 mm/s). The slow flow of blood in the capillaries creates 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 10-20 cm / s, and under loads it increases to 50 cm / s.

The linear speed of plasma movement 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 flow and move in it with 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 20-25 s in mowing, 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.

By analogy with the root system of plants, the blood inside a person transports nutrients through vessels of various sizes.

In addition to the nutritional function, work is carried out to transport oxygen from the air - cellular gas exchange is carried out.

circulatory system

If you look at the scheme of blood distribution throughout the body, then its cyclical path catches your eye. If we do not take into account the placental blood flow, then among the selected ones there is a small cycle that provides respiration and gas exchange of tissues and organs and affects the lungs of a person, as well as a second, large cycle that carries nutrients and enzymes.

The task of the circulatory system, which became known thanks to the scientific experiments of the scientist Harvey (in the 16th century, he discovered blood circles), in general, consists in organizing the movement of blood and lymphatic cells through the vessels.

Small circle of blood circulation

From above, venous blood from the right atrial chamber enters the right heart ventricle. Veins are medium-sized vessels. Blood passes in portions and is pushed out of the cavity cardiac ventricle through a valve that opens towards the pulmonary trunk.

From it, blood enters the pulmonary artery, and, as it moves away from the main muscle of the human body, the veins flow into the arteries. lung tissue, transforming and disintegrating into a multiple network of capillaries. Their role and primary function is to carry out gas exchange processes in which alveolocytes take in carbon dioxide.

As oxygen is distributed through the veins, arterial features become characteristic of the blood flow. So, through the venules, blood comes to the pulmonary veins, which open into the left atrium.

Systemic circulation

Let's trace the big blood cycle. The systemic circulation begins from the left cardiac ventricle, where the arterial flow enters, enriched with O 2 and depleted with CO 2, which is supplied from the pulmonary circulation. Where does blood go from the left ventricle of the heart?

After the left ventricle, the next aortic valve pushes arterial blood into the aorta. It distributes O 2 in high concentration throughout all arteries. Moving away from the heart, the diameter of the artery tube changes - it decreases.

All CO 2 is collected from the capillary vessels, and the large circle flows into the vena cava. From them, the blood again enters the right atrium, then into the right ventricle and pulmonary trunk.

Thus, the systemic circulation in the right atrium ends. And to the question - where does the blood go from the right ventricle of the heart, the answer is to the pulmonary artery.

Diagram of the human circulatory system

The diagram below with arrows of the process of blood flow briefly and clearly demonstrates the sequence of the implementation of the path of blood movement in the body, indicating the organs involved in the process.

Human circulatory organs

These include the heart and blood vessels(veins, arteries and capillaries). Consider the most main body in the human body.

The heart is a self-governing, self-regulating, self-correcting muscle. The size of the heart depends on the development skeletal muscle- the higher their development, the larger the heart. By structure, the heart has 4 chambers - 2 ventricles and 2 atria each, and is placed in the pericardium. The ventricles are separated from each other and between the atria by special heart valves.

Responsible for replenishing and saturating the heart with oxygen are coronary arteries or as they are called "coronary vessels".

The main function of the heart is to perform the work of a pump in the body. Failures are due to several reasons:

1. Insufficient/excessive volumes of incoming blood.
2. Injury to the heart muscle.
3. External pressure.

Second in importance in the circulatory system are the blood vessels.

Linear and volumetric blood flow velocity

When considering the speed parameters of blood, the concepts of linear and volumetric velocities are used. There is a mathematical relationship between these concepts.

Where does blood move the fastest? The linear velocity of blood flow is in direct proportion to the volumetric velocity, which varies depending on the type of vessels.

The highest rate of blood flow in the aorta.

Where does blood move at the slowest speed? The most low speed- in hollow veins.

Complete blood circulation time

For an adult, whose heart produces about 80 beats per minute, the blood makes the whole journey in 23 seconds, distributing 4.5-5 seconds for a small circle and 18-18.5 seconds for a large one.

The data is confirmed by experience. The essence of all research methods lies in the principle of labeling. A traceable substance that is uncharacteristic of the human body is injected into a vein and its location is dynamically determined.

So it is noted how much the substance will appear in the vein of the same name, located on the other side. This is the time of complete circulation of blood.

Conclusion

The human body is complex mechanism With various kinds systems. main role the circulatory system plays a role in its proper functioning and life support. Therefore, it is very important to understand its structure and maintain the heart and blood vessels in perfect order.

In humans, as in all mammals and birds, two circles of blood circulation - large and small. Four-chambered heart - two ventricles + two atria.

When looking at a drawing of a heart, imagine that you are looking at a person facing you. Then his left half of the body will be opposite your right, and the right half will be opposite your left. Left half the heart is closer to the left hand, and the right hand is closer to the middle of the body. Or imagine not a drawing, but yourself. "Feel" where you are left-hand side hearts, and where is the right one.

In turn, each half of the heart - left and right - consists of an atrium and a ventricle. The atria are at the top, the ventricles at the bottom.

Also remember the following thing. The left half of the heart is arterial, and the right half is venous.

One more rule. Blood is expelled from the ventricles and flows into the atria.

Now we turn to the circles of blood circulation themselves.

Small circle. Blood flows from the right ventricle to the lungs, from where it enters the left atrium. In the lungs, the blood turns from venous to arterial, because it gives off carbon dioxide and is saturated with oxygen.

Small circle of blood circulation
right ventricle → lungs → left atrium

Big circle. From the left ventricle arterial blood flows to all organs and parts of the body, where it becomes venous, after which it is collected and sent to the right atrium.

Systemic circulation
left ventricle → body → right atrium

This is a schematic presentation of the circles of blood circulation in order to explain briefly and clearly. However, it is often also required to know the names of the vessels through which blood is pushed out of the heart and flows into it. Here you should pay attention to the following. The vessels that carry blood from the heart to the lungs are called pulmonary arteries. But venous blood flows through them! The vessels that carry blood from the lungs to the heart are called pulmonary veins. But arterial blood flows through them! That is, in the case of a small circle of blood circulation, the opposite is true.

The large vessel that exits the left ventricle is called the aorta.

The superior and inferior vena cava flow into the right atrium, and not one vessel as in the diagram. One collects blood from the head, the other from the rest of the body.