Which organ of the circulatory system is capable of contracting? Organs of the circulatory system: structure and functions. Structure of the vascular system

Biology and Chemistry Teacher

MBOU Secondary School No. 48 named after. Hero of Russia of the city of Ulyanovsk

Option 1

I. Answer the questions

1. What tissue does blood belong to? _____

2. What function do red blood cells and platelets perform? ________________

3. Distinguish between the concepts of donor and recipient. ______________________________

4. What is the merit of Louis Pasteur? _________________________________________

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5. What is the significance of healing serums? _______________________________

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6. What is the significance of venous valves? _________________________________

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7. Indicate the role of heart valves in ensuring the movement of blood from the ventricles into the arteries. _____________________________________________

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8. Compare the speed of blood movement in arteries and veins. _________________

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9. First aid for nosebleeds. ___________________________

II. Complete the statements

1. For our body, microbes are _____________________________.

b) phagocytosis.

2. Gas exchange between pulmonary air and blood occurs:

a) in capillaries;

b) in the arteries;

c) in the veins.

3. The right half of the heart is filled with blood:

a) arterial;

b) venous;

c) mixed.

V. Name the organs of the circulatory system indicated in the figure with even numbers, determine which circulatory system they belong to.

2. _______________________________ ________________________________ 4. _______________________________ ________________________________ 6. _______________________________ ________________________________ 8. _______________________________ ________________________________ 10. ______________________________ ________________________________ 12. ______________________________ ________________________________ 14. ______________________________ ________________________________

Date____________ Last name, first name________________________ Class________

Option 2

I. Answer the questions

1. What role do lymph nodes play? _________________________

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2. What features of red blood cells distinguish mammals from other classes of invertebrate animals? _________________________________

3. What function do blood plasma and leukocytes perform? ________________

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4. In what cases should the Rh factor be taken into account? _______________________

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5. What is the merit of Ilya Ilyich Mechnikov? ______________________________

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6. What is the importance of vaccines? ___________________________________________

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7. Indicate the role of heart valves in ensuring the movement of blood from the atria to the ventricles. ___________________________________________

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8. Blood pressure measurement. __________________________________

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9. First aid for arterial bleeding. _______________________

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II. Complete the statements

1. For our body, the protective substances secreted by lymphocytes are ___________________________________________________________.

2. The introduction of medicinal serum creates ______________________ immunity.

3. Immunity obtained as a result of the use of medications is called __________________________________________________________.

III. Mark the correct statements

1. Arterial blood flows in all arteries without exception, and venous blood flows in all veins.

2. Nutrients in tissues pass from blood plasma into tissue fluid, and from there they enter cells.

IV. Choose the correct answer

1. Specific immunity is associated with:

a) with phagocytosis;

b) with the formation of antibodies.

2. In the arteries of the small circle there is blood:

a) arterial;

b) mixed;

c) venous.

3. The left half of the heart is filled with blood:

a) arterial;

b) venous;

c) mixed.

V. Name the organs of the circulatory system indicated in the figure with odd numbers, determine which circulatory system they belong to.

1. _______________________________ ________________________________ 3. _______________________________ ________________________________ 5. _______________________________ ________________________________ 7. _______________________________ ________________________________ 9. ______________________________ ________________________________ 11. ______________________________ ________________________________ 13. ______________________________ ________________________________

Job No.	Option I	Option II
	1. connecting. 2. red blood cells – transport of oxygen and carbon dioxide, platelets – participate in blood clotting. 3. The donor gives his blood, the recipient accepts. 4. Proved the involvement of microbes in infectious diseases. 5. Ready-made antibodies are injected into a person, passive immunity is created. 6. Prevent reverse blood flow. 7. Provide blood flow in one direction. 8. In the arteries, blood moves under high pressure; blood flows through the veins more slowly. 9. Sit the person down (you can’t throw your head back!), put a cold compress on the bridge of your nose, and put a piece of cotton wool soaked in peroxide in the nasal cavity.	1. Filtration, disinfection of lymph. 2. No core. 3. Plasma is nutritious, leukocytes are protective. 4. The Rh factor is taken into account during blood transfusions and pregnancy. 5.Discovered phagocytosis. 6. Develop active immunity. 7. Prevent reverse blood flow. 8. It is measured in the brachial artery with a special device - a tonometer. 9. Apply a tourniquet above the wound site (leave a note with the time!).
2. active. 3. phagocytosis.	1. antibodies. 2. passive. 3. artificial.
4. capillaries (BCC). 6. portal vein (PVV). 8. superior vena cava (SVC). 10. right ventricle (RV). 12. pulmonary capillaries (PCC). 14. left atrium (LA).	1. left ventricle (LVV). 3. arteries (BCC). 5. veins (BCV). 7. inferior vena cava (IVC). 9. right atrium (RA). 11. pulmonary artery (PAC). 13. pulmonary veins (PVC).

Question 1. What is the significance of the circulatory system?

The circulatory system circulates blood throughout the human body, thereby supplying our organs with oxygen and nutrients. Protects the body, and also some blood cells are involved in blood clotting.

Question 2. How are arteries different from veins?

The vessels through which blood flows from the heart are called arteries. Arteries have thick, strong and elastic walls. The largest artery is called the aorta. The vessels that carry blood to the heart are called veins. Their walls are thinner and softer than the walls of arteries.

Question 3. What function do capillaries perform?

It is the capillaries that form a huge branched network that permeates our entire body. Capillaries connect arteries and veins with each other, close the circulatory circle and ensure continuous blood circulation.

Question 4. How does the heart work?

The heart lies in the chest cavity between the lungs, slightly to the left of the midline of the body. Its size is small, approximately the size of a human fist, and the average heart weight is from 250 g (in women) to 300 g (in men). The shape of the heart resembles a cone.

The heart is a hollow muscular organ divided into four cavities - chambers: the right and left atria, the right and left ventricles. The right and left halves do not communicate. The heart is located inside a special sac of connective tissue - the pericardium. It contains a small amount of fluid inside, which wets its walls and the surface of the heart: this reduces the friction of the heart during its contractions.

The ventricles of the heart have well-developed muscular walls. The walls of the atria are much thinner. This is understandable: the atria do much less work, driving blood into the adjacent ventricles. The ventricles push blood into the circulation with great force so that it can reach the areas of the body most distant from the heart through the capillaries. The muscular wall of the left ventricle is especially strongly developed.

The movement of blood occurs in a certain direction, this is achieved by the presence of valves in the heart. The movement of blood from the atria into the ventricles is regulated by leaflet valves, which can only open towards the ventricles.

Question 5: What role do leaflet valves play?

The movement of blood from the atria into the ventricles is regulated by leaflet valves, which can only open towards the ventricles. Due to these valves, blood moves in a certain direction.

Question 6: How do semilunar valves work?

The return of blood from the arteries to the ventricles is prevented by the semilunar valves. They are located at the entrance to the arteries and have the appearance of deep semicircular pockets, which, under the pressure of blood, straighten, open, fill with blood, close tightly and thus block the return path of blood from the aorta and pulmonary trunk to the ventricles of the heart. When the ventricles contract, the semilunar valves are pressed against the walls, allowing blood to flow into the aorta and pulmonary trunk.

Question 7. Where does the systemic circulation begin and end?

The systemic circulation begins in the left ventricle, from where blood is pushed into the aorta. And it ends in the right atrium, where the superior and inferior vena cava bring venous blood.

Question 8. What happens to the blood in the pulmonary circulation?

From the right atrium, venous blood enters the right ventricle. The pulmonary circulation begins from it. Contracting, the right ventricle pushes blood into the pulmonary trunk, which divides into the right and left pulmonary arteries, which carry blood to the lungs. Here, in the pulmonary capillaries, gas exchange occurs: venous blood gives off carbon dioxide, is saturated with oxygen and becomes arterial. The four pulmonary veins return arterial blood to the left atrium.

Question 9. Why do arteries have thicker walls than veins?

In the arteries, blood is released under pressure and moves due to it. Thick walls allow them to withstand the pressure of blood being pushed out of the heart. But there is no such pressure in the veins.

Question 10. Why is the muscular wall of the left ventricle much thicker than the muscular wall of the right ventricle?

The muscular walls of the right and left ventricles differ in thickness: the walls of the left ventricle are much thicker than the walls of the right. The fact is that the left ventricle has to pump more blood and under higher pressure. The right ventricle, which pumps blood only through the lungs, does relatively little work. This is one example of an organ’s adaptation to the conditions of its activity.

THINK

Why is it harmful to wear tight shoes and tight belts?

If you put too much pressure on any part of the body (it doesn’t matter which one), blood circulation in it will be disrupted. Blood flows to the extremities, but it is difficult to return. And when wearing tight shoes, the foot is also deformed.

Each person plays a very significant role in providing the body with all the substances and vitamins that are necessary for the normal functioning and proper development of the person as a whole. Blood constantly circulates through the venous-arterial system, where the role of the main pump is played by the heart, which is constantly in constant motion throughout a person’s life. The heart itself consists of right and left halves, each of which in turn is divided into two internal chambers - a fleshy ventricle and a thin-walled atrium. which works in the correct rhythm, ensures the flow of oxygen not only to all internal organs, but also to all cells, simultaneously taking away carbon dioxide and other waste products. Thus, the importance of the circulatory system is extremely great.

It is noteworthy that the entire cardiovascular system is in constant development, thanks to which, when engaging in physical education and sports with the right selection of exercises, it is possible to maintain the body in a healthy state throughout almost your entire life. Unfortunately, many people do not always understand the importance of the circulatory system in human life and how lifestyle affects the heart. Proof of this is the sad statistics of an increase in the number of diseases associated with the cardiovascular system. These are hypertension, hypotension, heart attack, and so on. That is why all people, even from school, must realize that the importance of the circulatory system in a person’s life is very important, and they need to take care of their own health. The fact is that the blood gives the cells the necessary oxygen, which is vital for their growth and development.

Today, in many developed countries, interest in a healthy lifestyle is increasing every year, and the number of people giving up such bad habits as smoking and drinking alcohol is steadily increasing. In our country, the statistics, unfortunately, are not yet so favorable, but today there is already a part of young people who prefer to lead an active lifestyle, engage in tourism and sports. After all, many people simply do not know how destructive it is to the heart and blood vessels, and as for blood, as a result of poisoning, red blood cells stick together in the blood cells, which can lead to blockage of blood vessels, as well as internal hemorrhage. Thus, the enormous importance of the body’s circulatory system is proven by life itself, since so much depends on healthy blood. By the way, the composition of the blood is also affected by proper nutrition, therefore, if it is balanced and contains a large number of useful and nutritious elements, then there will be much less toxins in the body. A balanced approach to eating food promotes better absorption of nutrients and also prevents oxidative products from entering the bloodstream, which negatively affect blood composition. By the way, it will also be useful to know that fasting helps cleanse internal organs of toxins, since “hungry” blood cleanses the body, drawing out all harmful elements and substances from it

Every person wants to have good health, be able to run and jump, be beautiful and strong. All this wealth is in our hands from youth, and only over time, due to a careless attitude towards ourselves, do we gradually lose it. If people understood the role of the circulatory system in the body from an early age, then the health of the entire people would become much stronger. Sports exercises such as morning jogging and swimming have the best effect on the cardiovascular system, increasing the body's adaptive capabilities, as well as its resistance to various diseases. Healthy blood ensures the normal functioning of all human organs without exception, helping them overcome extreme stress at certain moments in life.

Thus, to summarize all of the above, it should be understood that the importance of the circulatory system in any organism is simply enormous, and the heart is the main organ that ensures the possibility of the existence of life as an integral biological system.

The circulatory system is a single anatomical and physiological formation, the main function of which is blood circulation, that is, the movement of blood in the body.
Thanks to blood circulation, gas exchange occurs in the lungs. During this process, carbon dioxide is removed from the blood, and oxygen from the inhaled air enriches it. Blood delivers oxygen and nutrients to all tissues, removing metabolic (decomposition) products from them.
The circulatory system also participates in heat exchange processes, ensuring the vital functions of the body in different environmental conditions. This system is also involved in the humoral regulation of organ activity. Hormones are secreted by endocrine glands and delivered to tissues susceptible to them. This is how blood unites all parts of the body into a single whole.

Parts of the vascular system

The vascular system is heterogeneous in morphology (structure) and function. It can, with a slight degree of convention, be divided into the following parts:

• aortoarterial chamber;
• resistance vessels;
• exchange vessels;
• arteriovenular anastomoses;
• capacitive vessels.

The aortoarterial chamber is represented by the aorta and large arteries (common iliac, femoral, brachial, carotid and others). Muscle cells are also present in the wall of these vessels, but elastic structures predominate, preventing their collapse during cardiac diastole. Elastic type vessels maintain a constant blood flow rate, regardless of pulse impulses.
Resistance vessels are small arteries whose walls are dominated by muscle elements. They are able to quickly change their lumen taking into account the oxygen needs of an organ or muscle. These vessels are involved in maintaining blood pressure. They actively redistribute blood volumes between organs and tissues.
Exchange vessels are capillaries, the smallest branches of the circulatory system. Their wall is very thin, gases and other substances easily penetrate through it. Blood can flow from the smallest arteries (arterioles) into venules, bypassing the capillaries, through arteriovenular anastomoses. These “connecting bridges” play a large role in heat transfer.
Capacitance vessels are so called because they are able to hold significantly more blood than arteries. These vessels include venules and veins. Through them, blood flows back to the central organ of the circulatory system - the heart.

Circulation circles

Circulation circles were described back in the 17th century by William Harvey.
The aorta emerges from the left ventricle, beginning the systemic circulation. Arteries that carry blood to all organs are separated from it. Arteries are divided into smaller and smaller branches, covering all tissues of the body. Thousands of tiny arteries (arterioles) break up into a huge number of the smallest vessels - capillaries. Their walls are characterized by high permeability, so gas exchange occurs in the capillaries. Here arterial blood is transformed into venous blood. Venous blood enters the veins, which gradually unite and eventually form the superior and inferior vena cava. The mouths of the latter open into the cavity of the right atrium.
In the pulmonary circulation, blood passes through the lungs. It gets there through the pulmonary artery and its branches. Gas exchange with air occurs in the capillaries that weave around the alveoli. Oxygen-enriched blood travels through the pulmonary veins to the left side of the heart.
Some important organs (brain, liver, intestines) have peculiarities of blood supply - regional circulation.

Structure of the vascular system

The aorta, emerging from the left ventricle, forms the ascending part, from which the coronary arteries are separated. Then it bends, and vessels extend from its arc, directing blood to the arms, head, and chest. The aorta then goes down along the spine, where it divides into vessels that carry blood to the organs of the abdominal cavity, pelvis, and legs.

Veins accompany arteries of the same name.
Separately, mention should be made of the portal vein. It drains blood away from the digestive organs. In addition to nutrients, it may contain toxins and other harmful agents. The portal vein delivers blood to the liver, where toxic substances are removed.

Structure of vascular walls

Arteries have outer, middle and inner layers. The outer layer is connective tissue. In the middle layer there are elastic fibers that maintain the shape of the vessel, and muscle fibers. Muscle fibers can contract and change the lumen of the artery. The inside of the arteries is lined with endothelium, which ensures a calm flow of blood without obstacles.

The walls of veins are much thinner than arteries. They have very little elasticity, so they stretch and fall easily. The inner wall of the veins forms folds: venous valves. They prevent the downward movement of venous blood. The outflow of blood through the veins is also ensured by the movement of skeletal muscles, which “squeeze” blood when walking or running.

Regulation of the circulatory system

The circulatory system almost instantly responds to changes in external conditions and the internal environment of the body. Under stress or strain, it responds by increasing heart rate, increasing blood pressure, improving blood supply to muscles, reducing the intensity of blood flow in the digestive organs, and so on. During periods of rest or sleep, the reverse processes occur.

Regulation of the function of the vascular system is carried out by neurohumoral mechanisms. Higher-level regulatory centers are located in the cerebral cortex and hypothalamus. From there, signals enter the vasomotor center, which is responsible for vascular tone. Through the fibers of the sympathetic nervous system, impulses enter the walls of blood vessels.

In regulating the function of the circulatory system, the feedback mechanism is very important. The walls of the heart and blood vessels contain a large number of nerve endings that sense changes in pressure (baroreceptors) and the chemical composition of the blood (chemoreceptors). Signals from these receptors enter higher regulatory centers, helping the circulatory system quickly adapt to new conditions.

Humoral regulation is possible with the help of the endocrine system. Most human hormones in one way or another affect the activity of the heart and blood vessels. The humoral mechanism involves adrenaline, angiotensin, vasopressin and many other active substances.

The circulatory system consists of a central organ, the heart, and closed tubes of various sizes connected to it, called blood vessels. The heart, with its rhythmic contractions, sets in motion the entire mass of blood contained in the vessels.

The circulatory system performs the following functions:

ü respiratory(participation in gas exchange) – the blood delivers oxygen to the tissues, and carbon dioxide enters the blood from the tissues;

ü trophic– blood carries nutrients obtained from food to organs and tissues;

ü protective– blood leukocytes participate in the absorption of microbes entering the body (phagocytosis);

ü transport– hormones, enzymes, etc. are distributed throughout the vascular system;

ü thermoregulatory– helps to equalize body temperature;

ü excretory– waste products of cellular elements are removed with the blood and transferred to the excretory organs (kidneys).

Blood is a liquid tissue consisting of plasma (intercellular substance) and formed elements suspended in it, which develop not in the vessels, but in the hematopoietic organs. Formed elements make up 36-40%, and plasma - 60-64% of blood volume (Fig. 32). The human body weighing 70 kg contains on average 5.5-6 liters of blood. Blood circulates in blood vessels and is separated from other tissues by the vascular wall, but formed elements and plasma can pass into the connective tissue surrounding the vessels. This system ensures the constancy of the internal environment of the body.

Blood plasma is a liquid intercellular substance consisting of water (up to 90%), a mixture of proteins, fats, salts, hormones, enzymes and dissolved gases, as well as end products of metabolism, which are excreted from the body by the kidneys and partly by the skin.

To the formed elements of blood include erythrocytes or red blood cells, leukocytes or white blood cells and platelets or platelets.

Fig.32. Blood composition.

Red blood cells – these are highly differentiated cells that do not contain a nucleus and individual organelles and are not capable of division. The lifespan of an erythrocyte is 2-3 months. The number of red blood cells in the blood is variable, it is subject to individual, age-related, daily and climatic fluctuations. Normally, in a healthy person, the number of red blood cells ranges from 4.5 to 5.5 million per cubic millimeter. Red blood cells contain a complex protein - hemoglobin. It has the ability to easily attach and detach oxygen and carbon dioxide. In the lungs, hemoglobin gives up carbon dioxide and accepts oxygen. Oxygen is delivered to tissues, and carbon dioxide is taken from them. Consequently, red blood cells in the body carry out gas exchange.

Leukocytes develop in the red bone marrow, lymph nodes and spleen and enter the blood in a mature state. The number of leukocytes in the blood of an adult ranges from 6000 to 8000 per cubic millimeter. Leukocytes are capable of active movement. Adhering to the wall of the capillaries, they penetrate through the gap between the endothelial cells into the surrounding loose connective tissue. The process of leukocytes leaving the bloodstream is called migration. Leukocytes contain a nucleus, the size, shape and structure of which are varied. Based on the structural features of the cytoplasm, two groups of leukocytes are distinguished: non-granular leukocytes (lymphocytes and monocytes) and granular leukocytes (neutrophils, basophils and eosinophils), containing granular inclusions in the cytoplasm.

One of the main functions of leukocytes is to protect the body from microbes and various foreign bodies and to form antibodies. The doctrine of the protective function of leukocytes was developed by I.I. Mechnikov. Cells that capture foreign particles or microbes have been called phagocytes, and the absorption process – phagocytosis. The place of reproduction of granular leukocytes is the bone marrow, and that of lymphocytes is the lymph nodes.

Platelets or blood platelets play an important role in blood clotting when the integrity of blood vessels is disrupted. A decrease in their amount in the blood causes slower clotting. A sharp decrease in blood clotting is observed in hemophilia, which is inherited through women, and only men are affected.

In plasma, the formed elements of blood are found in certain quantitative ratios, which are usually called the blood formula (hemogram), and the percentages of leukocytes in peripheral blood are called the leukocyte formula. In medical practice, a blood test is of great importance for characterizing the state of the body and diagnosing a number of diseases. The leukocyte formula allows you to assess the functional state of those hematopoietic tissues that supply various types of leukocytes into the blood. An increase in the total number of leukocytes in peripheral blood is called leukocytosis. It can be physiological and pathological. Physiological leukocytosis is transient, it is observed during muscle tension (for example, in athletes), during a rapid transition from a vertical to a horizontal position, etc. Pathological leukocytosis is observed in many infectious diseases, inflammatory processes, especially purulent ones, after operations. Leukocytosis has a certain diagnostic and prognostic significance for the differential diagnosis of a number of infectious diseases and various inflammatory processes, assessment of the severity of the disease, the reactivity of the body, and the effectiveness of therapy. Non-granular leukocytes include lymphocytes, among which T- and B-lymphocytes are distinguished. They participate in the formation of antibodies when a foreign protein (antigen) is introduced into the body and determine the body’s immunity.

Blood vessels are represented by arteries, veins and capillaries. The science of blood vessels is called angiology. Blood vessels that go from the heart to the organs and carry blood to them are called arteries, and the vessels carrying blood from organs to the heart are veins. Arteries arise from the branches of the aorta and go to the organs. Having entered the organ, the arteries branch, turning into arterioles, which branch into precapillaries And capillaries. Capillaries continue into postcapillaries, venules and finally in veins, which leave the organ and flow into the superior or inferior vena cava, carrying blood to the right atrium. Capillaries are the thinnest-walled vessels that perform an exchange function.

Individual arteries supply entire organs or parts thereof. In relation to an organ, there are arteries that go outside the organ before entering it - extraorgan (main) arteries and their continuations, branching inside the organ - intraorgan or intraorgan arteries. Branches extend from the arteries, which (before breaking up into capillaries) can connect with each other, forming anastomoses.

Rice. 33. The structure of the walls of blood vessels.

The structure of the vascular wall(Fig. 33). Arterial wall consists of three shells: inner, middle and outer.

Inner membrane (intima) lines the inside of the vessel wall. They consist of endothelium lying on an elastic membrane.

Middle shell (media) contains smooth muscle and elastic fibers. As they move away from the heart, the arteries divide into branches and become smaller and smaller. The arteries closest to the heart (the aorta and its large branches) primarily perform the function of conducting blood. In them, the foreground is counteraction to the stretching of the vessel wall by the mass of blood that is ejected by the heart impulse. Therefore, structures of a mechanical nature are more developed in the arterial wall, i.e. Elastic fibers predominate. Such arteries are called elastic arteries. In medium and small arteries, in which the inertia of the blood weakens and its own contraction of the vascular wall is required for further movement of blood, the contractile function predominates. It is ensured by greater development of muscle tissue in the vascular wall. Such arteries are called muscular arteries.

Outer shell (externa) represented by connective tissue that protects the vessel.

The last branches of the arteries become thin and small and are called arterioles. Their wall consists of endothelium lying on a single layer of muscle cells. The arterioles continue directly into the precapillary, from which numerous capillaries arise.

Capillaries(Fig. 33) are the thinnest vessels that perform an exchange function. In this regard, the capillary wall consists of a single layer of endothelial cells, which are permeable to substances and gases dissolved in the liquid. By anastomosing with each other, the capillaries form capillary networks, passing into postcapillaries. Postcapillaries continue into venules accompanying arterioles. Venules form the initial segments of the venous bed and pass into veins.

Vienna carry blood in the opposite direction to the arteries - from the organs to the heart. The walls of the veins are structured in the same way as the walls of the arteries, however, they are much thinner and have less muscle and elastic tissue (Fig. 33). The veins, merging with each other, form large venous trunks - the superior and inferior vena cava, which flow into the heart. The veins widely anastomose with each other, forming venous plexuses. The reverse flow of venous blood is prevented valves. They consist of a fold of endothelium containing a layer of muscle tissue. The valves face the free end towards the heart and therefore do not interfere with the flow of blood to the heart and keep it from returning back.

Factors that promote blood movement through vessels. As a result of ventricular systole, blood enters the arteries and they stretch. By contracting due to their elasticity and returning from a stretched state to their original position, the arteries contribute to a more uniform distribution of blood throughout the vascular bed. Blood flows continuously in the arteries, although the heart contracts and pumps out blood in spurts.

The movement of blood through the veins is carried out due to contractions of the heart and the suction action of the chest cavity, in which negative pressure is created during inhalation, as well as contraction of skeletal muscles, smooth muscles of organs and the muscular lining of the veins.

Arteries and veins usually run together, with small and medium-sized arteries accompanied by two veins, and large ones by one. The exception is the superficial veins, which run in the subcutaneous tissue and do not accompany the arteries.

The walls of blood vessels have their own thin arteries and veins serving them. They also contain numerous nerve endings (receptors and effectors) associated with the central nervous system, due to which the nervous regulation of blood circulation is carried out through the mechanism of reflexes. Blood vessels are large reflexogenic zones that play an important role in the neurohumoral regulation of metabolism.

The movement of blood and lymph in the microscopic part of the vascular bed is called microcirculation. It is carried out in the vessels of the microvasculature (Fig. 34). The microcirculatory bed includes five links:

1) arterioles ;

2) precapillaries, which ensure the delivery of blood to the capillaries and regulate their blood supply;

3) capillaries, through the wall of which exchange occurs between the cell and the blood;

4) postcapillaries;

5) venules through which blood flows into the veins.

Capillaries They constitute the main part of the microvasculature, where exchange between blood and tissues occurs. Oxygen, nutrients, enzymes, hormones come from the blood to the tissues, and waste metabolic products and carbon dioxide enter the blood from the tissues. The length of the capillaries is very long. If we expand the capillary network of the muscular system alone, its length will be equal to 100,000 km. The diameter of the capillaries is small - from 4 to 20 microns (average 8 microns). The sum of the cross sections of all functioning capillaries is 600-800 times the diameter of the aorta. This is due to the fact that the speed of blood flow in the capillaries is approximately 600-800 times less than the speed of blood flow in the aorta and amounts to 0.3-0.5 mm/s. The average speed of blood movement in the aorta is 40 cm/s, in medium-sized veins it is 6-14 cm/s, and in the vena cava it reaches 20 cm/s. The blood circulation time in humans is on average 20-23 seconds. Consequently, in 1 minute a complete blood circulation is completed three times, in 1 hour - 180 times, and in a day - 4320 times. And this is all with 4-5 liters of blood in the human body.

Rice. 34. Microcirculatory bed.

Circumferential or collateral circulation represents the flow of blood not along the main vascular bed, but through lateral vessels connected to it - anastomoses. In this case, the circumferential vessels expand and acquire the character of large vessels. The property of forming a roundabout circulation is widely used in surgical practice during operations on organs. Anastomoses are most developed in the venous system. In some places the veins have a large number of anastomoses called venous plexuses. The venous plexuses are especially well developed in the internal organs located in the pelvic area (bladder, rectum, internal genital organs).

The circulatory system is subject to significant age-related changes. They consist in a decrease in the elastic properties of the walls of blood vessels and the appearance of sclerotic plaques. As a result of such changes, the lumen of the vessels decreases, which leads to a deterioration in the blood supply to this organ.

From the microcirculatory bed, blood flows through the veins, and lymph through the lymphatic vessels flowing into the subclavian veins.

Venous blood containing attached lymph flows into the heart, first into the right atrium, then into the right ventricle. From the latter, venous blood enters the lungs through the pulmonary circulation.

Rice. 35. Pulmonary circulation.

Circulation diagram. Lesser (pulmonary) circulation(Fig. 35) serves to enrich the blood with oxygen in the lungs. It starts at right ventricle where it comes from pulmonary trunk. The pulmonary trunk, approaching the lungs, is divided into right and left pulmonary arteries. The latter branch in the lungs into arteries, arterioles, precapillaries and capillaries. In the capillary networks that weave around the pulmonary vesicles (alveoli), the blood gives off carbon dioxide and receives oxygen in return. Oxygen-enriched arterial blood flows from capillaries into venules and veins, which merge into four pulmonary veins, leaving the lungs and flowing into left atrium. The pulmonary circulation ends in the left atrium.

Rice. 36. Systemic circulation.

Arterial blood entering the left atrium is directed to the left ventricle, where the systemic circulation begins.

Systemic circulation(Fig. 36) serves to deliver nutrients, enzymes, hormones and oxygen to all organs and tissues of the body and remove metabolic products and carbon dioxide from them.

It starts at left ventricle of the heart, from which comes aorta, carrying arterial blood, which contains the nutrients and oxygen necessary for the body’s functioning, and has a bright scarlet color. The aorta branches into arteries that go to all organs and tissues of the body and pass into their thickness into arterioles and capillaries. Capillaries collect into venules and veins. Through the walls of capillaries, metabolism and gas exchange occurs 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). Therefore, the blood entering the venous bed is poor in oxygen and rich in carbon dioxide and has a dark color - venous blood. The veins branching from the organs merge into two large trunks - superior and inferior vena cava, which flow into right atrium, where the systemic circulation ends.

Rice. 37. Vessels supplying the heart.

Thus, “from heart to heart” the systemic circulation looks like this: left ventricle – aorta – main branches of the aorta – arteries of medium and small caliber – arterioles – capillaries – venules – veins of medium and small caliber – veins extending from organs – upper and the inferior vena cava - the right atrium.

The complement to the great circle is third (cardiac) circle of blood circulation, serving the heart itself (Fig. 37). It begins from the ascending aorta right and left coronary arteries and ends veins of the heart, which merge into coronary sinus, opening in right atrium.

The central organ of the circulatory system is the heart, the main function of which is to ensure continuous blood flow through the vessels.

Heart It is a hollow muscular organ that receives blood from the venous trunks flowing into it and drives the blood into the arterial system. Contraction of the heart chambers is called systole, relaxation is called diastole.

Rice. 38. Heart (front view).

The heart has the shape of a flattened cone (Fig. 38). It distinguishes between the top and the base. Top of the heart facing down, forward and to the left, reaching the fifth intercostal space at a distance of 8-9 cm to the left from the midline of the body. It is formed by the left ventricle. Base facing up, back and to the right. It is formed by the atria, and in front by the aorta and pulmonary trunk. The coronary groove, running transversely to the longitudinal axis of the heart, forms the boundary between the atria and ventricles.

In relation to the midline of the body, the heart is located asymmetrically: one third is on the right, two thirds on the left. The borders of the heart are projected onto the chest as follows:

§ apex of the heart determined in the fifth left intercostal space 1 cm medially from the midclavicular line;

§ upper limit(base of the heart) passes at the level of the upper edge of the third costal cartilages;

§ right border runs from the 3rd to the 5th ribs 2-3cm to the right from the right edge of the sternum;

§ bottom line runs transversely from the cartilage of the 5th right rib to the apex of the heart;

§ left border– from the apex of the heart to the 3rd left costal cartilage.

Rice. 39. Human heart (opened).

Heart cavity consists of 4 chambers: two atria and two ventricles - right and left (Fig. 39).

The right chambers of the heart are separated from the left by a solid septum and do not communicate with each other. The left atrium and left ventricle together constitute the left or arterial heart (according to the properties of the blood in it); the right atrium and right ventricle constitute the right or venous heart. Between each atrium and ventricle is the atrioventricular septum, which contains the atrioventricular orifice.

Right and left atria shaped like a cube. The right atrium receives venous blood from the systemic circulation and the walls of the heart, the left atrium receives arterial blood from the pulmonary circulation. On the posterior wall of the right atrium there are openings of the superior and inferior vena cava and the coronary sinus; in the left atrium there are openings of the 4 pulmonary veins. The atria are separated from each other by the interatrial septum. Upward, both atria continue into processes, forming the right and left ears, which cover the aorta and pulmonary trunk at the base.

The right and left atria communicate with the corresponding ventricles through the atrioventricular openings located in the atrioventricular septa. The holes are limited by the fibrous ring, so they do not collapse. Valves are located along the edge of the holes: on the right - tricuspid, on the left - bicuspid or mitral (Fig. 39). The free edges of the valves face the ventricular cavity. On the inner surface of both ventricles there are papillary muscles and chordae tendineae protruding into the lumen, from which tendon threads stretch to the free edge of the valve leaflets, preventing the valve leaflets from turning into the lumen of the atria (Fig. 39). In the upper part of each ventricle there is one more hole: in the right ventricle there is a hole in the pulmonary trunk, in the left there is an aorta, equipped with semilunar valves, the free edges of which are thickened due to small nodules (Fig. 39). Between the walls of the vessels and the semilunar valves there are small pockets - the sinuses of the pulmonary trunk and aorta. The ventricles are separated from each other by the interventricular septum.

When the atria contract (systole), the leaflets of the left and right atrioventricular valves are open towards the ventricular cavities, the blood flow presses them against their wall and does not interfere with the passage of blood from the atria to the ventricles. Following the contraction of the atria, contraction of the ventricles occurs (the atria are relaxed - diastole). When the ventricles contract, the free edges of the valve leaflets close under blood pressure and close the atrioventricular openings. In this case, blood from the left ventricle enters the aorta, and from the right - into the pulmonary trunk. The semilunar valve flaps are pressed against the walls of the blood vessels. Then the ventricles relax, and a general diastolic pause occurs in the cardiac cycle. In this case, the sinuses of the valves of the aorta and pulmonary trunk are filled with blood, due to which the valve flaps close, closing the lumen of the vessels and preventing the return of blood to the ventricles. Thus, the function of valves is to allow blood to flow in one direction or to prevent blood from flowing in the opposite direction.

Heart wall consists of three layers (shells):

ü internal – endocardium lining the cavities of the heart and forming the valves;

ü average – myocardium, making up most of the heart wall;

ü external – epicardium, which is the visceral layer of the serous membrane (pericardium).

The inner surface of the heart cavities is lined endocardium. It consists of a layer of connective tissue with a large number of elastic fibers and smooth muscle cells covered with an inner endothelial layer. All heart valves are duplications of the endocardium.

Myocardium formed by striated muscle tissue. It differs from skeletal muscles in its fiber structure and involuntary function. The degree of myocardial development in various parts of the heart is determined by the function they perform. In the atria, whose function is to expel blood into the ventricles, the myocardium is most poorly developed and is represented by two layers. The ventricular myocardium has a three-layer structure, and in the wall of the left ventricle, which ensures blood circulation in the vessels of the systemic circulation, it is almost twice as thick as the right ventricle, the main function of which is to ensure blood flow in the pulmonary circulation. The muscle fibers of the atria and ventricles are isolated from each other, which explains their separate contraction. First, both atria contract simultaneously, then both ventricles (the atria are relaxed when the ventricles contract).

Plays an important role in the rhythmic work of the heart and in coordinating the activity of the muscles of the individual chambers of the heart. conduction system of the heart , which is represented by specialized atypical muscle cells that form special bundles and nodes under the endocardium (Fig. 40).

Sinoatrial node located between the right ear and the confluence of the superior vena cava. It is associated with the muscles of the atria and is important for their rhythmic contraction. The sinoatrial node is functionally connected to atrioventricular node located at the base of the interatrial septum. From this node it extends into the interventricular septum atrioventricular bundle (bundle of His). This bundle is divided into right and left legs, going into the myocardium of the corresponding ventricles, where it branches into Purkinje fibers. Thanks to this, the regulation of the rhythm of heart contractions is established - first the atria, and then the ventricles. Excitation from the sinus-atrial node is transmitted through the atrial myocardium to the atrioventricular node, from which it spreads along the atrioventricular bundle to the ventricular myocardium.

Rice. 40. Conducting system of the heart.

The outside of the myocardium is covered epicardium, which is the serous membrane.

Blood supply to the heart carried out by the right and left coronary or coronary arteries (Fig. 37), extending from the ascending aorta. The outflow of venous blood from the heart occurs through the cardiac veins, which flow into the right atrium both directly and through the coronary sinus.

Innervation of the heart carried out by cardiac nerves arising from the right and left sympathetic trunks, and the cardiac branches of the vagus nerves.

Pericardium. The heart is located in a closed serous sac - the pericardium, in which two layers are distinguished: external fibrous And internal serous.

The inner layer is divided into two layers: visceral - epicardium (the outer layer of the heart wall) and parietal, fused with the inner surface of the fibrous layer. Between the visceral and parietal layers there is a pericardial cavity containing serous fluid.

The activity of the circulatory system and, in particular, the heart is influenced by numerous factors, including systematic exercise. With intense and prolonged muscular work, increased demands are placed on the heart, as a result of which certain structural changes occur in it. First of all, these changes are manifested by an increase in the size and mass of the heart (mainly the left ventricle) and are called physiological or working hypertrophy. The greatest increase in heart size is observed in cyclists, rowers, marathon runners, and the largest hearts in skiers. In short-distance runners and swimmers, boxers and football players, heart enlargement is found to a lesser extent.

VESSELS OF THE SMALL (PULMONARY) CIRCULATION

The pulmonary circulation (Fig. 35) serves to enrich the blood flowing from the organs with oxygen and remove carbon dioxide from it. This process takes place in the lungs, through which all the blood circulating in the human body passes. Venous blood flows through the superior and inferior vena cava into the right atrium, from it into the right ventricle, from which it exits pulmonary trunk. It goes left and up, crosses the underlying aorta and, at the level of the 4-5 thoracic vertebrae, divides into the right and left pulmonary arteries, which go to the corresponding lung. In the lungs, the pulmonary arteries are divided into branches that carry blood to the corresponding lobes of the lung. The pulmonary arteries accompany the bronchi along their entire length and, repeating their branches, the vessels are divided into smaller and smaller intrapulmonary vessels, which pass at the level of the alveoli into capillaries that entwine the pulmonary alveoli. Gas exchange occurs through the capillary wall. The blood gives off excess carbon dioxide and is saturated with oxygen, as a result of which it becomes arterial and acquires a scarlet color. Oxygen-enriched blood collects in small and then large veins, which follow the course of the arterial vessels. The blood flowing from the lungs collects in the four pulmonary veins that leave the lungs. Each pulmonary vein opens into the left atrium. The small circle vessels do not participate in the blood supply to the lung.

ARTERIES OF THE GREAT CIRCULATION

Aorta represents the main trunk of the arteries of the systemic circulation. It carries blood out of the left ventricle of the heart. As you move away from the heart, the cross-sectional area of ​​the arteries increases, i.e. the bloodstream becomes wider. In the area of ​​the capillary network, there is an increase of 600-800 times compared to the cross-sectional area of ​​the aorta.

The aorta has three sections: the ascending aorta, the aortic arch and the descending aorta. At the level of the 4th lumbar vertebra, the aorta is divided into the right and left common iliac arteries (Fig. 41).

Rice. 41. Aorta and its branches.

Branches of the ascending aorta are the right and left coronary arteries that supply blood to the wall of the heart (Fig. 37).

From the aortic arch from right to left: the brachiocephalic trunk, the left common carotid and the left subclavian arteries (Fig. 42).

Brachiocephalic trunk located in front of the trachea and behind the right sternoclavicular joint, it is divided into the right common carotid and right subclavian arteries (Fig. 42).

The branches of the aortic arch supply blood to the organs of the head, neck and upper limbs. Aortic arch projection- in the middle of the manubrium of the sternum, brachiocephalic trunk - from the aortic arch to the right sternoclavicular joint, common carotid artery - along the sternocleidomastoid muscle to the level of the upper edge of the thyroid cartilage.

Common carotid arteries(right and left) are directed upward on both sides of the trachea and esophagus and, at the level of the upper edge of the thyroid cartilage, are divided into the external and internal carotid arteries. The common carotid artery is pressed to stop bleeding to the tubercle of the 6th cervical vertebra.

Blood supply to organs, muscles and skin of the neck and head is carried out through the branches external carotid artery, which at the level of the neck of the lower jaw is divided into its terminal branches - the maxillary and superficial temporal arteries. The branches of the external carotid artery supply blood to the outer integuments of the head, face and neck, facial and masticatory muscles, salivary glands, teeth of the upper and lower jaws, tongue, pharynx, larynx, hard and soft palate, palatine tonsils, sternocleidomastoid muscle and other muscles necks located above the hyoid bone.

Internal carotid artery(Fig. 42), starting from the common carotid artery, rises to the base of the skull and penetrates the cranial cavity through the carotid canal. It does not produce branches in the neck area. The artery supplies blood to the dura mater, the eyeball and its muscles, the mucous membrane of the nasal cavity, and the brain. Its main branches are ophthalmic artery, front And middle cerebral arteries And posterior communicating artery(Fig. 42).

Subclavian arteries(Fig. 42) the left one extends from the aortic arch, the right one from the brachiocephalic trunk. Both arteries exit through the upper opening of the chest to the neck, lie on the 1st rib and penetrate into the axillary region, where they are called axillary arteries. The subclavian artery supplies blood to the larynx, esophagus, thyroid and thymus glands, and back muscles.

Rice. 42. Branches of the aortic arch. Brain vessels.

Originates from the subclavian artery vertebral artery, blood supply to the brain and spinal cord, deep muscles of the neck. In the cranial cavity, the right and left vertebral arteries fuse together to form basilar artery which, at the anterior edge of the pons (brain section), is divided into two posterior cerebral arteries (Fig. 42). These arteries, together with the branches of the carotid artery, participate in the formation of the arterial circle of the cerebrum.

The continuation of the subclavian artery is axillary artery. It lies deep in the armpit, passes along with the axillary vein and the trunks of the brachial plexus. The axillary artery supplies blood to the shoulder joint, skin and muscles of the upper limb and chest.

The continuation of the axillary artery is brachial artery, which supplies blood to the shoulder (muscles, bone and skin with subcutaneous tissue) and the elbow joint. It reaches the elbow and at the level of the neck of the radius is divided into terminal branches - radial and ulnar arteries. These arteries supply with their branches the skin, muscles, bones and joints of the forearm and hand. These arteries widely anastomose with each other and form two networks in the area of ​​the hand: dorsal and palmar. There are two arches on the palmar surface - superficial and deep. They represent an important functional device, because... Due to the varied functions of the hand, the vessels of the hand are often subject to compression. When the blood flow in the superficial palmar arch changes, the blood supply to the hand does not suffer, since blood delivery occurs in such cases through the arteries of the deep arch.

The projection of large arteries onto the skin of the upper limb and the places of their pulsation is important to know when stopping bleeding and applying tourniquets in cases of sports injuries. The projection of the brachial artery is determined in the direction of the medial groove of the shoulder to the ulnar fossa; radial artery - from the ulnar fossa to the lateral styloid process; ulnar artery - from the ulnar fossa to the pisiform bone; the superficial palmar arch is in the middle of the metacarpal bones, and the deep palmar arch is at their base. The place of pulsation of the brachial artery is determined in its medial groove, the radial one - in the distal forearm on the radius.

Descending aorta(continuation of the aortic arch) runs on the left along the spinal column from the 4th thoracic to the 4th lumbar vertebrae, where it divides into its terminal branches - the right and left common iliac arteries (Fig. 41, 43). The descending aorta is divided into thoracic and abdominal parts. All branches of the descending aorta are divided into parietal (parietal) and visceral (visceral).

Parietal branches of the thoracic aorta: a) 10 pairs of intercostal arteries running along the lower edges of the ribs and supplying blood to the muscles of the intercostal spaces, skin and muscles of the lateral chest, back, upper parts of the anterior abdominal wall, spinal cord and its membrane; b) superior phrenic arteries (right and left), supplying blood to the diaphragm.

To the organs of the chest cavity (lungs, trachea, bronchi, esophagus, pericardium, etc.) visceral branches of the thoracic aorta.

TO parietal branches of the abdominal aorta include the inferior phrenic arteries and 4 lumbar arteries, which supply blood to the diaphragm, lumbar vertebrae, spinal cord, muscles and skin of the lumbar and abdominal areas.

Visceral branches of the abdominal aorta(Fig. 43) are divided into paired and unpaired. Paired branches go to the paired organs of the abdominal cavity: the adrenal glands - the middle adrenal artery, the kidneys - the renal artery, the testicles (or ovaries) - the testicular or ovarian artery. The unpaired branches of the abdominal aorta go to the unpaired organs of the abdominal cavity, mainly the organs of the digestive system. These include the celiac trunk, superior and inferior mesenteric arteries.

Rice. 43. Descending aorta and its branches.

Celiac trunk(Fig. 43) departs from the aorta at the level of the 12th thoracic vertebra and is divided into three branches: the left gastric, common hepatic and splenic arteries, supplying blood to the stomach, liver, gall bladder, pancreas, spleen, duodenum.

Superior mesenteric artery departs from the aorta at the level of the 1st lumbar vertebra, it gives branches to the pancreas, small intestine and the initial parts of the large intestine.

Inferior mesenteric artery arises from the abdominal aorta at the level of the 3rd lumbar vertebra, it supplies blood to the lower parts of the colon.

At the level of the 4th lumbar vertebra, the abdominal aorta divides into right and left common iliac arteries(Fig. 43). When bleeding from the underlying arteries, the trunk of the abdominal aorta is pressed against the spinal column in the umbilical region, which is located above its bifurcation. At the superior edge of the sacroiliac joint, the common iliac artery divides into the external and internal iliac arteries.

Internal iliac artery descends into the small pelvis, where it gives off parietal and visceral branches. The parietal branches go to the muscles of the lumbar region, gluteal muscles, spinal column and spinal cord, muscles and skin of the thigh, and hip joint. The visceral branches of the internal iliac artery supply blood to the pelvic organs and external genitalia.

Rice. 44. External iliac artery and its branches.

External iliac artery(Fig. 44) goes outward and downward, passes under the inguinal ligament through the vascular lacuna to the thigh, where it is called the femoral artery. The external iliac artery gives off branches to the muscles of the anterior abdominal wall and to the external genitalia.

Its continuation is femoral artery which runs in the groove between the iliopsoas and pectineus muscles. Its main branches supply blood to the muscles of the abdominal wall, the ilium, the muscles of the thigh and femur, the hip and partially knee joints, and the skin of the external genitalia. The femoral artery penetrates the popliteal fossa and continues into the popliteal artery.

Popliteal artery and its branches supply blood to the lower thigh muscles and the knee joint. It runs from the back of the knee joint to the soleus muscle, where it divides into the anterior and posterior tibial arteries, which supply the skin and muscles of the anterior and posterior muscle groups of the lower leg, knee and ankle joints. These arteries pass into the arteries of the foot: the anterior one into the dorsal (dorsal) artery of the foot, the posterior one into the medial and lateral plantar arteries.

The projection of the femoral artery onto the skin of the lower limb is shown along the line connecting the middle of the inguinal ligament with the lateral epicondyle of the femur; popliteal - along the line connecting the upper and lower corners of the popliteal fossa; anterior tibial - along the front surface of the lower leg; posterior tibial - from the popliteal fossa in the middle of the back surface of the leg to the inner ankle; dorsal artery of the foot - from the middle of the ankle joint to the first interosseous space; lateral and medial plantar arteries - along the corresponding edge of the plantar surface of the foot.

VEINS OF THE SYSTEMIC CIRCULATION

The venous system is a system of vessels through which blood returns to the heart. Venous blood flows through the veins from organs and tissues, excluding the lungs.

Most veins go along with arteries, many of them have the same names as arteries. The total number of veins is much greater than the number of arteries, so the venous bed is wider than the arterial bed. Each large artery is usually accompanied by one vein, and the medium and small ones are accompanied by two veins. In some areas of the body, such as the skin, the saphenous veins run independently without arteries and are accompanied by cutaneous nerves. The lumen of the veins is wider than the lumen of the arteries. In the wall of internal organs that change their volume, veins form venous plexuses.

The veins of the systemic circulation are divided into three systems:

1) the superior vena cava system;

2) the inferior vena cava system, including the portal vein system and

3) the system of cardiac veins, forming the coronary sinus of the heart.

The main trunk of each of these veins opens with an independent opening into the cavity of the right atrium. The superior and inferior vena cava anastomose with each other.

Rice. 45. Superior vena cava and its tributaries.

Superior vena cava system. Superior vena cava 5-6 cm long, located in the chest cavity in the anterior mediastinum. It is formed as a result of the confluence of the right and left brachiocephalic veins behind the junction of the cartilage of the first right rib with the sternum (Fig. 45). From here the vein descends along the right edge of the sternum and, at the level of the 3rd rib, flows into the right atrium. The superior vena cava collects blood from the head, neck, upper limbs, walls and organs of the chest cavity (except the heart), partly from the back and abdominal wall, i.e. from those areas of the body that are supplied with blood by the branches of the aortic arch and the thoracic part of the descending aorta.

Each brachiocephalic vein is formed as a result of the confluence of the internal jugular and subclavian veins (Fig. 45).

Internal jugular vein collects blood from the organs of the head and neck. In the neck it runs as part of the neurovascular bundle of the neck along with the common carotid artery and the vagus nerve. The tributaries of the internal jugular vein are external And anterior jugular veins, collecting blood from the covers of the head and neck. The external jugular vein is clearly visible under the skin, especially when straining or when the body is positioned head down.

Subclavian vein(Fig. 45) is a direct continuation of the axillary vein. It collects blood from the skin, muscles and joints of the entire upper limb.

Veins of the upper limb(Fig. 46) are divided into deep and superficial or subcutaneous. They form numerous anastomoses.

Rice. 46. ​​Veins of the upper limb.

The deep veins accompany the arteries of the same name. Each artery is accompanied by two veins. The exceptions are the veins of the fingers and the axillary vein, formed by the union of two brachial veins. All deep veins of the upper limb have numerous tributaries in the form of small veins that collect blood from the bones, joints and muscles of the areas in which they pass.

The saphenous veins include (Fig. 46) include lateral saphenous vein of the arm or cephalic vein(begins in the radial part of the dorsum of the hand, runs along the radial side of the forearm and shoulder and flows into the axillary vein); 2) medial saphenous vein of the arm or basilar vein(starts on the ulnar side of the dorsum of the hand, goes to the medial part of the anterior surface of the forearm, runs to the middle of the shoulder and flows into the brachial vein); and 3) intermediate vein of the elbow, which is an obliquely located anastomosis connecting the main and cephalic veins in the elbow area. This vein is of great practical importance, as it serves as a place for intravenous infusions of drugs, blood transfusions and taking it for laboratory tests.

Inferior vena cava system. Inferior vena cava- the thickest venous trunk in the human body, located in the abdominal cavity to the right of the aorta (Fig. 47). It is formed at the level of the 4th lumbar vertebra from the confluence of two common iliac veins. The inferior vena cava runs up and to the right, passes through the opening in the tendinous center of the diaphragm into the chest cavity and flows into the right atrium. Tributaries flowing directly into the inferior vena cava correspond to the paired branches of the aorta. They are divided into parietal veins and sternal veins (Fig. 47). TO parietal veins These include the lumbar veins, four on each side, and the inferior phrenic veins.

TO veins of the innards These include testicular (ovarian), renal, adrenal and hepatic veins (Fig. 47). Hepatic veins, flowing into the inferior vena cava, carry blood from the liver, where it enters through the portal vein and hepatic artery.

Portal vein(Fig. 48) is a thick venous trunk. It is located behind the head of the pancreas, its tributaries are the splenic, superior and inferior mesenteric veins. At the porta hepatis, the portal vein divides into two branches, which extend into the liver parenchyma, where they break up into many small branches intertwining the hepatic lobules; Numerous capillaries penetrate the lobules and ultimately form central veins, which gather into 3–4 hepatic veins, flowing into the inferior vena cava. Thus, the portal vein system, unlike other veins, is inserted between two networks of venous capillaries.

Rice. 47. The inferior vena cava and its tributaries.

Portal vein collects blood from all unpaired organs of the abdominal cavity, with the exception of the liver - from the organs of the gastrointestinal tract, where absorption of nutrients occurs, the pancreas and spleen. Blood flowing from the organs of the gastrointestinal tract enters the portal vein into the liver for neutralization and deposition in the form of glycogen; insulin comes from the pancreas, regulating sugar metabolism; from the spleen - breakdown products of blood elements enter, used in the liver to produce bile.

Common iliac veins, right and left, merging with each other at the level of the 4th lumbar vertebra, form the inferior vena cava (Fig. 47). Each common iliac vein at the level of the sacroiliac joint is composed of two veins: the internal iliac and external iliac.

Internal iliac vein lies behind the artery of the same name and collects blood from the pelvic organs, its walls, external genitalia, from the muscles and skin of the gluteal region. Its tributaries form a series of venous plexuses (rectal, sacral, vesical, uterine, prostatic), anastomosing among themselves.

Rice. 48. Portal vein.

As on the upper limb, veins of the lower limb divided into deep and superficial or subcutaneous, which pass independently of the arteries. The deep veins of the foot and leg are double and accompany the arteries of the same name. Popliteal vein, composed of all the deep veins of the leg, is a single trunk located in the popliteal fossa. Moving onto the thigh, the popliteal vein continues into femoral vein, which is located medially from the femoral artery. Numerous muscular veins flow into the femoral vein, draining blood from the thigh muscles. After passing under the inguinal ligament, the femoral vein becomes external iliac vein.

The superficial veins form a rather dense subcutaneous venous plexus, which collects blood from the skin and superficial layers of the muscles of the lower extremities. The largest superficial veins are small saphenous vein of the leg(starts on the outside of the foot, runs along the back of the leg and flows into the popliteal vein) and great saphenous vein of the leg(starts at the big toe, runs along its inner edge, then along the inner surface of the leg and thigh and flows into the femoral vein). The veins of the lower extremities have numerous valves that prevent the blood from flowing back.

One of the important functional adaptations of the body, associated with the great plasticity of blood vessels and ensuring uninterrupted blood supply to organs and tissues, is collateral circulation. Collateral circulation refers to the lateral, parallel flow of blood through the lateral vessels. It is performed in case of temporary difficulties in blood flow (for example, when blood vessels are compressed during movement in the joints) and in pathological conditions (with blockage, wounds, ligation of blood vessels during operations). The lateral vessels are called collaterals. When blood flow through the main vessels is difficult, blood rushes through anastomoses into the nearest lateral vessels, which expand and their wall is rebuilt. As a result, impaired blood circulation is restored.

The systems of venous blood outflow pathways are interconnected kava-kavalnymi(between the inferior and superior vena cava) and porta cavalry(between the portal and vena cava) anastomoses, which provide a roundabout flow of blood from one system to another. Anastomoses are formed by the branches of the superior and inferior vena cava and the portal vein - where the vessels of one system directly communicate with the other (for example, the venous plexus of the esophagus). Under normal conditions of body activity, the role of anastomoses is small. However, if there is difficulty in the outflow of blood through one of the venous systems, anastomoses take an active part in the redistribution of blood between the main outflow lines.

REGULARITIES OF DISTRIBUTION OF ARTERIES AND VEINS

The distribution of blood vessels in the body has certain patterns. The arterial system reflects in its structure the laws of the structure and development of the body and its individual systems (P.F. Lesgaft). Supplying blood to various organs, it corresponds to the structure, function and development of these organs. Therefore, the distribution of arteries in the human body follows certain patterns.

Extraorgan arteries. These include arteries that extend outside the organ before entering it.

1. Arteries are located along the neural tube and nerves. Thus, the main arterial trunk runs parallel to the spinal cord - aorta, each segment of the spinal cord corresponds segmental arteries. Arteries are initially laid down in connection with the main nerves, so later they go along with the nerves, forming neurovascular bundles, which also include veins and lymphatic vessels. There is a relationship between nerves and vessels that contributes to the implementation of a unified neurohumoral regulation.

2. According to the division of the body into organs of plant and animal life, the arteries are divided into parietal(to the walls of body cavities) and visceral(to their contents, i.e. to the insides). An example is the parietal and visceral branches of the descending aorta.

3. There is one main trunk to each limb - to the upper limb subclavian artery, to the lower limb – external iliac artery.

4. Most of the arteries are located according to the principle of bilateral symmetry: paired arteries of the soma and viscera.

5. The arteries follow the skeleton, which forms the basis of the body. Thus, the aorta runs along the spinal column, and the intercostal arteries run along the ribs. In the proximal parts of the limbs that have one bone (shoulder, femur) there is one main vessel (brachial, femoral arteries); in the middle sections, which have two bones (forearm, tibia), there are two main arteries (radial and ulnar, tibia and tibia).

6. Arteries travel the shortest distance, giving off branches to nearby organs.

7. Arteries are located on the flexor surfaces of the body, since during extension the vascular tube stretches and collapses.

8. The arteries enter the organ on a concave medial or internal surface facing the source of nutrition, therefore all the gates of the viscera are on a concave surface directed towards the midline, where the aorta lies, sending them branches.

9. The caliber of the arteries is determined not only by the size of the organ, but also by its function. Thus, the renal artery is not inferior in diameter to the mesenteric arteries, which supply blood to the long intestine. This is explained by the fact that it carries blood to the kidney, the urinary function of which requires a large blood flow.

Intraorgan arterial bed corresponds to the structure, function and development of the organ in which these vessels branch. This explains that in different organs the arterial bed is structured differently, but in similar organs it is approximately the same.

Vein distribution patterns:

1. In veins, blood flows in most of the body (torso and limbs) against the direction of gravity and therefore slower than in arteries. Its balance in the heart is achieved by the fact that the venous bed is much wider in mass than the arterial bed. The greater width of the venous bed compared to the arterial bed is ensured by the large caliber of the veins, paired accompanying arteries, the presence of veins that do not accompany the arteries, a large number of anastomoses and the presence of venous networks.

2. The deep veins accompanying the arteries, in their distribution, obey the same laws as the arteries they accompany.

3. Deep veins participate in the formation of neurovascular bundles.

4. Superficial veins, lying under the skin, accompany the cutaneous nerves.

5. In humans, due to the vertical position of the body, a number of veins have valves, especially in the lower extremities.

FEATURES OF BLOOD CIRCULATION IN THE FETUS

In the early stages of development, the embryo receives nutrients from the vessels of the yolk sac (auxiliary extra-embryonic organ) - vitelline circulation. Until 7-8 weeks of development, the yolk sac also performs the function of hematopoiesis. Further development placental circulation– oxygen and nutrients are delivered to the fetus from the mother’s blood through the placenta. It happens as follows. Arterial blood enriched with oxygen and nutrients comes from the mother's placenta to umbilical vein, which enters the fetal body at the navel and goes up to the liver. At the level of the portal of the liver, the vein divides into two branches, one of which flows into the portal vein, and the other into the inferior vena cava, forming the ductus venosus. The branch of the umbilical vein, which flows into the portal vein, delivers pure arterial blood through it; this is due to the hematopoietic function necessary for the developing organism, which predominates in the fetus in the liver and decreases after birth. After passing through the liver, the blood flows through the hepatic veins into the inferior vena cava.

Thus, all the blood from the umbilical vein enters the inferior vena cava, where it mixes with venous blood flowing through the inferior vena cava from the lower half of the fetal body.

Mixed (arterial and venous) blood flows through the inferior vena cava into the right atrium and through the foramen ovale, located in the atrial septum, into the left atrium, bypassing the still non-functioning pulmonary circle. From the left atrium, mixed blood enters the left ventricle, then into the aorta, along the branches of which it is directed to the walls of the heart, head, neck and upper extremities.

The superior vena cava and coronary sinus of the heart also flow into the right atrium. Venous blood entering through the superior vena cava from the upper half of the body then enters the right ventricle, and from the latter into the pulmonary trunk. However, due to the fact that in the fetus the lungs do not yet function as a respiratory organ, only a small part of the blood enters the lung parenchyma and from there through the pulmonary veins into the left atrium. Most of the blood from the pulmonary trunk enters directly into the aorta through batalov duct, which connects the pulmonary artery to the aorta. From the aorta, through its branches, blood enters the organs of the abdominal cavity and lower extremities, and through two umbilical arteries, passing as part of the umbilical cord, it enters the placenta, carrying with it metabolic products and carbon dioxide. The upper body (head) receives blood richer in oxygen and nutrients. The lower half is fed worse than the upper half and lags behind in its development. This explains the small size of the pelvis and lower extremities of the newborn.

Act of birth represents a leap in the development of the organism, during which fundamental qualitative changes in vital processes occur. The developing fetus moves from one environment (the uterine cavity with its relatively constant conditions: temperature, humidity, etc.) to another (the outside world with its changing conditions), as a result of which metabolism, feeding and breathing methods change. Nutrients previously received through the placenta now come from the digestive tract, and oxygen begins to come not from the mother, but from the air due to the work of the respiratory system. When you first inhale and stretch the lungs, the pulmonary vessels greatly expand and fill with blood. Then the batallus duct collapses and during the first 8-10 days it becomes obliterated, turning into the batallus ligament.

The umbilical arteries close during the first 2-3 days of life, the umbilical vein - after 6-7 days. The flow of blood from the right atrium to the left through the foramen ovale stops immediately after birth, as the left atrium fills with blood coming from the lungs. Gradually this hole closes. In cases of non-closure of the foramen ovale and the batallo duct, the child develops a congenital heart defect, which is the result of improper formation of the heart during the prenatal period.