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Human blood vessels. Large human vessels Features of the structure of blood vessels

Structure and functions of the vascular wall


Blood in the human body flows through a closed system blood vessels. Vessels not only passively limit the volume of circulation and mechanically prevent blood loss, but also have a whole range of active functions in hemostasis. Under physiological conditions, an intact vascular wall helps maintain the fluid state of the blood. Intact endothelium in contact with blood does not have the ability to initiate the coagulation process. In addition, it contains on its surface and releases into the bloodstream substances that prevent clotting. This property prevents the formation of a blood clot on intact endothelium and limits the growth of a blood clot beyond the damage. When damaged or inflamed, the vessel wall takes part in the formation of a blood clot. Firstly, subendothelial structures, which come into contact with blood only when damaged or a pathological process develops, have a powerful thrombogenic potential. Secondly, the endothelium in the damaged area is activated and appears


procoagulant properties. The structure of the vessels is shown in Fig. 2.

Vascular wall in all vessels, except pre-capillaries, capillaries and post-capillaries, it consists of three layers: the inner shell (intima), the middle shell (media) and the outer shell (adventitia).

Intimacy. Throughout the bloodstream in physiological conditions the blood comes into contact with the endothelium, which forms the inner layer of the intima. The endothelium, which consists of a monolayer of endothelial cells, plays the most active role in hemostasis. The properties of the endothelium vary slightly in different areas circulatory systems s, determining the different hemostatic status of arteries, veins and capillaries. Under the endothelium there is an amorphous intercellular substance with smooth muscle cells, fibroblasts and macrophages. There are also inclusions of lipids in the form of droplets, most often located extracellularly. At the border of the intima and media there is an internal elastic membrane.


Rice. 2. Vascular wall consists of intima, the luminal surface of which is covered with a single-layer endothelium, media (smooth muscle cells) and adventitia (connective tissue frame): A - large muscular-elastic artery ( schematic illustration), B - arterioles (histological specimen), B - coronary artery in cross section

Vascular wall


Media consists of smooth muscle cells and intercellular substance. Its thickness varies significantly depending on various vessels, causing their different contractility, strength and elasticity.

Adventitia consists of connective tissue containing collagen and elastin.


Arterioles (arterial vessels with a total diameter of less than 100 μm) are transitional vessels from arteries to capillaries. The thickness of the walls of arterioles is slightly less than the width of their lumen. The vascular wall of the largest arterioles consists of three layers. As arterioles branch, their walls become thinner and the lumen narrower, but the ratio of lumen width to wall thickness remains the same. In the smallest arterioles, on a cross section, one or two layers of smooth muscle cells, endothelial cells and a thin outer membrane consisting of collagen fibers are visible.

Capillaries consist of a monolayer of endothelial cells surrounded by a basal plate. In addition, another type of cell is found in the capillaries around endothelial cells - pericytes, the role of which is not well understood.

Capillaries open at their venous end into postcapillary venules (diameter 8-30 µm), which are characterized by an increase in the number of pericytes in the vascular wall. Postcapillary venules, in turn, flow into


collecting venules (diameter 30-50 μm), the wall of which, in addition to pericytes, has an outer shell consisting of fibroblasts and collagen fibers. Collecting venules empty into muscle venules, which have one or two layers of smooth muscle fibers in the middle shell. In general, venules consist of an endothelial lining, a basement membrane directly adjacent to the outside of the endothelial cells, and pericytes, also surrounded by a basement membrane; Outside the basement membrane there is a layer of collagen. Veins are equipped with valves that are oriented to allow blood to flow towards the heart. Most valves are in the veins of the extremities, and in the veins of the chest and organs abdominal cavity they are missing.

Vascular function in hemostasis:

Mechanical restriction of blood flow.

Regulation of blood flow through vessels, including
le spastic reaction damaged from
ships.

Regulation of hemostatic reactions by
synthesis and representation on the surface
dothelium and in the subendothelial layer of proteins,
peptides and non-protein substances, directly
directly involved in hemostasis.

Presentation on cell surface recipe
tors for enzymatic complexes,
treated with coagulation and fibrinolysis.

Endothelium

Characteristics of the enlothelial cover


The vascular wall has an active surface, with inside lined with endothelial cells. The integrity of the endothelial lining is the basis for the normal functioning of blood vessels. The surface area of ​​the endothelial lining in the vessels of an adult is comparable to the area of ​​a football field. The cell membrane of endothelial cells has high turnover what is an important condition antithrombogenic properties of the vascular wall. High fluidity ensures a smooth inner surface of the endothelium (Fig. 3), which functions as an integral layer and excludes contact of blood plasma procoagulants with subendothelial structures.

Endotheliocytes synthesize, present on their surface and release into the blood and subendothelial space a whole range of biologically active substances. These are proteins, peptides and non-protein substances that regulate hemostasis. In table Table 1 lists the main products of endothelial cells involved in hemostasis.


Vascular wall

The walls of large arteries and small arterioles consist of three layers. The outer layer consists of loose connective tissue containing elastic and collagen fibers. The middle layer is represented by smooth muscle fibers that can provide narrowing and expansion of the lumen of the vessel. Internal - formed by one layer of epithelium (endothelium) and lines the vascular cavity.

The diameter of the aorta is 25 mm, arteries - 4 mm, arterioles - 0.03 mm. The speed of blood movement in large arteries is up to 50 cm/s.

Blood pressure in arterial system pulsating. Normally, in the human aorta it is greatest at the time of heart systole and is equal to 120 mm Hg. Art., the smallest - at the time of heart diastole - 70-80 mm Hg. Art.

Despite the fact that the heart pumps blood into the arteries in portions, the elasticity of the artery walls ensures a continuous flow of blood through the vessels.

The main resistance to blood flow occurs in arterioles due to contraction of the annular muscles and narrowing of the lumen of blood vessels. Arterioles are a kind of “faucets” of the cardiovascular system. The expansion of their lumen increases blood flow into the capillaries of the corresponding area, improving local blood circulation, and narrowing sharply worsens blood circulation.

Blood flow in capillaries

Capillaries are the thinnest (diameter 0.005-0.007 mm) vessels consisting of single-layer epithelium. They are located in the intercellular spaces, closely adjacent to the cells of tissues and organs. Such contact with the cells of organs and tissues allows for rapid exchange between the blood in the capillaries and the intercellular fluid. This is also facilitated by the low speed of blood movement in the capillaries, equal to 0.5-1.0 mm/s. The capillary wall has pores through which water and low molecular weight substances dissolved in it - inorganic salts, glucose, oxygen, etc. - can easily pass from blood plasma to tissue fluid at the arterial end of the capillary.

Blood flow in veins

The blood, having passed through the capillaries and enriched with carbon dioxide and other metabolic products, enters the venules, which, merging, form larger venous vessels. They carry blood to the heart due to the action of several factors:

  1. differences in pressure in the veins and in the right atrium;
  2. contraction of skeletal muscles, leading to rhythmic compression of the veins;
  3. negative pressure in chest cavity when inhaling, which promotes the outflow of blood from large veins to the heart;
  4. the presence of valves in the veins that prevent blood from flowing in the opposite direction.

The diameter of the vena cava is 30 mm, the veins are 5 mm, and the venules are 0.02 mm. The walls of the veins are thin, easily extensible, as they have a poorly developed muscle layer. Under the influence of gravity, blood in the veins of the lower extremities tends to stagnate, which causes varicose veins veins The speed of blood movement through the veins is 20 cm/s or less.

In maintaining normal blood flow from the veins to the heart big role muscle activity plays a role.

Structure of the vascular wall: endothelium, muscle and connective tissue

Vascular wall consists of three main structural components: endothelium, muscle and connective tissue, including elastic elements.

On the content and location of these fabrics the blood vessel system is influenced by mechanical factors, represented primarily by blood pressure, as well as metabolic factors that reflect the local needs of tissues. All these tissues are present in varying proportions in the vascular wall, with the exception of the wall of capillaries and postcapillary venules, in which the only structural elements present are the endothelium, its basal lamina and pericytes.

Vascular endothelium

Endothelium represents special type epithelium, which forms a semipermeable barrier between two compartments internal environment- blood plasma and interstitial fluid. The endothelium is a highly differentiated tissue capable of actively mediating and controlling extensive two-way exchange of small molecules and limiting the transport of certain macromolecules.

In addition to your roles In the exchange between blood and surrounding tissues, endothelial cells perform a number of other functions.
1. Conversion of angiotensin I (Greek angeion - vessel + tendere - to strain) into angiotensin II.
2. Conversion of bradykinin, serotonin, prostaglandins, norepinephrine, thrombin and other substances into biologically inert compounds.
3. Lipolysis of lipoproteins by enzymes located on the surface of endothelial cells, with the formation of triglycerides and cholesterol (substrates for the synthesis steroid hormones and membrane structures).

Angiology is the study of blood vessels.

Muscular artery (left) stained with hematoxylin and eosin and elastic artery (right) stained using the Weigert method (pictures). The tunica media of the muscular artery contains predominantly smooth muscle tissue, whereas the tunica media of the elastic artery is composed of layers of smooth muscle cells alternating with elastic membranes. In the adventitia and the outer part of the tunica media there are small blood vessels (vasa vasorum), as well as elastic and collagen fibers.

4. Production of vasoactive factors affecting vascular tone, such as endothelins, vasoconstrictors and nitric oxide - a relaxation factor.
Factors growth, such as vascular endothelial growth factors (VEGF), play a leading role in the formation of the vascular system during embryonic development, in the regulation of capillary growth under normal and pathological conditions in adults, as well as in maintaining the normal state of the vascular bed.

It should be noted that endothelial cells are functionally different depending on the vessel they line.

The endothelium also has antithrombogenic properties and prevents blood clotting. When endothelial cells are damaged, for example, in vessels affected by atherosclerosis, subendothelial connective tissue not covered by endothelium induces aggregation of blood platelets. This aggregation triggers a cascade of events, as a result of which fibrin is formed from blood fibrinogen. In this case, an intravascular blood clot, or a blood clot, which can grow until local blood flow is completely disrupted.

Dense pieces can separate from such a blood clot - emboli, - which are carried away with the bloodstream and can disrupt the patency of distant blood vessels. In both cases, blood flow may stop, resulting in a potentially life-threatening condition. Thus, the integrity of the endothelial layer, which prevents contact between platelets and subendothelial connective tissue, is a critical antithrombogenic mechanism.

Vascular smooth muscle tissue

Smooth muscle tissue present in all vessels, with the exception of capillaries and pericytic venules. Smooth muscle cells are numerous and arranged in spiral layers in the medial lining of blood vessels. Each muscle cell is surrounded by a basal lamina and a variable amount of connective tissue; both components are produced by the cell itself. Vascular smooth muscle cells, mainly in arterioles and small arteries, are often connected by communicative (gap) junctions.

Vascular connective tissue

Connective tissue present in the walls of blood vessels, and the quantity and proportions of its components vary significantly depending on local functional needs. Collagen fibers, an element ubiquitous in the wall of the vascular system, are found between the muscle cells of the tunica media, in the adventitia, and also in some subendothelial layers. Types IV, III and I collagens are present in basement membranes, tunica media and adventitia, respectively.

Elastic fibers provide elasticity during compression and stretching of the vascular wall. These fibers predominate in large arteries, where they are assembled into parallel membranes that are evenly distributed between muscle cells throughout the tunica media. The main substance forms a heterogeneous gel in the intercellular spaces of the vascular wall. It makes a certain contribution to the physical properties of the walls of blood vessels and probably affects their permeability and the diffusion of substances through them. The concentration of glycosaminoglycans is higher in the tissue of the arterial wall compared to that in the veins.

With aging, the intercellular substance undergoes disorganization due to increased production of collagen types I and III and some glycosaminoglycans. Changes in the molecular conformation of elastin and other glycoproteins also occur, resulting in the deposition of lipoproteins and calcium ions into the tissue, followed by calcification. Changes in the components of the intercellular substance associated with other more complex factors, can lead to the formation of an atherosclerotic plaque.

  1. Innervation of skeletal muscles. Mechanisms
  2. Muscle spindles and Golgi tendon organs. Histology
  3. Cardiac muscle: structure, histology
  4. Smooth muscle tissue: structure, histology
  5. Regeneration muscle tissue. Mechanisms of muscle healing
  6. Structure of the cardiovascular system. Microvasculature vessels
  7. Structure of the vascular wall: endothelium, muscle and connective tissue
  8. Tunica of blood vessels: intima, tunica media, adventitia
  9. Innervation of blood vessels
  10. Elastic arteries: structure, histology

Human cardiovascular system

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Types of Blood Vessels

All blood vessels in the human body are divided into two categories: vessels through which blood flows from the heart to organs and tissues ( arteries), and vessels through which blood returns from organs and tissues to the heart ( veins). The largest blood vessel in the human body is the aorta, which emerges from the left ventricle of the heart muscle. This is not surprising, since this is the “main pipe” through which the blood flow is pumped, supplying the entire body with oxygen and nutrients. The largest veins, which “collect” all the blood from organs and tissues before sending it back to the heart, form the superior and inferior vena cava, which enter the right atrium.

Between the veins and arteries there are smaller blood vessels: arterioles, precapillaries, capillaries, postcapillaries, venules. The actual exchange of substances between blood and tissues occurs in the so-called microcircular zone, which is formed by the small blood vessels listed earlier. As mentioned earlier, the transfer of substances from the blood to the tissues and back occurs due to the fact that the walls of the capillaries have microholes through which the exchange takes place.

The farther from the heart and closer to any organ, large blood vessels are divided into smaller ones: large arteries are divided into medium ones, which, in turn, are divided into small ones. This division can be compared to a tree trunk. At the same time, the arterial walls have complex structure, they have several membranes that ensure the elasticity of the vessels and the continuous movement of blood through them. From the inside, the arteries resemble rifled firearms - they are lined from the inside with spiral-shaped muscle fibers that form a swirling blood flow, allowing the walls of the arteries to withstand blood pressure, created by the heart muscle during systole.

All arteries are classified into muscular(arteries of the limbs), elastic(aorta), mixed(carotid arteries). The greater the need of a particular organ for blood supply, the larger the artery that approaches it. The most “gluttonous” organs in the human body are the brain (consumes the most oxygen) and the kidneys (pump large volumes of blood).

As mentioned above, large arteries are divided into medium ones, which are divided into small ones, etc., until the blood enters the smallest blood vessels - capillaries, where, in fact, metabolic processes take place - oxygen is given to tissues, which are released into the blood carbon dioxide, after which the capillaries gradually collect into veins, which deliver oxygen-poor blood to the heart.

Veins have a fundamentally different structure, unlike arteries, which, in general, is logical, since veins perform a completely different function. The walls of the veins are more fragile, the number of muscle and elastic fibers in them is much less, they lack elasticity, but they stretch much better. The only exception is portal vein, which has its own muscular membrane, which led to its second name - arterial vein. The speed and pressure of blood flow in the veins is much lower than in the arteries.

Unlike arteries, the diversity of veins in the human body is much higher: the main veins are called main veins; veins extending from the brain are villous; from the stomach - plexus-shaped; from the adrenal gland - throttle; from the guts - arcade, etc. All veins, except the main ones, form plexuses that envelop “their” organ from the outside or inside, thereby creating the most effective opportunities for blood redistribution.

Another distinctive feature of the structure of veins from arteries is the presence in some veins of internal valves, which allow blood to flow in only one direction - to the heart. Also, if the movement of blood through the arteries is ensured only by the contraction of the heart muscle, then the movement of venous blood is ensured as a result of the suction action chest, contractions of the thigh muscles, muscles of the leg and heart.

The largest number of valves is found in the veins of the lower extremities, which are divided into superficial (great and small saphenous veins) and deep (paired veins connecting arteries and nerve trunks). Between themselves, superficial and deep veins interact with the help of communicating veins that have valves that ensure the movement of blood from the superficial veins to the deep ones. It is the incompetence of the communicating veins that, in the vast majority of cases, is the cause of the development of varicose veins.

The great saphenous vein is the longest vein in the human body - its internal diameter reaches 5 mm, with 6-10 pairs of valves. Blood flow from the surfaces of the legs passes through the small saphenous vein.

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ANATOMY OF THE VASCULAR SYSTEM.

The branch of anatomy that studies blood vessels is called angiology. Angiology - the study of vascular system, which transports fluids in closed tubular systems: circulatory and lymphatic.

The circulatory system includes the heart and blood vessels. Blood vessels are divided into arteries, veins, and capillaries. Blood circulates in them. The lungs are connected to the circulatory system, providing oxygenation of the blood and removing carbon dioxide; the liver neutralizes toxic metabolic products contained in the blood and processes some of them; endocrine glands, releasing hormones into the blood; kidneys, which remove non-volatile substances from the blood and hematopoietic organs, which replenish lost blood elements.

Thus, the circulatory system ensures metabolism in the body, carries oxygen and nutrients, hormones and mediators in all organs and tissues; removes excretory products: carbon dioxide - through the lungs and aqueous solutions nitrogen waste – through the kidneys.

The central organ of the circulatory system is the heart. Knowledge of the anatomy of the heart is very important. Among the causes of death, cardiovascular diseases are in first place.

The heart is a hollow muscular four-chambered organ. It has two atria and two ventricles. The right atrium and right ventricle are called the right venous heart, containing venous blood. The left atrium and left ventricle are the arterial heart containing arterial blood. Normally, the right half of the heart does not communicate with the left. Between the atria is the interatrial septum, between the ventricles is the interventricular septum. The heart functions as a pump that moves blood throughout the body.

The vessels coming from the heart are called arteries, and those going to the heart are called veins. The veins flow into the atrium, that is, the atria receive blood. Blood is expelled from the ventricles.

Heart development.

The human heart in ontogenesis repeats phylogeny. Protozoa and invertebrates (molluscs) have an open circulatory system. In vertebrates, the main evolutionary changes in the heart and blood vessels are associated with the transition from the gill type of respiration to the pulmonary type. The heart of fish is two-chambered, in amphibians it is three-chambered, in reptiles, birds, and mammals it is four-chambered.

The human heart is formed at the embryonic shield stage, in the form of paired large vessels and consists of two epithelial rudiments arising from the mesenchyme. They are formed in the region of the cardiogenic plate located under the cranial end of the embryonic body. In the condensed mesoderm of the splanchnopleura, two longitudinally located endodermal tubes arise on the sides of the head gut. They are invaginated into the anlage of the pericardial cavity. As the embryonic shield transforms into a cylindrical body, both anlages come closer to each other and they merge with each other, the wall between them disappears, and a single straight heart tube is formed. This stage is called the simple tubular heart stage. Such a heart is formed by day 22 intrauterine development when the tube begins to pulsate. In a simple tubular heart, three sections are distinguished, separated by small grooves:

1. The cranial part is called the bulb of the heart and turns into an arterial trunk, which forms two ventral aortas. They bend in an arcuate manner and continue into the two dorsal descending aortas.

2) The caudal part is called the venous section and continues into

3) Venous sinus.

The next stage is the sigmoid heart. It is formed as a result of uneven growth of the heart tube. At this stage, there are 4 sections in the heart:

1) venous sinus– where the umbilical and vitelline veins drain;

2) venous section;

3) arterial section;

4) arterial trunk.

Stage of two-chamber heart.

The venous and arterial sections grow greatly, a constriction (deep) appears between them, at the same time, from the venous section, which is the common atrium, two outgrowths are formed - the future cardiac ears, which cover the arterial trunk on both sides. Both knees of the arterial section grow together, the wall separating them disappears and a common ventricle is formed. Both chambers are connected to each other by a narrow and short auricular duct. At this stage, in the venous sinus, in addition to the umbilical and vitelline veins, two pairs of cardiac veins flow into the sinus, that is, the big circle blood circulation At the 4th week of embryonic development, a fold appears on the inner surface of the common atrium, growing downwards and the primary interatrial septum is formed.

At week 6, an oval hole forms on this septum. At this stage of development, each atrium is connected by a separate opening to a common ventricle - the stage of a three-chambered heart.

At 8 weeks to the right of the primary interatrial septum a secondary one grows, in which there is a secondary oval foramen. It does not coincide with the primary one. This ensures blood flows in one direction, from the right atrium to the left. After birth, both septa fuse with each other and an oval fossa remains in place of the holes. The common ventricular cavity at the 5th week of embryonic development is divided into two halves with the help of a septum growing from below, towards the atria. It does not reach the atrium completely. The final function of the interventricular septum occurs after the arterial trunk is divided into 2 sections by the frontal septum: the pulmonary trunk and the aorta. After this, the continuation of the interatrial septum downwards connects with interventricular septum and the heart becomes four-chambered.

Disturbances in the embryonic development of the heart are associated with the occurrence of birth defects heart and large vessels. Congenital defects account for 1-2% of all defects. According to statistics, they are found from 4 to 8 per 1000 children. In children, congenital defects account for 30% of all congenital malformations. The vices are varied. They can be isolated or in various combinations.

There is an anatomical classification of congenital defects:

1) anomaly of the location of the heart;

2) vices anatomical structure heart (ASD, VSD)

3) defects of the great vessels of the heart ( open Batalov duct, coartation of the aorta);

4) anomalies of the coronary arteries;

5) combined defects (triads, pentads).

A newborn's heart has rounded shape. The heart grows especially intensively during the first year of life (more in length), the atria grow faster. Up to 6 years, the atria and ventricles grow at the same rate; after 10 years, the ventricles grow faster. By the end of the first year, the mass doubles, at 4-5 years - three times, at 9-10 years - five times, at 16 years - 10 times.

The myocardium of the left ventricle grows faster; at the end of the second year it is twice as thick. In children of the first year of life, the heart is located high and transversely, and then obliquely longitudinally.

Aristotle knew about the existence of such “blood receivers” as atreria and veins. According to the ideas of this time. according to their name, the arteries were supposed to contain only air, which was confirmed by the fact that the arteries of corpses usually turned out to be bloodless.

Arteries are vessels that carry blood from the heart. Anatomically, arteries of large, medium and small calibers and arterioles are distinguished. The arterial wall consists of 3 layers:

1) Internal - intima, consists of endothelium (flat cells) located on the subendothelial plate, which has an internal elastic membrane.

2) Medium - media

3) The outer layer is adventitia.

Depending on the structure of the middle layer, arteries are divided into 3 types:

Elastic arteries (aorta and pulmonary trunk) media consist of elastic fibers, which gives these vessels the elasticity necessary for the high pressure that develops during the ejection of blood.

2. Arteries mixed type- media consists of different quantities elastic fibers and smooth myocytes.

3. Arteries of the muscular type - the media consists of circularly located individual myocytes.

According to topography, arteries are divided into main, organ and intraorgan arteries.

The main arteries supply blood to individual parts of the body.

Organ - enrich individual organs with blood.

Intraorgan - they branch inside organs.

Arteries branching from the main organ vessels are called branches. There are two types of branching of arterial vessels.

1) main

2) loose

It depends on the structure of the organ. The topography of the arteries is not random, but regular. The laws of arterial topography were formulated by Lesgaft in 1881 under the title “General Laws of Angiology.” These have been supplemented subsequently:

1. Arteries are directed to organs along the shortest path.

2. The arteries in the limbs run on the flexor surface.

3. Arteries approach organs from their internal side, that is, from the side facing the source of blood supply. They enter the organs through the gate.

4. There is a correspondence between the skeletal plan and the structure of blood vessels. In the area of ​​the joints, arteries form arterial networks.

5. The number of arteries supplying blood to one organ depends not on the size of the organ, but on its function.

6. Inside organs, the division of arteries corresponds to the division plan of the organ. In lobular arteries there are interlobar arteries.

Vienna- vessels that carry blood to the heart. In most veins, blood flows against gravity. The speed of blood flow is slower.

Human circulatory system

The balance of venous blood of the heart with arterial blood is generally achieved by the fact that the venous bed is wider than the arterial bed due to the following factors:

1) larger number veins

2) larger caliber

3) high density of the venous network

4) formation of venous plexuses and anastomoses.

Venous blood flows to the heart through the superior and inferior vena cava and the coronary sinus. And it flows through one vessel - the pulmonary trunk. In accordance with the division of organs into vegetative and somatic (animal) veins, there are parietal and visceral.

On the extremities, veins are deep and superficial. The patterns of location of deep veins are the same as arteries. They go in one bundle along with arterial trunks, nerves and lymphatic vessels. Superficial veins accompanied by cutaneous nerves.

The veins of the body walls have a segmental structure

The veins follow the pattern of the skeleton.

Superficial veins contact the saphenous nerves

Veins in internal organs that change their volume form venous plexuses.

Differences between veins and arteries.

1) in shape - the arteries have a more or less regular cylindrical shape, and the veins either narrow or expand in accordance with the valves located in them, that is, they have a tortuous shape. The arteries are round in diameter, and the veins are flattened due to compression by neighboring organs.

2) According to the structure of the wall - in the wall of arteries smooth muscle well developed, more elastic fibers, thicker wall. Veins are thinner-walled because they have less blood pressure.

3) In terms of number, there are more veins than arteries. Most arteries of medium caliber are accompanied by two veins of the same name.

4) The veins form numerous anastomoses and plexuses among themselves, the significance of which is that they fill the space vacated in the body under certain conditions (emptying of hollow organs, changes in body position)

5) The total volume of veins is approximately twice that of arteries.

6) Availability of valves. Most veins have valves, which are a semilunar duplicate of the inner lining of the veins (intima). Smooth muscle bundles penetrate the base of each valve. The valves are located in pairs opposite each other, especially where some veins flow into others. The importance of valves is that they prevent blood from flowing back.

There are no valves in the following veins:

Vena cava

Portal veins

Brachiocephalic veins

Iliac veins

Veins of the brain

Veins of the heart parenchymal organs, red bone marrow

In the arteries, blood moves under the pressure of the ejected force of the heart, at the beginning the speed is higher, about 40 m/s, and then slows down.

The movement of blood in the veins is ensured by the following factors: this is the force of constant pressure, which depends on the push of the blood column from the heart and arteries, etc.

Supporting factors include:

1) the suction force of the heart during diastole - expansion of the atria due to which negative pressure is created in the veins.

2) the suction effect of the respiratory movements of the chest on the veins of the chest

3) muscle contraction, especially in the limbs.

Blood not only flows in the veins, but is also stored in the venous depots of the body. 1/3 of the blood is in the venous depots (spleen up to 200 ml, in the veins gate system up to 500 ml), in the walls of the stomach, intestines and skin. Blood from the venous depots is pushed out as needed - to increase blood flow during increased physical activity or large volume of blood loss.

The structure of capillaries.

Their total number is about 40 billion. The total area is about 11 thousand cm 2. capillaries have a wall consisting only of endothelium. The number of capillaries is not the same in various areas bodies. Not all capillaries are in the same working condition; some of them are closed and will fill with blood as needed. The sizes and diameter of capillaries are from 3-7 microns or more. The narrowest capillaries are in the muscles, and the widest are in the skin and mucous membranes of internal organs (in the organs of the immune and circulatory systems). The widest capillaries are called sinusoids

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Types of blood vessels, features of their structure and function.

Rice. 1. Human blood vessels (front view):
1 - dorsal artery of the foot; 2 - anterior tibial artery (with accompanying veins); 3 - femoral artery; 4 - femoral vein; 5 - superficial palmar arch; 6 - right external iliac artery and right external iliac vein; 7-right internal iliac artery and right internal iliac vein; 8 - anterior interosseous artery; 9 - radial artery (with accompanying veins); 10 - ulnar artery (with accompanying veins); 11 - lower vena cava; 12 - superior mesenteric vein; 13 - right renal artery and right renal vein; 14 - portal vein; 15 and 16 - saphenous veins of the forearm; 17- brachial artery (with accompanying veins); 18 - superior mesenteric artery; 19 - right pulmonary veins; 20 - right axillary artery and right axillary vein; 21 - right pulmonary artery; 22 - superior vena cava; 23 - right brachiocephalic vein; 24 - right subclavian vein and right subclavian artery; 25 - right general carotid artery; 26 - right inner jugular vein; 27 - external carotid artery; 28 - internal carotid artery; 29 - brachiocephalic trunk; 30 - external jugular vein; 31 - left common carotid artery; 32 - left internal jugular vein; 33 - left brachiocephalic vein; 34 - left subclavian artery; 35 - aortic arch; 36 - left pulmonary artery; 37 - pulmonary trunk; 38 - left pulmonary veins; 39 - ascending aorta; 40 - hepatic veins; 41 - splenic artery and vein; 42 - celiac trunk; 43 - left renal artery and left renal vein; 44 - inferior mesenteric vein; 45 - right and left artery testicle (with accompanying veins); 46 - inferior mesenteric artery; 47 - median vein of the forearm; 48 - abdominal aorta; 49 - left common iliac artery; 50 - left common iliac vein; 51 - left internal iliac artery and left internal iliac vein; 52 - left external iliac artery and left external iliac vein; 53 - left femoral artery and left femoral vein; 54 - venous palmar network; 55 - great saphenous (hidden) vein; 56 - small saphenous (hidden) vein; 57 - venous network of the dorsum of the foot.

Rice. 2. Human blood vessels (back view):
1 - venous network of the dorsum of the foot; 2 - small saphenous (hidden) vein; 3 - femoral-popliteal vein; 4-6 - venous network of the rear of the hand; 7 and 8 - saphenous veins of the forearm; 9 - posterior auricular artery; 10 - occipital artery; 11 - superficial cervical artery; 12 - transverse artery of the neck; 13 - suprascapular artery; 14 - posterior circumflex shoulder artery; 15 - artery circumflexing the scapula; 16 - deep brachial artery (with accompanying veins); 17 - posterior intercostal arteries; 18 - superior gluteal artery; 19 - inferior gluteal artery; 20 - posterior interosseous artery; 21 - radial artery; 22 - dorsal carpal branch; 23 - perforating arteries; 24 - external superior artery knee joint; 25 - popliteal artery; 26-popliteal vein; 27-outer inferior artery knee joint; 28 - posterior tibial artery (with accompanying veins); 29 - peroneal artery.

Arteries are blood vessels through which blood flows from the heart to organs and parts of the body. Arteries have thick walls consisting of three layers. The outer layer is represented by a connective tissue membrane and is called adventitia. The middle layer, or media, consists of smooth muscle tissue and contains connective tissue elastic fibers. The inner layer, or intima, is formed by the endothelium, under which there is a subendothelial layer and an internal elastic membrane. Elastic elements arterial wall form a single frame that works like a spring and determines the elasticity of the arteries. Depending on the organs and tissues supplied with blood, arteries are divided into parietal (parietal), which supply blood to the walls of the body, and visceral (visceral), which supply blood to internal organs. Before an artery enters an organ, it is called extraorgan; after entering an organ, it is called intraorgan, or intraorgan.

Depending on the development of the various layers of the wall, arteries of the muscular, elastic or mixed type are distinguished. Arteries of the muscular type have a well-developed middle tunica, the fibers of which are arranged spirally like a spring. These vessels include small arteries. Mixed arteries have approximately equal numbers of elastic and muscle fibers in their walls. These are the carotid, subclavian and other arteries of medium diameter. Elastic arteries have a thin outer shell and a thicker inner shell. They are represented by the aorta and pulmonary trunk, into which blood flows under high pressure. Lateral branches of one trunk or branches of different trunks can connect to each other. This connection of arteries before they break up into capillaries is called anastomosis, or anastomosis. The arteries that form anastomoses are called anastomosing (they are the majority). Arteries that do not have anastomoses are called terminal (for example, in the spleen). Terminal arteries are more easily clogged by a thrombus and are predisposed to the development of a heart attack.

After the birth of a child, the circumference, diameter, wall thickness and length of the arteries increase, and the level of discharge also changes arterial branches from the main vessels. Difference between diameter main arteries and their branches are small at first, but increase with age. The diameter of the main arteries grows faster than their branches. With age, the circumference of the arteries also increases, their length increases in proportion to the growth of the body and limbs. The levels of branches from the main arteries in newborns are located more proximally, and the angles at which these vessels depart are greater in children than in adults. The radius of curvature of the arcs formed by the vessels also changes. In proportion to the growth of the body and limbs and the increase in the length of the arteries, the topography of these vessels changes. As age increases, the type of branching of arteries changes: mainly from scattered to main. The formation, growth, tissue differentiation of vessels of the intraorgan bloodstream in various human organs occurs unevenly during ontogenesis. The wall of the arterial part of the intraorgan vessels, in contrast to the venous part, already has three membranes at the time of birth. After birth, the length and diameter of intraorgan vessels, the number of anastomoses, and the number of vessels per unit volume of the organ increase. This occurs especially intensively before the age of one year and from 8 to 12 years.

The smallest branches of the arteries are called arterioles. They differ from arteries in the presence of only one layer of muscle cells, thanks to which they perform a regulatory function. The arteriole continues into the precapillary, in which the muscle cells are scattered and do not form a continuous layer. The precapillary is not accompanied by a venule. Numerous capillaries extend from it.

At the points of transition of one type of vessel to another, smooth muscle cells are concentrated, forming sphincters that regulate blood flow at the microcirculatory level.

Capillaries are the smallest blood vessels with a lumen from 2 to 20 microns. The length of each capillary does not exceed 0.3 mm. Their number is very large: for example, there are several hundred capillaries per 1 mm2 of tissue. The total lumen of the capillaries of the whole body is 500 times larger than the lumen of the aorta. In the resting state of the organ, most of the capillaries do not function and the blood flow in them stops. The capillary wall consists of a single layer of endothelial cells. The surface of the cells facing the lumen of the capillary is uneven and folds form on it. This promotes phagocytosis and pinocytosis. There are feeding and specific capillaries. Feeding capillaries provide the organ with nutrients, oxygen and remove metabolic products from the tissues. Specific capillaries help the organ perform its functions (gas exchange in the lungs, excretion in the kidneys). Merging, the capillaries pass into postcapillaries, which are similar in structure to the precapillary. Postcapillaries merge into venules with a lumen of 4050 µm.

Veins are blood vessels that carry blood from organs and tissues to the heart. They, like arteries, have walls consisting of three layers, but contain fewer elastic and muscle fibers, therefore they are less elastic and collapse easily. Veins have valves that open as the blood flows, allowing blood to flow in one direction. The valves are semilunar folds of the inner membrane and are usually located in pairs at the confluence of two veins. In the veins lower limb blood moves against gravity, muscularis propria better developed and valves are more common. They are absent in the vena cava (hence their name), the veins of almost all internal organs, the brain, head, neck and small veins.

Arteries and veins usually go together, with large arteries supplied by one vein, and medium and small ones by two companion veins that anastomose with each other many times. As a result total capacity veins are 10-20 times larger than the volume of arteries. Superficial veins going to subcutaneous tissue, do not accompany the arteries. Veins, together with the main arteries and nerve trunks, form neurovascular bundles. According to their function, blood vessels are divided into pericardial, main and organ. The pericardium begins and ends both circles of blood circulation. These are the aorta, pulmonary trunk, vena cava and pulmonary veins. Main vessels serve to distribute blood throughout the body. These are large extraorgan arteries and veins. Organ vessels provide exchange reactions between blood and organs.

By the time of birth, the vessels are well developed, and the arteries are larger than the veins. The structure of blood vessels changes most intensively between the ages of 1 and 3 years. At this time, the middle shell is intensively developing, the final shape and size of the blood vessels are formed by 1418. Starting from 40-45 years, the inner membrane thickens, fat-like substances are deposited in it, and atherosclerotic plaques appear. At this time, the walls of the arteries become sclerotic, and the lumen of the vessels decreases.

General characteristics of the respiratory system. Fetal breathing. Pulmonary ventilation in children of different ages. Age-related changes depth, respiratory rate, vital capacity of the lungs, regulation of breathing.

The respiratory organs provide the body with oxygen necessary for oxidation processes and the release of carbon dioxide, which is the final product. metabolic processes. The need for oxygen is more important for humans than the need for food or water. Without oxygen, a person dies within 57 minutes, while without water he can live up to 710 days, and without food - up to 60 days. Cessation of breathing leads to the death of first of all nerve cells and then other cells. There are three main processes in breathing: the exchange of gases between the environment and the lungs ( external breathing), exchange of gases in the lungs between alveolar air and blood, exchange of gases between blood and interstitial fluid (tissue respiration).

The inhalation and exhalation phases make up the respiratory cycle. The volume of the thoracic cavity changes due to contractions of the inspiratory and expiratory muscles. The main inspiratory muscle is the diaphragm. During a quiet inhalation, the dome of the diaphragm lowers by 1.5 cm. The inspiratory muscles also include the external oblique intercostal and intercartilaginous muscles, with the contraction of which the ribs rise, the sternum moves forward, and the lateral parts of the ribs move to the sides. With very deep breathing, a number of auxiliary muscles are involved in the act of inhalation: sternocleidomastoid, scalene, pectoralis major and minor, serratus anterior, as well as muscles that extend the spine and fix the shoulder girdle (trapezius, rhomboid, levator scapula).

During active exhalation, muscles contract abdominal wall(oblique, transverse and straight), as a result, the volume of the abdominal cavity decreases and the pressure in it increases, it is transmitted to the diaphragm and raises it. Due to the contraction of the internal oblique and intercostal muscles, the ribs descend and move closer together. Accessory expiratory muscles include the spinal flexor muscles.

The respiratory tract is formed by the nasal cavity, nasal and oropharynx, larynx, trachea, bronchi of various calibers, including bronchioles.

Blood circulates throughout the body using complex system blood vessels. This transport system delivers blood to every cell in the body so it can “exchange” oxygen and nutrients for waste products and carbon dioxide.

Some numbers

There are more than 95 thousand kilometers of blood vessels in the body of a healthy adult. More than seven thousand liters of blood are pumped through them every day.

Blood vessel size varies from 25 mm(aortic diameter) up to eight microns(capillary diameter).

What types of vessels are there?

All vessels in human body can be roughly divided into arteries, veins and capillaries. Despite the difference in size, all vessels are constructed approximately the same.

The inside of their walls are lined with flat cells - endothelium. With the exception of capillaries, all vessels contain tough and elastic collagen fibers and smooth muscle fibers that can contract and dilate in response to chemical or nerve stimuli.

Arteries carry oxygen-rich blood from the heart to tissues and organs. This blood is bright red, so all the arteries look red.

Blood moves through arteries with great strength, so their walls are thick and elastic. They consist of large quantity collagen, which allows them to withstand blood pressure. The presence of muscle fibers helps turn the intermittent blood supply from the heart into a continuous flow to the tissues.

As they move away from the heart, the arteries begin to branch, and their lumen becomes thinner and thinner.

The most thin vessels, delivering blood to every corner of the body - these are capillaries. Unlike arteries, their walls are very thin, so oxygen and nutrients can pass through them into the cells of the body. The same mechanism allows waste products and carbon dioxide move from cells into the bloodstream.

The capillaries through which oxygen-poor blood flows are collected into thicker vessels - veins. Due to lack of oxygen venous blood is darker than arterial, and the veins themselves appear bluish. Through them, blood flows to the heart and from there to the lungs to be enriched with oxygen.

Vein walls are thinner than arterial walls because venous blood does not create as much pressure as arterial blood.

What are the largest vessels in the human body?

The two largest veins in the human body are inferior vena cava and superior vena cava. They bring blood to the right atrium: the superior vena cava from the upper part of the body, and the inferior vena cava from the lower.

Aorta- the largest artery of the body. It leaves the left ventricle of the heart. Blood enters the aorta through the aortic canal. The aorta branches into large arteries that carry blood throughout the body.

What is blood pressure?

Blood pressure is the force with which blood presses against the walls of the arteries. It increases when the heart contracts and pumps out blood, and decreases when the heart muscle relaxes. Blood pressure is stronger in the arteries and weaker in the veins.

Blood pressure is measured with a special device - tonometer. Pressure readings are usually recorded in two numbers. Thus, normal blood pressure for an adult is considered indicator 120/80.

The first number is systolic pressure is an indicator of pressure during heart rate. Second - diastolic pressure – pressure during relaxation of the heart.

Pressure is measured in the arteries and expressed in millimeters of mercury. In the capillaries, the pulsation of the heart becomes invisible and the pressure in them drops to approximately 30 mm Hg. Art.

A blood pressure reading can tell your doctor how your heart is working. If one or both numbers are higher than normal, this indicates high blood pressure. If it’s lower, it means it’s reduced.

High blood pressure indicates that the heart is working overload: it requires more effort to push blood through the vessels.

It also indicates that a person has an increased risk of heart disease.

Large vessels consist of three layers:

  • inner layer- endothelium, it reduces friction;
  • middle layer contains smooth muscle, regulating the lumen of the vessel, and elastic fibers, giving elasticity;
  • outer layer consists of loose fibrous connective tissue, provides protection, strengthening, blood supply and innervation of the vessel.

3 types of vessels:
Arteries- large three-layer vessels through which blood flows from the heart. They contain a well-developed middle layer, which allows them to withstand high pressure.
Capillaries- microscopic single-layer vessels consisting only of endothelium. In capillaries, the exchange of substances between blood and intercellular fluid occurs.
Vienna- large three-layer vessels through which blood flows to the heart. Contain semilunar valves that prevent backflow of blood. They have a poorly developed middle layer, which is why they easily stretch (to deposit blood) and contract (therefore, contraction of skeletal muscles increases venous blood flow).

Tests

1. Which blood vessel has a wall consisting of a single layer of cells?
A) intestinal artery
B) superior vena cava
B) portal vein of the liver
D) capillary of the nephron glomerulus

2. What factor ensures the movement of blood in the veins?
A) work of the leaflet valves of the heart
B) large branching of blood vessels
B) contraction of nearby skeletal muscles
D) different speeds of blood movement through the vessels

3. Valves located in the veins provide
A) regulation of blood pressure
B) redistribution of blood in the body
B) better blood clotting
D) blood movement in one direction

4. The thickest muscle layer of the vessel wall is characteristic of
A) blood capillaries
B) lymphatic vessels
B) arteries
D) veins

5. Strengthening and blood supply of the blood vessel provides(s)
A) smooth muscles
B) connective tissue
B) elastic fibers
D) endothelium