Help on Tele2, tariffs, questions

Two circles of blood circulation. The heart is made up of four cameras. The two right chambers are separated from the two left chambers by a solid partition. Left side the heart contains oxygen-rich arterial blood, and right- oxygen-poor, but carbon dioxide-rich venous blood. Each half of the heart consists of atria And ventricle Blood collects in the atria, then it is sent to the ventricles, and from the ventricles it is pushed into large vessels. Therefore, the ventricles are considered to be the beginning of blood circulation.

Like all mammals, human blood moves through two circles of blood circulation– big and small (Figure 13).

Great circle of blood circulation. The systemic circulation begins in the left ventricle. When the left ventricle contracts, blood is ejected into the aorta, the largest artery.

Arteries that supply blood to the head, arms and torso arise from the aortic arch. In the chest cavity, vessels depart from the descending aorta to the organs of the chest, and in the abdominal cavity - to the digestive organs, kidneys, muscles of the lower half of the body and other organs. Arteries supply blood to all organs and tissues. They branch repeatedly, narrow and gradually turn into blood capillaries.

In the capillaries of the large circle, the oxyhemoglobin of erythrocytes breaks down into hemoglobin and oxygen. Oxygen is absorbed by tissues and used for biological oxidation, and the released carbon dioxide is carried away by blood plasma and hemoglobin of red blood cells. Nutrients contained in the blood enter the cells. After this, the blood collects in the veins of the systemic circle. The veins of the upper half of the body drain into superior vena cava veins of the lower half of the body - in inferior vena cava. Both veins carry blood to the right atrium of the heart. This is where the large circle of blood circulation ends. Venous blood passes into the right ventricle, where the small circle begins.

Small (or pulmonary) circulation. When the right ventricle contracts, venous blood is directed into two pulmonary arteries. The right artery leads to the right lung, the left - to the left lung. Note: by pulmonary

arteries move venous blood! In the lungs, the arteries branch, becoming thinner and thinner. They approach the pulmonary vesicles - alveoli. Here, thin arteries divide into capillaries, weaving around the thin wall of each vesicle. The carbon dioxide contained in the veins goes into the alveolar air of the pulmonary vesicle, and oxygen from the alveolar air passes into the blood.

Figure 13 – Blood circulation diagram (arterial blood is shown in red, venous blood in blue, lymphatic vessels in yellow):

1 - aorta; 2 - pulmonary artery; 3 - pulmonary vein; 4 - lymphatic vessels;

5 - intestinal arteries; 6 - intestinal capillaries; 7 - portal vein; 8 - renal vein; 9 - lower and 10 - upper vena cava

Here it combines with hemoglobin. The blood becomes arterial: hemoglobin again turns into oxyhemoglobin and the blood changes color - from dark it becomes scarlet. Arterial blood through the pulmonary veins returns to the heart. From the left and right lungs, two pulmonary veins carrying arterial blood are directed to the left atrium. The pulmonary circulation ends in the left atrium. The blood passes into the left ventricle, and then the systemic circulation begins. So each drop of blood sequentially passes through first one circle of blood circulation, then another.

Blood circulation in the heart refers to a large circle. An artery branches off from the aorta to the muscles of the heart. It encircles the heart in the form of a crown and is therefore called coronary artery. Smaller vessels depart from it, breaking up into a capillary network. Here arterial blood gives up its oxygen and absorbs carbon dioxide. Venous blood collects in veins, which merge and flow into the right atrium through several ducts.

Lymph drainage carries away from the tissue fluid everything that is formed during the life of cells. Here are microorganisms that have entered the internal environment, dead parts of cells, and other residues unnecessary for the body. In addition, some nutrients from the intestines enter the lymphatic system. All these substances enter the lymphatic capillaries and are sent to the lymphatic vessels. Passing through the lymph nodes, the lymph is cleansed and, freed from foreign impurities, flows into the neck veins.

Thus, along with the closed circulatory system, there is an open lymphatic system, which allows you to cleanse the intercellular spaces of unnecessary substances.

The vessels in the human body form two closed circulatory systems. There are large and small circles of blood circulation. The vessels of the great circle supply blood to the organs, the vessels of the small circle provide gas exchange in the lungs.

Systemic circulation: arterial (oxygenated) blood flows from the left ventricle of the heart through the aorta, then through the arteries, arterial capillaries to all organs; from the organs, venous blood (saturated with carbon dioxide) flows through the venous capillaries into the veins, from there through the superior vena cava (from the head, neck and arms) and the inferior vena cava (from the torso and legs) into the right atrium.

Pulmonary circulation: venous blood flows from the right ventricle of the heart through the pulmonary artery into a dense network of capillaries entwining the pulmonary vesicles, where the blood is saturated with oxygen, then arterial blood flows through the pulmonary veins into the left atrium. In the pulmonary circulation, arterial blood flows through the veins, venous blood through the arteries. It begins in the right ventricle and ends in the left atrium. The pulmonary trunk emerges from the right ventricle, carrying venous blood to the lungs. Here the pulmonary arteries break up into vessels of smaller diameter, which turn into capillaries. Oxygenated blood flows through the four pulmonary veins into the left atrium.

Blood moves through the vessels due to the rhythmic work of the heart. During ventricular contraction, blood is forced under pressure into the aorta and pulmonary trunk. The highest pressure develops here - 150 mm Hg. Art. As blood moves through the arteries, the pressure drops to 120 mmHg. Art., and in capillaries - up to 22 mm. Lowest venous pressure; in large veins it is below atmospheric.

Blood is ejected from the ventricles in portions, and the continuity of its flow is ensured by the elasticity of the artery walls. At the moment of contraction of the ventricles of the heart, the walls of the arteries stretch, and then, due to elastic elasticity, return to their original state even before the next flow of blood from the ventricles. Thanks to this, the blood moves forward. Rhythmic fluctuations in the diameter of arterial vessels caused by the work of the heart are called pulse. It can be easily palpated in places where the arteries lie on the bone (radial, dorsal artery of the foot). By counting the pulse, you can determine the frequency of heart contractions and their strength. In a healthy adult, the pulse rate at rest is 60-70 beats per minute. With various heart diseases, arrhythmia is possible - interruptions in the pulse.

Blood flows at the highest speed in the aorta - about 0.5 m/s. Subsequently, the speed of movement drops and in the arteries reaches 0.25 m/s, and in the capillaries - approximately 0.5 mm/s. The slow flow of blood in the capillaries and the large extent of the latter favor metabolism (the total length of capillaries in the human body reaches 100 thousand km, and the total surface of all capillaries in the body is 6300 m2). The large difference in the speed of blood flow in the aorta, capillaries and veins is due to the unequal width of the overall cross-section of the bloodstream in its different sections. The narrowest such section is the aorta, and the total lumen of the capillaries is 600-800 times greater than the lumen of the aorta. This explains the slowdown in blood flow in the capillaries.

The movement of blood through the vessels is regulated by neurohumoral factors. Impulses sent along nerve endings can cause either a narrowing or expansion of the lumen of blood vessels. Two types of vasomotor nerves approach the smooth muscles of the walls of blood vessels: vasodilators and vasoconstrictors.

The impulses traveling along these nerve fibers arise in the vasomotor center of the medulla oblongata. In the normal state of the body, the walls of the arteries are somewhat tense and their lumen is narrowed. From the vasomotor center, impulses continuously flow through the vasomotor nerves, which determine constant tone. Nerve endings in the walls of blood vessels react to changes in pressure and chemical composition of the blood, causing excitement in them. This excitation enters the central nervous system, resulting in a reflex change in the activity of the cardiovascular system. Thus, an increase and decrease in the diameters of blood vessels occurs in a reflex way, but the same effect can also occur under the influence of humoral factors - chemical substances that are in the blood and come here with food and from various internal organs. Among them, vasodilators and vasoconstrictors are important. For example, the pituitary hormone - vasopressin, the thyroid hormone - thyroxine, the adrenal hormone - adrenaline, constrict blood vessels, enhance all functions of the heart, and histamine, formed in the walls of the digestive tract and in any working organ, acts in the opposite way: dilates capillaries without affecting other vessels . A significant effect on the functioning of the heart is exerted by changes in the content of potassium and calcium in the blood. An increase in calcium content increases the frequency and strength of contractions, increases the excitability and conductivity of the heart. Potassium causes exactly the opposite effect.

The expansion and contraction of blood vessels in various organs significantly affects the redistribution of blood in the body. More blood is sent to a working organ, where the vessels are dilated, and to a non-working organ - \ less. The depositing organs are the spleen, liver, and subcutaneous fat.

Lecture No. 9. Systemic and pulmonary circulation. Hemodynamics

Anatomical and physiological features of the vascular system

The human vascular system is closed and consists of two circles of blood circulation - large and small.

The walls of blood vessels are elastic. To the greatest extent, this property is inherent in arteries.

The vascular system is highly branched.

A variety of vessel diameters (diameter of the aorta - 20 - 25 mm, capillaries - 5 - 10 microns) (Slide 2).

Functional classification of vessels There are 5 groups of vessels (Slide 3):

Main (shock-absorbing) vessels – aorta and pulmonary artery.

These vessels are highly elastic. During ventricular systole, the great vessels stretch due to the energy of the ejected blood, and during diastole they restore their shape, pushing the blood further. Thus, they smooth out (cushion) the pulsation of blood flow and also ensure blood flow in diastole. In other words, due to these vessels, the pulsating blood flow becomes continuous.

Resistive vessels(resistance vessels) - arterioles and small arteries that can change their lumen and make a significant contribution to vascular resistance.

Exchange vessels (capillaries) - ensure the exchange of gases and substances between blood and tissue fluid.

Shunting (arteriovenous anastomoses) – connect arterioles

With venules directly, blood moves through them without passing through capillaries.

Capacitive (veins) – have high extensibility, due to which they are able to accumulate blood, performing the function of a blood depot.

Blood circulation diagram: systemic and pulmonary circulation

In humans, blood moves through two circles of blood circulation: large (systemic) and small (pulmonary).

Large (system) circle begins in the left ventricle, from where arterial blood is released into the largest vessel of the body - the aorta. Arteries branch off from the aorta and carry blood throughout the body. Arteries branch into arterioles, which in turn branch into capillaries. Capillaries gather into venules, through which venous blood flows; the venules merge into veins. The two largest veins (superior and inferior vena cava) empty into the right atrium.

Small (pulmonary) circle begins in the right ventricle, from where venous blood is released into the pulmonary artery (pulmonary trunk). As in the great circle, the pulmonary artery is divided into arteries, then into arterioles,

which branch into capillaries. In the pulmonary capillaries, venous blood is enriched with oxygen and becomes arterial. The capillaries form into venules, then into veins. Four pulmonary veins flow into the left atrium (Slide 4).

It should be understood that vessels are divided into arteries and veins not according to the blood flowing through them (arterial and venous), but according to the direction of its movement(from the heart or to the heart).

Structure of blood vessels

The wall of a blood vessel consists of several layers: the inner one, lined with endothelium, the middle one, formed by smooth muscle cells and elastic fibers, and the outer one, represented by loose connective tissue.

Blood vessels heading to the heart are usually called veins, and those leaving the heart are called arteries, regardless of the composition of the blood that flows through them. Arteries and veins differ in their external and internal structure (Slides 6, 7)

The structure of the walls of arteries. Types of arteries.The following types of artery structure are distinguished: elastic (includes the aorta, brachiocephalic trunk, subclavian, common and internal carotid arteries, common iliac artery), elastic-muscular, muscular-elastic (arteries of the upper and lower extremities, extraorgan arteries) and muscular (intraorgan arteries, arterioles and venules).

Vein wall structure has a number of features compared to arteries. Veins have a larger diameter than arteries of the same name. The wall of the veins is thin, easily collapses, it has a poorly developed elastic component, less developed smooth muscle elements in the middle tunica, while the outer tunica is well defined. Veins located below the level of the heart have valves.

Inner shell veins consists of endothelium and subendothelial layer. The internal elastic membrane is weakly expressed. Middle shell veins are represented by smooth muscle cells, which do not form a continuous layer, as in arteries, but are located in the form of separate bundles.

There are few elastic fibers. External adventitia

represents the thickest layer of the vein wall. It contains collagen and elastic fibers, vessels that feed the vein, and nerve elements.

Main main arteries and veins Arteries. Aorta (Slide 9) leaves the left ventricle and passes

in the back of the body along the spinal column. The part of the aorta that comes directly from the heart and goes upward is called

ascending. The right and left coronary arteries depart from it,

blood supply to the heart.

The ascending part bending to the left, passes into the aortic arch, which

spreads across the left main bronchus and continues into descending part aorta. Three large vessels arise from the convex side of the aortic arch. On the right is the brachiocephalic trunk, on the left are the left common carotid and left subclavian arteries.

Brachiocephalic trunk departs from the aortic arch upward and to the right, it is divided into the right common carotid and subclavian arteries. Left common carotid And left subclavian the arteries arise directly from the aortic arch to the left of the brachiocephalic trunk.

Descending aorta (Slides 10, 11) divided into two parts: thoracic and abdominal. Thoracic aorta located on the spine, to the left of the midline. From the thoracic cavity the aorta passes into abdominal aorta, passing through the aortic opening of the diaphragm. At the place of its division into two common iliac arteries at the level of the IV lumbar vertebra ( aortic bifurcation).

The abdominal part of the aorta supplies blood to the viscera located in the abdominal cavity, as well as the abdominal walls.

Arteries of the head and neck. The common carotid artery divides into the external

the carotid artery, which branches outside the cranial cavity, and the internal carotid artery, which passes through the carotid canal into the skull and supplies blood to the brain (Slide 12).

Subclavian artery on the left it departs directly from the aortic arch, on the right - from the brachiocephalic trunk, then on both sides it goes to the axillary cavity, where it passes into the axillary artery.

Axillary artery at the level of the lower edge of the pectoralis major muscle continues into the brachial artery (Slide 13).

Brachial artery(Slide 14) is located on the inside of the shoulder. In the cubital fossa, the brachial artery divides into the radial and ulnar artery.

Radiation and ulnar artery their branches supply blood to the skin, muscles, bones and joints. Moving onto the hand, the radial and ulnar arteries connect with each other and form the superficial and deep palmar arterial arches(Slide 15). Arteries extend from the palmar arches to the hand and fingers.

Abdominal h part of the aorta and its branches.(Slide 16) Abdominal aorta

located on the spine. Parietal and internal branches extend from it. Parietal branches are two going up to the diaphragm

inferior phrenic arteries and five pairs of lumbar arteries,

blood supply to the abdominal wall.

Internal branches The abdominal aorta is divided into unpaired and paired arteries. The unpaired splanchnic branches of the abdominal aorta include the celiac trunk, superior mesenteric artery and inferior mesenteric artery. The paired splanchnic branches are the middle adrenal, renal, and testicular (ovarian) arteries.

Pelvic arteries. The terminal branches of the abdominal aorta are the right and left common iliac arteries. Each common iliac

the artery, in turn, is divided into internal and external. Branches in internal iliac artery supply blood to the organs and tissues of the pelvis. External iliac artery at the level of the inguinal fold it becomes b single artery, which runs down the anterior inner surface of the thigh, and then enters the popliteal fossa, continuing into popliteal artery.

Popliteal artery at the level of the lower edge of the popliteus muscle it divides into the anterior and posterior tibial arteries.

The anterior tibial artery forms an arcuate artery, from which branches extend to the metatarsus and toes.

Vienna. From all organs and tissues of the human body, blood flows into two large vessels - the upper and inferior vena cava(Slide 19), which flow into the right atrium.

Superior vena cava located in the upper part of the chest cavity. It is formed by the fusion of the right and left brachiocephalic veins. The superior vena cava collects blood from the walls and organs of the chest cavity, head, neck, and upper extremities. Blood flows from the head through the external and internal jugular veins (Slide 20).

External jugular vein collects blood from the occipital and retroauricular regions and flows into the terminal section of the subclavian, or internal jugular, vein.

Internal jugular vein exits the cranial cavity through the jugular foramen. The internal jugular vein drains blood from the brain.

Veins of the upper limb. On the upper limb, deep and superficial veins are distinguished; they intertwine (anastomose) with each other. The deep veins have valves. These veins collect blood from bones, joints, and muscles; they are adjacent to the arteries of the same name, usually in twos. At the shoulder, both deep brachial veins merge and empty into the azygos axillary vein. Superficial veins of the upper limb form a network on the brush. axillary vein, located next to the axillary artery, at the level of the first rib passes into subclavian vein, which flows into the internal jugular.

Veins of the chest. The outflow of blood from the chest walls and organs of the chest cavity occurs through the azygos and semi-gypsy veins, as well as through the organ veins. All of them flow into the brachiocephalic veins and into the superior vena cava (Slide 21).

Inferior vena cava(Slide 22) is the largest vein in the human body; it is formed by the fusion of the right and left common iliac veins. The inferior vena cava flows into the right atrium; it collects blood from the veins of the lower extremities, walls and internal organs of the pelvis and abdomen.

Veins of the abdomen. The tributaries of the inferior vena cava in the abdominal cavity mostly correspond to the paired branches of the abdominal aorta. Among the tributaries there are parietal veins(lumbar and lower diaphragmatic) and splanchnic (hepatic, renal, right

adrenal, testicular in men and ovarian in women; the left veins of these organs flow into the left renal vein).

The portal vein collects blood from the liver, spleen, small and large intestine.

Veins of the pelvis. In the pelvic cavity there are tributaries of the inferior vena cava

The right and left common iliac veins, as well as the internal and external iliac veins flowing into each of them. The internal iliac vein collects blood from the pelvic organs. External - is a direct continuation of the femoral vein, which receives blood from all the veins of the lower limb.

By superficial veins of the lower limb blood flows away from the skin and underlying tissues. Superficial veins originate on the sole and dorsum of the foot.

The deep veins of the lower limb are adjacent to the arteries of the same name in pairs; blood flows through them from deep organs and tissues - bones, joints, muscles. The deep veins of the sole and dorsum of the foot continue to the lower leg and pass into the fore and posterior tibial veins, adjacent to the arteries of the same name. The tibial veins merge to form the unpaired popliteal vein, into which the veins of the knee (knee joint) flow. The popliteal vein continues into the femoral vein (Slide 23).

Factors ensuring constant blood flow

The movement of blood through the vessels is ensured by a number of factors, which are conventionally divided into main and auxiliary.

The main factors include:

the work of the heart, due to which a pressure difference is created between the arterial and venous systems (Slide 25).

elasticity of shock-absorbing vessels.

Auxiliary factors mainly promote blood movement

V venous system, where the pressure is low.

"Muscle pump" Contraction of skeletal muscles pushes blood through the veins, and the valves that are located in the veins prevent blood from moving away from the heart (Slide 26).

Suction action of the chest. During inhalation, the pressure in the chest cavity decreases, the vena cava dilates, and blood is sucked in

V them. In this regard, during inspiration, venous return increases, that is, the volume of blood entering the atria(Slide 27).

Suction action of the heart. During ventricular systole, the atrioventricular septum moves to the apex, as a result of which negative pressure arises in the atria, facilitating the flow of blood into them (Slide 28).

Blood pressure from behind - the next portion of blood pushes the previous one.

Volumetric and linear velocity of blood flow and factors influencing them

Blood vessels are a system of tubes, and the movement of blood through the vessels is subject to the laws of hydrodynamics (the science that describes the movement of fluid through pipes). According to these laws, the movement of a liquid is determined by two forces: the pressure difference at the beginning and end of the tube, and the resistance experienced by the flowing liquid. The first of these forces promotes the flow of fluid, the second hinders it. In the vascular system, this relationship can be represented as an equation (Poiseuille's law):

Q = P/R;

where Q – volumetric blood flow velocity, that is, blood volume,

flowing through a cross section per unit time, P is the quantity medium pressure in the aorta (pressure in the vena cava is close to zero), R –

the value of vascular resistance.

To calculate the total resistance of successively located vessels (for example, the brachiocephalic trunk departs from the aorta, the common carotid artery from it, the external carotid artery from it, etc.), the resistances of each of the vessels are added up:

R = R1 + R2 + … + Rn ;

To calculate the total resistance of parallel vessels (for example, intercostal arteries depart from the aorta), the reciprocal values ​​of the resistance of each vessel are added:

1/R = 1/R1 + 1/R2 + … + 1/Rn ;

Resistance depends on the length of the vessels, the lumen (radius) of the vessel, blood viscosity and is calculated using the Hagen-Poiseuille formula:

R= 8Lη/π r4 ;

where L is the length of the tube, η is the viscosity of the liquid (blood), π is the ratio of the circumference to the diameter, r is the radius of the tube (vessel). Thus, the volumetric velocity of blood flow can be represented as:

Q = ΔP π r4 / 8Lη;

The volumetric velocity of blood flow is the same throughout the entire vascular bed, since the blood inflow to the heart is equal in volume to the outflow from the heart. In other words, the amount of blood flowing per unit

time through the systemic and pulmonary circulation, through arteries, veins and capillaries equally.

Linear blood flow velocity– the path that a blood particle travels per unit time. This value is different in different parts of the vascular system. Volumetric (Q) and linear (v) blood flow velocities are related through

cross-sectional area (S):

v=Q/S;

The larger the cross-sectional area through which the liquid passes, the lower the linear velocity (Slide 30). Therefore, as the lumen of the vessels expands, the linear speed of blood flow slows down. The narrowest point of the vascular bed is the aorta; the greatest expansion of the vascular bed is observed in the capillaries (their total lumen is 500–600 times greater than in the aorta). The speed of blood movement in the aorta is 0.3 - 0.5 m/s, in the capillaries - 0.3 - 0.5 mm/s, in the veins - 0.06 - 0.14 m/s, in the vena cava -

0.15 – 0.25 m/s (Slide 31).

Characteristics of moving blood flow (laminar and turbulent)

Laminar (layered) current fluid under physiological conditions is observed in almost all parts of the circulatory system. With this type of flow, all particles move in parallel - along the axis of the vessel. The speed of movement of different layers of fluid is not the same and is determined by friction - the layer of blood located in close proximity to the vascular wall moves at a minimum speed, since friction is maximum. The next layer moves faster, and in the center of the vessel the fluid speed is maximum. As a rule, along the periphery of the vessel there is a layer of plasma, the speed of which is limited by the vascular wall, and a layer of erythrocytes moves along the axis at a higher speed.

The laminar flow of liquid is not accompanied by sounds, so if you apply a phonendoscope to a superficially located vessel, no noise will be heard.

Turbulent current occurs in places of narrowing of blood vessels (for example, if the vessel is compressed from the outside or there is an atherosclerotic plaque on its wall). This type of flow is characterized by the presence of turbulence and mixing of layers. Liquid particles move not only parallel, but also perpendicularly. More energy is required to ensure turbulent fluid flow compared to laminar flow. Turbulent blood flow is accompanied by sound phenomena (Slide 32).

Time for complete blood circulation. Blood depot

Blood circulation time- this is the time that is necessary for a particle of blood to pass through the systemic and pulmonary circulation. The blood circulation time in humans is on average 27 cardiac cycles, that is, at a frequency of 75–80 beats/min, it is 20–25 seconds. Of this time, 1/5 (5 seconds) is in the pulmonary circulation, 4/5 (20 seconds) is in the systemic circulation.

Blood distribution. Blood depots. In an adult, 84% of the blood is contained in the large circle, ~9% in the small circle and 7% in the heart. The arteries of the systemic circle contain 14% of the blood volume, the capillaries - 6% and the veins -

IN in a person’s resting state, up to 45–50% of the total blood mass available

V body, located in blood depots: spleen, liver, subcutaneous choroid plexus and lungs

Blood pressure. Blood pressure: maximum, minimum, pulse, average

Moving blood puts pressure on the walls of blood vessels. This pressure is called blood pressure. There are arterial, venous, capillary and intracardiac pressure.

Blood pressure (BP)- This is the pressure that blood exerts on the walls of the arteries.

Systolic and diastolic pressure are distinguished.

Systolic (SBP)– the maximum pressure at the moment the heart pushes blood into the vessels is normally 120 mm Hg. Art.

Diastolic (DBP)– the minimum pressure at the moment of opening of the aortic valve is about 80 mm Hg. Art.

The difference between systolic and diastolic pressure is called pulse pressure(PD), it is equal to 120 – 80 = 40 mm Hg. Art. Mean blood pressure (BPav)- the pressure that would be in the vessels without pulsation of blood flow. In other words, it is the average pressure over the entire cardiac cycle.

ADsr = SBP+2DBP/3;

BP avg = SBP+1/3PP;

(Slide 34).

During physical activity, systolic pressure can increase to 200 mm Hg. Art.

Factors affecting blood pressure

The value of blood pressure depends on cardiac output And vascular resistance, which, in turn, is determined

elastic properties of blood vessels and their lumen . Blood pressure is also affected by volume of circulating blood and its viscosity (as viscosity increases, resistance increases).

As you move away from the heart, the pressure drops because the energy that creates the pressure is spent on overcoming resistance. The pressure in small arteries is 90 – 95 mm Hg. Art., in the smallest arteries – 70 – 80 mm Hg. Art., in arterioles – 35 – 70 mm Hg. Art.

In postcapillary venules the pressure is 15–20 mmHg. Art., in small veins – 12 – 15 mm Hg. Art., in large ones – 5 – 9 mm Hg. Art. and in hollows – 1 – 3 mm Hg. Art.

Blood pressure measurement

Blood pressure can be measured by two methods - direct and indirect.

Direct method (bloody)(Slide 35 ) – a glass cannula is inserted into the artery and connected with a rubber tube to a pressure gauge. This method is used in experiments or during heart surgery.

Indirect (indirect) method.(Slide 36 ). A cuff is fixed around the shoulder of a seated patient, to which two tubes are attached. One of the tubes is connected to a rubber bulb, the other to a pressure gauge.

Then a phonendoscope is installed in the area of ​​the ulnar fossa on the projection of the ulnar artery.

Air is injected into the cuff to a pressure that obviously exceeds systolic pressure, while the lumen of the brachial artery is blocked and the blood flow in it stops. At this moment, the pulse in the ulnar artery is not detected, there are no sounds.

After this, the air is gradually released from the cuff, and the pressure in it decreases. At the moment when the pressure drops slightly below systolic, blood flow in the brachial artery resumes. However, the lumen of the artery is narrowed, and the blood flow in it is turbulent. Since the turbulent movement of the fluid is accompanied by sound phenomena, a sound appears - a vascular tone. Thus, the pressure in the cuff at which the first vascular sounds appear corresponds to maximum, or systolic, pressure.

Tones are heard as long as the lumen of the vessel remains narrowed. At the moment when the pressure in the cuff decreases to diastolic, the lumen of the vessel is restored, the blood flow becomes laminar, and the sounds disappear. Thus, the moment the sounds disappear corresponds to the diastolic (minimum) pressure.

Microcirculation

Microcirculatory bed. The vessels of the microvasculature include arterioles, capillaries, venules and arterilovenular anastomoses

(Slide 39).

Arterioles are arteries of the smallest caliber (diameter 50 - 100 microns). Their inner shell is lined with endothelium, the middle shell is represented by one or two layers of muscle cells, and the outer shell consists of loose fibrous connective tissue.

Venules are veins of very small caliber; their middle membrane consists of one or two layers of muscle cells.

Arteriolovenular anastomoses - these are vessels that carry blood bypassing the capillaries, that is, directly from the arterioles to the venules.

Blood capillaries– the most numerous and thinnest vessels. In most cases, capillaries form a network, but they can form loops (in the papillae of the skin, intestinal villi, etc.), as well as glomeruli (vascular glomeruli in the kidney).

The number of capillaries in a particular organ is related to its functions, and the number of open capillaries depends on the intensity of the organ’s work at a given moment.

The total cross-sectional area of ​​the capillary bed in any region is many times greater than the cross-sectional area of ​​the arteriole from which they emerge.

There are three thin layers in the capillary wall.

The inner layer is represented by flat polygonal endothelial cells located on the basement membrane, the middle layer consists of pericytes enclosed in the basement membrane, and the outer layer consists of sparsely located adventitial cells and thin collagen fibers immersed in an amorphous substance (Slide 40).

Blood capillaries carry out the main metabolic processes between blood and tissues, and in the lungs they participate in ensuring gas exchange between blood and alveolar gas. The thinness of the capillary walls, the huge area of ​​their contact with tissues (600 - 1000 m2), slow blood flow (0.5 mm/s), low blood pressure (20 - 30 mm Hg) provide the best conditions for metabolic processes.

Transcapillary exchange(Slide 41). Metabolic processes in the capillary network occur due to the movement of fluid: exit from the vascular bed into the tissue ( filtration ) and reabsorption from the tissue into the lumen of the capillary ( reabsorption ). The direction of fluid movement (from a vessel or into a vessel) is determined by filtration pressure: if it is positive, filtration occurs, if negative, reabsorption occurs. Filtration pressure, in turn, depends on the values ​​of hydrostatic and oncotic pressure.

Hydrostatic pressure in the capillaries is created by the work of the heart, it promotes the release of fluid from the vessel (filtration). The oncotic pressure of plasma is caused by proteins, it promotes the movement of fluid from the tissue into the vessel (reabsorption).

In the circulatory system, there are two circles of blood circulation: large and small. They begin in the ventricles of the heart and end in the atria (Fig. 232).

Systemic circulation begins with the aorta from the left ventricle of the heart. Through it, arterial vessels bring blood rich in oxygen and nutrients to the capillary system of all organs and tissues.

Venous blood from the capillaries of organs and tissues enters small, then larger veins, and ultimately, through the superior and inferior vena cava, it collects in the right atrium, where the systemic circulation ends.

Pulmonary circulation begins in the right ventricle with the pulmonary trunk. Through it, venous blood reaches the capillary bed of the lungs, where it is freed from excess carbon dioxide, enriched with oxygen and returns to the left atrium through four pulmonary veins (two veins from each lung). The pulmonary circulation ends in the left atrium.

Vessels of the pulmonary circulation. The pulmonary trunk (truncus pulmonalis) begins from the right ventricle on the anterior superior surface of the heart. It rises up and to the left and crosses the aorta lying behind it. The length of the pulmonary trunk is 5-6 cm. Under the aortic arch (at the level of the IV thoracic vertebra), it is divided into two branches: the right pulmonary artery (a. pulmonalis dextra) and the left pulmonary artery (a. pulmonalis sinistra). From the terminal part of the pulmonary trunk to the concave surface of the aorta there is a ligament (arterial ligament) *. The pulmonary arteries are divided into lobar, segmental and subsegmental branches. The latter, accompanying the branches of the bronchi, form a capillary network that densely entwines the alveoli of the lungs, in the area of ​​which gas exchange occurs between the blood and the air in the alveoli. Due to the difference in partial pressure, carbon dioxide passes from the blood into the alveolar air, and oxygen enters the blood from the alveolar air. Hemoglobin contained in red blood cells plays an important role in this gas exchange.

* (The ligament arteriosus is a remnant of the overgrown ductus arteriosus of the fetus. During the period of embryonic development, when the lungs do not function, most of the blood from the pulmonary trunk is transferred through the ductus botallus into the aorta and thus bypasses the pulmonary circulation. During this period, only small vessels - the rudiments of the pulmonary arteries - go to the non-breathing lungs from the pulmonary trunk.)

From the capillary bed of the lungs, oxygenated blood passes sequentially into the subsegmental, segmental and then lobar veins. The latter in the area of ​​the gate of each lung form two right and two left pulmonary veins (vv. pulmonales dextra et sinistra). Each of the pulmonary veins usually drains separately into the left atrium. Unlike veins in other areas of the body, the pulmonary veins contain arterial blood and do not have valves.

Vessels of the systemic circulation. The main trunk of the systemic circulation is the aorta (aorta) (see Fig. 232). It starts from the left ventricle. It distinguishes between the ascending part, the arc and the descending part. The ascending part of the aorta in the initial section forms a significant expansion - the bulb. The length of the ascending part of the aorta is 5-6 cm. At the level of the lower edge of the manubrium of the sternum, the ascending part passes into the aortic arch, which goes back and to the left, spreads through the left bronchus and at the level of the IV thoracic vertebra passes into the descending part of the aorta.

The right and left coronary arteries of the heart depart from the ascending aorta in the region of the bulb. From the convex surface of the aortic arch, the brachiocephalic trunk (innominate artery), then the left common carotid artery and the left subclavian artery depart successively from right to left.

The final vessels of the systemic circulation are the superior and inferior vena cava (vv. cavae superior et inferior) (see Fig. 232).

The superior vena cava is a large but short trunk, its length is 5-6 cm. It lies to the right and somewhat posterior to the ascending aorta. The superior vena cava is formed by the confluence of the right and left brachiocephalic veins. The confluence of these veins is projected at the level of the connection of the first right rib with the sternum. The superior vena cava collects blood from the head, neck, upper extremities, organs and walls of the chest cavity, from the venous plexuses of the spinal canal and partially from the walls of the abdominal cavity.

The inferior vena cava (Fig. 232) is the largest venous trunk. It is formed at the level of the IV lumbar vertebra by the confluence of the right and left common iliac veins. The inferior vena cava, rising upward, reaches the opening of the same name in the tendon center of the diaphragm, passes through it into the chest cavity and immediately flows into the right atrium, which in this place is adjacent to the diaphragm.

In the abdominal cavity, the inferior vena cava lies on the anterior surface of the right psoas major muscle, to the right of the lumbar vertebral bodies and the aorta. The inferior vena cava collects blood from the paired organs of the abdominal cavity and the walls of the abdominal cavity, the venous plexuses of the spinal canal and the lower extremities.

Pulmonary circulation

Circulation circles- this concept is conditional, since only fish have a completely closed blood circulation. In all other animals, the end of the systemic circulation is the beginning of the small one and vice versa, which makes it impossible to talk about their complete isolation. In fact, both circles of blood circulation form a single whole bloodstream, in two sections of which (the right and left heart), kinetic energy is imparted to the blood.

Circulation is a vascular pathway that has its beginning and end in the heart.

Systemic (systemic) circulation

Structure

It begins with the left ventricle, which ejects blood into the aorta during systole. Numerous arteries arise from the aorta, resulting in blood flow distributed among several parallel regional vascular networks, each of which supplies a separate organ. Further division of the arteries occurs into arterioles and capillaries. The total area of ​​all capillaries in the human body is approximately 1000 m².

After passing through the organ, the process of capillaries merging into venules begins, which in turn gather into veins. Two vena cavae approach the heart: superior and inferior, which, when fused, form part of the right atrium of the heart, which is the end of the systemic circulation. The circulation of blood in the systemic circulation occurs in 24 seconds.

Exceptions in the structure

• Blood circulation of the spleen and intestines. The general structure does not include blood circulation in the intestines and spleen, since after the formation of the splenic and intestinal veins, they merge to form the portal vein. The portal vein re-disintegrates in the liver into a capillary network, and only after that the blood flows to the heart.
• Kidney circulation. In the kidney, there are also two capillary networks - the arteries break up into afferent arterioles of the Shumlyansky-Bowman capsule, each of which breaks up into capillaries and gathers into an efferent arteriole. The efferent arteriole reaches the convoluted tubule of the nephron and re-disintegrates into a capillary network.

Functions

Blood supply to all organs of the human body, including the lungs.

Lesser (pulmonary) circulation

Structure

It begins in the right ventricle, which ejects blood into the pulmonary trunk. The pulmonary trunk is divided into the right and left pulmonary artery. Arteries are dichotomously divided into lobar, segmental and subsegmental arteries. Subsegmental arteries are divided into arterioles, which break up into capillaries. The outflow of blood goes through veins, collecting in the reverse order, which in the amount of 4 flow into the left atrium. Blood circulation in the pulmonary circulation occurs in 4 seconds.

The pulmonary circulation was first described by Miguel Servetus in the 16th century in his book “The Restoration of Christianity.”

Functions

• Heat dissipation

Small circle function is not nutrition of lung tissue.

“Additional” circulation circles

Depending on the physiological state of the body, as well as practical expediency, additional circles of blood circulation are sometimes distinguished:

• placental,
• cordial.

Placental circulation

Exists in the fetus located in the uterus.

Blood that is not fully oxygenated drains through the umbilical vein, which runs in the umbilical cord. From here, most of the blood flows through the ductus venosus into the inferior vena cava, mixing with unoxygenated blood from the lower body. A smaller portion of the blood enters the left branch of the portal vein, passes through the liver and hepatic veins, and enters the inferior vena cava.

Mixed blood flows through the inferior vena cava, the oxygen saturation of which is about 60%. Almost all of this blood flows through the foramen ovale in the wall of the right atrium into the left atrium. From the left ventricle, blood is ejected into the systemic circulation.

Blood from the superior vena cava first enters the right ventricle and pulmonary trunk. Since the lungs are in a collapsed state, the pressure in the pulmonary arteries is greater than in the aorta, and almost all the blood passes through the ductus arteriosus into the aorta. The ductus arteriosus flows into the aorta after the arteries of the head and upper extremities depart from it, which provides them with more enriched blood. A very small part of the blood enters the lungs, which subsequently enters the left atrium.

Part of the blood (~60%) from the systemic circulation enters the placenta through two umbilical arteries; the rest goes to the organs of the lower body.

Cardiac circulatory system or coronary circulatory system

Structurally, it is part of the large circle of blood circulation, but due to the importance of the organ and its blood supply, you can sometimes find mention of this circle in the literature.

Arterial blood flows to the heart through the right and left coronary arteries. They begin at the aorta above its semilunar valves. Smaller branches extend from them, enter the muscle wall and branch to the capillaries. The outflow of venous blood occurs in 3 veins: large, middle, small, and cardiac vein. Merging they form the coronary sinus and it opens into the right atrium.

Wikimedia Foundation. 2010.