All useful substances circulate through the cardiovascular system, which, like a kind of transport system, needs a trigger mechanism. The main motor impulse enters the human circulatory system from the heart. As soon as we overwork or experience a spiritual experience, our heartbeat quickens.
The heart is connected to the brain, and it is no coincidence that the ancient philosophers believed that all our spiritual experiences are hidden in the heart. The main function of the heart is to pump blood throughout the body, nourish every tissue and cell, and remove waste products from them. Having made the first beat, this occurs in the fourth week after the conception of the fetus, the heart then beats at a frequency of 120,000 beats per day, which means that our brain works, the lungs breathe, and the muscles act. A person's life depends on the heart.
The human heart is the size of a fist and weighs 300 grams. The heart is located in chest, it is surrounded by the lungs, and protected by the ribs, sternum and spine. This is a fairly active and durable muscular organ. The heart has strong walls and is made up of intertwined muscle fibers that are not at all like other muscle tissues in the body. In general, our heart is a hollow muscle made up of a pair of pumps and four cavities. The two upper cavities are called the atria, and the two lower cavities are called the ventricles. Each atrium is connected directly to the lower ventricle by thin but very strong valves, they ensure the correct direction of blood flow.
The right heart pump, in other words, the right atrium with the ventricle, sends blood through the veins to the lungs, where it is enriched with oxygen, and the left pump, as strong as the right one, pumps the blood to the most distant organs of the body. With each heartbeat, both pumps work in a two-stroke mode - relaxation and concentration. Throughout our lives, this mode is repeated 3 billion times. Blood enters the heart through the atria and ventricles when the heart is in a relaxed state.
As soon as it is filled with blood entirely, it passes through the atrium electrical impulse, it causes a sharp contraction of the atrial systole, as a result of which blood enters through the open valves into the relaxed ventricles. In turn, as soon as the ventricles fill with blood, they contract and push the blood out of the heart through the external valves. All this takes about 0.8 seconds. Blood flows through the arteries in time with the heartbeat. With each beat of the heart, blood flow presses on the walls of the arteries, giving the heart a characteristic sound - this is how the pulse sounds. At healthy person the pulse rate is usually 60-80 beats per minute, but the heart rate depends not only on our physical activity at the moment, but also on the state of mind.
Some heart cells are capable of self-irritation. In the right atrium there is a natural focus of automatism of the heart, it produces approximately one electrical impulse per second when we rest, then this impulse travels throughout the heart. Although the heart is able to work completely on its own, the heart rate depends on signals received from nerve stimuli and commands from the brain.
Circulatory system
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Circulatory system human is a closed circuit through which blood is supplied to all organs. Upon exiting the left ventricle, the blood passes through the aorta and begins its circulation throughout the body. First of all, it flows through the smallest arteries, and enters the network of thin blood vessels- capillaries. There, the blood exchanges oxygen and nutrients with the tissue. From the capillaries, blood flows into the vein, and from there into the paired wide veins. The upper and lower cavities of the vein are connected directly to the right atrium.
Further, the blood enters the right ventricle, and then into the pulmonary arteries and lungs. The pulmonary arteries gradually expand, and form microscopic cells - alveoli, covered with a membrane only one cell thick. Under the pressure of gases on the membrane, on both sides, the process of interchange takes place in the blood, as a result, the blood is cleared of carbon dioxide and saturated with oxygen. Enriched with oxygen, the blood passes through the four pulmonary veins and enters the left atrium - this is how a new circulation cycle begins.
Blood makes one complete revolution in about 20 seconds. Following, thus, through the body, the blood enters the heart twice. All this time, it moves along a complex tubular system, the total length of which is approximately twice the circumference of the Earth. There are many more veins in our circulatory system than arteries, although muscle the veins are less developed, but the veins are more elastic than the arteries, and about 60% of the blood flow passes through them. The veins are surrounded by muscles. As the muscles contract, they push blood towards the heart. Veins, especially those located on the legs and arms, are equipped with a system of self-regulating valves.
After passing through the next portion of the blood flow, they close, preventing the backflow of blood. In a complex, our circulatory system is more reliable than any modern high-precision technical device; it not only enriches the body with blood, but also removes waste from it. Due to continuous blood flow, we maintain a constant body temperature. Evenly distributed through the blood vessels of the skin, the blood protects the body from overheating. Through the blood vessels, blood is equally distributed throughout the body. Normally, the heart pumps 15% of the blood flow to the bone muscles, because they account for the lion's share physical activity.
In the circulatory system, the intensity of blood flow entering the muscle tissue increases by 20 times, or even more. To produce vital energy for the body, the heart needs a lot of blood, even more than the brain. It is estimated that the heart receives 5% of the blood it pumps, and absorbs 80% of the blood it receives. Through a very complex circulatory system, the heart also receives oxygen.
human heart
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Human health, as well as the normal functioning of the whole organism, depends mainly on the state of the heart and circulatory system, on their clear and well-coordinated interaction. However, a violation in the activity of the cardiovascular system, and related diseases, thrombosis, heart attack, atherosclerosis, are quite frequent phenomena. Arteriosclerosis, or atherosclerosis, occurs due to hardening and blockage of blood vessels, which impedes blood flow. If some vessels are completely clogged, blood stops flowing to the brain or heart, and this can cause a heart attack, in fact, complete paralysis of the heart muscle.
Fortunately, in the past decade, cardiovascular disease has been curable. Armed modern technologies, surgeons can restore the affected focus of automatism of the heart. They can, and replace a damaged blood vessel, and even transplant the heart of one person to another. Worldly troubles, smoking, fatty foods adversely affect cardiovascular system. But playing sports, quitting smoking and a calm lifestyle provide the heart with a healthy working rhythm.
circulatory system, or circulatory, or cardiovascular, is a large branched transport system. It continuously, throughout a person's life, carries oxygen, nutrients, hormones throughout the body, taking waste products of metabolism from cells, tissues and organs, that is, it carries out hemodynamics(the movement of blood in the body). Consequently, the circulatory system provides: nutrition of the body, gas exchange, its release from metabolic products and humoral regulation of the functioning of the body.
Blood moves through the blood vessels mainly due to the contractions of the heart. And its path in the body is as follows: heart → arteries → capillaries → veins → heart. The circulatory system is a closed system. It consists of two circles of blood circulation — big And small.
They were first described by the outstanding English scientist William Harvey.
A heart- a hollow muscular organ. Its mass in an adult is 250-300 g. The heart is located in chest cavity and shifted to the left of the midline of the chest. It is contained in a pericardial sac formed by connective tissue. On the inner surface the pericardial sac releases a fluid that moisturizes the heart and reduces friction during its contractions.
The structure of the heart corresponds to its inherent function. It is divided by a solid partition into two parts - left and right, and each of them is divided into two interconnected sections: the upper - atrium and bottom - ventricle. Consequently, The human heart, like all mammals, has four chambers: it consists of two atria and two ventricles.. The walls of the atria are much thinner than the walls of the ventricles. This is due to the fact that the work performed by the atria is relatively small. During their contraction, blood enters the ventricles, which do much more work: they push blood along the entire length of the vessels. muscular wall (myocardium) of the left ventricle is thicker than the wall of the right ventricle because it does a lot of work. On the border between each atrium and ventricle there are valves in the form of valves, which are attached to the walls of the heart by tendon threads. This flap valves(Fig. 58).
During atrial contraction, the valve leaflets hang down into the ventricles. Blood flows freely from the atria to the ventricles. When the ventricles contract, the valve flaps rise and close the entrance to the atrium. Therefore, blood moves in only one direction: from the atria to the ventricles. From the ventricles, it is pushed into the vessels.
The whole human body is permeated blood vessels. In their structure, they are not the same.
arteries are the vessels that carry blood away from the heart. They have strong elastic walls, which include smooth muscles. As the heart contracts, it ejects blood under high pressure into the arteries. Due to their density and elasticity, the walls of the arteries withstand this pressure and stretch.
Large arteries branch to the extent of distance from the heart. The smallest arteries ( arterioles) branch into thin capillaries(Fig. 59), of which there are approximately 150 billion in the human body. The walls of the capillaries are formed by one layer of flat cells. Substances dissolved in the blood plasma pass into the tissue fluid, and from it enter the cells through these walls. The waste products of cells penetrate through the walls of the capillaries from the tissue fluid into the blood. Blood flows from capillaries to veins- Vessels through which it flows to the heart. The pressure in the veins is small, their walls are much thinner than the walls of the arteries. material from the site
On this page, material on the topics:
Report on the topic of the circulatory system Grade 4
Report on the circulatory system Grade 4
Importance of the circulatory system grade 4 report
What is called blood circulation. structure of the function of blood vessels abstract
A short report on the circulatory system
Questions about this item:
Name the organs and departments that make up the cardiovascular system.
Describe the biological functions of the cardiovascular system.
Diagrammatically depict the direction of blood flow in the cardiovascular system.
What type does the human circulatory system belong to?
Name the advantages of a four-chambered heart.
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Human circulatory system
1. General information, historical background
2. Heart - general information
2.1 Anatomy of the heart
2.2. Physiology of the heart
3. Blood vessels - general information
3.1. Arteries - general information
3.1.1. Artery anatomy
3.2. Veins - general information
3.2.1. Vein Anatomy
3.3. Blood capillaries - general information
3.3.1. Anatomy of blood capillaries
4. Blood circulation - general information, the concept of circulatory circles
4.1. Physiology of circulation
5. Lymphatic system - general information, historical background
5.1. Lymphatic capillaries - general information
5.1.1. Anatomy of the lymphatic capillaries
5.2. Lymphatic vessels - general information
5.2.1. Anatomy of the lymphatic vessels
5.3. Lymph nodes - general information
5.3.1. Anatomy of the lymph nodes
5.4. Lymphatic trunks and ducts - general information
5.5. Physiology of the lymphatic system
- CIRCULATORY SYSTEM
The circulatory system is the system of vessels and cavities through which blood circulates. Through the circulatory system, the cells and tissues of the body are supplied with nutrients and oxygen and are released from metabolic products. Therefore, the circulatory system is sometimes called the transport or distribution system.
The heart and blood vessels form a closed system through which blood moves due to contractions of the heart muscle and myocytes of the vessel walls. Blood vessels are represented by arteries that carry blood from the heart, veins through which blood flows to the heart, and a microvasculature consisting of arterioles, capillaries, postcopillary venules, and arteriovenular anastomoses.
As you move away from the heart, the caliber of the arteries gradually decreases down to the smallest arterioles, which in the thickness of the organs pass into a network of capillaries. The latter, in turn, continue into small, gradually enlarging
veins that carry blood to the heart. The circulatory system is divided into two circles of blood circulation - large and small. The first begins in the left ventricle and ends in the right atrium, the second begins in the right ventricle and ends in the left atrium. Blood vessels are absent only in the epithelium of the skin and mucous membranes, in hair, nails, the cornea of the eye and articular cartilage.
Blood vessels get their name from the organs they supply (renal artery, splenic vein), their origin from a larger vessel (superior mesenteric artery, inferior mesenteric artery), the bone to which they are attached (ulnar artery), direction (medial artery surrounding the thigh), depth of occurrence (superficial or deep artery). Many small arteries are called branches, and veins are called tributaries.
Depending on the area of branching, the arteries are divided into parietal (parietal), blood-supplying walls of the body, and visceral (internal), blood-supplying internal organs. Before an artery enters an organ, it is called an organ, and after entering an organ, it is called an intraorgan. The latter branches within and supplies its individual structural elements.
Each artery splits into smaller vessels. With the main type of branching, lateral branches depart from the main trunk - the main artery, the diameter of which gradually decreases. With a tree-like type of branching, the artery immediately after its discharge is divided into two or more terminal branches, while resembling the crown of a tree.
1.1 Cardiovascular system
The human cardiovascular system consists of the heart, blood vessels through which blood circulates, and the lymphatic system through which lymph flows. The function of the cardiovascular system is to supply organs and tissues with oxygen and nutrients, as well as to remove waste products and carbon dioxide from organs and tissues.
History. Information about the structure of the heart was available in the ancient Egyptian papyri (17-2 centuries BC). In ancient Greece, the physician Hippocrates (5-4 centuries BC) described the heart as a muscular organ. Aristotle (fourth century BC) believed that the heart contained air that was circulated through the arteries. The Roman physician Galen (2nd century AD) proved that arteries contain blood, not air. The heart was described in detail by Andreas Vesalius (16th century A.D.).
For the first time, correct information about the work of the heart and blood circulation was reported by Harvey in 1628. Since the 18th century, detailed studies of the structure and function of the cardiovascular system began.
2.Heart
The heart is the central organ of the circulatory system, which is a hollow muscular organ that functions as a pump and ensures the movement of blood in the circulatory system.
2.1 Anatomy of the heart
The heart is a muscular hollow cone-shaped organ. In relation to the midline of a person (the line dividing the human body into left and right halves), the human heart is located asymmetrically - about 2/3 - to the left of the middle line of the body, about 1/3 of the heart - to the right of the midline of the human body. The heart is located in the chest, enclosed in a pericardial sac - the pericardium, located between the right and left pleural cavities containing the lungs.
The longitudinal axis of the heart goes obliquely from top to bottom, from right to left and from back to front. The position of the heart is different: transverse, oblique or vertical.
The vertical position of the heart most often occurs in people with a narrow and long chest, the transverse position - in people with a wide and short chest.
Distinguish the base of the heart, directed anteriorly, downwards and to the left. At the base of the heart are the atria. From the base of the heart exit: the aorta and the pulmonary trunk, into the base of the heart enter: the superior and inferior vena cava, right and left pulmonary veins. Thus, the heart is fixed on the large vessels listed above.
With its posterior-lower surface, the heart is adjacent to the diaphragm (a jumper between the chest and abdominal cavities), and the sternocostal surface is facing the sternum and costal cartilages. Three grooves are distinguished on the surface of the heart - one coronal; between the atria and ventricles and two longitudinal (anterior and posterior) between the ventricles.
The length of the heart of an adult varies from 100 to 150 mm, the width at the base is 80–110 mm, and the anteroposterior distance is 60–85 mm. The weight of the heart on average in men is 332 g, in women - 253 g. In newborns, the weight of the heart is 18-20 g.
The heart consists of four chambers: right atrium, right ventricle, left atrium, left ventricle. The atria are located above the ventricles. The atrial cavities are separated from each other by the interatrial septum, and the ventricles are separated by the interventricular septum. The atria communicate with the ventricles through openings.
The right atrium has a capacity of 100–140 ml in an adult, and a wall thickness of 2–3 mm. The right atrium communicates with the right ventricle through the right atrioventricular orifice, which has a tricuspid valve. Behind, the superior vena cava flows into the right atrium above, below - the inferior vena cava. The mouth of the inferior vena cava is limited by a flap. The coronary sinus of the heart, which has a valve, flows into the posterior-lower part of the right atrium. The coronary sinus of the heart collects venous blood from the heart's own veins.
The right ventricle of the heart has the shape of a trihedral pyramid, with its base facing up. The capacity of the right ventricle in adults is 150-240 ml, the wall thickness is 5-7 mm.
The weight of the right ventricle is 64-74 g. Two parts are distinguished in the right ventricle: the ventricle itself and the arterial cone located in the upper part of the left half of the ventricle. The arterial cone passes into the pulmonary trunk - a large venous vessel that carries blood to the lungs. Blood from the right ventricle enters the pulmonary trunk through the tricuspid valve.
The left atrium has a capacity of 90-135 ml, a wall thickness of 2-3 mm. On the back wall of the atrium are the mouths of the pulmonary veins (vessels carrying oxygen-enriched blood from the lungs), two on the right and two on the left.
the left ventricle has a conical shape; its capacity is from 130 to 220 ml; wall thickness 11 - 14 mm. The weight of the left ventricle is 130-150 g. There are two openings in the cavity of the left ventricle: the atrioventricular (left and front), equipped with a bicuspid valve, and the opening of the aorta (the main artery of the body), equipped with a tricuspid valve. In the right and left ventricles there are numerous muscular protrusions in the form of crossbars - trabeculae. The valves are controlled by the papillary muscles.
The wall of the heart consists of three layers: the outer one - the epicardium, the middle one - the myocardium (muscle layer), and the inner one - the endocardium. Both the right and left atrium have small protruding parts on the sides - ears. The source of innervation of the heart is the cardiac plexus - part of the general thoracic vegetative plexus. In the heart itself there are many nerve plexuses and ganglions that regulate the frequency and strength of heart contractions, the work of heart valves.
The blood supply to the heart is carried out by two arteries: the right coronary and the left coronary, which are the first branches of the aorta. The coronary arteries divide into smaller branches that enclose the heart. The diameter of the mouths of the right coronary artery ranges from 3.5 to 4.6 mm, the left - from 3.5 to 4.8 mm. Sometimes, instead of two coronary arteries, there may be one.
The outflow of blood from the veins of the walls of the heart mainly occurs in the coronary sinus, which flows into the right atrium. Lymphatic fluid flows through the lymphatic capillaries from the endocardium and myocardium to the lymph nodes located under the epicardium, and from there the lymph enters the lymphatic vessels and nodes of the chest.
2.2 Physiology of the heart
The work of the heart as a pump is the main source of mechanical energy for the movement of blood in the vessels, which maintains the continuity of metabolism and energy in the body.
The activity of the heart occurs due to the conversion of chemical energy into mechanical energy of myocardial contraction.
In addition, the myocardium has the property of excitability.
Excitation impulses arise in the heart under the influence of the processes occurring in it. This phenomenon is called automation. There are centers in the heart that generate impulses leading to excitation of the myocardium with its subsequent contraction (i.e., the process of automation is carried out with subsequent excitation of the myocardium). Such centers (nodes) provide rhythmic contraction in the required order of the atria and ventricles of the heart. The contractions of both atria, and then both ventricles, are carried out almost simultaneously.
Inside the heart, due to the presence of valves, the blood moves in one direction. In the diastole phase (expansion of the cavities of the heart associated with relaxation of the myocardium), blood flows from the atria into the ventricles. In the systole phase (consecutive contractions of the atrial myocardium, and then the ventricles), blood flows from the right ventricle to the pulmonary trunk, from the left ventricle to the aorta.
In the diastolic phase of the heart, the pressure in its chambers is close to zero; 2/3 of the volume of blood entering in the diastolic phase flows due to positive pressure in the veins outside the heart and 1/3 is pumped into the ventricles in the atrial systole phase. The atria are a reservoir for incoming blood; atrial volume may increase due to the presence of atrial lugs.
A change in pressure in the chambers of the heart and the vessels departing from it causes the movement of the heart valves, the movement of blood. During contraction, the right and left ventricles expel 60-70 ml of blood each.
Compared to other organs (with the exception of the cerebral cortex), the heart absorbs oxygen most intensively. In men, the size of the heart is 10-15% larger than in women, and the heart rate is 10-15% lower.
Physical activity causes an increase in blood flow to the heart due to its displacement from the veins of the extremities during muscle contraction and from the veins of the abdominal cavity. This factor acts mainly under dynamic loads; static loads insignificantly change venous blood flow. An increase in the flow of venous blood to the heart leads to an increase in the work of the heart.
With maximum physical activity, the value of the energy costs of the heart can increase by 120 times compared to the state of rest. Prolonged exposure to physical activity causes an increase in the reserve capacity of the heart.
Negative emotions cause the mobilization of energy resources and increase the release of adrenaline (hormone of the adrenal cortex) into the blood - this leads to an increase in heart rate (normal heart rate is 68-72 per minute), which is an adaptive reaction of the heart.
The heart is also affected by environmental factors. So, in conditions of high mountains, with a low oxygen content in the air, oxygen starvation of the heart muscle develops with a simultaneous reflex increase in blood circulation as a response to this oxygen starvation.
Sharp fluctuations in temperature, noise, ionizing radiation, magnetic fields, electromagnetic waves, infrasound, many chemicals (nicotine, alcohol, carbon disulfide, organometallic compounds, benzene, lead) have a negative effect on the activity of the heart.
3. Blood vessels - general information
Blood vessels are elastic tubes of various diameters that make up a closed system through which blood flows in the body from the heart to the periphery and from the periphery to the heart. Depending on the direction of the blood flow and the saturation of the blood with oxygen, arteries, veins, and the capillaries connecting them are isolated.
3.1. Arteries - general information
Arteries are blood vessels that carry oxygenated blood from the heart to all parts of the body. The exception is the pulmonary trunk, which carries venous blood from the right ventricle to the lungs. The collection of arteries makes up the arterial system.
The arterial system starts from the left ventricle of the heart, from which the largest and main arterial vessel, the aorta, emerges. Numerous branches extend from the aorta from the heart to the fifth lumbar vertebra: to the head - the common carotid arteries; to the upper limbs - subclavian arteries; to the digestive organs - the celiac trunk and mesenteric arteries; to the kidneys - renal arteries. In its lower part, in the abdominal region, the aorta divides into two common iliac arteries, which supply blood to the pelvic organs and lower limbs.
Arteries supply blood to all organs, dividing into branches of different diameters. Arteries or their branches are designated either by the name of the organ (renal artery) or by topography (subclavian artery). Some large arteries are called trunks (celiac trunk). Small arteries are called branches, and the smallest arteries are called arterioles.
Passing through the smallest arterial vessels, oxygenated blood reaches any part of the body, where, along with oxygen, these smallest arteries supply the nutrients necessary for the vital activity of tissues and organs.
3.1.1. Artery anatomy
Arteries are cylindrical tubes with a very complex wall structure. In the course of branching of the arteries, the diameter of their lumen gradually decreases, but the total diameter increases. There are large, medium and small arteries. There are three membranes in the walls of arteries.
Inner shell - the inner cell layer is formed by the endothelium and the underlying subendothelial layer. In the aorta - the thickest cell layer. As the arteries branch, the cell layer becomes thinner.
The middle shell is formed mainly by smooth muscle tissue and elastic tissues. As the arteries branch, the elastic tissue becomes less pronounced. In the smallest arteries, elastic tissue is weakly expressed. In the walls of the precapillary arterioles, the elastic tissue disappears, and the muscle cells are arranged in one row. Muscle fibers also disappear in the capillaries.
The outer shell is built of loose connective tissue with a high content of elastic fibers. This membrane performs the function of an artery: it is rich in vessels and nerves.
The walls of the arteries have their own blood and lymphatic vessels that feed the walls of the arteries. These vessels come from branches of nearby arteries and lymphatic vessels. Venous blood from the walls of the arteries flows into the nearest veins.
The walls of blood vessels are permeated with numerous and diverse in structure and functions of nerve endings. Sensitive nerve endings (angioreceptors) respond to changes in the chemical composition of the blood, to changes in pressure in the arteries and send nerve impulses to the corresponding parts of the nervous system. The motor nerve endings located in the muscular layer of the artery, with appropriate irritation, cause contraction of the muscle fibers, thereby reducing the lumen of the arteries.
The branching of large arteries into smaller ones occurs in three main types: main, loose or mixed.
branches branch out in succession. At the same time, as the branches branch off, the diameter of the main trunk decreases. In the second type, the vessel is divided into several branches (similar to a bush). Branching can be mixed, when the main trunk gives off branches, and then splits into several arteries. The main (main) arteries usually lie between the muscles, on the bones.
According to P.F. Lesgaft, the arterial trunks are divided according to the bone basis. So, on the shoulder there is one arterial trunk; on the forearm - two, and on the hand - five.
According to M.G. Weight gain, the distribution of arterial trunks is subject to a certain pattern. In organs such as the liver, kidney, spleen, the artery enters through the gates in them and sends branches in all directions. The artery sends branches to the muscle sequentially and stepwise, along its length. Finally, arteries can penetrate into the organ from several sources along the radii (an example is the thyroid gland).
Arterial blood supply to hollow organs occurs in three types - radial, circular, and longitudinal. In this case, the arterial vessels form arches along the hollow organ (stomach, intestines, trachea, etc.) and send their branches to its walls. Arterial networks are formed on the wall.
The arterial system, as part of the cardiovascular system, is characterized by the presence in all organs and parts of the body of connections between arteries and their branches - anastomoses, due to which roundabout (collateral) blood circulation is carried out.
In addition to anastomoses, there are direct connections between small arteries or arterioles and veins - fistulas. Through these fistulas, blood, bypassing the capillaries, directly passes from the artery into the vein. Anastomoses and anastomoses play an important role in the redistribution of blood between organs.
3.2 Veins - general information
Veins are blood vessels that carry venous blood (low in oxygen and high in carbon dioxide) from organs and tissues to the right atrium. The exception is the pulmonary veins that carry blood from the lungs to the left atrium: the blood in them is enriched with oxygen.
The totality of all veins is the venous system, which is part of the cardiovascular system. A network of tiny vessels - capillaries (see below "capillaries") pass into postcapillary venules, which merge to form larger venules. Venules form a network in organs. Veins originate from this network, which in turn form more powerful venous plexuses or venous network, located in or near the organ.
3.2.1. Vein Anatomy
There are superficial and deep veins.
Superficial veins are located in the subcutaneous tissue and originate from the superficial venous plexuses or venous arches of the head, trunk, and limbs.
Deep veins, often paired, begin in certain parts of the body, accompany the arteries, which is why they are called companion veins.
The veins that carry blood from the head and neck are the internal jugular veins. They connect with the veins that carry blood from the upper limbs - the subclavian veins, forming the brachiocephalic veins. The brachiocephalic veins form the superior vena cava. The veins of the walls of the chest and, partially, the abdominal cavities flow into it. The veins that collect blood from the lower extremities, parts of the abdominal cavity and from the paired organs of the abdomen (kidneys, gonads) form the inferior vena cava.
From unpaired abdominal organs (digestive organs, spleen, pancreas, greater omentum, bile ducts, gallbladder), blood flows through the portal vein to the liver, where digestion products from the gastrointestinal tract are utilized and restructured. From the liver, venous blood through the hepatic veins (3-4 trunks) enters the inferior vena cava.
The veins of the heart wall flow into the common drain of the cardiac veins - the coronary sinus (see anatomy of the heart).
In the venous network, a system of venous messages (communications) and venous plexuses is widely developed, which ensures the outflow of blood from one venous system to another. Small and medium veins, as well as some large ones, have venous valves (flaps) - semilunar folds on the inner shell, which are usually located in pairs. A small number of valves have veins of the lower extremities. Valves allow blood to flow towards the heart and prevent it from flowing back. Both vena cava, veins of the head and neck do not have valves.
In the brain there are venous sinuses - sinuses located in the clefts of the dura mater of the brain, which have non-contiguous walls. The venous sinuses provide an unimpeded outflow of venous blood from the cranial cavity into the cranial veins.
The wall of the vein, like the wall of the artery, consists of three layers. However, the elastic elements in it are poorly developed due to low pressure and low blood flow velocity in the veins.
The arteries that feed the vein wall are branches of nearby arteries. In the wall of the vein are nerve endings that respond to the chemical composition of the blood, blood flow velocity and other factors. The wall also contains motor nerve fibers that affect the tone of the muscular membrane of the vein, causing it to contract. In this case, the lumen of the vein changes slightly.
3.3. Blood capillaries - general information
Blood capillaries are the thinnest-walled vessels through which blood moves. They are present in all organs and tissues and are a continuation of arterioles. Separate capillaries, uniting with each other, pass into postcapillary venules. The latter, merging with each other, give rise to collective venules, passing into larger veins.
The exceptions are the sinusoidal (with a wide lumen) capillaries of the liver, located between the venous microvessels, and the glomerular capillaries of the kidneys, located between the arterioles. In all other organs and tissues, capillaries serve as a “bridge between the arterial and venous systems.
Blood capillaries provide the tissues of the body with oxygen and nutrients, take waste products of tissues and carbon dioxide from the tissues.
3.3.1. Anatomy of blood capillaries
According to microscopic studies, capillaries look like narrow tubes, the walls of which are penetrated by submicroscopic “pores”. Capillaries are straight, curved and twisted into a ball. The average capillary length reaches 750 µm, and the cross-sectional area is 30 µm. sq. The diameter of the capillary lumen corresponds to the size of the erythrocyte (on average). According to electron microscopy, the capillary wall consists of two layers: inner - endothelial and outer - basal.
The endothelial layer (shell) consists of flattened cells - endotheliocytes. The basal layer (shell) consists of cells - pericytes and a membrane that envelops the capillary. The walls of capillaries are permeable to metabolic products of the organism (water, molecules). Along the capillaries, there are sensitive nerve endings that send signals about the state of metabolic processes to the corresponding centers of the nervous system.
4. Blood circulation - general information, the concept of circulatory circles
Oxygenated blood flows from the lungs into the left atrium through the pulmonary veins. From the left atrium, arterial blood through the left atrioventricular bicuspid valve enters the left ventricle of the heart, and from it into the largest artery - the aorta.
Through the aorta and its branches, arterial blood containing oxygen and nutrients is sent to all parts of the body. Arteries are divided into arterioles, and the latter into capillaries - the circulatory system. Through the capillaries, the exchange of the circulatory system with organs and tissues is carried out with oxygen, carbon dioxide, nutrients and waste products (see "capillaries").
The capillaries of the circulatory system gather into venules that carry venous blood with a low oxygen content and a high carbon dioxide content. Venules are further united into venous vessels. Ultimately, the veins form the two largest venous vessels - the superior vena cava, the inferior vena cava (see "veins"). Both hollow veins flow into the right atrium, where the own veins of the heart also flow (see "heart").
From the right atrium, venous blood, passing through the right atrioventricular tricuspid valve, enters the right ventricle of the heart, and from it through the pulmonary trunk, then through the pulmonary arteries into the lungs.
In the lungs, through the blood capillaries surrounding the alveoli of the lungs (see “respiratory organs, section “lungs”), gas exchange occurs - the blood is enriched with oxygen and gives off carbon dioxide, becomes arterial again and again enters the left atrium through the pulmonary veins. This whole cycle of blood circulation in the body is called the general circle of blood circulation.
Considering the features of the structure and function of the heart, blood vessels, the general circulation is divided into large and small circles of blood circulation.
Systemic circulation
The systemic circulation begins in the left ventricle, from which the aorta exits, and ends in the right atrium, where the superior and inferior vena cava empties.
Small circle of blood circulation
The pulmonary circulation begins in the right ventricle, from which the pulmonary trunk exits to the lungs, and ends in the left atrium, where the pulmonary veins flow. By means of a small circle of blood circulation, gas exchange of blood is carried out. Venous blood in the lungs gives off carbon dioxide, is saturated with oxygen - it becomes arterial.
4.1. Physiology of circulation
The source of energy necessary for the movement of blood through the vascular system is the work of the heart. The contraction of the heart muscle informs it of the energy expended on overcoming the elastic forces of the walls of the vessels and giving speed to its jet. Part of the supplied energy accumulates in the elastic walls of the arteries due to their stretching.
During the diastole of the heart, the walls of the arteries contract; and the energy concentrated in them passes into the kinetic energy of the moving blood. The oscillation of the arterial wall is defined as the pulsation of the artery (pulse). The pulse rate corresponds to the heart rate. In some heart conditions, the pulse rate does not match the heart rate.
The pulse is determined on the carotid arteries, subclavian or limb arteries. The pulse rate is counted for at least 30 seconds. In healthy people, the pulse rate in a horizontal position is 60-80 per minute (in adults). An increase in heart rate is called tachysphygmia, and a slow pulse is called bradysphygmia.
Due to the elasticity of the arterial wall, which accumulates the energy of heart contractions, the continuity of blood flow in the blood vessels is maintained. In addition, other factors contribute to the return of venous blood to the heart: negative pressure in the chest cavity at the time of entry (2-5 mm Hg below atmospheric pressure), which ensures suction of blood to the heart; contractions of the muscles of the skeleton and diaphragm, contributing to the pushing of blood to the heart.
The state of the function of the circulatory system can be judged on the basis of the following main indicators.
Blood pressure (BP) is the pressure developed by blood in arterial vessels. When measuring pressure, a unit of pressure is used, equal to 1 mmHg.
Blood pressure is an indicator consisting of two values - the pressure in the arterial system during systole of the heart (systolic pressure), corresponding to the highest level of pressure in the arterial system, and the pressure in the arterial system during diastole of the heart (diastolic pressure), corresponding to the minimum blood pressure in the arterial system. In healthy people 17-60 years old, systolic blood pressure is in the range of 100-140 mm Hg. Art., diastolic pressure - 70-90 mm Hg. Art.
Emotional stress, physical activity cause a temporary increase in blood pressure. In healthy people, the daily fluctuation of blood pressure can be 10 mm Hg. Art. An increase in blood pressure is called hypertension, and a decrease is called hypotension.
Minute blood volume is the amount of blood ejected by the heart in one minute. At rest, the minute volume (MO) is 5.0-5.5 liters. With physical activity, it increases by 2-4 times, for athletes - by 6-7 times. In some heart diseases, MO decreases to 2.5-1.5 liters.
The volume of circulating blood (VCC) is normally 75-80 ml of blood per 1 kg of human weight. With physical exertion, the BCC increases, and with blood loss and shock, it decreases.
Blood circulation time - the time during which a particle of blood passes through the large and small circles of blood circulation. Normally, this time is 20-25 seconds, it decreases with physical exertion and increases with circulatory disorders up to 1 minute. The circuit time in a small circle is 7-11 seconds.
The distribution of blood in the body is characterized by a pronounced unevenness. In humans, blood flow in ml per 100 g of organ weight is at rest for 1 minute (on average): in the kidneys - 420 ml, in the heart - 84 ml, in the liver - 57 ml, in striated muscles - 2.7 ml. Veins contain 70-80% of the body's blood. During physical exertion, the vessels of the skeletal muscles expand; the blood supply to the muscles during exercise will be 80-85% of the total blood supply. The rest of the organs will have 15-20% of the total blood volume.
The structure of the vessels of the heart, brain and lungs provides a relatively privileged blood supply to these organs. So, to the muscle of the heart, whose mass is 0.4% of body weight, about 5% of it enters at rest, that is, 10 times more than the average to all tissues. The brain, which weighs 2% of body weight, receives almost 15% of all blood at rest. The brain consumes 20% of the oxygen that enters the body.
In the lungs, blood circulation is facilitated due to the large diameter of the pulmonary arteries, the high extensibility of the vessels of the lungs and the small length of the path along which the blood passes in the pulmonary circulation.
Regulation of blood circulation provides the amount of blood flow in tissues and organs corresponding to the level of their functions. There is a cardiovascular center in the brain, which regulates the activity of the heart and the tone of the muscular membrane of the blood vessels.
The cardiovascular center receives nerve impulses from nerve endings (receptors) located in the blood vessels and responding to changes in pressure in the vessels, changes in blood flow velocity, blood chemistry, etc.
Then the circulatory system is an area of necessary knowledge related to health.
Humans are 60% liquid. It is found in all organs, even in those that at first glance seem dry - nail plates and. Neither, nor, nor even are possible without the participation of lymph and tissue fluid.
circulatory system
Blood circulation is an important factor in the life of the human body and a number of animals. Blood can perform its various functions only when it is in constant motion.
Blood circulation occurs along two main paths, called circles, connected in a sequential chain: a small and a large circle of blood circulation.
In a small circle, blood circulates through the lungs: from the right ventricle it enters the lungs, where it is saturated with oxygen and returns to the left atrium.
Then the blood enters the left ventricle and is sent through the systemic circulation to all organs of the body. From there, the blood carries carbon dioxide and decay products through the veins to the right atrium.
Closed circulatory system
A closed circulatory system is a circulatory system in which there are veins, arteries and capillaries (in which the exchange of substances between blood and tissues takes place), and blood flows exclusively through the vessels.
A closed system differs from an open circulatory system by the presence of a well-developed four-chambered, three-chambered, or two-chambered heart.
The movement of blood in a closed circulatory system is provided by the constant contraction of the heart. Blood vessels in a closed circulatory system are located throughout the body. In an open one, there is only one open blood path.
Human circulatory system
Colorless cells that look like amoebas are called leukocytes. They are protectors, as they fight against harmful microorganisms. The smallest platelets are called platelets.
Their main task is to prevent blood loss in case of damage to blood vessels, so that any cut does not become a mortal threat to humans. Erythrocytes, leukocytes and platelets are called blood cells.
Blood cells float in plasma - a light yellow liquid, which is 90% composed of. Plasma also contains proteins, various salts, enzymes, hormones, and glucose.
The blood in our body moves through a system of large and small vessels. The total length of blood vessels in the human body is approximately 100,000 km.
main organ of the circulatory system
The main organ of the human circulatory system is the heart. It consists of two atria and two ventricles. Arteries leave the heart, through which it pushes blood. Blood returns to the heart through the veins.
With the slightest injury, blood begins to flow from the damaged vessels. Blood clotting is provided by platelets. They accumulate at the site of injury and secrete a substance that promotes blood clotting and the formation of a blood clot (clot).
- For more accurate diagnosis diseases do blood tests. One of them is clinical. It shows the quantity and quality of blood cells.
- Since blood enriched with oxygen moves through the arteries, the arterial membrane, unlike the venous one, is more powerful and has muscle layer. This allows it to withstand high pressure.
- One drop of blood contains more than 250 million erythrocytes, 375 thousand leukocytes and 16 million platelets.
- The contractions of the heart ensure the movement of blood through the vessels to all organs and tissues. At rest, the heart beats 60-80 times per minute, which means that about 3 billion contractions occur in a lifetime.
Now you know everything you need to know about the human circulatory system. educated person. Of course, if your specialization is medicine, then you can tell much more about this topic.
The content of the article
CIRCULATORY SYSTEM(circulatory system), a group of organs involved in the circulation of blood in the body. The normal functioning of any animal organism requires efficient blood circulation as it carries oxygen, nutrients, salts, hormones and other vital substances to all organs of the body. In addition, the circulatory system returns blood from tissues to those organs where it can be enriched with nutrients, as well as to the lungs, where it is saturated with oxygen and released from carbon dioxide (carbon dioxide). Finally, the blood must bathe a number of special organs, such as the liver and kidneys, which neutralize or excrete the end products of metabolism. The accumulation of these products can lead to chronic ill health and even death.
This article discusses the human circulatory system. ( For circulatory systems in other species, see the article COMPARATIVE ANATOMY.)
Components of the circulatory system.
In its most general form, this transport system consists of a muscular four-chamber pump (heart) and many channels (vessels), the function of which is to deliver blood to all organs and tissues and then return it to the heart and lungs. According to the main components of this system, it is also called the cardiovascular, or cardiovascular.
Blood vessels are divided into three main types: arteries, capillaries, and veins. Arteries carry blood away from the heart. They branch into vessels of ever smaller diameter, through which blood enters all parts of the body. Closer to the heart, the arteries have the largest diameter (approximately thumb hands), in the limbs they are the size of a pencil. In the parts of the body farthest from the heart, the blood vessels are so small that they can only be seen under a microscope. It is these microscopic vessels, capillaries, that supply cells with oxygen and nutrients. After their delivery, blood loaded with end products of metabolism and carbon dioxide is sent to the heart through a network of vessels called veins, and from the heart to the lungs, where gas exchange occurs, as a result of which the blood is released from the load of carbon dioxide and saturated with oxygen.
In the process of passing through the body and its organs, some part of the liquid seeps through the walls of the capillaries into the tissues. This opalescent, plasma-like fluid is called lymph. return of lymph to common system blood circulation is carried out through the third system of channels - the lymphatic pathways, which merge into large ducts that flow into the venous system in close proximity to the heart. ( Detailed description lymph and lymphatic vessels see article LYMPHATIC SYSTEM.)
WORK OF THE CIRCULATION SYSTEM
Pulmonary circulation.
It is convenient to begin describing the normal movement of blood through the body from the moment when it returns to the right half of the heart through two large veins. One of them, the superior vena cava, brings blood from the upper half of the body, and the second, the inferior vena cava, from the bottom. Blood from both veins enters the collecting section of the right side of the heart, the right atrium, where it mixes with the blood brought by the coronary veins, which open into the right atrium through the coronary sinus. The coronary arteries and veins circulate the blood necessary for the work of the heart itself. The atrium fills, contracts, and pushes blood into the right ventricle, which contracts to force blood through the pulmonary arteries into the lungs. The constant flow of blood in this direction is maintained by the operation of two important valves. One of them, tricuspid, located between the ventricle and the atrium, prevents the return of blood to the atrium, and the second, the valve pulmonary artery, closes at the moment of relaxation of the ventricle and thereby prevents the return of blood from the pulmonary arteries. In the lungs, blood passes through the ramifications of the vessels, falling into a network of thin capillaries that are in direct contact with the smallest air sacs - the alveoli. An exchange of gases takes place between the capillary blood and the alveoli, which completes the pulmonary phase of blood circulation, i.e. phase of blood entering the lungs see also RESPIRATORY ORGANS).
Systemic circulation.
From this moment, the systemic phase of blood circulation begins, i.e. phase of blood transfer to all tissues of the body. The carbon dioxide-free and oxygenated (oxygenated) blood returns to the heart through the four pulmonary veins (two from each lung) and enters the left atrium at low pressure. The path of blood flow from the right ventricle of the heart to the lungs and return from them to the left atrium is the so-called. small circle of blood circulation. The blood-filled left atrium contracts simultaneously with the right and pushes it into the massive left ventricle. The latter, having filled up, contracts, sending blood under high pressure into the largest artery, the aorta. All arterial branches that supply the tissues of the body depart from the aorta. As on right side heart, on the left there are two valves. The bicuspid (mitral) valve directs blood flow to the aorta and prevents blood from returning to the ventricle. The entire path of blood from the left ventricle up to its return (through the superior and inferior vena cava) to the right atrium is referred to as the systemic circulation.
arteries.
In a healthy person, the aorta is approximately 2.5 cm in diameter. This large vessel extends upward from the heart, forms an arc, and then descends through the chest into abdominal cavity. Along the aorta, all the major arteries that enter the systemic circulation branch off from it. The first two branches, extending from the aorta almost at the very heart, are the coronary arteries that supply blood to the tissue of the heart. In addition to them, the ascending aorta (the first part of the arch) does not give branches. However, at the top of the arc, three important vessels depart from it. The first - the innominate artery - immediately divides into the right carotid artery, which supplies blood to the right half of the head and brain, and the right subclavian artery, passing under the clavicle in right hand. The second branch from the aortic arch is the left carotid artery, the third is the left subclavian artery; these branches carry blood to the head, neck, and left arm.
From the aortic arch, the descending aorta begins, which supplies blood to the organs of the chest, and then penetrates into the abdominal cavity through a hole in the diaphragm. Two renal arteries supplying the kidneys are separated from the abdominal aorta, as well as the abdominal trunk with the superior and inferior mesenteric arteries extending to the intestines, spleen and liver. The aorta then divides into two iliac arteries that supply blood to the pelvic organs. In the groin area, the iliac arteries pass into the femoral; the latter, going down the thighs, at the level of the knee joint, pass into the popliteal arteries. Each of them, in turn, is divided into three arteries - the anterior tibial, posterior tibial and peroneal arteries, which feed the tissues of the legs and feet.
Throughout the course of the bloodstream, the arteries become smaller and smaller as they branch, and finally acquire a caliber that is only a few times the size of the blood cells they contain. These vessels are called arterioles; continuing to divide, they form a diffuse network of vessels (capillaries), the diameter of which is approximately equal to the diameter of an erythrocyte (7 microns).
The structure of the arteries.
Although large and small arteries differ somewhat in their structure, the walls of both consist of three layers. outer layer(adventitia) is a relatively loose layer of fibrous, elastic connective tissue; the smallest blood vessels (the so-called vascular vessels) pass through it, feeding the vascular wall, as well as branches of the autonomic nervous system that regulate the lumen of the vessel. The middle layer (media) consists of elastic tissue and smooth muscles that provide elasticity and contractility of the vascular wall. These properties are essential for regulating blood flow and maintaining normal blood pressure under changing physiological conditions. Usually the walls large vessels, such as the aorta, contain more elastic tissue than the walls of the smaller arteries, which are dominated by muscle tissue. According to this tissue feature, the arteries are divided into elastic and muscular. The inner layer (intima) rarely exceeds the diameter of several cells in thickness; it is this layer, lined with endothelium, that gives the inner surface of the vessel a smoothness that facilitates blood flow. Through it, nutrients enter the deep layers of the media.
As the diameter of arteries decreases, their walls become thinner and the three layers become less and less distinct, until - at the arteriolar level - they remain mostly coiled muscle fibers, some elastic tissue, and an inner lining of endothelial cells.
capillaries.
Finally, the arterioles imperceptibly pass into the capillaries, the walls of which are expelled only by the endothelium. Although these tiny tubes contain less than 5% of the volume of circulating blood, they are extremely important. The capillaries form an intermediate system between arterioles and venules, and their networks are so dense and wide that no part of the body can be pierced without piercing a huge number of them. It is in these networks that, under the action of osmotic forces, oxygen and nutrients are transferred to individual cells of the body, and in return, the products of cellular metabolism enter the bloodstream.
In addition, this network (the so-called capillary bed) plays an important role in the regulation and maintenance of body temperature. The constancy of the internal environment (homeostasis) of the human body depends on maintaining body temperature within the narrow limits of the norm (36.8–37 °). Usually, blood from arterioles enters the venules through the capillary bed, but in cold conditions capillaries close and blood flow decreases, primarily in the skin; at the same time, blood from the arterioles enters the venules, bypassing the many branches of the capillary bed (shunting). On the contrary, if heat transfer is necessary, for example, in the tropics, all capillaries open, and skin blood flow increases, which contributes to heat loss and preservation normal temperature body. This mechanism exists in all warm-blooded animals.
Vienna.
On the opposite side of the capillary bed, the vessels merge into numerous small channels, venules, which are comparable in size to arterioles. They continue to connect to form larger veins that carry blood from all parts of the body back to the heart. Constant blood flow in this direction is facilitated by a system of valves found in most veins. Venous pressure, unlike pressure in the arteries, does not depend directly on the tension of the muscles of the vascular wall, so the flow in the right direction is determined mainly by other factors: the pushing force created by arterial pressure great circle blood circulation; "Sucking" effect of negative pressure that occurs in the chest during inspiration; pumping action of the muscles of the limbs, which during normal contractions push venous blood to the heart.
The walls of the veins are similar in structure to the arterial ones in that they also consist of three layers, expressed, however, much weaker. The movement of blood through the veins, which occurs practically without pulsation and at a relatively low pressure, does not require such thick and elastic walls as those of arteries. Another important difference between veins and arteries is the presence of valves in them that maintain blood flow in one direction at low pressure. IN most valves are contained in the veins of the extremities, where muscle contractions play a particularly important role in moving blood back to the heart; large veins, such as hollow, portal and iliac, valves are deprived.
On the way to the heart, the veins collect blood flowing from gastrointestinal tract on portal vein, from the liver through the hepatic veins, from the kidneys through the renal veins, and from upper limbs through the subclavian veins. Near the heart, two hollow veins are formed, through which blood enters the right atrium.
The vessels of the pulmonary circulation (pulmonary) resemble the vessels of the systemic circulation, with the only exception that they lack valves, and the walls of both arteries and veins are much thinner. In contrast to the systemic circulation, venous, non-oxygenated blood flows through the pulmonary arteries into the lungs, and arterial blood flows through the pulmonary veins, i.e. saturated with oxygen. The terms "arteries" and "veins" refer to the direction of blood flow in the vessels - from the heart or to the heart, and not to what kind of blood they contain.
subsidiary bodies.
A number of organs perform functions that complement the work of the circulatory system. The spleen, liver and kidneys are most closely associated with it.
Spleen.
With repeated passage through the circulatory system, red blood cells (erythrocytes) are damaged. Such "waste" cells are removed from the blood in many ways, but the main role here belongs to the spleen. The spleen not only destroys damaged red blood cells, but also produces lymphocytes (related to white blood cells). In lower vertebrates, the spleen also plays the role of a reservoir of erythrocytes, but in humans this function is poorly expressed. see also SPLEEN.
Liver.
To carry out its more than 500 functions, the liver needs a good blood supply. Therefore, it occupies an important place in the circulatory system and is provided by its own vascular system, which is called the portal. A number of liver functions are directly related to the blood, such as removing waste red blood cells from it, producing blood clotting factors, and regulating blood sugar levels by storing excess sugar in the form of glycogen. see also LIVER .
Kidneys.
BLOOD (ARTERIAL) PRESSURE
With each contraction of the left ventricle of the heart, the arteries fill with blood and stretch. This phase cardiac cycle is called ventricular systole, and the relaxation phase of the ventricles is called diastole. During diastole, however, the elastic forces of large blood vessels come into play, maintaining blood pressure and not allowing interruption of the blood flow to the various parts body. The change of systoles (contractions) and diastole (relaxations) gives the blood flow in the arteries a pulsating character. The pulse can be found in any major artery, but is usually felt at the wrist. In adults, the pulse rate is usually 68-88, and in children - 80-100 beats per minute. The existence of arterial pulsation is also evidenced by the fact that when an artery is cut, bright red blood flows out in jerks, and when a vein is cut, bluish (due to a lower oxygen content) blood flows evenly, without visible shocks.
To ensure proper blood supply to all parts of the body during both phases of the cardiac cycle, a certain level of blood pressure is needed. Although this value varies considerably even in healthy people, normal blood pressure averages 100–150 mmHg. during systole and 60–90 mm Hg. during diastole. The difference between these indicators is called pulse pressure. For example, in a person with a blood pressure of 140/90 mmHg. pulse pressure is 50 mm Hg. Another indicator - mean arterial pressure - can be approximately calculated by averaging systolic and diastolic pressure or adding half the pulse pressure to diastolic.
Normal blood pressure is determined, maintained and regulated by many factors, the main of which are the strength of heart contractions, the elastic "recoil" of the walls of the arteries, the volume of blood in the arteries and the resistance of small arteries (muscular type) and arterioles to blood flow. All these factors together determine the lateral pressure on the elastic walls of the arteries. It can be measured very accurately by using a special electronic probe inserted into the artery and recording the results on paper. Such devices, however, are quite expensive and are used only for special studies, and doctors, as a rule, make indirect measurements using the so-called. sphygmomanometer (tonometer).
The sphygmomanometer consists of a cuff that is wrapped around the limb where the measurement is made, and a recording device, which can be a mercury column or a simple aneroid manometer. Usually the cuff is wrapped tightly around the arm above the elbow and inflated until the pulse at the wrist disappears. The brachial artery is found at the level of the elbow bend and a stethoscope is placed over it, after which air is slowly released from the cuff. When the pressure in the cuff is reduced to a level that allows blood to flow through the artery, a sound is heard with a stethoscope. The readings of the measuring device at the time of the appearance of this first sound (tone) correspond to the level of systolic blood pressure. With further release of air from the cuff, the nature of the sound changes significantly or it completely disappears. This moment corresponds to the level of diastolic pressure.
In a healthy person, blood pressure fluctuates throughout the day depending on emotional state, stress, sleep and many other physical and mental factors. These fluctuations reflect certain shifts in the fine balance that exists in the norm, which is maintained as nerve impulses coming from the centers of the brain through the sympathetic nervous system, and changes in chemical composition blood, which have a direct or indirect regulatory effect on blood vessels. With a strong emotional stress sympathetic nerves cause small, muscular-type arteries to constrict, resulting in an increase in blood pressure and pulse rate. Yet greater value has a chemical balance, the influence of which is mediated not only by the brain centers, but also by individual nerve plexuses associated with the aorta and carotid arteries. The sensitivity of this chemical regulation is illustrated, for example, by the effect of accumulation of carbon dioxide in the blood. With an increase in its level, the acidity of the blood increases; this both directly and indirectly causes the contraction of the walls of the peripheral arteries, which is accompanied by an increase in blood pressure. At the same time, the heart rate increases, but the vessels of the brain paradoxically expand. The combination of these physiological reactions ensures a stable supply of oxygen to the brain due to an increase in the volume of incoming blood.
It is the fine regulation of blood pressure that allows you to quickly change horizontal position the body to a vertical position without significant movement of blood to the lower extremities, which could cause fainting due to insufficient blood supply to the brain. In such cases, the walls of the peripheral arteries contract and oxygenated blood is directed mainly to the vital organs. Vasomotor (vasomotor) mechanisms are even more important for animals such as the giraffe, whose brain, when it raises its head after drinking, moves up almost 4 m in a few seconds. A similar decrease in blood content in the vessels of the skin, digestive tract and liver occurs in moments of stress emotional experiences, shock and injury, which allows the brain, heart and muscles to receive more oxygen and nutrients.
Such fluctuations in blood pressure are normal, but its changes are also observed with a number of pathological conditions. In heart failure, the force of contraction of the heart muscle can drop so much that blood pressure is too low ( arterial hypotension). Similarly, loss of blood or other fluids due to severe burns or bleeding can cause both systolic and diastolic blood pressure to drop to dangerous levels. With some congenital heart defects (for example, non-closure of the arterial duct) and a number of lesions of the valvular apparatus of the heart (for example, aortic valve insufficiency) drops sharply peripheral resistance. In such cases, systolic pressure may remain normal, but diastolic pressure drops significantly, which means an increase in pulse pressure.
The regulation of blood pressure in the body and the maintenance of the necessary blood supply to the organs are the best way to understand the enormous complexity of the organization and operation of the circulatory system. This truly wonderful transport system is a real "lifeline" of the body, since the lack of blood supply to any vital organ, primarily the brain, for at least a few minutes leads to its irreversible damage and even death.
DISEASES OF THE BLOOD VESSELS
Diseases of the blood vessels (vascular diseases) are conveniently considered according to the type of vessels in which pathological changes develop. Stretching of the walls of blood vessels or the heart itself leads to the formation of aneurysms (saccular protrusions). Usually this is a consequence of the development of scar tissue in a number of diseases of the coronary vessels, syphilitic lesions or hypertension. Aortic or ventricular aneurysm is the most serious complication cardiovascular disease; it can rupture spontaneously, causing fatal bleeding.
Aorta.
The largest artery, the aorta, must contain the blood ejected under pressure from the heart and, due to its elasticity, move it to smaller arteries. Infectious (most often syphilitic) and arteriosclerotic processes can develop in the aorta; rupture of the aorta due to trauma or congenital weakness of its walls is also possible. high blood pressure often leads to chronic dilatation of the aorta. However, aortic disease is less important than heart disease. Her most severe lesions are extensive atherosclerosis and syphilitic aortitis.
Atherosclerosis.
Aortic atherosclerosis is a form of simple arteriosclerosis of the inner lining of the aorta (intima) with granular (atheromatous) fatty deposits in and under this layer. One of the severe complications of this disease of the aorta and its main branches (innominate, iliac, carotid and renal arteries) is the formation of blood clots on the inner layer, which can interfere with blood flow in these vessels and lead to a catastrophic disruption of the blood supply to the brain, legs and kidneys. This kind of obstructive (obstructing blood flow) lesions of some large vessels can be eliminated surgically(vascular surgery).
Syphilitic aortitis.
The decrease in the prevalence of syphilis itself makes the inflammation of the aorta caused by it more rare. It manifests itself approximately 20 years after infection and is accompanied by a significant expansion of the aorta with the formation of aneurysms or the spread of infection to the aortic valve, which leads to its insufficiency (aortic regurgitation) and overload of the left ventricle of the heart. Narrowing of the mouth of the coronary arteries is also possible. Any of these conditions can lead to death, sometimes very quickly. The age at which aortitis and its complications appear ranges from 40 to 55 years; the disease is more common in men.
Arteriosclerosis
of the aorta, accompanied by a loss of elasticity of its walls, is characterized by damage not only to the intima (as in atherosclerosis), but also to the muscular layer of the vessel. This is a disease of the elderly, and with increasing life expectancy of the population, it is becoming more common. The loss of elasticity reduces the efficiency of blood flow, which in itself can lead to aneurysm-like expansion of the aorta and even to its rupture, especially in the abdominal region. Currently, sometimes it is possible to cope with this condition surgically ( see also ANEURYSM).
Pulmonary artery.
Lesions of the pulmonary artery and its two main branches are not numerous. In these arteries, arteriosclerotic changes sometimes occur, and there are also birth defects. The two most important changes are: 1) expansion of the pulmonary artery due to an increase in pressure in it due to any obstruction to blood flow in the lungs or on the way of blood to the left atrium and 2) blockage (embolism) of one of its main branches due to the passage of a blood clot from inflamed large veins of the lower leg (phlebitis) through the right half of the heart, which is common cause sudden death.
Arteries of medium caliber.
by the most common illness medium arteries is arteriosclerosis. With its development in the coronary arteries of the heart, the inner layer of the vessel (intima) is affected, which can lead to complete blockage of the artery. Depending on the degree of injury and general condition The patient is undergoing either balloon angioplasty or coronary bypass surgery. In balloon angioplasty, a catheter with a balloon at the end is inserted into the affected artery; inflation of the balloon leads to flattening of the deposits along the arterial wall and expansion of the lumen of the vessel. During shunting operations, a section of the vessel is cut out from another part of the body and sewn into coronary artery bypassing the narrowed area, restoring normal blood flow.
When the arteries of the legs and arms are affected, the middle, muscular layer of the vessels (media) thickens, which leads to their thickening and curvature. The defeat of these arteries has relatively less severe consequences.
Arterioles.
Damage to arterioles creates an obstacle to free blood flow and leads to an increase in blood pressure. However, even before the arterioles are sclerosed, spasms of unknown origin may occur, which is a common cause of hypertension.
Vienna.
Vein diseases are very common. Most common varicose veins veins lower extremities; this condition develops under the influence of gravity during obesity or pregnancy, and sometimes due to inflammation. In this case, the function of the venous valves is disturbed, the veins are stretched and overflowed with blood, which is accompanied by swelling of the legs, the appearance of pain and even ulceration. Various surgical procedures are used for treatment. Relief of the disease is facilitated by training the muscles of the lower leg and reducing body weight. Another pathological process - inflammation of the veins (phlebitis) - is also most often observed in the legs. In this case, there are obstructions to blood flow with a violation of local circulation, but the main danger of phlebitis is the separation of small blood clots (emboli), which can pass through the heart and cause circulatory arrest in the lungs. This condition, called pulmonary embolism, is very serious and often fatal. The defeat of large veins is much less dangerous and is much less common.
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