Heart. Systemic and pulmonary circulation
The heart has complex structure and performs no less complex and important work. Contracting rhythmically, it ensures blood flow through the vessels.
The heart is located behind the sternum, in the middle section of the chest cavity and is almost completely surrounded by the lungs. It may move slightly to the side as it hangs freely on the blood vessels. The heart is located asymmetrically. Its long axis is inclined and forms an angle of 40° with the axis of the body. It is directed from top to right, forward, down to the left, and the heart is rotated so that its right section is tilted more forward, and the left one – back. Two-thirds of the heart is to the left of the midline and one-third (the vena cava and right atrium) is to the right. Its base is turned towards the spine, and its apex is facing the left ribs, to be more precise, the fifth intercostal space.
Anatomy of the heart
Sternocostal surface the hearts are more convex. It is located behind the sternum and cartilages of the III-VI ribs and is directed forward, upward, and to the left. The transverse coronary groove runs along it, which separates the ventricles from the atria and thereby divides the heart into top part, formed by the atria, and the lower one, consisting of the ventricles. Another groove of the sternocostal surface - the anterior longitudinal - runs along the border between the right and left ventricles, with the right one forming the largest part of the anterior surface, the left one the smaller one.
Diaphragmatic surface flatter and adjacent to the tendon center of the diaphragm. A longitudinal posterior groove runs along this surface, separating the surface of the left ventricle from the surface of the right. In this case, the left one makes up the majority of the surface, and the right one makes up the smaller part.
Anterior and posterior longitudinal grooves they merge at their lower ends and form a cardiac notch to the right of the cardiac apex.
There are also side surfaces located on the right and left and facing the lungs, which is why they are called pulmonary.
Right and left edges hearts are not the same. The right edge is more pointed, the left is more blunt and rounded due to the thicker wall of the left ventricle.
The boundaries between the four chambers of the heart are not always clearly defined. The landmarks are the grooves in which the blood vessels of the heart are located, covered with fatty tissue and the outer layer of the heart - the epicardium. The direction of these grooves depends on how the heart is located (obliquely, vertically, transversely), which is determined by the body type and the height of the diaphragm. In mesomorphs (normosthenics), whose proportions are close to the average, it is located obliquely, in dolichomorphs (asthenics) with a thin physique - vertically, in brachymorphs (hypersthenics) with wide short forms - transversely.
The heart seems to be suspended by the base on large vessels, while the base remains motionless, and the apex is in a free state and can move.
Structure of heart tissue
The heart wall is made up of three layers:
- Endocardium - inner layer epithelial tissue, lining the cavities of the heart chambers from the inside, accurately repeating their relief.
- Myocardium is a thick layer formed muscle tissue(cross-striped). The cardiac myocytes of which it consists are connected by many bridges that link them into muscle complexes. This muscle layer ensures the rhythmic contraction of the chambers of the heart. The myocardium is thinnest at the atria, the greatest is at the left ventricle (about 3 times thicker than the right), since it needs more force to push blood into the systemic circulation, in which the resistance to flow is several times greater than in the small circle. The atrial myocardium consists of two layers, the ventricular myocardium - of three. The atrial myocardium and ventricular myocardium are separated by fibrous rings. The conduction system that provides rhythmic contraction of the myocardium is one for the ventricles and atria.
- Epicardium – outer layer, which is the visceral petal of the heart sac (pericardium), which is a serous membrane. It covers not only the heart, but also the initial parts of the pulmonary trunk and aorta, as well as the final parts of the pulmonary and vena cava.
Anatomy of the atria and ventricles
The cardiac cavity is divided by a septum into two parts - right and left, which do not communicate with each other. Each of these parts consists of two chambers - the ventricle and the atrium. The septum between the atria is called the interatrial septum, and the septum between the ventricles is called the interventricular septum. Thus, the heart consists of four chambers - two atria and two ventricles.
Right atrium
It is shaped like an irregular cube, with an additional cavity in front called the right ear. The atrium has a volume of 100 to 180 cubic meters. cm. It has five walls, 2 to 3 mm thick: anterior, posterior, superior, lateral, medial.
The inferior vena cava (below) also flows into the right atrium (from above, from behind). On the lower right is the coronary sinus, where the blood of all the cardiac veins drains. Between the openings of the superior and inferior vena cava there is an intervenous tubercle. In the place where the inferior vena cava flows into the right atrium, there is a fold of the inner layer of the heart - the valve of this vein. The sinus of the vena cava is the posterior dilated section of the right atrium, into which both of these veins flow.
The chamber of the right atrium has a smooth internal surface, and only in the right appendage with the adjacent anterior wall the surface is uneven.
Many pinpoint openings of the small veins of the heart open into the right atrium.
Right ventricle
It consists of a cavity and an arterial cone, which is a funnel directed upward. The right ventricle has the shape of a triangular pyramid, the base of which faces upward and the apex faces downward. The right ventricle has three walls: anterior, posterior, medial.
The front is convex, the back is flatter. Medial is interventricular septum, consisting of two parts. The larger one, the muscular one, is located at the bottom, the smaller one, the membranous one, is at the top. The pyramid faces the atrium with its base and has two openings: posterior and anterior. The first is between the cavity of the right atrium and the ventricle. The second goes into the pulmonary trunk.
Left atrium
It has the appearance of an irregular cube, is located behind and adjacent to the esophagus and the descending aorta. Its volume is 100-130 cubic meters. cm, wall thickness – from 2 to 3 mm. Like the right atrium, it has five walls: anterior, posterior, superior, literal, medial. The left atrium continues anteriorly into an additional cavity called the left appendage, which is directed towards the pulmonary trunk. Four pulmonary veins flow into the atrium (back and above), in the openings of which there are no valves. The medial wall is interatrial septum. The inner surface of the atrium is smooth, the pectineus muscles are present only in the left appendage, which is longer and narrower than the right one, and is noticeably separated from the ventricle by an interception. It communicates with the left ventricle via the atrioventricular orifice.
Left ventricle
It is shaped like a cone, the base of which faces upward. The walls of this chamber of the heart (anterior, posterior, medial) have the greatest thickness - from 10 to 15 mm. There is no clear boundary between the front and back. At the base of the cone are the openings of the aorta and the left atrioventricular opening.
The round opening of the aorta is located in front. Its valve consists of three valves.
Heart size
The size and weight of the heart varies from person to person. The average values are as follows:
- length is from 12 to 13 cm;
- greatest width – from 9 to 10.5 cm;
- anteroposterior size – from 6 to 7 cm;
- weight in men - about 300 g;
- weight in women is about 220 g.
Functions of the cardiovascular system and heart
The heart and blood vessels make up the cardiovascular system, the main function of which is transport. It consists of supplying tissues and organs with nutrition and oxygen and returning metabolic products.
The heart acts as a pump - it ensures continuous circulation of blood in the circulatory system and delivery of nutrients and oxygen to organs and tissues. Under stress or physical exertion, its work immediately changes: it increases the number of contractions.
The work of the heart muscle can be described as follows: its right part(venous heart) receives waste blood saturated with carbon dioxide from the veins and gives it to the lungs to be saturated with oxygen. From the lungs, O2-enriched blood is sent to left side heart (arterial) and from there is forcefully pushed into the bloodstream.
The heart produces two circles of blood circulation - large and small.
The large one supplies blood to all organs and tissues, including the lungs. It begins in the left ventricle and ends in the right atrium.
The pulmonary circulation produces gas exchange in the alveoli of the lungs. It begins in the right ventricle and ends in the left atrium.
Blood flow is regulated by valves: they prevent it from flowing in the opposite direction.
The heart has such properties as excitability, conductivity, contractility and automaticity (excitation without external stimuli under the influence of internal impulses).
Thanks to the conduction system, sequential contraction of the ventricles and atria occurs, and the synchronous inclusion of myocardial cells in the contraction process.
Rhythmic contractions of the heart ensure a portioned flow of blood into the circulatory system, but its movement in the vessels occurs without interruption, which is due to the elasticity of the walls and the resulting small vessels resistance to blood flow.
The circulatory system has a complex structure and consists of a network of vessels for different purposes: transport, shunting, exchange, distribution, capacitance. There are veins, arteries, venules, arterioles, capillaries. Together with the lymphatic ones, they maintain the constancy of the internal environment in the body (pressure, body temperature, etc.).
Arteries move blood from the heart to the tissues. As they move away from the center, they become thinner, forming arterioles and capillaries. Arterial bed circulatory system carries out transportation necessary substances to organs and maintains constant pressure in the vessels.
The venous bed is more extensive than the arterial bed. Veins move blood from tissues to the heart. Veins are formed from venous capillaries, which, merging, first become venules, then veins. They form large trunks near the heart. Distinguish superficial veins, located under the skin, and deep, located in the tissues near the arteries. The main function of the venous part of the circulatory system is the outflow of blood, rich in products metabolism and carbon dioxide.
To assess the functional capabilities of the cardiovascular system and the permissibility of stress, special tests are carried out, which make it possible to assess the performance of the body and its compensatory capabilities. Functional tests of the cardiovascular system are included in the physical examination to determine the degree of fitness and general physical fitness. The assessment is based on such indicators of the heart and blood vessels as blood pressure, pulse pressure, blood flow speed, minute and stroke volumes of blood. Such tests include Letunov's tests, step tests, Martinet's test, Kotov's - Demin's test.
The heart begins to beat from the fourth week after conception and does not stop until the end of life. It does a gigantic job: per year it pumps about three million liters of blood and makes about 35 million heartbeats. At rest, the heart uses only 15% of its resource, and under load – up to 35%. Over an average lifespan, it pumps about 6 million liters of blood. Another interesting fact: The heart supplies blood to 75 trillion cells in the human body, excluding the cornea of the eyes.
Circulation circles in humans: evolution, structure and work of large and small, additional features
IN human body the circulatory system is designed to fully meet its internal needs. An important role in the movement of blood is played by the presence of a closed system in which arterial and venous blood flows are separated. And this is done through the presence of blood circulation circles.
Historical reference
In the past, when scientists did not yet have informative instruments at hand capable of studying physiological processes in a living organism, the greatest scientists were forced to search anatomical features at the corpses. Naturally, the heart of a deceased person does not contract, so some nuances had to be figured out on their own, and sometimes simply fantasized. So, back in the second century AD Claudius Galen, self-learner Hippocrates, assumed that the arteries contained air instead of blood in their lumen. Over the next centuries, many attempts were made to combine and link together the existing anatomical data from the standpoint of physiology. All scientists knew and understood how the circulatory system works, but how does it work?
Scientists have made a tremendous contribution to the systematization of data on heart function. Miguel Servet and William Harvey in the 16th century. Harvey, scientist who first described the systemic and pulmonary circulation , in 1616 determined the presence of two circles, but he could not explain in his works how the arterial and venous beds were connected to each other. And only later, in the 17th century, Marcello Malpighi, one of the first to use a microscope in his practice, discovered and described the presence of tiny capillaries, invisible to the naked eye, which serve as a connecting link in the blood circulation.
Phylogeny, or the evolution of blood circulation
Due to the fact that, as animals of the vertebrate class evolved, they became more and more progressive in anatomical and physiological terms, they required a complex structure of the cardiovascular system. Thus, for faster movement of the liquid internal environment in the body of a vertebrate animal, the need for a closed blood circulation system arose. Compared to other classes of the animal kingdom (for example, arthropods or worms), the rudiments of a closed vascular system appear in chordates. And if the lancelet, for example, does not have a heart, but there is an abdominal and dorsal aorta, then in fish, amphibians (amphibians), reptiles (reptiles) a two- and three-chambered heart appears, respectively, and in birds and mammals a four-chambered heart appears, the peculiarity of which is is the focus in it of two circles of blood circulation that do not mix with each other.
Thus, the presence in birds, mammals and humans, in particular, of two separated circulatory circles is nothing more than the evolution of the circulatory system, necessary for better adaptation to conditions environment.
Anatomical features of the blood circulation
The circulatory system is a set of blood vessels, which is a closed system for the supply of oxygen and nutrients to the internal organs through gas exchange and nutrient exchange, as well as for the removal of carbon dioxide and other metabolic products from cells. The human body is characterized by two circles - the systemic, or large circle, and the pulmonary, also called the small circle.
Video: blood circulation circles, mini-lecture and animation
Systemic circulation
The main function of the large circle is to ensure gas exchange in all internal organs except the lungs. It begins in the cavity of the left ventricle; represented by the aorta and its branches, the arterial bed of the liver, kidneys, brain, skeletal muscles and other organs. Further, this circle continues with the capillary network and venous bed of the listed organs; and through the entry of the vena cava into the cavity of the right atrium it ends in the latter.
So, as already said, the beginning of the great circle is the cavity of the left ventricle. Arterial blood flow, which contains more oxygen than carbon dioxide, is sent here. This flow enters the left ventricle directly from the circulatory system of the lungs, that is, from the small circle. The arterial flow from the left ventricle is pushed through the aortic valve into the largest great vessel - the aorta. The aorta can be figuratively compared to a kind of tree, which has many branches, because arteries extend from it to the internal organs (liver, kidneys, gastrointestinal tract, to the brain - through the system carotid arteries, to skeletal muscles, to subcutaneous fat, etc.). Organ arteries, which also have numerous branches and bear names corresponding to their anatomy, carry oxygen to each organ.
In tissues internal organs arterial vessels are divided into vessels of smaller and smaller diameter, and as a result a capillary network is formed. Capillaries are the smallest vessels that practically do not have a middle muscular layer, and are represented inner shell- intima, lined with endothelial cells. The gaps between these cells at the microscopic level are so large compared to other vessels that they allow proteins, gases and even shaped elements into the intercellular fluid of surrounding tissues. Thus, intense gas exchange and exchange of other substances occurs between the capillary with arterial blood and the liquid intercellular medium in a particular organ. Oxygen penetrates from the capillary, and carbon dioxide, as a product of cell metabolism, enters the capillary. The cellular stage of respiration occurs.
After more oxygen has passed into the tissues and all carbon dioxide has been removed from the tissues, the blood becomes venous. All gas exchange occurs with each new influx of blood, and during the period of time while it moves along the capillary towards the venule - a vessel that collects venous blood. That is, with each cardiac cycle, in one or another part of the body, oxygen enters the tissues and carbon dioxide is removed from them.
These venules unite into larger veins, and a venous bed is formed. Veins, similar to arteries, are named according to the organ in which they are located (renal, cerebral, etc.). From large venous trunks, tributaries of the superior and inferior vena cava are formed, and the latter then flow into the right atrium.
Features of blood flow in the organs of the systemic circle
Some of the internal organs have their own characteristics. So, for example, in the liver there is not only a hepatic vein, which “carries” the venous flow away from it, but also a portal vein, which, on the contrary, brings blood to the liver tissue, where blood purification is performed, and only then the blood collects in the tributaries of the hepatic vein to enter to a big circle. Portal vein brings blood from the stomach and intestines, so everything that a person eats or drinks must undergo a kind of “cleaning” in the liver.
In addition to the liver, certain nuances exist in other organs, for example, in the tissues of the pituitary gland and kidneys. Thus, in the pituitary gland the presence of a so-called “wonderful” capillary network is noted, because the arteries that bring blood to the pituitary gland from the hypothalamus are divided into capillaries, which then collect into venules. The venules, after the blood with the molecules of releasing hormones are collected, are again divided into capillaries, and then veins are formed that carry the blood from the pituitary gland. In the kidneys, the arterial network is divided twice into capillaries, which is associated with the processes of excretion and reabsorption in the kidney cells - in the nephrons.
Pulmonary circulation
Its function is to carry out gas exchange processes in lung tissue in order to saturate the “waste” venous blood with oxygen molecules. It begins in the cavity of the right ventricle, where venous blood flow with an extremely small amount of oxygen and with high content carbon dioxide. This blood moves through the pulmonary valve into one of the large vessels called the pulmonary trunk. Next, the venous flow moves along the arterial bed in the lung tissue, which also breaks up into a network of capillaries. By analogy with capillaries in other tissues, gas exchange occurs in them, only oxygen molecules enter the lumen of the capillary, and carbon dioxide penetrates into the alveolocytes (cells of the alveoli). With each act of breathing, air enters the alveoli from the environment, from which oxygen penetrates through the cell membranes into the blood plasma. When exhaling, the carbon dioxide that enters the alveoli is expelled with the exhaled air.
After being saturated with O2 molecules, the blood acquires the properties of arterial blood, flows through the venules and ultimately reaches the pulmonary veins. The latter, consisting of four or five pieces, open into the cavity of the left atrium. As a result, venous blood flows through the right half of the heart, and through left half- arterial; and normally these flows should not mix.
Lung tissue has a double network of capillaries. With the help of the first, gas exchange processes are carried out in order to enrich the venous flow with oxygen molecules (relationship directly with the small circle), and in the second, the lung tissue itself is supplied with oxygen and nutrients (relationship with the large circle).
Additional circulation circles
These concepts are used to distinguish the blood supply of individual organs. For example, to the heart, which needs oxygen more than others, arterial inflow is carried out from the branches of the aorta at its very beginning, which are called the right and left coronary (coronary) arteries. Intense gas exchange occurs in the capillaries of the myocardium, and venous drainage carried out into the coronary veins. The latter collect in the coronary sinus, which opens directly into the right atrial chamber. In this way it is carried out cardiac or coronary circulation.
coronary (coronary) circle of blood circulation in the heart
Circle of Willis is a closed arterial network of cerebral arteries. The medulla provides additional blood supply to the brain when cerebral blood flow through other arteries is disrupted. This protects such an important organ from lack of oxygen, or hypoxia. The cerebral circulation is represented by the initial segment of the anterior cerebral artery, the initial segment of the posterior cerebral artery, anterior and posterior communicating arteries, and internal carotid arteries.
Circle of Willis in the brain (classical variant of the structure)
Placental circulation functions only during pregnancy by a woman and performs the function of “breathing” in a child. The placenta is formed starting from 3-6 weeks of pregnancy, and begins to function fully from the 12th week. Due to the fact that the fetus's lungs do not work, oxygen enters its blood through the flow of arterial blood into the baby's umbilical vein.
fetal circulation before birth
Thus, the entire human circulatory system can be divided into separate interconnected sections that perform their functions. The proper functioning of such areas, or blood circulation circles, is the key to the healthy functioning of the heart, blood vessels and the entire body as a whole.
Blood circulation is the continuous movement of blood along a closed cardiac circuit. vascular system, providing vital important functions body. The cardiovascular system includes organs such as the heart and blood vessels.
Heart
The heart is the central circulatory organ that ensures the movement of blood through the vessels.
The heart is a hollow four-chambered muscular organ, shaped like a cone, located in the chest cavity, in the mediastinum. It is divided into right and left halves by a continuous partition. Each half consists of two sections: the atrium and the ventricle, connected to each other by an opening that is closed by a leaflet valve. In the left half, the valve consists of two valves, in the right - of three. The valves open towards the ventricles. This is facilitated by tendon filaments, which are attached at one end to the valve leaflets, and at the other to the papillary muscles located on the walls of the ventricles. During ventricular contraction, tendon threads prevent the valves from everting towards the atrium. Blood enters the right atrium from the superior and inferior vena cava and the coronary veins of the heart itself; four pulmonary veins flow into the left atrium.
The ventricles give rise to vessels: the right one - the pulmonary trunk, which is divided into two branches and carries venous blood to the right and left lungs, that is, to the pulmonary circulation; the left ventricle gives rise to the left aortic arch, but which arterial blood enters the systemic circulation. At the border of the left ventricle and the aorta, the right ventricle and the pulmonary trunk, there are semilunar valves (three cusps in each). They close the lumens of the aorta and pulmonary trunk and allow blood to pass from the ventricles into the vessels, but prevent the reverse flow of blood from the vessels to the ventricles.
The wall of the heart consists of three layers: the inner - endocardium, formed by epithelial cells, the middle - myocardium, muscle and outer - epicardium, consisting of connective tissue.
The heart lies freely in the pericardial sac of connective tissue, where fluid is constantly present, moisturizing the surface of the heart and ensuring its free contraction. The main part of the heart wall is muscular. The greater the force of muscle contraction, the more powerfully developed is the muscular layer of the heart, for example, the greatest thickness of the walls is in the left ventricle (10–15 mm), the walls of the right ventricle are thinner (5–8 mm), and the walls of the atria are even thinner (23 mm).
The structure of the heart muscle is similar to the striated muscles, but differs from them in the ability to automatically contract rhythmically due to impulses arising in the heart itself, regardless of external conditions- automaticity of the heart. This is due to special nerve cells located in the heart muscle, in which excitations occur rhythmically. The automatic contraction of the heart continues even when it is isolated from the body.
Normal metabolism in the body is ensured by the continuous movement of blood. Blood in the cardiovascular system flows in only one direction: from the left ventricle through the systemic circulation it enters the right atrium, then into the right ventricle and then through the pulmonary circulation it returns to the left atrium, and from there to the left ventricle. This movement of blood is determined by the work of the heart due to the sequential alternation of contractions and relaxations of the heart muscle.
There are three phases in the work of the heart: the first is contraction of the atria, the second is contraction of the ventricles (systole), the third is the simultaneous relaxation of the atria and ventricles, diastole, or pause. The heart beats rhythmically about 70–75 times per minute when the body is at rest, or 1 time every 0.8 seconds. Of this time, contraction of the atria accounts for 0.1 seconds, contraction of the ventricles accounts for 0.3 seconds, and the total pause of the heart lasts 0.4 seconds.
The period from one atrial contraction to another is called the cardiac cycle. The continuous activity of the heart consists of cycles, each of which consists of contraction (systole) and relaxation (diastole). The heart muscle, the size of a fist and weighing about 300 g, works continuously for decades, contracts about 100 thousand times a day and pumps more than 10 thousand liters of blood. Such high performance of the heart is due to its increased blood supply and high level metabolic processes occurring in it.
Nervous and humoral regulation of the activity of the heart coordinates its work with the needs of the body at each this moment regardless of our will.
The heart as a working organ is regulated by the nervous system in accordance with the influences of the external and internal environment. Innervation occurs with the participation of the autonomic nervous system. However, a pair of nerves (sympathetic fibers), when irritated, strengthen and speed up heart contractions. When another pair of nerves (parasympathetic, or vagus) is irritated, impulses entering the heart weaken its activity.
The activity of the heart is also influenced by humoral regulation. Thus, adrenaline produced by the adrenal glands has the same effect on the heart as the sympathetic nerves, and an increase in potassium in the blood inhibits the heart, just like the parasympathetic (vagus) nerves.
Circulation
The movement of blood through vessels is called circulation. Only by being constantly in motion does blood carry out its main functions: delivery of nutrients and gases and removal from tissues and organs final products decay.
Blood moves through blood vessels - hollow tubes of various diameters, which, without interruption, pass into others, forming a closed circulatory system.
Three types of vessels of the circulatory system
There are three types of vessels: arteries, veins and capillaries. Arteries called the vessels through which blood flows from the heart to the organs. The largest of them is the aorta. In organs, arteries branch into vessels of smaller diameter - arterioles, which in turn break up into capillaries. Moving through the capillaries, arterial blood gradually turns into venous blood, which flows through veins.
Two circles of blood circulation
All arteries, veins and capillaries in the human body are combined into two circles of blood circulation: large and small. Systemic circulation begins in the left ventricle and ends in the right atrium. Pulmonary circulation begins in the right ventricle and ends in the left atrium.
Blood moves through the vessels due to the rhythmic work of the heart, as well as the difference in pressure in the vessels when blood leaves the heart and in the veins when it returns to the heart. Rhythmic fluctuations in the diameter of arterial vessels caused by the work of the heart are called pulse.
Using your pulse, you can easily determine the number of heartbeats per minute. The pulse wave propagation speed is about 10 m/s.
The speed of blood flow in the vessels is about 0.5 m/s in the aorta, and only 0.5 mm/s in the capillaries. Due to such a low speed of blood flow in the capillaries, the blood has time to give oxygen and nutrients to the tissues and accept their waste products. The slowdown in blood flow in the capillaries is explained by the fact that their number is huge (about 40 billion) and, despite their microscopic size, their total lumen is 800 times larger than the lumen of the aorta. In the veins, with their enlargement as they approach the heart, the total lumen of the bloodstream decreases, and the speed of blood flow increases.
Blood pressure
When the next portion of blood is ejected from the heart into the aorta and into the pulmonary artery, high blood pressure is created in them. Blood pressure rises when the heart pumps faster and harder into the aorta. more blood, as well as with narrowing of arterioles.
If the arteries dilate, blood pressure drops. Blood pressure is also affected by the amount of circulating blood and its viscosity. As you move away from the heart, blood pressure decreases and becomes lowest in the veins. Difference between high pressure blood in the aorta and pulmonary artery and low, even negative pressure in the vena cava and pulmonary veins ensures a continuous flow of blood throughout the entire circulation.
In healthy people, the maximum blood pressure in the brachial artery at rest is normally about 120 mmHg. Art., and the minimum is 70–80 mm Hg. Art.
A persistent increase in blood pressure at rest is called hypertension, and a decrease in blood pressure is called hypotension. In both cases, the blood supply to the organs is disrupted and their working conditions worsen.
First aid for blood loss
First aid for blood loss is determined by the nature of the bleeding, which can be arterial, venous or capillary.
The most dangerous arterial bleeding occurs when the arteries are injured, and the blood is bright scarlet in color and flows in a strong stream (spring). If an arm or leg is injured, it is necessary to raise the limb, keep it in a bent position, and press the damaged artery with a finger above the wound site (closer to the heart); then you need to apply a tight bandage made of a bandage, towel, or piece of cloth above the wound site (also closer to the heart). A tight bandage should not be left in place for more than an hour and a half, so the victim must be taken to a medical facility as soon as possible.
With venous bleeding, the flowing blood is darker in color; to stop it, the damaged vein is pressed with a finger at the wound site, the arm or leg is bandaged below it (further from the heart).
With a small wound, capillary bleeding appears, to stop which it is enough to apply a tight sterile bandage. The bleeding will stop due to the formation of a blood clot.
Lymph circulation
It's called lymph circulation, moving lymph through the vessels. Lymphatic system promotes additional outflow of fluid from organs. Lymph movement is very slow (03 mm/min). It moves in one direction - from the organs to the heart. Lymphatic capillaries become larger vessels, which collect in the right and left thoracic ducts, which flow into large veins. Along the course of the lymphatic vessels there are The lymph nodes: in the groin, popliteal and armpits, under the lower jaw.
The lymph nodes contain cells (lymphocytes) that have a phagocytic function. They neutralize microbes and utilize foreign substances that have entered the lymph, causing the lymph nodes to swell and become painful. Tonsils are lymphoid accumulations in the pharynx area. Sometimes they are stored pathogens, metabolic products of which negatively affect the function of internal organs. Often resort to surgical removal of the tonsils.
In the body's blood supply system there are two main circles, one of which, the pulmonary one, is called the pulmonary circulation circle, since its extent is small. This element of the blood supply system covers only the lungs of the body. This blood supply system is typical for mammals.
Features of the structure of the body's blood supply system
Before talking about the small circle, it is worth saying a few words about what the circulatory circuit consists of. In warm-blooded animals, the blood supply system is of the completely closed type. It is considered complete because there is no mixing of arterial and venous blood. Closed type means that the blood circulation process does not involve communication with the external environment.
Even though blood is connective tissue, it is in constant motion: it flows through an extensive network of vessels to all parts of the body, organs, and tissues. The circulatory system includes blood vessels and the heart. Vessels can be divided into several types: arteries, veins, and the third type of vessels - capillaries.
Arteries are vessels that carry blood away from the heart. Distinctive feature arteries have elastic, but very thick walls. The aorta is the largest artery in the body.
Veins carry blood to the heart. Their walls are much thinner than those of arteries.
Capillaries are the thinnest vessels that form a branched blood network that passes to all tissues throughout the body. The capillaries have a small diameter - thinner than a hair. Their walls consist of only one layer of tissue, through which gas, white blood cells and various soluble substances can easily pass.
The direction of blood flow is determined by valves. The valves open towards the ventricles, they regulate the movement of blood from the atria. Lunates prevent arterial blood from returning to the ventricle. They are semicircular pockets located at the exit of the artery. Under the influence of blood, the semilunar valves straighten, fill with blood and close. As a result, the passage into the ventricle from the pulmonary circle and the aorta closes. The work of the circulatory system is carried out by special regulatory systems. The body has nervous and humoral regulation of blood circulation.
The central organ of the circulatory system is the heart, which is a pump that forces blood to move through the vessels. This organ has a cone shape and is located in the chest, slightly to the left of center, between the lungs. Heart size approx. equal to the value fist, and the mass can be from 250 to 300 g.
The heart is located in the cardiac sac - a special sac containing a certain amount of fluid that wets the surface of the heart. This allows you to reduce friction during heart contractions.
The heart is a hollow organ consisting of four chambers: two atria, left and right, and two ventricles, left and right. The ventricles are different from the atria large size and greater thickness of the walls, and the wall of the left ventricle is best developed. Both parts of the organ do not communicate with each other.
This structure of the organ is explained by the purpose of the cavities: the atria only drive blood into the ventricles, which means they perform less work. The ventricles push blood into the circulation so that under the influence of great force it diverges to the most distant areas.
The concept of blood circulation
The general circuit of blood supply in the body includes the systemic and pulmonary circulation. This structural feature of the circulatory system of mammals or warm-blooded animals and humans became known after the discovery of blood circulation in two circles by William Harvey in the 17th century. He came to the idea that blood returns to the heart after completing its circuit in the same way as the Earth revolves around the Sun. Since the microscope had not yet been invented at that time and nothing was known about the existence of capillaries, Harvey’s discovery of the systemic and pulmonary circulation became a scientific foresight.
The circulatory system is closed circles, through which nutrients and oxygen are delivered to cells and metabolic products and carbon dioxide are carried away.
The blood circulation consists of two “loops” of vessels connected to each other. Blood first passes through the pulmonary circulation and then through the systemic circulation. Consistency is ensured by special valves.
At the same time, “additional” circles are distinguished:
- placental;
- coronary;
- Circle of Willis.
The placental circle exists only while the fetus is in the uterus. In this case, blood from the mother’s body passes into the fetal placenta, where it transfers nutrients to the capillaries of the baby’s umbilical vein.
Coronary circle of blood supply - heart circle blood circulation It is a component of the great circle, but due to the importance of the heart, in some sources it is singled out as a separate element.
The circle of Willis runs at the base of the brain and is necessary to compensate for the lack of blood supply.
The systemic circulation starts from the left ventricle and ends at the right atrium. (arterial, bright scarlet) is pushed out and pumped into the aorta, the widest vessel. The aorta divides into a large number of arteries, forming parallel vascular networks. Through them, blood flows to organs and tissues: the brain, organs abdominal cavity. IN lumbar region the artery branches: one “connects” the lower limbs to the circulatory network, the other - the genitals.
Already in organs, arteries branch into capillaries, through the walls of which nutrients and oxygen enter the tissue fluid from the blood. There, the blood is saturated with carbon dioxide, collects metabolic products, becoming venous, darker than arterial.
From capillaries deoxygenated blood passes into veins, which, connecting, make up larger veins.
From the lower extremities, trunk and abdominal cavity, venous blood enters the vein, from where it passes into the right atrium. This is where blood comes from the head, upper limbs and neck through the superior vena cava. This is where the systemic circulation ends.
Vessels belonging to the great circle can be seen on the folds, for example, they are usually clearly visible on the elbow bends.
What is the pulmonary circulation?
The path that blood takes from the right ventricle to the atrium is much shorter than the large one. That's why it got the name "small". The main task of this circle is to carry out gas exchange in the alveoli of the lungs and heat transfer.
At the same time, the pulmonary circle performs several more functions:
- Gas exchange between blood and alveolar air.
- Delay of various foreign blood particles coming from the systemic circulation (thrombi, emboli). When the volume of blood vessels changes, blood is deposited.
The pulmonary circulation begins in the right atrium. From there, venous blood, containing very little oxygen, is released into a large vessel (but thinner than the aorta) - the pulmonary trunk. Directly in the lungs, the pulmonary trunk is divided into two pulmonary arteries, right and left. From the left artery blood flows into the left lung, from the right - into the right.
The lungs are considered the central part of the pulmonary circulation.
These arteries, in turn, branch repeatedly into many capillaries surrounding the respiratory vesicles. In these sinusoidal capillaries with a diameter of 30 microns, gas exchange occurs: the process of oxygenation of the blood occurs, that is, saturation with oxygen, here it gives off carbon dioxide and turns into arterial blood.
Blood in the pulmonary capillaries moves at a constant speed due to constant pressure. Slow current in the capillaries allows the blood to receive the required amount of oxygen and have time to give off carbon dioxide. The vessels of the pulmonary circulation have very thin walls, so in normal conditions do not create obstacles for the passage of oxygen and carbon dioxide.
An obstacle to blood flow in the capillaries can be an air bubble that clogs the lumen. This situation may arise when intravenous administration medicine if air gets into the blood along with it. The result is an air embolism.
Arterial blood, already rich in oxygen, flows through the four pulmonary veins. Smaller veins gather into 4 large pulmonary veins and enter the left atrium. This ends the pulmonary circulation. Then the blood enters the left atrium through the atrioventricular opening, and a systemic circulation begins, thanks to which oxygen reaches all organs and tissues human body.
Features of the pulmonary circulation
The time it takes for blood to pass through the pulmonary circle can be 4-5 seconds. This time is enough to provide oxygen to the body in calm state. When oxygen consumption increases, for example during heavy physical activity or intense sports, the pressure in the heart increases and blood flow accelerates.
An important feature of the small (pulmonary) circle is that it is a system low pressure. The average pressure in the arteries can be up to 25 mm Hg. Art. in the pulmonary artery and 6-8 mm. rt. Art. in the veins.
Dividing the circulatory system into two circulation circles has an important advantage: it allows you to “unload” the heart, since used blood, which has very little oxygen, is separated from oxygen-enriched blood. Therefore, the heart experiences much less stress than it would with one circle of blood circulation, since in this case it would have to pump both venous and arterial blood.
Veins carry only venous blood containing carbon dioxide, and arteries carry oxygen-rich arterial blood. But there is only one exception: in a small circle everything happens exactly the opposite: “fresh” blood flows through the veins, and “used” blood through the arteries.
Regulation of blood flow in the pulmonary circulation
Large vessels of the lungs are a reflexogenic zone. They provide a reflex response of the vessels of the small circle. When pressure increases, a reflex decrease is observed blood pressure.
Act as sensors for regulating blood flow nerve cells, which monitor certain blood parameters, including the concentration of carbon dioxide, oxygen and various liquids, pH (acidity) levels, and the presence of hormones. This information enters the brain, where data processing occurs.
To regulate, the brain sends appropriate impulses to the heart, blood, and vessels. In addition, blood flow is regulated with the help of internal lumens that are located in the arteries. They provide constant regulation of the speed of blood flow. As soon as the heartbeat slows down, the arteries begin to narrow, and if it speeds up, the arteries dilate.
Another factor influencing the speed of blood flow is adrenaline. It can cause vasodilation or constriction by acting on a- and b-adrenergic receptors. The effect of adrenaline depends on several conditions, on which type of receptor (a- or b-) predominates in the blood, and the concentration of the substance. At low concentrations, adrenaline acts mainly on b-adrenergic receptors, as they are the most sensitive.
In some vessels, for example in the vessels of skeletal muscles, b-adrenergic receptors predominate, but group a receptors are more common. Therefore, adrenaline, if produced in physical concentration, causes constriction of most blood vessels and dilation muscle vessels. As a result, blood flow is redistributed in favor of skeletal muscles. In this way, the body prepares for intense work under stress.
The heart is one of the most perfect organs of the human body, which was created with special thought and care. He has excellent qualities: fantastic power, rare tirelessness and an inimitable ability to adapt to external environment. It’s not for nothing that many people call the heart the human motor, because in fact, it is so. If you just think about the colossal work of our “engine”, then this is a most amazing organ.
What is the heart and what are its functions?
The heart is a muscular organ that, through rhythmic, repeated contractions, ensures blood flow through the blood vessels.
The main function of the heart is to ensure constant and uninterrupted blood flow throughout the body.. Therefore, the heart is a kind of pump that circulates blood throughout the body, and this is its main function. Thanks to the work of the heart, blood flows to all parts of the body and organs, saturates the tissues nutrients and oxygen, while also saturating the blood itself with oxygen. At physical activity, increasing the speed of movement (running) and under stress - the heart must produce an instant reaction and increase the speed and number of contractions.
We have become familiar with what the heart is and what its functions are, now let’s look at the structure of the heart.
To begin with, it is worth saying that the human heart is on the left side chest. It is important to note that there is a group in the world unique people whose heart is located not on the left side, as usual, but on the right side, such people, as a rule, have a mirror structure of the body, as a result of which the heart is located on the opposite side from its usual location.
The heart consists of four separate chambers (cavities):
- Left atrium;
- Right atrium;
- Left ventricle;
- Right ventricle.
The valves located in the heart are responsible for the flow of blood.. The left atrium contains the pulmonary veins and the right atrium - the hollow veins (superior vena cava and inferior vena cava). The pulmonary trunk and the ascending aorta emerge from the left and right ventricles.
The left ventricle shares with the left atrium mitral valve (bicuspid valve). The right ventricle and right atrium are separated tricuspid valve. Also in the very heart are pulmonary and aortic valves, which are responsible for the flow of blood from the left and right ventricles.
Circulation circles of the heart
As you know, the heart produces 2 types of blood circulation circles - this, in turn, is the systemic circulation and the small one. Systemic circulation originates from the left ventricle and ends in the right atrium.The task of the systemic circulation is to supply blood to all organs of the body, as well as directly to the lungs themselves.
Pulmonary circulation originates from the right ventricle and ends in the left atrium.
As for the pulmonary circulation, it is responsible for gas exchange in the pulmonary alveoli.
Here's a brief summary of what concerns the blood circulation.
What does the heart do?
What is a heart for? As you already understand, the heart produces continuous blood flow throughout the body. A three-hundred-gram ball of muscle, elastic and mobile, is a constantly working suction and discharge pump, the right half of which takes the blood used in the body from the veins and directs it to the lungs for enrichment with oxygen. The blood from the lungs then enters the left side of the heart and, with a certain degree of force, measured by the level of blood pressure, ejects the blood.Blood circulation during blood circulation occurs approximately 100 thousand times a day, at a distance of over 100 thousand kilometers (this is the total length of the vessels of the human body). Over the course of a year, the number of heartbeats reaches an astronomical value - 34 million. During this time, 3 million liters of blood are pumped. Gigantic work! What amazing reserves are hidden in this biological engine!
Interesting to know: one contraction requires enough energy to lift a 400 g load to a height of one meter. Moreover, a calm heart uses only 15% of all the energy it has. With hard work, this figure increases to 35%.
Unlike skeletal muscles, which can remain at rest for hours, the contractile cells of the myocardium work tirelessly for many years. This gives rise to one important requirement: their air supply must be continuous and optimal. If there are no nutrients and oxygen, the cell dies instantly. It cannot stop and wait for delayed doses of life-giving gas and glucose, since it does not create the reserves necessary for the so-called maneuver. Her life lies in a saving breath of fresh blood.
But can a muscle saturated with blood starve? Yes maybe. The fact is that the myocardium does not feed on the blood that fills its cavities. It is supplied with oxygen and essential nutrients through two “pipelines” that branch from the base of the aorta and crown the muscle like a crown (hence their name “coronary” or “coronary”). They, in turn, form a dense network of capillaries that nourish its own tissue. There are a lot of spare branches here - collaterals that duplicate the main vessels and run parallel with them - something like the branches and ducts of a large river. In addition, the basins of the main “blood rivers” are not separated, but are connected into a single whole thanks to transverse vessels - anastomoses. If something bad happens: a blockage or rupture, the blood will rush along the alternate channel and the loss will be more than compensated for. Thus, nature has provided not only the hidden powers of the pumping mechanism, but also a perfect system of replacement blood supply.
This process, common to all vessels, is especially pathological for the coronary arteries. After all, they are very thin, the largest of them is no wider than the straw through which you drink a cocktail. The peculiarity of blood circulation in the myocardium also plays a role. Oddly enough, blood periodically stops in these intensely circulating arteries. Scientists explain this strangeness as follows. Unlike other vessels coronary arteries experience the influence of two forces that are opposite to each other: the pulse pressure of the blood entering through the aorta, and the counter pressure that arises at the moment of contraction of the heart muscle and tends to push the blood back to the aorta. When the opposing forces become equal, blood flow stops for a split second. This time is enough for some of the clot-forming material to precipitate from the blood. This is why atherosclerosis coronary vessels develops many years before it occurs in other arteries.
Heart diseases
Now cardiovascular diseases attack people at an active pace, especially the elderly. Millions of deaths a year - this is the outcome of heart disease. This means: three out of five patients die directly from heart attacks. Statistics note two alarming facts: the trend of increasing diseases and their rejuvenation.Heart diseases include 3 groups of diseases that affect:
- Heart valves (congenital or acquired heart defects);
- Cardiac vessels;
- Tissues of the membranes of the heart.
Heart failure. This term refers to a disease in which a complex of disorders occurs due to a decrease in myocardial contractility, which is a consequence of the development of stagnant processes. In heart failure, blood stagnates in both the small and big circle blood circulation
Heart defects. With heart defects, defects in the functioning of the valve apparatus may be observed, which can lead to heart failure. Heart defects can be either congenital or acquired.
Heart arythmy. This heart pathology is caused
