There is 1 circle of blood circulation. Small and systemic circulation diagrams. Small and large circle of human blood circulation. What is cardiosclerosis? Types and classification

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Historical reference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. Thus, back in the second century AD, Claudius Galen, studying from the works of Hippocrates himself, 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 Miguel Servetus and William Harvey made a tremendous contribution to the systematization of data on the work of the heart in the 16th century. Harvey, the 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 evolved, the vertebrate class became more and more progressive in anatomical and physiological terms, they required a complex structure and cordially- vascular 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 of two separated circulatory circles in birds, mammals and humans, in particular, is nothing more than evolution circulatory system necessary for better adaptation to environmental conditions.

Anatomical features of the blood circulation

Circulation circles are a set of blood vessels, which is a closed system for admission to internal organs oxygen and nutrients through gas and nutrient exchange, as well as for removing 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. Arterial flow from the left ventricle is pushed through the aortic valve into the largest main vessel- into 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 of 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 the tissues of 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, practically without a middle muscular layer, and are represented by an inner membrane - 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 formed elements to easily penetrate into the intercellular fluid of the 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. Implemented cellular stage breathing.

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. The portal vein brings blood from the stomach and intestines, so everything that a person eats or drinks must undergo a kind of “purification” 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 the 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 a large content of carbon dioxide enters from the right atrial chamber (from the “end point” of the great circle). 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 myocardial capillaries, and venous outflow occurs into the coronary veins. The latter collect in the coronary sinus, which opens directly into the right atrial chamber. In this way, the cardiac or coronary circulation is carried out.

The 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 so much important organ from lack of oxygen, or hypoxia. The cerebral circulation is represented by the initial segment of the anterior cerebral artery, initial segment of the posterior cerebral artery, anterior and posterior communicating arteries, internal carotid arteries.

The placental circulation functions only during pregnancy by a woman and performs the function of “breathing” in the child. The placenta is formed starting from 3-6 weeks of pregnancy and begins to function in full force 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.

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.

Why does post-infarction cardiosclerosis (PICS) develop and how does it manifest?

The group of heart diseases includes post-infarction cardiosclerosis. This is one of the types of IHD. It is based on the replacement of functional muscle tissue of the heart with connective tissue. If left untreated, cardiosclerosis leads to heart failure and premature death.

Development of post-infarction cardiosclerosis in adults

Not everyone knows what PICS is. Post-infarction cardiosclerosis is a chronic cardiac pathology that develops mainly against the background acute form IHD. In such people, the number of muscle cells decreases. This contributes to impaired myocardial contractility and circulatory disorders. U healthy person The heart works by contracting muscle cells and generating nerve impulses.

With IHD, oxygen starvation of tissues is observed. The most dangerous is cardiosclerosis against the background acute heart attack, since this results in the formation of an area of necrosis. Subsequently, it is replaced by connective tissue and is disabled. In severe cases, such people need to have a pacemaker installed. The ventricles and atria dilate with cardiosclerosis. The organ itself increases in volume. Often, with cardiosclerosis, valves are involved in the process.

What is cardiosclerosis? Types and classification

Highlight the following types post-infarction cardiosclerosis:

Focal;
Widespread (diffuse);
Involving valves.

An experienced cardiologist knows that the focal form of the disease most often develops. It is characterized by the presence of a limited area of connective tissue, next to which functioning cardiomyocytes are located. The lesions can be single or multiple. This pathology may be no less serious than diffuse cardiosclerosis. Cardiosclerosis is most dangerous in the area of the left ventricle of the heart, since the systemic circulation begins there. Less commonly, diffuse cardiosclerosis develops against the background of a heart attack. With it, the connective tissue is distributed evenly. The cause may be a massive heart attack.

Main etiological factors and causes

Large-focal post-infarction cardiosclerosis develops against the background of an acute form coronary disease hearts. Other causes of the development of this pathology include bruise and injury to the heart, myocardial dystrophy, rheumatism, and myocarditis. The following risk factors are identified:

atherosclerosis of the coronary arteries;
poor nutrition;
blood lipid disorder;
diabetes;
hypertonic disease;
obesity;
nervous tension;
addiction to alcohol and cigarettes.

A common cause of heart attack is atherosclerosis. With it, plaques form in the lumen of the coronary arteries that supply the heart. They impede blood flow, leading to acute ischemia. A heart attack can also develop against the background of thrombosis, when the lumen of the vessel is blocked. This pathology is detected mainly in people over 40 years of age.

After suffered a heart attack scars are formed consisting of connective tissue. These are areas of sclerosis. This tissue is not capable of contracting and conducting impulses. The consequence of all this is a decrease in cardiac output. Subsequently, rhythm and conduction are disrupted.

How does cardiosclerosis occur?

This form of chronic ischemic heart disease is manifested by the following symptoms:

shortness of breath;
a feeling of interruptions in the work of the heart;
cough;
increased heartbeat;
swelling;
dizziness;
weakness;
decreased performance;
sleep disturbance;
chest pain.

The most consistent symptom of the disease is shortness of breath. It is more pronounced if there is an atherosclerotic process. It does not appear immediately, but several years after the start of the growth of connective tissue. Shortness of breath has the following distinctive features:

accompanied by cough;
appears in a lying position, during stress and physical activity;
disappears when sitting;
progresses over time.

Patients often experience nocturnal attacks of cardiac asthma. With a combination of cardiosclerosis and arterial hypertension there is a high probability of developing left ventricular failure. In this situation, pulmonary edema develops. If, against the background of a heart attack, foci of necrosis have formed in the area of the right ventricle and a violation of its function is observed, then the following symptoms occur:

liver enlargement;
swelling;
pulsation and swelling of the veins in the neck;
acrocyanosis.

Fluid may accumulate in the chest and pericardial sac. Stagnation of blood in the lungs against the background of cardiosclerosis leads to coughing. It is dry and paroxysmal. Damage to the nerve fibers of the pathways leads to heart rhythm disturbances. Cardiosclerosis becomes the cause atrial fibrillation and extrasystoles. The most dangerous consequences of this disease are complete blockade and ventricular tachycardia.

Examination for suspected cardiosclerosis

Diagnosis is made based on the results of laboratory, physical and instrumental studies, as well as collecting anamnesis. The patient's medical history is of great value. This pathology can be suspected if there is a history of ischemic heart disease. In case of post-infarction cardiosclerosis, treatment is carried out after the following studies:

echocardiography;
electrocardiography;
positron emission tomography;
rhythmocardiography;
coronary angiography;
X-ray examination;
load tests.

A physical examination of the patient reveals the following changes:

displacement of the apical impulse;
weakening of the first tone;
systolic murmur.

The ischemic type of cardiosclerosis always leads to cardiac hypertrophy due to the left side. This can be revealed when conducting an ECG and ultrasound. Electrocardiography can detect focal changes cardiac muscle, left ventricular enlargement, signs of bundle branch block.

A comprehensive examination necessarily includes a treadmill test and bicycle ergometry. With their help, changes in heart activity are assessed and general condition at physical activity. All patients were prescribed Holter monitoring.

Conservative treatment of patients

After the medical history is completed and a diagnosis is made, treatment of the patient begins. It can be conservative and radical. Treatment has the following objectives:

elimination of symptoms of the disease;
relief of the patient's condition;
prevention of complications;
slowing the development of heart failure;
prevention of progression of sclerosis.

Due to the fact that the heart muscle contracts weakly, the technique is indicated medicines. The most commonly used groups of medications are:

ACE inhibitors (Captopril, Perindopril);
beta-blockers (Metoprolol, Bisoprolol);
antiplatelet agents (Aspirin, Clopidogrel);
nitrates (Nitrosorbide);
diuretics;
potassium preparations (Panangin);
medications that reduce hypoxia and improve metabolic processes (Riboxin).

ACE inhibitors are indicated for high blood pressure. These medications reduce the chance repeated heart attacks. A medical history of a previous AMI is the basis for lifestyle changes. All patients with cardiosclerosis should adhere to the following recommendations:

eliminate physical and emotional stress;
lead a healthy and active lifestyle;
do not skip taking medications prescribed by your doctor;
give up alcoholic drinks and cigarettes;
normalize nutrition.

With myomalacia, the diet has great importance. It is necessary to exclude fatty and salty foods. This is especially useful for concomitant atherosclerosis. Treatment for cardiosclerosis is aimed at slowing the progression of heart failure. Glycosides are used for this purpose. In this case, the stage of CHF is taken into account.

Radical treatment methods

In severe post-infarction cardiosclerosis, the causes of death lie in heart rhythm disturbances and a pronounced decrease in myocardial contractility. Against the background of this pathology, the development of an aneurysm is possible. Severely ill patients may require a cardioverter-defibrillator or pacemaker. The first is implanted if a person has ventricular fibrillation and to prevent sudden cardiac arrest.

In case of persistent bradycardia and complete blockade, a pacemaker is indicated. Persistent attacks of angina after an acute heart attack require minimally invasive interventions (bypass surgery, stenting or angioplasty). In case of formation of an aneurysm, resection is organized.

With advanced cardiosclerosis, a heart transplant may be required. The following indications for transplantation are distinguished:

Decrease in cardiac output to 20% or less;
Ineffectiveness of drug therapy;
Young age.

This operation is performed on people under 65 years of age. In exceptional cases, heart transplantation is performed at an older age.

Health prognosis and prevention

The prognosis depends on the size of the sclerosis zone, the presence of complications and the magnitude of cardiac output. It worsens with the development of the following complications:

acute heart failure;
ventricular tachycardia;
atrioventricular block;
aneurysms;
tamponade;
atrial fibrillation.

Patients with cardiosclerosis have an increased risk of developing thromboembolism. The post-infarction form of cardiosclerosis can be prevented. Preventive actions aimed at the underlying disease. In order to reduce the risk of developing a heart attack, you must follow these rules:

promptly treat arterial hypertension;
do not abuse fatty foods, salt and alcohol;
do not smoke or use drugs;
do psychological relief;
go to bed no later than 11 pm.

If a heart attack develops, you must consult a doctor promptly. In the future you need to do therapeutic exercises, eliminate stressful situations. Rehabilitation measures include balneotherapy, rest in a sanatorium and constant medical observation. Most often, cardiosclerosis and heart attack develop against the background hypertension. To prevent complications, lifelong medication is required. Thus, cardiosclerosis is a consequence of acute myocardial infarction.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Continuous movement of blood through closed system cavities of the heart and blood vessels is called blood circulation. The circulatory system helps provide vital life to all important functions body.

The movement of blood through the blood vessels occurs due to contractions of the heart. In humans, there are large and small circles of blood circulation.

Systemic and pulmonary circulation

Systemic circulation begins with the largest artery - the aorta. Due to the contraction of the left ventricle of the heart, blood is ejected into the aorta, which then breaks up into arteries, arterioles that supply blood to the upper and lower limbs, head, torso, all internal organs and ending with capillaries.

Passing through the capillaries, the blood gives oxygen and nutrients to the tissues and takes away dissimilation products. From the capillaries, blood collects into small veins, which, merging and increasing their cross-section, form the superior and inferior vena cava.

A large circle of blood circulation ends in the right atrium. Arterial blood flows in all arteries of the systemic circulation, and venous blood flows in the veins.

Pulmonary circulation begins in the right ventricle, where venous blood enters from the right atrium. The right ventricle contracts and pushes blood into the pulmonary trunk, which divides into two pulmonary arteries that carry blood to the right and left lungs. In the lungs they are divided into capillaries surrounding each alveoli. In the alveoli, the blood releases carbon dioxide and is saturated with oxygen.

Through four pulmonary veins (there are two veins in each lung), oxygenated blood enters the left atrium(where the pulmonary circulation ends), and then into the left ventricle. Thus, venous blood flows in the arteries of the pulmonary circulation, and arterial blood flows in its veins.

The pattern of blood movement through the circulation was discovered by the English anatomist and physician W. Harvey in 1628.

Blood vessels: arteries, capillaries and veins

There are three types of blood vessels in humans: arteries, veins and capillaries.

Arteries- cylindrical tubes through which blood moves from the heart to organs and tissues. The walls of the arteries consist of three layers, which give them strength and elasticity:

Outer connective tissue membrane;
middle layer formed by smooth muscle fibers, between which elastic fibers lie
inner endothelial membrane. Thanks to the elasticity of the arteries, the periodic pushing of blood from the heart into the aorta turns into a continuous movement of blood through the vessels.

Capillaries are microscopic vessels whose walls consist of a single layer of endothelial cells. Their thickness is about 1 micron, length 0.2-0.7 mm.

Due to the structural features, it is in the capillaries that blood performs its main functions: it gives oxygen and nutrients to tissues and removes carbon dioxide and other dissimilation products that need to be excreted.

Due to the fact that the blood in the capillaries is under pressure and moves slowly, in the arterial part of it, water and nutrients dissolved in it seep into the intercellular fluid. At the venous end of the capillary, blood pressure decreases and intercellular fluid flows back into the capillaries.

Vienna- vessels that carry blood from capillaries to the heart. Their walls consist of the same membranes as the walls of the aorta, but are much weaker than arterial ones and have fewer smooth muscle and elastic fibers.

Blood in the veins flows under low pressure, so the movement of blood through the veins is more influenced by surrounding tissues, especially skeletal muscles. Unlike arteries, veins (with the exception of hollow veins) have valves in the form of pockets that prevent the reverse flow of blood.

Lymph
- colorless liquid; formed from
tissue fluid that has leaked into
lymphatic capillaries and vessels;
contains 3-4 times less proteins than
blood plasma; lymph reaction is alkaline.
There are no red blood cells in lymph, small
numbers of leukocytes contained,
penetrating from blood capillaries
into tissue fluid.

Lymphatic
system
includes lymphatic
vessels
(lymphatic capillaries, large
lymphatic vessels, lymphatic
ducts - the largest vessels) and
lymphatic
nodes.

Functions
lymphatic system: additional
outflow of fluid from organs; hematopoietic
and protective functions (in lymphatic
lymphocytes multiply in nodes
and phagocytosis of pathogens
microorganisms, as well as the production
immune bodies); participation in metabolism
(absorption of fat breakdown products).

This system includes a group of muscular organs that have a hollow structure. They are responsible for the process of blood circulation through the vessels located in the body. It is represented, in particular, by the heart and vessels of different sizes. These muscular organs form the pulmonary and systemic circulation. The diagram given in the article helps to visualize the mechanism of operation.

A key feature of the circulatory system, which consists of two circles, is the need for a heart with two or more chambers. For example, fish have only one blood circulation, since they do not have lungs, and gas exchange occurs in the gill vessels. Thus, the heart of fish is single-chambered and plays the role of a pump that pushes blood moving in one direction.

Amphibians and reptiles have lungs, so they have blood circulation. They work according to a simple scheme: blood from the ventricle is directed into vessels that form a large circle, from arteries directly into capillaries and veins. In addition, venous return is also realized, but from the right atrium blood flows into the ventricle, which is common to both circles.

Mammals and humans have a four-chambered heart. The presence of septa in it ensures the division into two atria and two ventricles. It is the absence of mixing of venous and arterial that provides mammals with warm blood.

The concept of blood circulation

The system consists of two circles. One of them is called large, or bodily, and the second is called small, or pulmonary. The blood circulation includes arterial, capillary, lymphatic and venous vessels. This system ensures the supply of blood to the vessels from the heart, as well as its reverse movement. The heart represents central authority. It is here that the pulmonary and systemic circulations intersect (the diagram is presented below), without mixing venous and arterial blood.

Systemic and pulmonary circulation

The major circle is a system that supplies peripheral tissues with arterial blood and then returns it back. It starts from the left ventricle. From it through aortic orifice, which has a tricuspid valve, blood exits into the aorta. Then it goes to other, smaller arteries, reaching the capillaries. These organs together make up the adductor link.

It is here that oxygen enters the tissues, from which red blood cells then take up carbon dioxide. In addition, blood transports glucose, lipoproteins, amino acids and metabolic products into the tissues, carried into the venules and then into the veins from the capillaries. The veins, in turn, empty into the vena cava, which returns blood to the right atrium of the heart.

The small, large and cardiac circulation circles have a unique structure.

The body circle ends precisely at the atrium. The circulatory diagram looks like this, if we consider it in the direction of blood flow: it begins with the left ventricle, then goes the aorta, elastic arteries, then muscular-elastic and muscular arteries, then arterioles and capillaries. They connect to venules, veins and vena cava, which return blood to the right atrium of the heart.

Diagrams of the pulmonary and systemic circulation can also be found on the Internet.

The systemic circulation begins with the largest artery - the aorta. Due to the contraction of the left ventricle of the heart, blood is ejected into the aorta, which then breaks up into arteries, arterioles, supplying blood to the upper and lower extremities, head, torso, all internal organs and ending in capillaries.

A large circle of blood circulation ends in the right atrium. Arterial blood flows in all arteries of the systemic circulation, and venous blood flows in the veins.

The pulmonary circulation begins in the right ventricle, where venous blood enters from the right atrium. The right ventricle contracts and pushes blood into the pulmonary trunk, which divides into two pulmonary arteries that carry blood to the right and left lungs. In the lungs they are divided into capillaries surrounding each alveoli. In the alveoli, the blood releases carbon dioxide and is saturated with oxygen.

Through four pulmonary veins (there are two veins in each lung), oxygenated blood enters the left atrium (where the pulmonary circulation ends), and then into the left ventricle. Thus, venous blood flows in the arteries of the pulmonary circulation, and arterial blood flows in its veins.

Structure

It begins from the left ventricle, which ejects blood into the aorta during systole. Numerous arteries depart from the aorta, as a result, blood flow is distributed according to the segmental structure along the vascular networks, providing oxygen and nutrients to all organs and tissues. Further division of the arteries occurs into arterioles and capillaries.

The total surface area of all capillaries in the human body is approximately 1500 m2. Through the thin walls of capillaries, arterial blood gives nutrients and oxygen to the cells of the body, and takes carbon dioxide and metabolic products from them, enters the venules, becoming venous. Venules collect into veins.

Venous drainage from unpaired organs abdominal cavity carried out not directly into the inferior vena cava, but through the portal vein (formed by the superior, inferior mesenteric and splenic veins). The portal vein, having entered the portal of the liver (hence the name) together with the hepatic artery, is divided in the hepatic beams into a capillary network, where the blood is purified and only after that it enters the inferior vena cava through the hepatic veins.
The pituitary gland also has a portal or “miraculous network”: the anterior lobe of the pituitary gland ( adenohypophysis) receives nutrition from the superior pituitary artery, which breaks up into a primary capillary network in contact with the axovasal synapses of neurosecretory neurons of the mediobasal hypothalamus, producing releasing hormones. The capillaries of the primary capillary network and axovasal synapses form the first neurohemal organ of the pituitary gland. Capillaries collect in portal veins, which go to the anterior lobe of the pituitary gland and re-branch there, forming a secondary capillary network through which releasing hormones reach adenocytes. Tropic hormones of the adenohypophysis are secreted into the same network, after which the capillaries merge into the anterior pituitary veins, carrying blood with hormones of the adenohypophysis to the target organs. Since the capillaries of the adenohypophysis lie between two veins (portal and pituitary), they belong to the “miraculous” capillary network. The posterior lobe of the pituitary gland (neurohypophysis) receives nutrition from the inferior pituitary artery, on the capillaries of which axovasal synapses of neurosecretory neurons are formed - the second neurohemal organ of the pituitary gland. The capillaries collect in the posterior pituitary veins. Thus, the posterior lobe of the pituitary gland (neurohypophysis), unlike the anterior lobe (adenohypophysis), does not produce its own hormones, but deposits and secretes into the blood hormones produced in the nuclei of the hypothalamus.
There are also two capillary networks in the kidneys - the arteries are divided into afferent arterioles Shumlyansky-Bowman capsules, each of which breaks up into capillaries and gathers into an efferent arteriole. The efferent arteriole reaches the convoluted tubule of the nephron and re-disintegrates into a capillary network.
The lungs also have a double capillary network - one belongs to the systemic circulation and supplies the lungs with oxygen and energy, taking metabolic products, and the other belongs to the small circle and serves for oxygenation (displacing carbon dioxide from the venous blood and saturating it with oxygen).
The heart also has its own vascular network: through the coronary arteries in diastole, blood enters the cardiac muscle, the conduction system of the heart, and so on, and in systole through the capillary network it is squeezed into the coronary veins, which flow into the coronary sinus, which opens into the right atrium.

Functions

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

Small (pulmonary) circulation

Structure

It begins in the right ventricle, which discharges venous blood into the pulmonary trunk. The pulmonary trunk is divided into the right and left pulmonary arteries. The pulmonary arteries branch into lobar, segmental and subsegmental arteries. Subsegmental arteries are divided into arterioles, which break up into capillaries. The outflow of blood goes through the veins, which collect in reverse order and four in number flow into the left atrium, where the pulmonary circulation ends. Blood circulation in the pulmonary circulation occurs in 4-5 seconds.

The pulmonary circulation was first described by Miguel Servetus in 1553 in his book The Restoration of Christianity.

Functions

The main task of the small circle is gas exchange in the pulmonary alveoli and heat transfer.

The second circle, called the pulmonary circle, starts from the right ventricle. Blood enters it from the right atrium through the atrioventricular opening. Oxygen-depleted blood, called venous, from the cavity of the right ventricle enters the pulmonary trunk through the pulmonary (outflow) tract. This artery is much thinner than the aorta. It is divided into two branches directed to both lungs.

The central organ that forms a small circle is the lungs. Pulmonary blood flow is required for oxygenation of the blood. This is where carbon dioxide is released and oxygen taken in. Gas exchange takes place in sinusoidal pulmonary capillaries, which have an atypical diameter for the body - about 30 microns. This can be seen in the diagram of the pulmonary and systemic circulation.

After oxygenation, the blood is sent through the intrapulmonary vein system to the pulmonary veins. There are four of them, all of them are attached to the left atrium, carrying oxygenated blood into it. The blood circulation ends here. The diagram of the pulmonary circle can be described as follows: the beginning is the right ventricle, after which it goes pulmonary artery and intrapulmonary arteries, then – pulmonary arterioles, as well as pulmonary sinusoids, then – venules and pulmonary veins. It ends with the left atrium.

What else does the diagram of the pulmonary and systemic circulation reflect?

“Additional” circulation circles

Exists in the fetus located in the uterus.

The mother's blood enters the placenta, where it gives oxygen and nutrients to the capillaries of the fetal umbilical vein, which runs along with two arteries in the umbilical cord. The umbilical vein gives off two branches: most of the blood flows through the ductus venosus directly into the inferior vena cava, mixing with unoxygenated blood from the lower body. A smaller portion of the blood enters the left branch of the portal vein, passes through the liver and hepatic veins and then also enters the inferior vena cava.

After birth, the umbilical vein empties and turns into the round ligament of the liver (ligamentum teres hepatis). The ductus venosus also turns into a scar cord. In premature infants, the ductus venosus may function for some time (it usually becomes scarred after some time. If not, there is a risk of developing hepatic encephalopathy). In portal hypertension, the umbilical vein and the Arantian duct can recanalize and serve as bypass pathways (porto-caval shunts).

Mixed (arterial-venous) blood flows through the inferior vena cava, the oxygen saturation of which is about 60%; Venous blood flows through the superior vena cava. Almost all the blood from the right atrium flows through the foramen ovale into the left atrium and then into the left ventricle. From the left ventricle, blood is ejected into the systemic circulation.

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

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

pushing and the passage of the placenta through the birth canal contribute to the pushing of maternal blood into the umbilical cord (especially if the birth took place “unusually” or there was a pathology of pregnancy). To accurately determine the blood type and Rh factor of a newborn, blood should be taken not from the umbilical cord, but from the child.

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

Arterial blood enters the heart through the right and left coronary arteries, originating from the aorta above its semilunar valves. The left coronary artery is divided into two or three, rarely four arteries, of which the most clinically significant are the anterior descending (LAD) and circumflex branches (OB).

The anterior descending branch is a direct continuation of the left coronary artery and descends to the apex of the heart. The circumflex branch departs from the left coronary artery at its beginning at approximately a right angle, bends around the heart from front to back, sometimes reaching back wall interventricular groove.

The myocardium is characterized by increased oxygen consumption. About 1% of the minute blood volume enters the coronary vessels.

Since the coronary vessels begin directly from the aorta, they fill with blood during cardiac diastole. During systole, the coronary vessels are compressed. The capillaries of the blood vessels are terminal and do not have anastomoses. Therefore, when a precapillary vessel is blocked by a thrombus, an infarction (bleeding) of a significant area of the heart muscle occurs.

The circle of Willis is an arterial ring formed by the arteries of the vertebral and internal carotid arteries, located at the base of the brain, helps compensate for insufficient blood supply. Normally, the circle of Willis is closed. The anterior communicating artery, initial segment of the anterior cerebral artery (A-1), supraclinoid part of the internal carotid artery, posterior communicating artery, initial segment of the posterior cerebral artery participate in the formation of the circle of Willis

Blood supply to the heart and lungs

The lungs cannot be fed from the right sections, despite the fact that some of the oxygen diffuses from them. Thus, we can conclude that two circles of blood circulation perform different functions: the first enriches the blood with oxygen, and the second carries it to all organs, and takes deoxygenated blood from them.

The heart is fed directly from the vessels of the systemic circle. The blood that is in its cavities supplies the endocardium with oxygen. In this case, some myocardial veins, mostly small ones, flow into the cardiac chambers.

We examined the diagram of the pulmonary and systemic circulation.

Fish

The heart of fish has 4 cavities connected in series: sinus venosus, atrium, ventricle and conus arteriosus/bulb.

The venous sinus (sinus venosus) is a simple extension of a vein that receives blood.
In sharks, ganoids and lungfishes, the conus arteriosus contains muscle tissue, several valves and is capable of contraction.
In bony fishes, the conus arteriosus is reduced (has no muscle tissue and valves), therefore it is called the “arterial bulb”.

The blood in the heart of fish is venous, from the bulb/cone it flows to the gills, there it becomes arterial, flows to the organs of the body, becomes venous, returns to the venous sinus.

Lungfish

In lungfishes, a “pulmonary circulation” appears: from the last (fourth) gill artery, blood flows through the pulmonary artery (PA) into the respiratory sac, where it is additionally enriched with oxygen and returns through the pulmonary vein (PV) to the heart, in left part of the atrium. Venous blood from the body flows, as it should, into the venous sinus. To limit the mixing of arterial blood from the “pulmonary circle” with venous blood from the body, there is an incomplete septum in the atrium and partially in the ventricle.

Thus, arterial blood in the ventricle appears before venous, therefore it enters the anterior branchial arteries, from which a direct road leads to the head. The smart fish brain receives blood that has passed through the gas exchange organs three times in a row! Bathing in oxygen, the rogue.

Amphibians

The circulatory system of tadpoles is similar to that of bony fish.

In an adult amphibian, the atrium is divided by a septum into left and right, resulting in a total of 5 chambers:

venous sinus (sinus venosus), in which, like in lungfishes, blood flows from the body
the left atrium (left atrium), into which, like in lungfishes, blood flows from the lung
right atrium
ventricle
arterial cone (conus arteriosus).

1) The left atrium of amphibians receives arterial blood from the lungs, and the right atrium receives venous blood from organs and arterial blood from the skin, so in the right atrium of frogs the blood is mixed.

2) As can be seen in the figure, the mouth of the arterial cone is shifted towards the right atrium, so blood from the right atrium enters there first, and from the left - last.

3) Inside the conus arteriosus there is a spiral valve that distributes three portions of blood:

the first portion of blood (from the right atrium, the most venous of all) goes to the pulmonary cutaneous artery (pulmocutaneous artery), to be oxygenated
the second portion of blood (a mixture of mixed blood from the right atrium and arterial blood from the left atrium) goes to the body organs through the systemic artery
the third portion of blood (from the left atrium, the most arterial of all) goes to the carotid artery (carotid artery) to the brain.

4) In lower amphibians (tailed and legless) amphibians

the septum between the atria is incomplete, so mixing of arterial and mixed blood occurs more strongly;
the skin is supplied with blood not from the cutaneous pulmonary arteries (where the most venous blood is possible), but from the dorsal aorta (where the blood is average) - this is not very beneficial.

5) When a frog sits under water, venous blood flows from the lungs into the left atrium, which, in theory, should go to the head. There is an optimistic version that the heart begins to work in a different mode (the ratio of the pulsation phases of the ventricle and the arterial cone changes), complete mixing of the blood occurs, due to which not completely venous blood from the lungs enters the head, but mixed blood consisting of venous blood of the left atrium and mixed blood of the right. There is another (pessimistic) version, according to which the brain of an underwater frog receives the most venous blood and becomes dull.

Reptiles

In reptiles, the pulmonary artery (“to the lung”) and two aortic arches emerge from a ventricle partially divided by a septum. The division of blood between these three vessels occurs in the same way as in lungfish and frogs:

The most arterial blood (from the lungs) enters the right aortic arch. To make it easier for children to learn, the right aortic arch begins from the very left part of the ventricle, and it is called the “right arch” because it goes around the heart on right, it is included in the spinal artery (you can see what it looks like in the next and subsequent figures). Depart from the right arc carotid arteries- the most arterial blood enters the head;
mixed blood enters the left aortic arch, which bends around the heart on the left and connects with the right aortic arch - the spinal artery is obtained, carrying blood to the organs;
The most venous blood (from the body organs) enters the pulmonary arteries.

Crocodiles

Crocodiles have a four-chambered heart, but they still mix blood through a special foramen of Panizza between the left and right aortic arches.

It is believed, however, that mixing does not normally occur: due to the fact that in the left ventricle there is more high pressure, blood from there flows not only into the right aortic arch (Right aorta), but also - through the panicia foramen - into the left aortic arch (Left aorta), thus, the crocodile's organs receive almost entirely arterial blood.

When a crocodile dives, the blood flow through its lungs decreases, the pressure in the right ventricle increases, and the flow of blood through the foramen of panicia stops: the left aortic arch of an underwater crocodile flows blood from the right ventricle. I don’t know what the point is in this: all the blood in the circulatory system at this moment is venous, why should it be redistributed where? In any case, blood enters the head of the underwater crocodile from the right aortic arch - when the lungs are not working, it is completely venous. (Something tells me that the pessimistic version is also true for underwater frogs.)

Birds and mammals

The circulatory systems of animals and birds in school textbooks are presented very close to the truth (all other vertebrates, as we have seen, are not so lucky with this). The only little thing that you are not supposed to talk about in school is that in mammals (B) only the left aortic arch is preserved, and in birds (B) only the right one is preserved (under the letter A is the circulatory system of reptiles, in which both arches are developed) - There is nothing else interesting in the circulatory system of either chickens or people. Except for the fruits...

Fruit

Arterial blood received by the fetus from the mother comes from the placenta through the umbilical vein. Part of this blood enters the portal system of the liver, part bypasses the liver, both of these portions ultimately flow into the inferior vena cava (interior vena cava), where they mix with venous blood flowing from the fetal organs. Entering the right atrium (RA), this blood is once again diluted with venous blood from the superior vena cava (superior vena cava), thus resulting in hopelessly mixed blood in the right atrium. At the same time, some venous blood from the non-functioning lungs enters the left atrium of the fetus - just like a crocodile sitting under water. What shall we do, colleagues?

The good old incomplete septum, which the authors of school textbooks on zoology laugh at so loudly, comes to the rescue - in the human fetus, right in the septum between the left and right atria, there is an oval hole (Foramen ovale), through which mixed blood from the right atrium enters the left atrium. In addition, there is a ductus arteriosus (Dictus arteriosus), through which mixed blood from the right ventricle enters the aortic arch. Thus, mixed blood flows through the fetal aorta to all its organs. And to the brain too! And you and I pestered frogs and crocodiles!! And themselves.

Tests

1. Cartilaginous fish lack:
a) swim bladder;
b) spiral valve;
c) conus arteriosus;
d) chord.

2. The circulatory system in mammals contains:
a) two aortic arches, which then merge into the dorsal aorta;
b) only the right aortic arch
c) only the left aortic arch
d) only abdominal aorta, and there are no aortic arches.

3. The circulatory system of birds contains:
A) two aortic arches, which then merge into the dorsal aorta;
B) only the right aortic arch;
B) only the left aortic arch;
D) only the abdominal aorta, and there are no aortic arches.

4. The arterial cone is present in
A) cyclostomes;
B) cartilaginous fish;
B) cartilaginous fish;
D) bony ganoid fish;
D) bony fish.

5. Classes of vertebrates in which blood moves directly from the respiratory organs to the tissues of the body, without first passing through the heart (select all correct options):
A) Bony fish;
B) adult amphibians;
B) Reptiles;
D) Birds;
D) Mammals.

6. The heart of a turtle in its structure:
A) three-chamber with an incomplete septum in the ventricle;
B) three-chamber;
B) four-chamber;
D) four-chamber with a hole in the septum between the ventricles.

7. Number of blood circulation in frogs:
A) one in tadpoles, two in adult frogs;
B) one in adult frogs, tadpoles have no blood circulation;
C) two in tadpoles, three in adult frogs;
D) two in tadpoles and adult frogs.

8. So that the carbon dioxide molecule that has passed into the blood from the tissues of your left foot can exit into environment through the nose, it must pass through all of the listed structures of your body except:
A) right atrium;
B) pulmonary vein;
B) alveoli of the lungs;
D) pulmonary artery.

9. There are two circles of blood circulation (choose all the correct options):
A) cartilaginous fish;
B) ray-finned fish;
B) lungfishes;
D) amphibians;
D) reptiles.

10. A four-chambered heart has:
A) lizards;
B) turtles;
B) crocodiles;
D) birds;
D) mammals.

11. Here is a schematic drawing of a mammalian heart. Oxygenated blood enters the heart through the following vessels:

A) 1;
B) 2;
AT 3;
D) 10.

12. The figure shows arterial arches:
A) lungfish;
B) tailless amphibian;
B) tailed amphibian;
D) reptile.