Physiology of the human cardiovascular system. Description
Lecture 7.
Systemic circulation
Pulmonary circulation
Heart.
endocardium myocardium epicardium Pericardium
bicuspid valve tricuspid valve . Valve aorta pulmonary valve
systole (reduction) and diastole (relaxation
During atrial diastole atrial systole. By the end ventricular systole
Myocardium
Excitability.
Conductivity.
Contractility.
Refractoriness.
Automaticity -
Atypical myocardium
1. sinoatrial node
2.
3. Purkinje fibers .
Normally, the atrioventricular node and the His bundle are only transmitters of excitations from the leading node to the heart muscle. Automaticity in them manifests itself only in those cases when they do not receive impulses from the sinoatrial node.
Indicators of cardiac activity.
Stroke, or systolic, volume of the heart- the amount of blood ejected by the ventricle of the heart into the corresponding vessels with each contraction. In a healthy adult at relative rest, the systolic volume of each ventricle is approximately 70-80 ml . Thus, when the ventricles contract, 140-160 ml of blood enters the arterial system.
Minute volume- the amount of blood ejected by the ventricle of the heart in 1 minute. The minute volume of the heart is the product of the stroke volume and the heart rate per minute. On average, minute volume is 3-5l/min . Cardiac output can increase due to an increase in stroke volume and heart rate.
Cardiac index– the ratio of minute blood volume in l/min to body surface in m². For a “standard” man it is 3 l/min m².
Electrocardiogram.
In the beating heart, conditions are created for the generation of electric current. During systole, the atria become electronegative with respect to the ventricles, which are in diastole at this time. Thus, when the heart operates, a potential difference arises. Biopotentials of the heart recorded using an electrocardiograph are called electrocardiograms.
To register the biocurrents of the heart they use standard leads, for which areas on the surface of the body are selected that give the greatest potential difference. Three classic standard leads are used, in which the electrodes are strengthened: I - on the inner surface of the forearms of both hands; II - on the right hand and in the area of the calf muscle of the left leg; III – on the left limbs. Chest leads are also used.
A normal ECG consists of a series of waves and the intervals between them. When analyzing an ECG, the height, width, direction, shape of the waves, as well as the duration of the waves and the intervals between them, reflect the speed of impulses in the heart, are taken into account. The ECG has three upward (positive) waves - P, R, T and two negative waves, the tops of which are directed downwards - Q and S .
P wave– characterizes the occurrence and spread of excitation in the atria.
Q wave– reflects excitation of the interventricular septum
R wave– corresponds to the period of excitation coverage of both ventricles
S wave– characterizes the completion of the propagation of excitation in the ventricles.
T wave– reflects the process of repolarization in the ventricles. Its height characterizes the state of metabolic processes occurring in the heart muscle.
Nervous regulation.
The heart, like all internal organs, is innervated by the autonomic nervous system.
Parasympathetic nerves are fibers of the vagus nerve. The central neurons of the sympathetic nerves lie in the lateral horns of the spinal cord at the level of the I-IV thoracic vertebrae; the processes of these neurons are directed to the heart, where they innervate the myocardium of the ventricles and atria, forming the conduction system.
The centers of the nerves innervating the heart are always in a state of moderate excitement. Due to this, nerve impulses constantly flow to the heart. Neuronal tone is maintained by impulses entering the central nervous system from receptors located in the vascular system. These receptors are located in the form of a cluster of cells and are called reflexogenic zone of cardio-vascular system. The most important reflexogenic zones are located in the area of the carotid sinus and in the area of the aortic arch.
The vagus and sympathetic nerves have opposite effects on the activity of the heart in 5 directions:
1. chronotropic (changes heart rate);
2. inotropic (changes the strength of heart contractions);
3. bathmotropic (influences excitability);
4. dromotropic (changes the ability to conduct);
5. tonotropic (regulates the tone and intensity of metabolic processes).
The parasympathetic nervous system has a negative effect in all five directions, and the sympathetic nervous system has a positive effect.
Thus, with stimulation of the vagus nerves there is a decrease in the frequency and strength of heart contractions, a decrease in the excitability and conductivity of the myocardium, and a decrease in the intensity of metabolic processes in the heart muscle.
When the sympathetic nerves are stimulated there is an increase in the frequency and strength of heart contractions, an increase in the excitability and conductivity of the myocardium, and stimulation of metabolic processes.
Blood vessels.
Based on their functioning characteristics, there are 5 types of blood vessels:
1. Trunk- the largest arteries in which rhythmically pulsating blood flow turns into a more uniform and smooth one. This smoothes out sharp fluctuations in pressure, which contributes to an uninterrupted supply of blood to organs and tissues. The walls of these vessels contain few smooth muscle elements and many elastic fibers.
2. Resistive(resistance vessels) - include precapillary (small arteries, arterioles) and postcapillary (venules and small veins) resistance vessels. The relationship between the tone of pre- and post-capillary vessels determines the level of hydrostatic pressure in the capillaries, the magnitude of filtration pressure and the intensity of fluid exchange.
3. True capillaries(metabolic vessels) – the most important department of the cardiovascular system. Through the thin walls of capillaries, exchange occurs between blood and tissues.
4. Capacitive vessels– venous section of the cardiovascular system. They hold about 70-80% of all blood.
5. Shunt vessels– arteriovenous anastomoses, providing a direct connection between small arteries and veins, bypassing the capillary bed.
Basic hemodynamic law: the amount of blood flowing per unit time through the circulatory system is greater, the greater the pressure difference at its arterial and venous ends and the less resistance to blood flow.
During systole, the heart pumps blood into the vessels, the elastic wall of which stretches. During diastole, the wall returns to its original state, since there is no ejection of blood. As a result, stretching energy is converted into kinetic energy, which ensures further movement of blood through the vessels.
Arterial pulse.
Arterial pulse– periodic expansion and lengthening of arterial walls, caused by the flow of blood into the aorta during systole of the left ventricle.
The pulse is characterized by the following signs: frequency – number of beats in 1 minute, rhythm – correct alternation of pulse beats, filling – degree of change in arterial volume, determined by the strength of the pulse beat, voltage - characterized by the force that must be applied to compress the artery until the pulse completely disappears.
The curve obtained by recording pulse oscillations of the artery wall is called sphygmogram.
The smooth muscle elements of the blood vessel wall are constantly in a state of moderate tension - vascular tone . There are three mechanisms for regulating vascular tone:
1. autoregulation
2. neural regulation
3. humoral regulation.
Autoregulation ensures a change in the tone of smooth muscle cells under the influence of local excitation. Myogenic regulation is associated with changes in the state of vascular smooth muscle cells depending on the degree of their stretching - the Ostroumov-Beilis effect. When blood pressure increases, smooth muscle cells in the walls of blood vessels respond by contracting to stretch and relaxing to decrease pressure in the blood vessels. Meaning: maintaining a constant level of blood volume entering the organ (the most pronounced mechanism is in the kidneys, liver, lungs, and brain).
Nervous regulation vascular tone is carried out by the autonomic nervous system, which has a vasoconstrictor and vasodilator effect.
Sympathetic nerves are vasoconstrictors (constrict blood vessels) for the vessels of the skin, mucous membranes, gastrointestinal tract and vasodilators (dilate blood vessels) for the vessels of the brain, lungs, heart and working muscles. The parasympathetic part of the nervous system has a dilating effect on blood vessels.
Humoral regulation carried out by substances of systemic and local action. Systemic substances include calcium, potassium, sodium ions, and hormones. Calcium ions cause vasoconstriction, while potassium ions have a dilating effect.
Action hormones on vascular tone:
1. vasopressin – increases the tone of smooth muscle cells of arterioles, causing vasoconstriction;
2. adrenaline has both a constricting and dilating effect, acting on alpha1-adrenergic receptors and beta1-adrenergic receptors, therefore, at low concentrations of adrenaline, dilation of blood vessels occurs, and at high concentrations, narrowing occurs;
3. thyroxine – stimulates energy processes and causes constriction of blood vessels;
4. renin - produced by cells of the juxtaglomerular apparatus and enters the bloodstream, influencing the protein angiotensinogen, which turns into angiotensin II, causing vasoconstriction.
Metabolites (carbon dioxide, pyruvic acid, lactic acid, hydrogen ions) affect the chemoreceptors of the cardiovascular system, leading to a reflex narrowing of the lumen of blood vessels.
To substances local impact relate:
1. mediators of the sympathetic nervous system - vasoconstrictor, parasympathetic (acetylcholine) - dilating;
2. biologically active substances – histamine dilates blood vessels, and serotonin constricts;
3. kinins – bradykinin, kalidin – have an expanding effect;
4. prostaglandins A1, A2, E1 dilate blood vessels, and F2α constricts.
Redistribution of blood.
Redistribution of blood in the vascular bed leads to increased blood supply to some organs and a decrease in others. Redistribution of blood occurs mainly between the vessels of the muscular system and internal organs, especially the abdominal organs and skin. During physical work, the increased amount of blood in the vessels of skeletal muscles ensures their effective functioning. At the same time, the blood supply to the organs of the digestive system decreases.
During the digestion process, the vessels of the organs of the digestive system dilate, their blood supply increases, which creates optimal conditions for the physical and chemical processing of the contents of the gastrointestinal tract. During this period, the vessels of the skeletal muscles narrow and their blood supply decreases.
Physiology of microcirculation.
Promotes normal metabolism microcirculation processes– directed movement of body fluids: blood, lymph, tissue and cerebrospinal fluids and secretions of the endocrine glands. The set of structures that ensure this movement is called microcirculatory bed. The main structural and functional units of the microvasculature are blood and lymphatic capillaries, which, together with the surrounding tissues, form three links of the microcirculatory bed : capillary circulation, lymph circulation and tissue transport.
The capillary wall is perfectly adapted to perform metabolic functions. In most cases, it consists of a single layer of endothelial cells, between which there are narrow gaps.
Exchange processes in capillaries are provided by two main mechanisms: diffusion and filtration. The driving force of diffusion is the ion concentration gradient and the movement of the solvent following the ions. The diffusion process in blood capillaries is so active that when blood passes through the capillary, plasma water manages to exchange up to 40 times with the fluid of the intercellular space. In a state of physiological rest, up to 60 liters of water passes through the walls of all capillaries in 1 minute. Of course, as much water comes out of the blood, the same amount comes back.
Blood capillaries and adjacent cells are structural elements histohematic barriers between the blood and surrounding tissues of all internal organs without exception. These barriers regulate the flow of nutrients, plastic and biologically active substances from the blood into the tissues, carry out the outflow of products of cellular metabolism, thus contributing to the preservation of organ and cellular homeostasis, and, finally, prevent the flow of foreign and toxic substances, toxins, from the blood into the tissues. microorganisms, some medicinal substances.
Transcapillary exchange. The most important function of histohematic barriers is transcapillary exchange. The movement of fluid through the capillary wall occurs due to the difference in the hydrostatic pressure of the blood and the hydrostatic pressure of the surrounding tissues, as well as under the influence of the difference in the osmo-oncotic pressure of the blood and intercellular fluid.
Tissue transport. The capillary wall is morphologically and functionally closely connected with the loose connective tissue surrounding it. The latter transports the liquid coming from the lumen of the capillary with substances dissolved in it and oxygen to the rest of the tissue structures.
Lymph and lymph circulation.
The lymphatic system consists of capillaries, vessels, lymph nodes, thoracic and right lymphatic ducts, from which lymph enters the venous system. Lymphatic vessels are a drainage system through which tissue fluid flows into the bloodstream.
In an adult, under conditions of relative rest, about 1 ml of lymph flows from the thoracic duct into the subclavian vein every minute, from 1.2 to 1.6 liters per day.
Lymph is a fluid contained in lymph nodes and vessels. The speed of lymph movement through lymphatic vessels is 0.4-0.5 m/s.
In terms of chemical composition, lymph and blood plasma are very similar. The main difference is that lymph contains significantly less protein than blood plasma.
The source of lymph is tissue fluid. Tissue fluid is formed from blood in capillaries. It fills the intercellular spaces of all tissues. Tissue fluid is an intermediate medium between blood and body cells. Through tissue fluid, cells receive all the nutrients and oxygen necessary for their life, and metabolic products, including carbon dioxide, are released into it.
The constant flow of lymph is ensured by the continuous formation of tissue fluid and its transition from the interstitial spaces to the lymphatic vessels.
The activity of organs and the contractility of lymphatic vessels are essential for the movement of lymph. Lymphatic vessels contain muscle elements, due to which they have the ability to actively contract. The presence of valves in the lymphatic capillaries ensures the movement of lymph in one direction (to the thoracic and right lymphatic ducts).
Auxiliary factors promoting the movement of lymph include: contractile activity of striated and smooth muscles, negative pressure in large veins and the chest cavity, an increase in the volume of the chest during inhalation, which causes the absorption of lymph from the lymphatic vessels.
Main functions lymphatic capillaries are drainage, suction, transport-eliminative, protective and phagocytosis.
Drainage function carried out in relation to the plasma filtrate with colloids, crystalloids and metabolites dissolved in it. Absorption of emulsions of fats, proteins and other colloids is carried out mainly by the lymphatic capillaries of the villi of the small intestine.
Transport-eliminative– this is the transfer of lymphocytes and microorganisms into the lymphatic ducts, as well as the removal of metabolites, toxins, cell debris, and small foreign particles from tissues.
Protective function The lymphatic system is performed by unique biological and mechanical filters - lymph nodes.
Phagocytosis consists of trapping bacteria and foreign particles.
The lymph nodes. Lymph in its movement from capillaries to central vessels and ducts passes through the lymph nodes. An adult has 500-1000 lymph nodes of various sizes - from the head of a pin to the small grain of a bean.
Lymph nodes perform a number of important functions functions : hematopoietic, immunopoietic (plasma cells that produce antibodies are formed in the lymph nodes, T- and B-lymphocytes responsible for immunity are also located there), protective-filtration, exchange and reservoir. The lymphatic system as a whole ensures the outflow of lymph from tissues and its entry into the vascular bed.
Coronary circulation.
Blood flows to the heart through two coronary arteries. Blood flow in the coronary arteries occurs primarily during diastole.
Blood flow in the coronary arteries depends on cardiac and extracardiac factors:
Cardiac factors: the intensity of metabolic processes in the myocardium, the tone of the coronary vessels, the pressure in the aorta, heart rate. The best conditions for coronary circulation are created when blood pressure in an adult is 110-140 mm Hg.
Extracardiac factors: the influence of sympathetic and parasympathetic nerves innervating the coronary vessels, as well as humoral factors. Adrenaline, norepinephrine in doses that do not affect the functioning of the heart and blood pressure, contribute to the expansion of the coronary arteries and an increase in coronary blood flow. The vagus nerves dilate the coronary vessels. Nicotine, overstrain of the nervous system, negative emotions, poor nutrition, and lack of constant physical training sharply worsen coronary circulation.
Pulmonary circulation.
The lungs are organs in which blood circulation, along with trophic, also performs a specific – gas exchange – function. The latter is a function of the pulmonary circulation. The trophism of the lung tissue is provided by the vessels of the systemic circulation. Arterioles, precapillaries and subsequent capillaries are closely associated with the alveolar parenchyma. When they entwine the alveoli, they form such a dense network that under intravital microscopy it is difficult to determine the boundaries between individual vessels. Thanks to this, in the lungs the blood washes the alveoli in an almost continuous continuous flow.
Hepatic circulation.
The liver has two networks of capillaries. One network of capillaries ensures the activity of the digestive organs, the absorption of food digestion products and their transport from the intestines to the liver. Another network of capillaries is located directly in the liver tissue. It helps the liver perform functions related to metabolic and excretory processes.
Blood entering the venous system and the heart must first pass through the liver. This is a feature of the portal circulation, which ensures that the liver performs its neutralizing function.
Cerebral circulation.
The brain has a unique feature of blood circulation: it occurs in the confined space of the skull and is in relationship with the blood circulation of the spinal cord and the movements of cerebrospinal fluid.
Up to 750 ml of blood passes through the vessels of the brain in 1 minute, which is about 13% of the IOC, with a brain weight of about 2-2.5% of body weight. Blood flows to the brain through four main vessels - two internal carotid and two vertebral, and flows out through two jugular veins.
One of the most characteristic features of cerebral blood flow is its relative constancy and autonomy. The total volumetric blood flow depends little on changes in central hemodynamics. Blood flow in the vessels of the brain can change only with pronounced deviations of central hemodynamics from normal conditions. On the other hand, an increase in the functional activity of the brain, as a rule, does not affect central hemodynamics and the volume of blood flowing to the brain.
The relative constancy of blood circulation in the brain is determined by the need to create homeostatic conditions for the functioning of neurons. There are no oxygen reserves in the brain, and the reserves of the main oxidation metabolite, glucose, are minimal, so their constant supply by blood is necessary. In addition, the constancy of microcirculation conditions ensures the constancy of water exchange between brain tissue and blood, blood and cerebrospinal fluid. Increased production of cerebrospinal fluid and intercellular water can lead to compression of the brain enclosed in a closed cranium.
1. Structure of the heart. The role of the valve apparatus
2. Properties of the heart muscle
3. Cardiac conduction system
4. Indicators and methods for studying cardiac activity
5. Regulation of heart activity
6. Types of blood vessels
7. Blood pressure and pulse
8. Regulation of vascular tone
9. Physiology of microcirculation
10. Lymph and lymph circulation
11. Activity of the cardiovascular system during physical activity
12. Features of regional blood circulation.
1. Functions of the blood system
2. Blood composition
3. Osmotic and oncotic blood pressure
4. Blood reaction
5. Blood groups and Rh factor
6. Red blood cells
7. Leukocytes
8. Platelets
9. Hemostasis.
1. Three parts of breathing
2. Mechanism of inhalation and exhalation
3. Tidal volumes
4. Transport of gases by blood
5. Regulation of breathing
6. Breathing during physical activity.
Physiology of the cardiovascular system.
Lecture 7.
The circulatory system consists of the heart, vessels (blood and lymphatic), blood storage organs, and mechanisms for regulating the circulatory system. Its main function is to ensure constant movement of blood through the vessels.
Blood in the human body circulates in two circulatory circles.
Systemic circulation It begins with the aorta, which arises from the left ventricle, and ends with the superior and inferior vena cava, which flow into the right atrium. The aorta gives rise to large, medium and small arteries. Arteries become arterioles, which end in capillaries. Capillaries permeate all organs and tissues of the body in a wide network. In the capillaries, the blood gives oxygen and nutrients to the tissues, and from them metabolic products, including carbon dioxide, enter the blood. The capillaries turn into venules, the blood from which enters small, medium and large veins. Blood from the upper part of the body enters the superior vena cava, and from the lower part - into the inferior vena cava. Both of these veins flow into the right atrium, where the systemic circulation ends.
Pulmonary circulation(pulmonary) begins with the pulmonary trunk, which arises from the right ventricle and carries venous blood to the lungs. The pulmonary trunk branches into two branches going to the left and right lung. In the lungs, the pulmonary arteries are divided into smaller arteries, arterioles, and capillaries. In the capillaries, the blood releases carbon dioxide and is enriched with oxygen. Pulmonary capillaries become venules, which then form veins. The four pulmonary veins carry arterial blood to the left atrium.
Heart.
The human heart is a hollow muscular organ. A solid vertical septum divides the heart into left and right halves ( which in an adult healthy person do not communicate with each other). The horizontal septum, together with the vertical septum, divides the heart into four chambers. The upper chambers are the atria, the lower chambers are the ventricles.
The wall of the heart consists of three layers. Inner layer ( endocardium ) is represented by the endothelial membrane. Middle layer ( myocardium ) consists of striated muscle. The outer surface of the heart is covered with a serous membrane ( epicardium ), which is the inner layer of the pericardial sac - the pericardium. Pericardium (heart shirt) surrounds the heart like a bag and ensures its free movement.
Inside the heart there is a valve apparatus that is designed to regulate blood flow.
The left atrium is separated from the left ventricle bicuspid valve . At the border between the right atrium and the right ventricle is tricuspid valve . Valve aorta separates it from the left ventricle, and pulmonary valve separates it from the right ventricle.
The valve apparatus of the heart ensures the movement of blood in the cavities of the heart in one direction. The opening and closing of heart valves is associated with changes in pressure in the cavities of the heart.
The cycle of cardiac activity lasts 0.8 - 0.86 seconds and consists of two phases - systole (reduction) and diastole (relaxation). Atrial systole lasts 0.1 seconds, diastole 0.7 seconds. Ventricular systole is stronger than atrial systole and lasts about 0.3-0.36 s, diastole - 0.5 s. The total pause (simultaneous diastole of the atria and ventricles) lasts 0.4 s. During this period the heart rests.
During atrial diastole the atrioventricular valves are open and the blood coming from the corresponding vessels fills not only their cavities, but also the ventricles. During atrial systole the ventricles are completely filled with blood . By the end ventricular systole the pressure in them becomes greater than the pressure in the aorta and pulmonary trunk. This promotes the opening of the semilunar valves of the aorta and pulmonary trunk, and blood from the ventricles enters the corresponding vessels.
Myocardium It is represented by striated muscle tissue, consisting of individual cardiomyocytes, which are connected to each other using special contacts and form muscle fiber. As a result, the myocardium is anatomically continuous and functions as a single unit. Thanks to this functional structure, rapid transfer of excitation from one cell to another is ensured. Based on the characteristics of their functioning, the working (contracting) myocardium and the atypical muscles are distinguished.
Basic physiological properties of the heart muscle.
Excitability. Cardiac muscle is less excitable than skeletal muscle.
Conductivity. Excitation travels through the fibers of the heart muscle at a lower speed than through the fibers of the skeletal muscle.
Contractility. The heart, unlike skeletal muscle, obeys the “all or nothing” law. The heart muscle contracts as much as possible to both threshold and stronger stimulation.
To physiological features cardiac muscle include an extended refractory period and automaticity
Refractoriness. The heart has a significantly pronounced and prolonged refractory period. It is characterized by a sharp decrease in tissue excitability during the period of its activity. Due to the pronounced refractory period, which lasts longer than the systole period, the heart muscle is not capable of tetanic (long-term) contraction and performs its work as a single muscle contraction.
Automaticity - the ability of the heart to contract rhythmically under the influence of impulses arising within itself.
Atypical myocardium forms the conduction system of the heart and ensures the generation and conduction of nerve impulses. In the heart, atypical muscle fibers form nodes and bundles, which are combined into a conduction system consisting of the following sections:
1. sinoatrial node , located on the posterior wall of the right atrium at the junction of the superior vena cava;
2. atrioventricular node (atrioventricular node), located in the wall of the right atrium near the septum between the atria and ventricles;
3. atrioventricular bundle (bundle of His), extending from the atrioventricular node in one trunk. The bundle of His, passing through the septum between the atria and ventricles, divides into two legs going to the right and left ventricles. The bundle of His ends thicker than the muscles Purkinje fibers .
The sinoatrial node is the leader in the activity of the heart (pacemaker), impulses arise in it that determine the frequency and rhythm of heart contractions. Normally, the atrioventricular node and the His bundle are only transmitters of excitations from the leading
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MINISTRY OF EDUCATION AND SCIENCE
MURMANSK STATE HUMANITIES UNIVERSITY
DEPARTMENT OF LIFE SAFETY AND FUNDAMENTALS OF MEDICAL KNOWLEDGE
Course work
Discipline: Anatomy and age-related physiology
On the topic of: " Physiology of the cardiovascular system»
Performed:
1st year student
Faculty of PPI, Group 1-PPO
Rogozhina L.V.
Checked:
k. ped. Sc., associate professor Sivkov E.P.
Murmansk 2011
Plan
Introduction
1.1 Anatomical structure of the heart. Cardiac cycle. The value of the valve apparatus
1.2 Basic physiological properties of the heart muscle
1.3 Heart rhythm. Cardiac performance indicators
1.4 External manifestations of heart activity
1.5 Regulation of cardiac activity
II. Blood vessels
2.1 Types of blood vessels, features of their structure
2.2 Blood pressure in various parts of the vascular bed. Movement of blood through vessels
III. Age-related features of the circulatory system. Cardiovascular hygiene
Conclusion
List of used literature
Introduction
From the basics of biology, I know that all living organisms consist of cells, cells, in turn, are combined into tissues, tissues form various organs. And anatomically homogeneous organs that provide any complex acts of activity are combined into physiological systems. In the human body there are systems: blood, blood and lymph circulation, digestion, bone and muscle, respiration and excretion, endocrine glands, or endocrine, and nervous system. I will consider in more detail the structure and physiology of the cardiovascular system.
I.Heart
1. 1 Anatomicalstructure of the heart. Heart cyclel. The value of the valve apparatus
The human heart is a hollow muscular organ. A solid vertical partition divides the heart into two halves: left and right. The second septum, running horizontally, forms four cavities in the heart: the upper cavities are the atria, the lower cavities are the ventricles. The average weight of a newborn's heart is 20 g. The weight of an adult's heart is 0.425-0.570 kg. The length of the heart in an adult reaches 12-15 cm, the transverse size is 8-10 cm, the anteroposterior size is 5-8 cm. The weight and size of the heart increase in certain diseases (heart defects), as well as in people who engage in strenuous physical labor or sports for a long time .
The wall of the heart consists of three layers: inner, middle and outer. The inner layer is represented by the endothelial membrane (endocardium), which lines the inner surface of the heart. The middle layer (myocardium) consists of striated muscle. The musculature of the atria is separated from the musculature of the ventricles by a connective tissue septum, which consists of dense fibrous fibers - the fibrous ring. The muscular layer of the atria is much less developed than the muscular layer of the ventricles, which is due to the peculiarities of the functions that each part of the heart performs. The outer surface of the heart is covered with a serous membrane (epicardium), which is the inner layer of the pericardial sac. Under the serosa are the largest coronary arteries and veins, which provide blood supply to the tissues of the heart, as well as a large accumulation of nerve cells and nerve fibers that innervate the heart.
Pericardium and its significance. The pericardium (heart sac) surrounds the heart like a sac and ensures its free movement. The pericardium consists of two layers: the inner (epicardium) and the outer, facing the chest organs. Between the layers of the pericardium there is a gap filled with serous fluid. The liquid reduces friction of the pericardial layers. The pericardium limits the stretching of the heart by filling it with blood and provides support for the coronary vessels.
There are two types of valves in the heart: atrioventricular (atrioventricular) and semilunar. Atrioventricular valves are located between the atria and the corresponding ventricles. The left atrium is separated from the left ventricle by the bicuspid valve. At the border between the right atrium and the right ventricle is the tricuspid valve. The edges of the valves are connected to the papillary muscles of the ventricles by thin and strong tendon threads that hang into their cavity.
The semilunar valves separate the aorta from the left ventricle and the pulmonary trunk from the right ventricle. Each semilunar valve consists of three valves (pockets), in the center of which there are thickenings - nodules. These nodules, adjacent to each other, provide complete sealing when closing the semilunar valves.
Cardiac cycle and its phases. The activity of the heart can be divided into two phases: systole (contraction) and diastole (relaxation). Atrial systole is weaker and shorter than ventricular systole: in the human heart it lasts 0.1 s, and ventricular systole lasts 0.3 s. Atrial diastole takes 0.7 s, and ventricular diastole - 0.5 s. The general pause (simultaneous diastole of the atria and ventricles) of the heart lasts 0.4 s. The entire cardiac cycle lasts 0.8 s. The duration of the various phases of the cardiac cycle depends on the heart rate. With more frequent heartbeats, the activity of each phase decreases, especially diastole.
I have already mentioned the presence of valves in the heart. I will dwell in a little more detail on the importance of valves in the movement of blood through the chambers of the heart.
The importance of the valve apparatus in the movement of blood through the chambers of the heart. During atrial diastole, the atrioventricular valves are open and blood coming from the corresponding vessels fills not only their cavities, but also the ventricles. During atrial systole, the ventricles are completely filled with blood. This prevents the reverse movement of blood into the vena cava and pulmonary veins. This is due to the fact that the muscles of the atria, which form the mouths of the veins, contract first. As the cavities of the ventricles fill with blood, the leaflets of the atrioventricular valves close tightly and separate the cavity of the atria from the ventricles. As a result of contraction of the papillary muscles of the ventricles at the time of their systole, the tendon threads of the atrioventricular valve leaflets are stretched and do not allow them to turn towards the atria. Towards the end of ventricular systole, the pressure in them becomes greater than the pressure in the aorta and pulmonary trunk.
This promotes the opening of the semilunar valves, and blood from the ventricles enters the corresponding vessels. During ventricular diastole, the pressure in them drops sharply, which creates conditions for the reverse movement of blood towards the ventricles. In this case, blood fills the pockets of the semilunar valves and causes them to close.
Thus, the opening and closing of the heart valves is associated with changes in the pressure in the cavities of the heart.
Now I want to talk about the basic physiological properties of the heart muscle.
1. 2 Basic physiological properties of the heart muscle
Cardiac muscle, like skeletal muscle, has excitability, the ability to conduct excitation and contractility.
Excitability of the heart muscle. Cardiac muscle is less excitable than skeletal muscle. For excitation to occur in the cardiac muscle, it is necessary to apply a stronger stimulus than for the skeletal muscle. It has been established that the magnitude of the reaction of the heart muscle does not depend on the strength of the applied stimulation (electrical, mechanical, chemical, etc.). The heart muscle contracts as much as possible to both threshold and stronger stimulation.
Conductivity. Excitation waves are carried through the fibers of the heart muscle and the so-called special heart tissue at unequal speeds. Excitation propagates through the fibers of the atrium muscles at a speed of 0.8-1.0 m/s, through the fibers of the ventricular muscles - 0.8-0.9 m/s, through special heart tissue - 2.0-4.2 m/s .
Contractility. The contractility of the heart muscle has its own characteristics. The atrial muscles contract first, then the papillary muscles and the subendocardial layer of the ventricular muscles. Subsequently, the contraction also covers the inner layer of the ventricles, thereby ensuring the movement of blood from the cavities of the ventricles into the aorta and pulmonary trunk.
The physiological characteristics of the heart muscle are an extended refractory period and automaticity. Now about them in more detail.
Refractory period. In the heart, unlike other excitable tissues, there is a significantly pronounced and extended refractory period. It is characterized by a sharp decrease in tissue excitability during its activity. There are absolute and relative refractory periods (r.p.). During absolute r.p. No matter how much force is applied to the heart muscle, it does not respond to it with excitation and contraction. It corresponds in time to systole and the beginning of diastole of the atria and ventricles. During the relative r.p. the excitability of the heart muscle gradually returns to its original level. During this period, the muscle can respond to a stimulus stronger than the threshold. It is detected during atrial and ventricular diastole.
Myocardial contraction lasts about 0.3 s, approximately coinciding in time with the refractory phase. Consequently, during the period of contraction, the heart is unable to respond to stimuli. Due to the pronounced r.p.r., which lasts longer than the period of systole, the heart muscle is incapable of a titanic (long-term) contraction and performs its work as a single muscle contraction.
Automaticity of the heart. Outside the body, under certain conditions, the heart is able to contract and relax, maintaining the correct rhythm. Consequently, the reason for the contractions of an isolated heart lies in itself. The ability of the heart to contract rhythmically under the influence of impulses arising within itself is called automaticity.
In the heart, a distinction is made between working muscles, represented by striated muscle, and atypical, or special, tissue in which excitation occurs and is carried out.
In humans, atypical tissue consists of:
The sinoauricular node, located on the posterior wall of the right atrium at the confluence of the vena cava;
Atrioventricular (atrioventricular) node located in the right atrium near the septum between the atria and ventricles;
The bundle of His (atrioventricular bundle), extending from the atrioventricular node in one trunk.
The bundle of His, passing through the septum between the atria and ventricles, is divided into two legs going to the right and left ventricles. The bundle of His ends in the thickness of the muscles with Purkinje fibers. The bundle of His is the only muscular bridge connecting the atria to the ventricles.
The sinoauricular node is the leader in the activity of the heart (pacemaker), impulses arise in it that determine the frequency of heart contractions. Normally, the atrioventricular node and the His bundle are only transmitters of excitation from the leading node to the heart muscle. However, they have an inherent ability for automaticity, only it is expressed to a lesser extent than in the sinoauricular node, and manifests itself only in pathological conditions.
Atypical tissue consists of poorly differentiated muscle fibers. In the area of the sinoauricular node, a significant number of nerve cells, nerve fibers and their endings were found, which here form a nerve network. Nerve fibers from the vagus and sympathetic nerves approach the nodes of atypical tissue.
1. 3 Heart rhythm. Cardiac performance indicators
Heart rhythm and factors influencing it. The heart rhythm, i.e. the number of contractions per minute, depends mainly on the functional state of the vagus and sympathetic nerves. When the sympathetic nerves are stimulated, the heart rate increases. This phenomenon is called tachycardia. When the vagus nerves are stimulated, the heart rate decreases - bradycardia.
The state of the cerebral cortex also affects the heart rhythm: with increased inhibition, the heart rhythm slows down, with increased excitatory process it is stimulated.
The rhythm of the heart can change under the influence of humoral influences, in particular the temperature of the blood flowing to the heart. Experiments have shown that local irritation of the region of the right atrium with heat (localization of the leading node) leads to an increase in heart rate; when cooling this region of the heart, the opposite effect is observed. Local irritation by heat or cold of other parts of the heart does not affect the heart rate. However, it can change the speed of excitations through the conduction system of the heart and affect the strength of heart contractions.
The heart rate in a healthy person depends on age. These data are presented in the table.
Indicators of cardiac activity. Indicators of cardiac performance are systolic and cardiac output.
Systolic, or stroke, volume of the heart is the amount of blood that the heart pumps into the corresponding vessels with each contraction. The size of the systolic volume depends on the size of the heart, the condition of the myocardium and the body. In a healthy adult at relative rest, the systolic volume of each ventricle is approximately 70-80 ml. Thus, when the ventricles contract, 120-160 ml of blood enters the arterial system.
Cardiac minute volume is the amount of blood that the heart pumps into the pulmonary trunk and aorta in 1 minute. The minute volume of the heart is the product of the systolic volume and the heart rate per minute. On average, the minute volume is 3-5 liters.
Systolic and cardiac output characterizes the activity of the entire circulatory system.
1. 4 External manifestations of heart activity
How can you determine the work of the heart without special equipment?
There is data by which the doctor judges the work of the heart by the external manifestations of its activity, which include the apical impulse, heart sounds. More details about this data:
Apex impulse. During ventricular systole, the heart performs a rotational movement, turning from left to right. The apex of the heart rises and presses on the chest in the area of the fifth intercostal space. During systole, the heart becomes very dense, so pressure of the apex of the heart on the intercostal space can be seen (bulging, protrusion), especially in thin subjects. The apical impulse can be felt (palpated) and thereby determined its boundaries and strength.
Heart sounds are sound phenomena that occur in the beating heart. There are two tones: I - systolic and II - diastolic.
Systolic tone. The atrioventricular valves are mainly involved in the origin of this tone. During ventricular systole, the atrioventricular valves close, and vibrations of their valves and the tendon threads attached to them cause the first sound. In addition, sound phenomena that occur during contraction of the ventricular muscles take part in the origin of the first tone. According to its sound characteristics, the first tone is drawn-out and low.
Diastolic sound occurs at the beginning of ventricular diastole during the protodiastolic phase, when the semilunar valves close. The vibration of the valve flaps is the source of sound phenomena. According to the sound characteristics, tone II is short and high.
Also, the work of the heart can be judged by the electrical phenomena that occur in it. They are called cardiac biopotentials and are obtained using an electrocardiograph. They are called electrocardiograms.
1. 5 Regulusation of cardiac activity
Any activity of an organ, tissue, cell is regulated by neurohumoral pathways. The activity of the heart is no exception. I will tell you more about each of these paths below.
Nervous regulation of heart activity. The influence of the nervous system on the activity of the heart is due to the vagus and sympathetic nerves. These nerves belong to the autonomic nervous system. The vagus nerves go to the heart from nuclei located in the medulla oblongata at the bottom of the fourth ventricle. Sympathetic nerves approach the heart from nuclei localized in the lateral horns of the spinal cord (I-V thoracic segments). The vagus and sympathetic nerves end in the sinoauricular and atrioventricular nodes, as well as in the musculature of the heart. As a result, when these nerves are excited, changes are observed in the automation of the sinoauricular node, the speed of excitation through the conduction system of the heart, and the intensity of heart contractions.
Weak irritations of the vagus nerves lead to a slowdown in the heart rate, while strong ones cause cardiac contractions to stop. After cessation of irritation of the vagus nerves, heart activity can be restored again.
When the sympathetic nerves are irritated, the heart rate increases and the strength of heart contractions increases, the excitability and tone of the heart muscle increases, as well as the speed of excitation.
Tone of the centers of the cardiac nerves. The centers of cardiac activity, represented by the nuclei of the vagus and sympathetic nerves, are always in a state of tone, which can be strengthened or weakened depending on the conditions of existence of the organism.
The tone of the centers of the cardiac nerves depends on afferent influences coming from the mechano- and chemoreceptors of the heart and blood vessels, internal organs, receptors of the skin and mucous membranes. Humoral factors also influence the tone of the centers of the cardiac nerves.
There are also certain features in the functioning of the cardiac nerves. One of the reasons is that with an increase in the excitability of the neurons of the vagus nerves, the excitability of the nuclei of the sympathetic nerves decreases. Such functionally interconnected relationships between the centers of the cardiac nerves contribute to better adaptation of the activity of the heart to the conditions of existence of the body.
Reflex influences on the activity of the heart. I have conditionally divided these influences into: those carried out from the heart; carried out through the autonomic nervous system. Now in more detail about each:
Reflex influences on the activity of the heart are carried out from the heart itself. Intracardiac reflex influences are manifested in changes in the strength of heart contractions. Thus, it has been established that stretching the myocardium of one of the parts of the heart leads to a change in the force of contraction of the myocardium of its other part, which is hemodynamically disconnected from it. For example, when the myocardium of the right atrium is stretched, increased work of the left ventricle is observed. This effect can only be the result of reflex intracardiac influences.
Extensive connections of the heart with various parts of the nervous system create conditions for a variety of reflex effects on the activity of the heart, carried out through the autonomic nervous system.
The walls of blood vessels contain numerous receptors that are able to be excited when the blood pressure and chemical composition of the blood changes. There are especially many receptors in the area of the aortic arch and carotid sinuses (slight expansion, protrusion of the vessel wall on the internal carotid artery). They are also called vascular reflexogenic zones.
When blood pressure decreases, these receptors are excited, and impulses from them enter the medulla oblongata to the nuclei of the vagus nerves. Under the influence of nerve impulses, the excitability of neurons in the nuclei of the vagus nerves decreases, which increases the influence of sympathetic nerves on the heart (I already spoke about this feature above). As a result of the influence of sympathetic nerves, the heart rhythm and the force of heart contractions increase, the blood vessels narrow, which is one of the reasons for the normalization of blood pressure.
With an increase in blood pressure, nerve impulses generated in the receptors of the aortic arch and carotid sinuses increase the activity of neurons in the vagus nerve nuclei. The influence of the vagus nerves on the heart is detected, the heart rhythm slows down, heart contractions weaken, blood vessels dilate, which is also one of the reasons for restoring the original level of blood pressure.
Thus, reflex influences on the activity of the heart, carried out from receptors in the area of the aortic arch and carotid sinuses, should be classified as self-regulatory mechanisms that manifest themselves in response to changes in blood pressure.
Excitation of the receptors of internal organs, if strong enough, can change the activity of the heart.
Naturally, it is necessary to note the influence of the cerebral cortex on the functioning of the heart. The influence of the cerebral cortex on the activity of the heart. The cerebral cortex regulates and corrects the activity of the heart through the vagus and sympathetic nerves. Evidence of the influence of the cerebral cortex on the activity of the heart is the possibility of the formation of conditioned reflexes. Conditioned reflexes on the heart are quite easily formed in humans, as well as in animals.
You can give an example of an experience with a dog. The dog formed a conditioned reflex on the heart, using a flash of light or sound stimulation as a conditioned signal. The unconditioned stimulus was pharmacological substances (for example, morphine), which typically alter the activity of the heart. Shifts in heart function were monitored by recording an ECG. It turned out that after 20-30 injections of morphine, the complex of irritations associated with the administration of this drug (flash of light, laboratory environment, etc.) led to conditioned reflex bradycardia. A slowdown in heart rate was also observed when the animal was administered an isotonic sodium chloride solution instead of morphine.
In humans, various emotional states (excitement, fear, anger, anger, joy) are accompanied by corresponding changes in the activity of the heart. This also indicates the influence of the cerebral cortex on the functioning of the heart.
Humoral influences on the activity of the heart. Humoral influences on the activity of the heart are realized by hormones, some electrolytes and other highly active substances that enter the blood and are waste products of many organs and tissues of the body.
There are a lot of these substances, I will look at some of them:
Acetylcholine and norepinephrine - mediators of the nervous system - have a pronounced effect on the functioning of the heart. The action of acetylcholine is inseparable from the functions of the parasympathetic nerves, since it is synthesized in their endings. Acetylcholine reduces the excitability of the heart muscle and the force of its contractions.
Catecholamines, which include norepinephrine (a transmitter) and adrenaline (a hormone), are important for the regulation of heart activity. Catecholamines have effects on the heart similar to those of the sympathetic nerves. Catecholamines stimulate metabolic processes in the heart, increase energy consumption and thereby increase the myocardium's need for oxygen. Adrenaline simultaneously causes dilation of the coronary vessels, which improves the nutrition of the heart.
Hormones of the adrenal cortex and thyroid gland play a particularly important role in regulating the activity of the heart. Hormones of the adrenal cortex - mineralocorticoids - increase the force of myocardial heart contractions. The thyroid hormone - thyroxine - increases metabolic processes in the heart and increases its sensitivity to the effects of sympathetic nerves.
I noted above that the circulatory system consists of the heart and blood vessels. I examined the structure, functions and regulation of the heart. Now it’s worth focusing on blood vessels.
II. Blood vessels
2. 1 Types of blood vessels, features of their structure
heart vessel blood circulation
In the vascular system, there are several types of vessels: main, resistive, true capillaries, capacitive and shunt.
The great vessels are the largest arteries in which rhythmically pulsating, variable blood flow turns into a more uniform and smooth one. The blood in them moves from the heart. The walls of these vessels contain few smooth muscle elements and many elastic fibers.
Resistance vessels (vessels of resistance) include precapillary (small arteries, arterioles) and postcapillary (venules and small veins) resistance vessels.
True capillaries (exchange vessels) are the most important part of the cardiovascular system. Through the thin walls of capillaries, exchange occurs between blood and tissues (transcapillary exchange). The walls of the capillaries do not contain smooth muscle elements; they are formed by a single layer of cells, outside of which there is a thin connective tissue membrane.
Capacitive vessels are the venous section of the cardiovascular system. Their walls are thinner and softer than the walls of arteries, and they also have valves in the lumen of the vessels. Blood in them moves from organs and tissues to the heart. These vessels are called capacitive because they hold approximately 70-80% of all blood.
Shunt vessels are arteriovenous anastomoses that provide a direct connection between small arteries and veins, bypassing the capillary bed.
2. 2 Blood pressure in differentindividual parts of the vascular bed. Movement of blood through vessels
Blood pressure in different parts of the vascular bed is not the same: in the arterial system it is higher, in the venous system it is lower.
Blood pressure is the pressure of blood on the walls of blood vessels. Normal blood pressure is necessary for blood circulation and proper blood supply to organs and tissues, for the formation of tissue fluid in capillaries, as well as for the processes of secretion and excretion.
The amount of blood pressure depends on three main factors: the frequency and strength of heart contractions; the value of peripheral resistance, i.e. the tone of the walls of blood vessels, mainly arterioles and capillaries; volume of circulating blood.
There are arterial, venous and capillary blood pressure.
Arterial blood pressure. The value of blood pressure in a healthy person is fairly constant, however, it is always subject to slight fluctuations depending on the phases of the heart and breathing.
There are systolic, diastolic, pulse and mean arterial pressure.
Systolic (maximum) pressure reflects the state of the myocardium of the left ventricle of the heart. Its value is 100-120 mm Hg. Art.
Diastolic (minimum) pressure characterizes the degree of tone of the arterial walls. It is equal to 60-80 mm Hg. Art.
Pulse pressure is the difference between systolic and diastolic pressure. Pulse pressure is necessary to open the semilunar valves during ventricular systole. Normal pulse pressure is 35-55 mmHg. Art. If systolic pressure becomes equal to diastolic pressure, blood movement will be impossible and death will occur.
Mean arterial pressure is equal to the sum of diastolic and 1/3 of pulse pressure.
The value of blood pressure is influenced by various factors: age, time of day, state of the body, central nervous system, etc.
With age, the maximum pressure increases to a greater extent than the minimum.
During the day there is a fluctuation in pressure: during the day it is higher than at night.
A significant increase in maximum blood pressure can be observed during heavy physical activity, during sports competitions, etc. After stopping work or finishing competitions, blood pressure quickly returns to its original values.
High blood pressure is called hypertension. A decrease in blood pressure is called hypotension. Hypotension can occur due to drug poisoning, severe injuries, extensive burns, or large blood losses.
Arterial pulse. These are periodic expansions and lengthenings of the walls of the arteries, caused by the flow of blood into the aorta during systole of the left ventricle. The pulse is characterized by a number of qualities that are determined by palpation, most often of the radial artery in the lower third of the forearm, where it is located most superficially;
The following qualities of the pulse are determined by palpation: frequency - the number of beats per minute, rhythm - the correct alternation of pulse beats, filling - the degree of change in the volume of the artery, determined by the strength of the pulse beat, tension - characterized by the force that must be applied to compress the artery until the pulse completely disappears .
Blood circulation in capillaries. These vessels lie in the intercellular spaces, closely adjacent to the cells of the organs and tissues of the body. The total number of capillaries is enormous. The total length of all human capillaries is about 100,000 km, i.e. a thread that could encircle the globe along the equator 3 times.
The speed of blood flow in the capillaries is low and amounts to 0.5-1 mm/s. Thus, each blood particle remains in the capillary for approximately 1 s. The small thickness of this layer and its close contact with the cells of organs and tissues, as well as the continuous change of blood in the capillaries, provide the possibility of exchange of substances between the blood and the intercellular fluid.
There are two types of functioning capillaries. Some of them form the shortest path between arterioles and venules (main capillaries). Others are lateral branches from the first; they arise from the arterial end of the main capillaries and flow into their venous end. These side branches form capillary networks. Trunk capillaries play an important role in the distribution of blood in capillary networks.
In each organ, blood flows only in “standby” capillaries. Some capillaries are excluded from the blood circulation. During periods of intense activity of organs (for example, during muscle contraction or secretory activity of glands), when the metabolism in them increases, the number of functioning capillaries increases significantly. At the same time, blood rich in red blood cells, oxygen carriers, begins to circulate in the capillaries.
The regulation of capillary blood circulation by the nervous system and the influence of physiologically active substances - hormones and metabolites - on it are carried out through effects on arteries and arterioles. Their narrowing or expansion changes the number of functioning capillaries, the distribution of blood in the branching capillary network, and changes the composition of the blood flowing through the capillaries, i.e., the ratio of red blood cells and plasma.
The amount of pressure in the capillaries is closely related to the state of the organ (rest and activity) and the functions that it performs.
Arteriovenous anastomoses. In some areas of the body, such as the skin, lungs and kidneys, there are direct connections between arterioles and veins - arteriovenous anastomoses. This is the shortest path between arterioles and veins. Under normal conditions, the anastomoses are closed and blood flows through the capillary network. If the anastomoses open, some of the blood can flow into the veins, bypassing the capillaries.
Thus, arteriovenous anastomoses play the role of shunts regulating capillary blood circulation. An example of this is the change in capillary blood circulation in the skin with an increase (over 35 °C) or decrease (below 15 °C) in external temperature. Anastomoses in the skin open and blood flow is established from the arterioles directly into the veins, which plays an important role in the processes of thermoregulation.
Movement of blood in the veins. Blood from the microvasculature (venules, small veins) enters the venous system. Blood pressure in the veins is low. If at the beginning of the arterial bed the blood pressure is 140 mm Hg. Art., then in the venules it is 10-15 mm Hg. Art. In the final part of the venous bed, blood pressure approaches zero and may even be below atmospheric pressure.
A number of factors contribute to the movement of blood through the veins. Namely: the work of the heart, the valve apparatus of the veins, the contraction of skeletal muscles, the suction function of the chest.
The work of the heart creates a difference in blood pressure in the arterial system and the right atrium. This ensures venous return of blood to the heart. The presence of valves in the veins promotes the movement of blood in one direction - towards the heart. Alternating contraction and relaxation of muscles is an important factor in promoting the movement of blood through the veins. When muscles contract, the thin walls of the veins compress and blood moves towards the heart. Relaxation of skeletal muscles promotes the flow of blood from the arterial system into the veins. This pumping action of the muscles is called the muscle pump, which is an assistant to the main pump - the heart. It is quite clear that the movement of blood through the veins is facilitated while walking, when the muscle pump of the lower extremities works rhythmically.
Negative intrathoracic pressure, especially during the inspiratory phase, promotes venous return of blood to the heart. Intrathoracic negative pressure causes dilation of the venous vessels in the neck and chest cavity, which have thin and pliable walls. The pressure in the veins decreases, making it easier for blood to move towards the heart.
In small and medium veins there are no pulse fluctuations in blood pressure. In large veins near the heart, pulse fluctuations are observed - a venous pulse, which has a different origin than the arterial pulse. It is caused by difficulty in the flow of blood from the veins to the heart during systole of the atria and ventricles. During systole of these parts of the heart, the pressure inside the veins increases and their walls vibrate.
III. Age-related waspsbenefits of the circulatory system.Cardiovascular hygiene
The human body has its own individual development from the moment of fertilization to the natural end of life. This period is called ontogenesis. It distinguishes two independent stages: prenatal (from the moment of conception to the moment of birth) and postnatal (from the moment of birth to the death of a person). Each of these stages has its own characteristics in the structure and functioning of the circulatory system. Let's look at some of them:
Age characteristics in the prenatal stage. The formation of the embryonic heart begins from the 2nd week of prenatal development, and its development generally ends by the end of the 3rd week. The blood circulation of the fetus has its own characteristics, primarily associated with the fact that before birth, oxygen enters the fetus’s body through the placenta and the so-called umbilical vein. The umbilical vein branches into two vessels, one supplies the liver, the other connects to the inferior vena cava. As a result, in the inferior vena cava, oxygen-rich blood is mixed with blood that has passed through the liver and contains metabolic products. Blood enters the right atrium through the inferior vena cava. Next, the blood passes into the right ventricle and is then pushed into the pulmonary artery; a smaller part of the blood flows into the lungs, and most of it through the ductus botalli enters the aorta. The presence of the ductus botallus connecting the artery to the aorta is the second specific feature in the fetal circulation. As a result of the connection of the pulmonary artery and the aorta, both ventricles of the heart pump blood into the systemic circulation. Blood with metabolic products returns to the maternal body through the umbilical arteries and placenta.
Thus, the circulation of mixed blood in the fetal body, its connection through the placenta with the mother’s circulatory system and the presence of the ductus botallus are the main features of the fetal circulation.
Age-related features in the postnatal stage. In a newborn child, the connection with the mother’s body ceases and its own circulatory system takes on all the necessary functions. The ductus botallus loses its functional significance and soon becomes overgrown with connective tissue. In children, the relative mass of the heart and the total lumen of blood vessels are larger than in adults, which greatly facilitates blood circulation processes.
Are there any patterns in the growth of the heart? It may be noted that the growth of the heart is closely related to the overall growth of the body. The most intensive growth of the heart is observed in the first years of development and at the end of adolescence.
The shape and position of the heart in the chest also changes. In newborns, the heart is spherical and located much higher than in an adult. These differences are eliminated only by the age of 10.
Functional differences in the cardiovascular system of children and adolescents persist up to 12 years. The heart rate in children is higher than in adults. Heart rate in children is more susceptible to external influences: physical exercise, emotional stress, etc. Blood pressure in children is lower than in adults. Stroke volume in children is significantly less than in adults. With age, minute blood volume increases, which provides the heart with adaptation capabilities to physical activity.
During puberty, the rapid processes of growth and development occurring in the body affect the internal organs and, especially, the cardiovascular system. At this age, there is a discrepancy between the size of the heart and the diameter of the blood vessels. With the rapid growth of the heart, the blood vessels grow more slowly, their lumen is not wide enough, and therefore the adolescent’s heart bears an additional load, pushing blood through narrow vessels. For the same reason, a teenager may have a temporary disturbance in the nutrition of the heart muscle, increased fatigue, mild shortness of breath, and discomfort in the heart area.
Another feature of the adolescent’s cardiovascular system is that the adolescent’s heart grows very quickly, and the development of the nervous system that regulates the functioning of the heart does not keep pace with it. As a result, teenagers sometimes experience palpitations, irregular heart rhythms, etc. All of these changes are temporary and occur due to characteristics of growth and development, and not as a result of illness.
Hygiene of the cardiovascular system. For the normal development of the heart and its activity, it is extremely important to eliminate excessive physical and mental stress that disrupts the normal pace of the heart, as well as to ensure its training through rational and accessible physical exercises for children.
Gradual training of cardiac activity ensures improvement of the contractile and elastic properties of the muscle fibers of the heart.
Cardiovascular training is achieved by daily physical exercise, sports activities and moderate physical labor, especially when they are carried out in the fresh air.
Hygiene of the circulatory system in children places certain demands on their clothing. Tight clothes and tight dresses compress the chest. Narrow collars compress the blood vessels of the neck, which affects blood circulation in the brain. Tight belts compress the blood vessels of the abdominal cavity and thereby impede blood circulation in the circulatory organs. Tight shoes have an adverse effect on blood circulation in the lower extremities.
Conclusion
The cells of multicellular organisms lose direct contact with the external environment and are in the surrounding liquid medium - intercellular, or tissue fluid, from where they draw the necessary substances and where they secrete metabolic products.
The composition of tissue fluid is constantly updated due to the fact that this fluid is in close contact with continuously moving blood, which carries out a number of its inherent functions. Oxygen and other substances necessary for cells penetrate from the blood into the tissue fluid; products of cell metabolism enter the blood flowing from the tissues.
The diverse functions of blood can only be carried out with its continuous movement in the vessels, i.e. in the presence of blood circulation. Blood moves through the vessels due to periodic contractions of the heart. When the heart stops, death occurs because the delivery of oxygen and nutrients to tissues, as well as the release of tissues from metabolic products, stops.
Thus, the circulatory system is one of the most important systems of the body.
WITHlist of used literature
1. S.A. Georgieva and others. Physiology. - M.: Medicine, 1981.
2. E.B. Babsky, G.I. Kositsky, A.B. Kogan et al. Human physiology. - M.: Medicine, 1984.
3. Yu.A. Ermolaev Age physiology. - M.: Higher. School, 1985
4. S.E. Sovetov, B.I. Volkov and others. School hygiene. - M.: Education, 1967
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Structure and functions of the cardiovascular system
The cardiovascular system- physiological system, including the heart, blood vessels, lymphatic vessels, lymph nodes, lymph, regulatory mechanisms (local mechanisms: peripheral nerves and nerve centers, in particular the vasomotor center and the center for regulating the activity of the heart).
Thus, the cardiovascular system is a combination of 2 subsystems: the circulatory system and the lymph circulation system. The heart is the main component of both subsystems.
Blood vessels form 2 circles of blood circulation: small and large.
Pulmonary circulation - 1553 Servet - begins in the right ventricle with the pulmonary trunk, which carries venous blood. This blood enters the lungs, where the gas composition is regenerated. The end of the pulmonary circulation is in the left atrium with four pulmonary veins, through which arterial blood flows to the heart.
Systemic circulation - 1628 Harvey - begins in the left ventricle with the aorta and ends in the right atrium with veins: v.v.cava superior et interior. Functions of the cardiovascular system: movement of blood through the vessel, since blood and lymph perform their functions during movement.
Factors that ensure blood movement through vessels
- The main factor ensuring the movement of blood through the vessels: the work of the heart as a pump.
- Supporting factors:
- closedness of the cardiovascular system;
- pressure difference in the aorta and vena cava;
- elasticity of the vascular wall (transformation of the pulsating release of blood from the heart into continuous blood flow);
- valve apparatus of the heart and blood vessels, ensuring unidirectional blood movement;
- the presence of intrathoracic pressure is a “suction” action that ensures venous return of blood to the heart.
- Muscle work - pushing blood and a reflex increase in the activity of the heart and blood vessels as a result of activation of the sympathetic nervous system.
- Activity of the respiratory system: the more often and deeper the breathing, the more pronounced the suction effect of the chest.
Morphological features of the heart. Phases of heart activity
1. Main morphological features of the heart
A person has a 4-chambered heart, but from a physiological point of view, a 6-chambered one: the additional chambers are the auricles, since they contract 0.03-0.04 s before the atria. Due to their contractions, the atria are completely filled with blood. The size and weight of the heart are proportional to the overall size of the body.
In an adult, the volume of the cavity is 0.5-0.7 l; heart weight is equal to 0.4% of body weight.
The wall of the heart consists of 3 layers.
The endocardium is a thin connective tissue layer that passes into the tunica intima of the vessels. Provides non-wetting of the heart wall, facilitating intravascular hemodynamics.
Myocardium - the atrial myocardium is separated from the ventricular myocardium by a fibrous ring.
Epicardium - consists of 2 layers - fibrous (outer) and cardiac (inner). The fibrous leaf surrounds the heart from the outside - it performs a protective function and protects the heart from stretching. The heart leaf consists of 2 parts:
Visceral (epicardium);
Parietal, which fuses with the fibrous layer.
Between the visceral and parietal layers there is a cavity filled with fluid (reduces injuries).
Pericardium meaning:
Protection from mechanical damage;
Overextension protection.
The optimal level of heart contraction is achieved when the length of muscle fibers increases by no more than 30-40% of the initial value. Provides an optimal level of functioning of the cells of the synsatrial node. When the heart is overstretched, the process of generating nerve impulses is disrupted. Support for large vessels (prevents the collapse of the vena cava).
Phases of cardiac activity and the work of the heart valve apparatus in various phases of the cardiac cycle
The entire cardiac cycle lasts 0.8-0.86 s.
Two main phases of the cardiac cycle:
Systole is the ejection of blood from the cavities of the heart as a result of contraction;
Diastole - relaxation, rest and nutrition of the myocardium, filling the cavities with blood.
These main phases are divided into:
Atrial systole - 0.1 s - blood enters the ventricles;
Atrial diastole - 0.7 s;
Ventricular systole - 0.3 s - blood enters the aorta and pulmonary trunk;
Ventricular diastole - 0.5 s;
The total cardiac pause is 0.4 s. Ventricles and atria in diastole. The heart rests, feeds, the atria fill with blood and the ventricles are 2/3 full.
The cardiac cycle begins in atrial systole. Ventricular systole begins simultaneously with atrial diastole.
The ventricular cycle (Chauveau and Morely (1861)) - consists of ventricular systole and diastole.
Ventricular systole: period of contraction and period of ejection.
The contraction period is carried out in 2 phases:
1) asynchronous contraction (0.04 s) - uneven contraction of the ventricles. Contraction of the interventricular septal muscle and papillary muscles. This phase ends with complete closure of the atrioventricular valve.
2) isometric contraction phase - begins from the moment the atrioventricular valve closes and proceeds when all valves close. Since blood is incompressible, during this phase the length of muscle fibers does not change, but their tension increases. As a result, the pressure in the ventricles increases. The result is the opening of the semilunar valves.
The expulsion period (0.25 s) - consists of 2 phases:
1) rapid expulsion phase (0.12 s);
2) slow expulsion phase (0.13 s);
The main factor is the pressure difference, which promotes the release of blood. During this period, isotonic contraction of the myocardium occurs.
Ventricular diastole.
Consists of the following phases.
Protodiastolic period is the time interval from the end of systole to the closure of the semilunar valves (0.04 s). Due to the pressure difference, the blood returns to the ventricles, but filling the pockets of the semilunar valves closes them.
Isometric relaxation phase (0.25 s) - carried out with the valves completely closed. The length of the muscle fiber is constant, their tension changes and the pressure in the ventricles decreases. As a result, the atrioventricular valves open.
The filling phase is carried out during a general pause of the heart. First, fast filling, then slow - the heart is filled by 2/3.
Presystole is the filling of the ventricles with blood due to the atrium system (1/3 of the volume). By changing the pressure in the various cavities of the heart, a pressure difference is ensured on both sides of the valves, which ensures the functioning of the valvular apparatus of the heart.
PHYSIOLOGY OF THE CARDIOVASCULAR SYSTEM
PartI. GENERAL PLAN OF THE STRUCTURE OF THE CARDIOVASCULAR SYSTEM. PHYSIOLOGY OF THE HEART
1. General plan of the structure and functional significance of the cardiovascular system
The cardiovascular system, along with respiratory, is key life support system of the body because it provides continuous blood circulation through a closed vascular bed. Blood, only being in constant movement, is able to perform its numerous functions, the main of which is transport, which predetermines a number of others. Constant blood circulation through the vascular bed makes possible its continuous contact with all organs of the body, which ensures, on the one hand, the maintenance of the constancy of the composition and physicochemical properties of the intercellular (tissue) fluid (the actual internal environment for tissue cells), and on the other, the preservation homeostasis of the blood itself.
From a functional point of view, the cardiovascular system is divided into:
Ø heart - pump of periodic rhythmic type of action
Ø vessels- blood circulation pathways.
The heart provides rhythmic periodic pumping of portions of blood into the vascular bed, providing them with the energy necessary for the further movement of blood through the vessels. Rhythmic work of the heart is collateral continuous blood circulation in the vascular bed. Moreover, the blood in the vascular bed moves passively along the pressure gradient: from the area where it is higher to the area where it is lower (from arteries to veins); the minimum is the pressure in the veins returning blood to the heart. Blood vessels are present in almost all tissues. They are absent only in epithelia, nails, cartilage, tooth enamel, in some areas of the heart valves and in a number of other areas that are nourished by the diffusion of necessary substances from the blood (for example, cells of the inner wall of large blood vessels).
In mammals and humans, the heart four-chamber(consists of two atria and two ventricles), the cardiovascular system is closed, there are two independent circles of blood circulation - big(system) and small(pulmonary). Circulation circles start at ventricles with arterial type vessels (aorta and pulmonary trunk ), and end in atria veins (superior and inferior vena cava and pulmonary veins ). Arteries- vessels that carry blood from the heart, and veins- returning blood to the heart.
Systemic (systemic) circulation begins in the left ventricle with the aorta, and ends in the right atrium with the superior and inferior vena cava. The blood flowing from the left ventricle into the aorta is arterial. Moving through the vessels of the systemic circulation, it ultimately reaches the microcirculatory bed of all organs and structures of the body (including the heart and lungs itself), at the level of which it exchanges substances and gases with tissue fluid. As a result of transcapillary exchange, the blood becomes venous: it is saturated with carbon dioxide, final and intermediate products of metabolism, perhaps some hormones or other humoral factors enter it, and partly releases oxygen, nutrients (glucose, amino acids, fatty acids), vitamins and etc. Venous blood flowing from various tissues of the body through the venous system returns to the heart (namely, through the superior and inferior vena cava - into the right atrium).
Lesser (pulmonary) circulation begins in the right ventricle with the pulmonary trunk, which branches into two pulmonary arteries, which deliver venous blood to the microvasculature that encircles the respiratory part of the lungs (respiratory bronchioles, alveolar ducts and alveoli). At the level of this microvasculature, transcapillary exchange occurs between venous blood flowing to the lungs and alveolar air. As a result of this exchange, the blood is saturated with oxygen, partially releases carbon dioxide and turns into arterial blood. Through the system of pulmonary veins (two exit from each lung), arterial blood flowing from the lungs returns to the heart (to the left atrium).
Thus, in the left half of the heart the blood is arterial, it enters the vessels of the systemic circulation and is delivered to all organs and tissues of the body, ensuring their supply
The final product" href="/text/category/konechnij_produkt/" rel="bookmark">the final products of metabolism. In the right half of the heart there is venous blood, which is released into the pulmonary circulation and at the level of the lungs turns into arterial blood.
2. Morpho-functional characteristics of the vascular bed
The total length of the human vascular bed is about 100 thousand. kilometers; usually most of them are empty, and only the hard-working and constantly working organs (heart, brain, kidneys, respiratory muscles and some others) are intensively supplied. Vascular bed begins large arteries , carrying blood out of the heart. The arteries branch along their course, giving rise to arteries of smaller caliber (medium and small arteries). Having entered the blood-supplying organ, the arteries branch repeatedly until arterioles , which are the smallest vessels of the arterial type (diameter - 15-70 µm). From the arterioles, in turn, the metarteroyls (terminal arterioles) extend at a right angle, from which they originate true capillaries , forming net. At the sites where the capillaries separate from the metarterols, there are precapillary sphincters that control the local volume of blood passing through the true capillaries. Capillaries represent the smallest vessels in the vascular bed (d = 5-7 µm, length - 0.5-1.1 mm), their wall does not contain muscle tissue, but is formed just one layer of endothelial cells and a surrounding basement membrane. A person has 100-160 billion. capillaries, their total length is 60-80 thousand. kilometers, and the total surface area is 1500 m2. Blood from the capillaries sequentially enters the postcapillary (diameter up to 30 µm), collecting and muscular (diameter up to 100 µm) venules, and then into small veins. Small veins unite with each other to form medium and large veins.
Arterioles, metarterioles, precapillary sphincters, capillaries and venules make up microvasculature, which is the path of local blood flow of the organ, at the level of which exchange takes place between blood and tissue fluid. Moreover, this exchange occurs most effectively in capillaries. Venules, like no other vessels, are directly related to the course of inflammatory reactions in tissues, since it is through their wall that masses of leukocytes and plasma pass through inflammation.
Coll" href="/text/category/koll/" rel="bookmark">collateral vessels of one artery connecting with branches of other arteries, or intrasystemic arterial anastomoses between different branches of the same artery)
Ø venous(connecting vessels between different veins or branches of the same vein)
Ø arteriovenous(anastomoses between small arteries and veins, allowing blood to flow bypassing the capillary bed).
The functional purpose of arterial and venous anastomoses is to increase the reliability of the blood supply to the organ, while arteriovenous ones are to ensure the possibility of blood movement bypassing the capillary bed (they are found in large quantities in the skin, the movement of blood along which reduces heat loss from the surface of the body).
Wall everyone vessels, excluding capillaries , comprises three shells:
Ø inner shell, educated endothelium, basement membrane and subendothelial layer(a layer of loose fibrous connective tissue); this shell is separated from the middle shell internal elastic membrane;
Ø middle shell, which includes smooth muscle cells and dense fibrous connective tissue, the intercellular substance of which contains elastic and collagen fibers; separated from the outer shell outer elastic membrane;
Ø outer shell(adventitia), formed loose fibrous connective tissue, feeding the vessel wall; in particular, small vessels pass through this membrane, providing nutrition to the cells of the vascular wall itself (the so-called vascular vessels).
In vessels of various types, the thickness and morphology of these shells has its own characteristics. Thus, the walls of arteries are much thicker than those of veins, and it is their middle layer that differs most in thickness between arteries and veins, due to which the walls of arteries are more elastic than those of veins. At the same time, the outer lining of the wall of the veins is thicker than that of the arteries, and they, as a rule, have a larger diameter compared to the arteries of the same name. Small, medium and some large veins have venous valves , which are semilunar folds of their inner membrane and prevent the reverse flow of blood in the veins. The veins of the lower extremities have the largest number of valves, while both vena cava, veins of the head and neck, renal veins, portal and pulmonary veins do not have valves. The walls of large, medium and small arteries, as well as arterioles, are characterized by some structural features relating to their medial shell. In particular, in the walls of large and some medium-sized arteries (vessels of the elastic type), elastic and collagen fibers predominate over smooth muscle cells, as a result of which such vessels are characterized by very high elasticity, which is necessary to convert pulsating blood flow into constant one. The walls of small arteries and arterioles, on the contrary, are characterized by a predominance of smooth muscle fibers over connective tissue, which allows them to change the diameter of their lumen within a fairly wide range and thus regulate the level of blood filling of the capillaries. Capillaries, which do not have middle and outer membranes as part of their walls, are not able to actively change their lumen: it changes passively depending on the degree of their blood supply, which depends on the size of the lumen of the arterioles.
Fig.4. Diagram of the structure of the wall of an artery and vein
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Aorta" href="/text/category/aorta/" rel="bookmark">aorta, pulmonary arteries, common carotid and iliac arteries;
Ø resistive type vessels (resistance vessels)– mainly arterioles, the smallest vessels of the arterial type, in the wall of which there is a large number of smooth muscle fibers, which allows them to change their lumen within a wide range; ensure the creation of maximum resistance to blood movement and take part in its redistribution between organs working with different intensities
Ø exchange vessels(mainly capillaries, partly arterioles and venules, at the level of which transcapillary exchange occurs)
Ø vessels of capacitive (depositing) type(veins), which, due to the small thickness of their middle membrane, are characterized by good compliance and can stretch quite strongly without an accompanying sharp increase in pressure in them, due to which they often serve as a blood depot (as a rule, about 70% of the volume of circulating blood is in the veins)
Ø anastomosing type vessels(or shunt vessels: artreioarterial, venovenous, arteriovenous).
3. Macro-microscopic structure of the heart and its functional significance
Heart(cor) is a hollow muscular organ that pumps blood into the arteries and receives it from the veins. It is located in the chest cavity, as part of the organs of the middle mediastinum, intrapericardially (inside the heart sac - pericardium). Has a conical shape; its longitudinal axis is directed obliquely - from right to left, from top to bottom and from back to front, so it lies two-thirds in the left half of the thoracic cavity. The apex of the heart faces down, left and forward, and the wider base faces up and back. The heart has four surfaces:
Ø anterior (sternocostal), convex, facing the posterior surface of the sternum and ribs;
Ø lower (diaphragmatic or posterior);
Ø lateral or pulmonary surfaces.
The average heart weight in men is 300g, in women – 250g. The largest transverse size of the heart is 9-11 cm, the anteroposterior size is 6-8 cm, the length of the heart is 10-15 cm.
The heart begins to form at the 3rd week of intrauterine development, its division into the right and left halves occurs by the 5-6th week; and it begins to work soon after its initiation (on the 18-20th day), making one contraction every second.
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Rice. 7. Heart (front and side views)
The human heart consists of 4 chambers: two atria and two ventricles. The atria receive blood from the veins and push it into the ventricles. In general, their pumping capacity is much less than that of the ventricles (the ventricles are mainly filled with blood during a general pause of the heart, while contraction of the atria only contributes to additional pumping of blood), the main role atria is that they are temporary blood reservoirs . Ventricles receive blood flowing from the atria and pump it into the arteries (aorta and pulmonary trunk). The wall of the atria (2-3mm) is thinner than that of the ventricles (5-8mm in the right ventricle and 12-15mm in the left). At the border between the atria and ventricles (in the atrioventricular septum) there are atrioventricular openings, in the area of which there are leaflet atrioventricular valves(bicuspid or mitral in the left half of the heart and tricuspid in the right), preventing the reverse flow of blood from the ventricles into the atria during ventricular systole . At the site where the aorta and pulmonary trunk exit from the corresponding ventricles, they are localized semilunar valves, preventing the reverse flow of blood from the vessels into the ventricles during ventricular diastole . In the right half of the heart the blood is venous, and in the left half it is arterial.
Heart wall comprises three layers:
Ø endocardium– a thin inner membrane that lines the inside of the heart cavity, repeating their complex relief; it consists mainly of connective (loose and dense fibrous) and smooth muscle tissue. Endocardial duplications form the atrioventricular and semilunar valves, as well as the valves of the inferior vena cava and coronary sinus
Ø myocardium– the middle layer of the heart wall, the thickest, is a complex multi-tissue membrane, the main component of which is cardiac muscle tissue. The myocardium is thickest in the left ventricle and thinnest in the atria. Atrial myocardium comprises two layers: superficial (general for both atria, in which the muscle fibers are located transversely) And deep (separate for each atrium, in which muscle fibers follow longitudinally, here there are also circular fibers, loop-shaped in the form of sphincters covering the mouths of the veins flowing into the atria). Ventricular myocardium three-layer: outer (educated obliquely oriented muscle fibers) and interior (educated longitudinally oriented muscle fibers) layers are common to the myocardium of both ventricles, and located between them middle layer (educated circular fibers) – separate for each of the ventricles.
Ø epicardium– the outer membrane of the heart, is a visceral layer of the serous membrane of the heart (pericardium), built like serous membranes and consists of a thin plate of connective tissue covered with mesothelium.
Myocardium of the heart, providing periodic rhythmic contraction of its chambers, is formed cardiac muscle tissue (a type of striated muscle tissue). The structural and functional unit of cardiac muscle tissue is cardiac muscle fiber. It is striated (the contractile apparatus is represented myofibrils , oriented parallel to its longitudinal axis, occupying a peripheral position in the fiber, while the nuclei are located in the central part of the fiber), is characterized by the presence well developed sarcoplasmic reticulum And T-tubule systems . But him distinctive feature is the fact that it is multicellular formation , which is a collection of sequentially arranged and connected by intercalary disks of cardiac muscle cells - cardiomyocytes. In the area of insertion discs there is a large number gap junctions (nexuses), arranged like electrical synapses and providing the ability to directly conduct excitation from one cardiomyocyte to another. Due to the fact that the cardiac muscle fiber is a multicellular formation, it is called a functional fiber.
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Rice. 9. Scheme of the structure of a gap junction (nexus). The gap contact provides ionic And metabolic cell coupling. The plasma membranes of cardiomyocytes in the area of gap junction formation are brought together and separated by a narrow intercellular gap 2-4 nm wide. The connection between the membranes of neighboring cells is provided by a transmembrane protein of a cylindrical configuration - connexon. The connexon molecule consists of 6 connexin subunits, arranged radially and bounding a cavity (connexon channel, diameter 1.5 nm). Two connexon molecules of neighboring cells are connected to each other in the intermembrane space, resulting in the formation of a single nexus channel that can pass ions and low molecular weight substances with Mr up to 1.5 kDa. Consequently, nexuses make it possible to move not only inorganic ions from one cardiomyocyte to another (which ensures direct transmission of excitation), but also low-molecular organic substances (glucose, amino acids, etc.)
Blood supply to the heart carried out coronary arteries(right and left), extending from the aortic bulb and components together with the microvasculature and coronary veins (collected into the coronary sinus, which flows into the right atrium) coronary (coronary) circulation, which is part of a large circle.
Heart refers to the number of organs that work continuously throughout life. Over 100 years of human life, the heart makes about 5 billion contractions. Moreover, the intensity of the heart’s work depends on the level of metabolic processes in the body. Thus, in an adult, the normal heart rate at rest is 60-80 beats/min, while in smaller animals with a larger relative body surface area (surface area per unit mass) and, accordingly, a higher level of metabolic processes, the intensity of cardiac activity is much higher . So in a cat (average weight 1.3 kg) the heart rate is 240 beats/min, in a dog - 80 beats/min, in a rat (200-400g) - 400-500 beats/min, and in a tit (weight about 8g) – 1200 beats/min. The heart rate of large mammals with a relatively low level of metabolic processes is much lower than that of humans. In a whale (weight 150 tons), the heart beats 7 times per minute, and in an elephant (3 tons) - 46 beats per minute.
The Russian physiologist calculated that during a human life the heart performs work equal to the effort that would be enough to lift a train to the highest peak in Europe - Mount Mont Blanc (height 4810m). During the day, in a person who is at relative rest, the heart pumps 6-10 tons of blood, and during life - 150-250 thousand tons.
The movement of blood in the heart, as well as in the vascular bed, occurs passively along a pressure gradient. So, the normal cardiac cycle begins with atrial systole , as a result of which the pressure in the atria increases slightly, and portions of blood are pumped into the relaxed ventricles, the pressure in which is close to zero. At the moment following atrial systole ventricular systole the pressure in them increases, and when it becomes higher than that in the proximal vascular bed, blood from the ventricles is expelled into the corresponding vessels. In the moment general cardiac pause the main filling of the ventricles occurs with blood passively returning to the heart through the veins; contraction of the atria provides additional pumping of a small amount of blood into the ventricles.
https://pandia.ru/text/78/567/images/image011_14.jpg" width="552" height="321 src=">Fig. 10. Scheme of the heart
Rice. 11. Diagram showing the direction of blood flow in the heart
4. Structural organization and functional role of the cardiac conduction system
The conduction system of the heart is represented by a set of conductive cardiomyocytes that form
Ø sinoatrial node(sinoatrial node, Keith-Fluck node, located in the right atrium, at the junction of the vena cava),
Ø atrioventricular node(the atrioventricular node, the Aschoff-Tawar node, is located in the thickness of the lower part of the interatrial septum, closer to the right half of the heart),
Ø His bundle(atrioventricular bundle, located in the upper part of the interventricular septum) and his legs(descend from the bundle of His along the inner walls of the right and left ventricles),
Ø network of diffuse conducting cardiomyocytes, forming Prukinje fibers (pass through the thickness of the working myocardium of the ventricles, usually adjacent to the endocardium).
Cardiomyocytes of the cardiac conduction system are atypical myocardial cells(the contractile apparatus and the T-tubule system are poorly developed in them, they do not play a significant role in the development of tension in the cavities of the heart at the time of their systole), which have the ability to independently generate nerve impulses with a certain frequency ( automation).
Involvement" href="/text/category/vovlechenie/" rel="bookmark">involving the myocradiocytes of the interventricular septum and the apex of the heart in excitation, and then along the branches of the legs and Purkinje fibers returns to the base of the ventricles. Due to this, the apices of the ventricles contract first, and then their foundations.
Thus, the conduction system of the heart provides:
Ø periodic rhythmic generation of nerve impulses, initiating contraction of the heart chambers at a certain frequency;
Ø a certain sequence in the contraction of the heart chambers(first the atria excite and contract, pumping blood into the ventricles, and only then the ventricles, pumping blood into the vascular bed)
Ø almost synchronous coverage of the working ventricular myocardium by excitation, and hence the high efficiency of ventricular systole, which is necessary to create a certain pressure in their cavities, slightly higher than that in the aorta and pulmonary trunk, and, consequently, to ensure a certain systolic ejection of blood.
5. Electrophysiological characteristics of myocardial cells
Conducting and working cardiomyocytes are excitable structures, i.e., they have the ability to generate and conduct action potentials (nerve impulses). And for conducting cardiomyocytes characteristic automatic (ability for independent periodic rhythmic generation of nerve impulses), while working cardiomyocytes are excited in response to excitation coming to them from conductive or other already excited working myocardial cells.
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Rice. 13. Diagram of the action potential of a working cardiomyocyte
IN action potential of working cardiomyocytes The following phases are distinguished:
Ø rapid initial depolarization phase, due to fast incoming voltage-gated sodium current , occurs due to activation (opening of fast activation gates) of fast voltage-gated sodium channels; is characterized by a high steepness of increase, since the current causing it has the ability to self-renew.
Ø AP plateau phase, due to voltage dependent slow incoming calcium current . The initial depolarization of the membrane caused by the incoming sodium current leads to the opening of slow calcium channels, through which calcium ions enter the cardiomyocyte along a concentration gradient; these channels are to a much lesser extent, but still permeable to sodium ions. The entry of calcium and partly sodium into the cardiomyocyte through slow calcium channels somewhat depolarizes its membrane (but much weaker than the fast incoming sodium current preceding this phase). During this phase, fast sodium channels, which provide the phase of rapid initial depolarization of the membrane, are inactivated, and the cell enters the state absolute refractoriness. During this period, gradual activation of voltage-gated potassium channels also occurs. This phase is the longest AP phase (0.27 s with a total AP duration of 0.3 s), as a result of which the cardiomyocyte is in a state of absolute refractoriness most of the time during the AP generation period. Moreover, the duration of a single contraction of the myocardial cell (about 0.3 s) is approximately equal to that of the AP, which, together with a long period of absolute refractoriness, makes it impossible for the development of tetanic contraction of the heart muscle, which would be equivalent to cardiac arrest. Therefore, the heart muscle is capable of developing only single contractions.
Physiology of the cardiovascular system
Performing one of the main functions - transport - the cardiovascular system ensures the rhythmic flow of physiological and biochemical processes in the human body. All necessary substances (proteins, carbohydrates, oxygen, vitamins, mineral salts) are delivered to tissues and organs through blood vessels and metabolic products and carbon dioxide are removed. In addition, hormonal substances produced by the endocrine glands, which are specific regulators of metabolic processes, and antibodies necessary for the body’s protective reactions against infectious diseases are carried through the blood vessels into organs and tissues. Thus, the vascular system also performs regulatory and protective functions. In collaboration with the nervous and humoral systems, the vascular system plays an important role in ensuring the integrity of the body.
The vascular system is divided into circulatory and lymphatic. These systems are anatomically and functionally closely related and complement each other, but there are certain differences between them. Blood in the body moves through the circulatory system. The circulatory system consists of the central circulatory organ - the heart, the rhythmic contractions of which allow blood to move through the vessels.
Vessels of the pulmonary circulation
Pulmonary circulation begins in the right ventricle, from which the pulmonary trunk emerges, and ends in the left atrium, into which the pulmonary veins flow. The pulmonary circulation is also called pulmonary, it ensures gas exchange between the blood of the pulmonary capillaries and the air of the pulmonary alveoli. It consists of the pulmonary trunk, the right and left pulmonary arteries with their branches, and the vessels of the lungs, which gather into two right and two left pulmonary veins, flowing into the left atrium.
Pulmonary trunk(truncus pulmonalis) originates from the right ventricle of the heart, diameter 30 mm, goes obliquely upward, to the left and at the level of the IV thoracic vertebra it divides into the right and left pulmonary arteries, which go to the corresponding lung.
Right pulmonary artery with a diameter of 21 mm, it goes to the right to the gate of the lung, where it is divided into three lobar branches, each of which in turn is divided into segmental branches.
Left pulmonary artery shorter and thinner than the right one, runs from the bifurcation of the pulmonary trunk to the hilum of the left lung in the transverse direction. On its way, the artery crosses the left main bronchus. At the gate, according to the two lobes of the lung, it is divided into two branches. Each of them breaks up into segmental branches: one - within the boundaries of the upper lobe, the other - the basal part - with its branches provides blood to the segments of the lower lobe of the left lung.
Pulmonary veins. Venules begin from the capillaries of the lungs, which merge into larger veins and form two pulmonary veins in each lung: the right upper and right lower pulmonary veins; left superior and left inferior pulmonary veins.
Right superior pulmonary vein collects blood from the upper and middle lobes of the right lung, and lower right - from the lower lobe of the right lung. The common basal vein and the superior vein of the inferior lobe form the right inferior pulmonary vein.
Left superior pulmonary vein collects blood from the upper lobe of the left lung. It has three branches: apical-posterior, anterior and lingular.
Left lower pulmonary the vein carries blood from the lower lobe of the left lung; it is larger than the superior one, consists of the superior vein and the common basal vein.
Vessels of the systemic circulation
Systemic circulation begins in the left ventricle, from where the aorta emerges, and ends in the right atrium.
The main purpose of the vessels of the systemic circulation is the delivery of oxygen, nutrients, and hormones to organs and tissues. Metabolism between blood and organ tissues occurs at the level of capillaries, and metabolic products are removed from organs through the venous system.
The blood vessels of the systemic circulation include the aorta with the arteries of the head, neck, trunk and limbs branching off from it, branches of these arteries, small vessels of organs, including capillaries, small and large veins, which then form the superior and inferior vena cava.
Aorta(aorta) is the largest unpaired arterial vessel in the human body. It is divided into the ascending part, the aortic arch and the descending part. The latter, in turn, is divided into thoracic and abdominal parts.
Ascending aorta begins with an extension - a bulb, leaves the left ventricle of the heart at the level of the third intercostal space on the left, goes up behind the sternum and at the level of the second costal cartilage passes into the aortic arch. The length of the ascending aorta is about 6 cm. The right and left coronary arteries depart from it, which supply blood to the heart.
Aortic arch starts from the second costal cartilage, turns left and back to the body of the fourth thoracic vertebra, where it passes into the descending part of the aorta. There is a slight narrowing in this place - aortic isthmus. Large vessels depart from the aortic arch (brachiocephalic trunk, left common carotid and left subclavian arteries), which supply blood to the neck, head, upper torso and upper limbs.
Descending aorta - the longest part of the aorta, starts from the level of the IV thoracic vertebra and goes to the IV lumbar vertebra, where it divides into the right and left iliac arteries; this place is called bifurcation of the aorta. The descending aorta is divided into the thoracic and abdominal aorta.
Physiological characteristics of the heart muscle. The main features of the heart muscle include automaticity, excitability, conductivity, contractility, and refractoriness.
Automaticity of the heart - the ability to rhythmically contract the myocardium under the influence of impulses that appear in the organ itself.
The composition of cardiac striated muscle tissue includes typical contractile muscle cells - cardiomyocytes and atypical cardiac myocytes (pacemakers), forming the conduction system of the heart, which ensures the automaticity of heart contractions and coordination of the contractile function of the myocardium of the atria and ventricles of the heart. The first sinoatrial node of the conduction system is the main center of cardiac automaticity - a first-order pacemaker. From this node, excitation spreads to the working cells of the atria myocardium and through special intracardiac conduction bundles reaches the second node - atrioventricular (atrioventricular), which is also capable of generating impulses. This node is a second-order pacemaker. Excitation through the atrioventricular node under normal conditions is possible only in one direction. Retrograde conduction of impulses is impossible.
The third level, which ensures the rhythmic activity of the heart, is located in the His bundle and Purkin fibers.
Automation centers located in the conduction system of the ventricles are called third-order pacemakers. Under normal conditions, the frequency of myocardial activity of the entire heart is generally determined by the sinoatrial node. It subjugates all the underlying formations of the conduction system and imposes its own rhythm.
A necessary condition for ensuring the functioning of the heart is the anatomical integrity of its conduction system. If excitability does not occur in the first-order pacemaker or its transmission is blocked, the second-order pacemaker takes on the role of pacemaker. If the transfer of excitability to the ventricles is impossible, they begin to contract in the rhythm of third-order pacemakers. With transverse blockade, the atria and ventricles each contract in their own rhythm, and damage to the pacemakers leads to complete cardiac arrest.
Excitability of the heart muscle occurs under the influence of electrical, chemical, thermal and other stimuli of the heart muscle, which is capable of entering a state of excitation. This phenomenon is based on the negative electrical potential in the initial excited area. As in any excitable tissue, the membrane of the working cells of the heart is polarized. It is positively charged on the outside and negatively charged on the inside. This condition occurs as a result of different concentrations of Na + and K + on both sides of the membrane, as well as as a result of different permeability of the membrane to these ions. At rest, Na + ions do not penetrate through the cardiomyocyte membrane, but K + ions only partially penetrate. Due to diffusion, K + ions leaving the cell increase the positive charge on its surface. The inner side of the membrane becomes negative. Under the influence of a stimulus of any nature, Na + enters the cell. At this moment, a negative electrical charge appears on the surface of the membrane and potential reversal develops. The action potential amplitude for cardiac muscle fibers is about 100 mV or more. The resulting potential depolarizes the membranes of neighboring cells, their own action potentials appear - excitation spreads throughout the myocardial cells.
The action potential of a cell in the working myocardium is many times longer than in skeletal muscle. During the development of an action potential, the cell is not excited to subsequent stimuli. This feature is important for the function of the heart as an organ, since the myocardium can respond with only one action potential and one contraction to repeated stimulation. All this creates conditions for rhythmic contraction of the organ.
In this way, excitation spreads throughout the entire organ. This process is the same in the working myocardium and in pacemakers. The ability to excite the heart with an electric current has found practical application in medicine. Under the influence of electrical impulses, the source of which are electrical stimulators, the heart begins to excite and contract in a given rhythm. When electrical stimulation is applied, regardless of the magnitude and strength of the stimulation, the beating heart will not respond if this stimulation is applied during systole, which corresponds to the time of the absolute refractory period. And during diastole, the heart responds with a new extraordinary contraction - an extrasystole, after which a long pause occurs, called compensatory.
Cardiac muscle conductivity lies in the fact that excitation waves travel through its fibers at unequal speeds. Excitation propagates through the fibers of the atrium muscles at a speed of 0.8-1.0 m/s, through the fibers of the ventricular muscles - 0.8-0.9 m/s, and through special heart tissue - 2.0-4.2 m/s With. Excitation travels along skeletal muscle fibers at a speed of 4.7-5.0 m/s.
Contractility of the heart muscle has its own characteristics as a result of the structure of the organ. The atrial muscles contract first, then the papillary muscles and the subendocardial layer of the ventricular muscles. Further, the contraction also covers the inner layer of the ventricles, which thereby ensures the movement of blood from the cavities of the ventricles into the aorta and pulmonary trunk.
Changes in the contractile force of the heart muscle, which occur periodically, are carried out using two self-regulation mechanisms: heterometric and homeometric.
At the core heterometric mechanism lies the change in the initial dimensions of the length of the myocardial fibers, which occurs when the flow of venous blood changes: the more the heart expands during diastole, the more it contracts during systole (Frank-Starling law). This law is explained as follows. The cardiac fiber consists of two parts: contractile and elastic. During excitation, the first one contracts, and the second one stretches depending on the load.
Homeometric mechanism is based on the direct effect of biologically active substances (such as adrenaline) on the metabolism of muscle fibers and the production of energy in them. Adrenaline and norepinephrine increase the entry of Ca2 into the cell during the development of an action potential, thereby causing increased heart contractions.
Refractoriness of the heart muscle characterized by a sharp decrease in tissue excitability throughout its activity. There are absolute and relative refractory periods. In the absolute refractory period, when electrical stimulation is applied, the heart will not respond to them with irritation and contraction. The refractory period lasts as long as systole lasts. During the relative refractory period, the excitability of the heart muscle gradually returns to its original level. During this period, the heart muscle can respond to the stimulus with a contraction stronger than the threshold. The relative refractory period is found during diastole of the atria and ventricles of the heart. After the phase of relative refractoriness, a period of increased excitability begins, which coincides in time with diastolic relaxation and is characterized by the fact that the heart muscle responds with a flash of excitation and to impulses of low strength.
Cardiac cycle. The heart of a healthy person contracts rhythmically at rest with a frequency of 60-70 beats per minute.
The period that includes one contraction and subsequent relaxation is cardiac cycle. A contraction rate above 90 beats is called tachycardia, and below 60 beats is called bradycardia. With a heart rate of 70 beats per minute, the full cycle of cardiac activity lasts 0.8-0.86 s.
The contraction of the heart muscle is called systole, relaxation - diastole. The cardiac cycle has three phases: atrial systole, ventricular systole and a general pause. The beginning of each cycle is considered atrial systole, the duration of which is 0.1-0.16 s. During systole, the pressure in the atria increases, which leads to the ejection of blood into the ventricles. The latter are relaxed at this moment, the leaflets of the atrioventricular valves hang down and blood freely passes from the atria to the ventricles.
After the end of atrial systole begins ventricular systole lasting 0.3 s. During ventricular systole, the atria are already relaxed. Like the atria, both ventricles - right and left - contract simultaneously.
Ventricular systole begins with contractions of their fibers, resulting from the spread of excitation throughout the myocardium. This period is short. At the moment, the pressure in the cavities of the ventricles has not yet increased. It begins to increase sharply when excitability covers all fibers, and reaches 70-90 mm Hg in the left atrium. Art., and in the right - 15-20 mm Hg. Art. As a result of increased intraventricular pressure, the atrioventricular valves quickly close. At this moment, the semilunar valves are also still closed and the ventricular cavity remains closed; the volume of blood in it is constant. Excitation of the myocardial muscle fibers leads to an increase in blood pressure in the ventricles and an increase in tension in them. The appearance of a cardiac impulse in the fifth left intercostal space is due to the fact that with an increase in myocardial tension, the left ventricle (heart) takes on a rounded shape and produces an impact on the inner surface of the chest.
If the blood pressure in the ventricles exceeds the pressure in the aorta and pulmonary artery, the semilunar valves open, their valves are pressed against the inner walls and period of exile(0.25 s). At the beginning of the expulsion period, the blood pressure in the ventricular cavity continues to increase and reaches approximately 130 mm Hg. Art. in the left and 25 mm Hg. Art. in the right. As a result, blood quickly flows into the aorta and pulmonary trunk, and the volume of the ventricles quickly decreases. This rapid expulsion phase. After the opening of the semilunar valves, the ejection of blood from the heart cavity slows down, the contraction of the ventricular myocardium weakens and begins slow expulsion phase. With a drop in pressure, the semilunar valves close, impeding the reverse flow of blood from the aorta and pulmonary artery, and the ventricular myocardium begins to relax. A short period begins again, during which the aortic valves are still closed and the atrioventricular valves are not open. If the pressure in the ventricles is slightly less than in the atria, then the atrioventricular valves open and the ventricles are filled with blood, which will again be ejected in the next cycle, and diastole of the whole heart begins. Diastole continues until the next atrial systole. This phase is called general pause(0.4 s). Then the cycle of cardiac activity is repeated.
