Lecture 6. Blood circulation
Circulatory organs. Heart
The circulatory organs include blood vessels(arteries, veins, capillaries) and heart. Arteries are vessels through which blood flows from the heart, veins are vessels through which blood returns to the heart. The walls of arteries and veins consist of three layers: the inner layer is made of flat endothelium, the middle layer is made of smooth muscle tissue and elastic fibers, and the outer layer is made of connective tissue(Fig. 197). Large arteries located near the heart have to withstand a lot of pressure, so they have thick walls, their middle layer consists mainly of elastic fibers. Arteries carry blood to the organs, branch into arterioles, then the blood enters the capillaries and flows through the venules into the veins.Capillaries consist of a single layer of endothelial cells located on the basement membrane. Through the walls of capillaries, oxygen and nutrients diffuse from the blood into the tissues, and carbon dioxide and metabolic products enter. Veins, unlike arteries, have semilunar valves, thanks to which blood flows only towards the heart. The pressure in the veins is low, their walls are thinner and softer.
The heart is located in chest between the lungs, two thirds located to the left of the midline of the body, and one third to the right. The weight of the heart is about 300 g, the base is at the top, the apex is at the bottom. The outside is covered with the pericardium, the pericardium. The bag is formed by two leaves, between which there is a small cavity. One of the leaves covers the heart muscle (myocardium). The endocardium lines the heart cavity and forms the valves. The heart consists of four chambers, two upper - thin-walled atria and two lower thick-walled ventricles, and the wall of the left ventricle is 2.5 times thicker than the wall of the right ventricle (Fig. 198). This is due to the fact that the left ventricle pumps blood into the big circle blood circulation, right - into the small circle.
In the left half of the heart there is arterial blood, in the right - venous. In the left atrioventricular orifice there is a bicuspid valve, in the right - a tricuspid valve. When the ventricles contract, the valves close under blood pressure and prevent blood from flowing back into the atria. Tendon threads attached to the valves and papillary muscles of the ventricles prevent the valves from everting out. At the border of the ventricles with the pulmonary artery and aorta there are pocket-shaped semilunar valves. When the ventricles contract, these valves are pressed against the walls of the arteries, and blood is released into the aorta and pulmonary artery. When the ventricles relax, the pockets fill with blood and prevent blood from flowing back into the ventricles.
About 10% of the blood ejected by the left ventricle enters the coronary vessels that supply the heart muscle. When there is a blockage of some kind coronary vessel death of a portion of the myocardium (infarction) may occur. Impairment of the patency of an artery can occur as a result of blockage of the vessel by a blood clot or due to its severe narrowing - spasm.
Work of the heart. Work regulation
There are three phases of cardiac activity: contraction (systole) of the atria, ventricular systole and general relaxation(diastole). With a heart rate of 75 times per minute, one cycle takes 0.8 seconds. In this case, atrial systole lasts 0.1 s, ventricular systole - 0.3 s, total diastole- 0.4 s.
Thus, in one cycle the atria work for 0.1 s and rest for 0.7 s, the ventricles work for 0.3 s and rest for 0.5 s. This allows the heart to work without getting tired throughout your life.
With one contraction of the heart, about 70 ml of blood is ejected into the pulmonary trunk and aorta; in a minute, the volume of ejected blood will be more than 5 liters. At physical activity the frequency and strength of heart contractions increases and cardiac output reaches 20 - 40 l/min.
Automaticity of the heart. Even an isolated heart, when a physiological solution is passed through it, is capable of contracting rhythmically without external stimulation, under the influence of impulses arising in the heart itself. Impulses arise in the sinoatrial and atrioventricular nodes (pacemakers), located in the right atrium, then are carried through the conduction system (branch branches and Purkinje fibers) to the atria and ventricles, causing their contraction (Fig. 199). Both the pacemakers and the conduction system of the heart are formed by muscle cells of a special structure. The rhythm of the isolated heart is set by the sinoatrial node; it is called the 1st order pacemaker. If you interrupt the transmission of impulses from the sinoatrial node to the atrioventricular node, the heart will stop, then resume work in the rhythm set by the atrioventricular node, the 2nd order pacemaker.
Nervous regulation. The activity of the heart, like other internal organs, is regulated by the autonomic (vegetative) part of the nervous system:
Firstly, the heart has its own nervous system hearts with reflex arcs in the heart itself - the metasympathetic part of the nervous system. Its work is visible when the atria of an isolated heart are overfilled, in this case the frequency and strength of heart contractions increases.
Secondly, the sympathetic and parasympathetic nerves approach the heart. Information from stretch receptors in the vena cava and aortic arch is transmitted to medulla, to the center of regulation of cardiac activity. The weakening of the heart is caused by the parasympathetic nerves as part of the vagus nerve, while the strengthening of the heart is caused by the sympathetic nerves, the centers of which are located in the spinal cord.
Humoral regulation. The activity of the heart is also affected by a number of substances entering the blood. Increased heart function is caused by adrenaline secreted by the adrenal glands, thyroxine secreted by the thyroid gland, and excess Ca2+ ions. Weakening of the heart is caused by acetylcholine, an excess of K+ ions.
Circulation circles
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The systemic circulation begins in the left ventricle, arterial blood is thrown into the left aortic arch, from which the subclavian and carotid arteries, carrying blood to upper limbs and head. From them, venous blood returns through the superior vena cava to the right atrium. The aortic arch passes into the abdominal aorta, from which blood flows through the arteries to the internal organs, releases oxygen and nutrients, and venous blood returns through the inferior vena cava to the right atrium. Blood from digestive system By portal vein enters the liver hepatic vein flows into the inferior vena cava (Fig. 200).
The minimum time for a complete circuit is 20-23 seconds. In this case, it takes about 4 seconds to pass through the pulmonary circulation, and the rest - to pass through the large one. The pulmonary circulation begins in the right ventricle, venous blood through the pulmonary arteries enters the capillaries that encircle the alveoli of the lungs, gas exchange occurs and arterial blood returns through the four pulmonary veins to the left atrium.
The heart of an adult is cone-shaped. Its weight is 220-300 g.
Topography of the heart
The heart is located in the chest cavity, behind the sternum, in the space between the lungs, called the mediastinum, so that its base faces up and its apex faces down and to the left. The base of the heart is projected onto the surface of the chest along a line connecting two points. One of them is located on the cartilage of the 3rd rib at a distance of 12.5 mm from the right edge of the sternum, the other is on the cartilage of the second rib at 18 mm from the left edge of the sternum. The apex of the heart is formed by the left ventricle; is projected in the fifth left intercostal space at a distance of 3 cm from the median plane.
Macrostructure
The human heart is a hollow muscular four-chamber organ consisting of two atria and two ventricles. The right and left halves of the heart are separated by a solid septum. The atria and ventricles communicate through the atrioventricular openings, in which there are valves that open towards the ventricles: tricuspid on the right and bicuspid (mitral) on the left. Atrioventricular valves allow blood to flow in only one direction, along the pressure gradient. The outside of the heart is covered with pericardium. Its outer fibrous layer descends from the base of the heart and encloses it like a sac. The inner (serous) layer of the pericardium forms two layers - visceral (covers the myocardium) and parietal (adjacent from the inside to the fibrous pericardium). The space between the pericardial layers is a narrow gap filled with fluid that facilitates the movements of the heart. The inside of the heart cavity is lined with endocardium. It consists of connective tissue covered with endothelium and is involved in the formation of valve leaflets. Between the pericardium and endocardium there is a middle layer - the myocardium, which is formed muscle tissue. The thickness of the myocardium of the left ventricle is much greater than that of the right. The walls of the atria are thinner than the walls of the ventricles. On the inner surface of the ventricles there are muscle cords - papillary muscles. From their tops begin thin tendinous chords - strings, which at their other end are attached to the lower edges of the tricuspid and bicuspid valves. The tension of the tendon threads at the moment of contraction of the ventricles prevents the valves from everting towards the atria.
Myocardial microstructure
The myocardium is a complex multi-tissue structure. The main component of the myocardium is the transversely striated contractile cardiomyocytes (typical) that form the system. A characteristic feature of the myocardial microstructure is the presence of intercalated discs, where neighboring cardiomyocytes form zones of tight contact. In the area of close contact of cardiomyocytes electrical resistance is insignificant compared to other areas, so excitation easily and quickly spreads throughout the entire mass of the myocardium. The myocardium has several properties that are extremely important for cardiac contraction: automaticity, excitability, conductivity, contractility and internal secretion.
Blood in the cardiovascular system flows in only one direction: from the left ventricle through the systemic circulation to the right atrium, then from the right atrium to the right ventricle, from where through the pulmonary circulation to the left atrium and from the left atrium to the left ventricle. The one-sidedness of blood flow depends on the sequential contraction of the parts of the heart and on its valve apparatus. The heart contracts rhythmically (in humans, 70-80 beats/min). In this case, there is a stereotypical alternation of the phases of contraction (systole) and relaxation (diastole) of various chambers of the heart, which is called cardiac cycle. A single cycle of human heart activity consists of three phases: atrial systole, ventricular systole and pause.
Phase analysis of a single cycle of human heart activity
First phase cardiac cycle- this is atrial systole: the atria contract, and the blood in them enters the ventricles. The leaflet valves open freely towards the ventricles and therefore do not interfere with the flow of blood from the atria to the ventricles. During atrial systole, blood cannot flow back into the veins, since the mouths of the veins are compressed by the annular muscles. Atrial systole lasts 0.12 seconds. After contraction, the atria begin to relax, that is, atrial diastole occurs, which lasts 0.7 seconds. The physiological essence of diastole is as follows: the duration of diastole is necessary to ensure the initial polarization of myocardial cells due to the operating time of the Na-K pump; ensuring the removal of Ca ++ from the sarcoplasm; ensuring glycogen resynthesis; ensuring ATP resynthesis; ensuring diastolic filling of the heart with blood.
Atrial systole is followed by second phase - ventricular systole. Ventricular systole, in turn, consists of two phases: the tension phase and the expulsion phase of blood. During the tension phase (which is divided into the asynchronous contraction phase and the isometric contraction phase), the ventricular muscles tense (their tone increases), and the pressure in the ventricles increases. The flap valves then slam shut. The papillary muscles of the ventricles contract, the tendon threads are stretched and prevent the valves from everting towards the atria. The tension of the ventricular muscles increases, the pressure rises, and when it becomes higher than in the aorta and pulmonary trunk (approximately 150 mm Hg), the semilunar valves open and blood is released into the vessels under high pressure. This begins the phase of expulsion of blood from the ventricles (which is divided into a phase of rapid expulsion and a phase of slow expulsion). The tension phase lasts 0.03-0.08 seconds, and the expulsion phase lasts 0.25 seconds. The entire ventricular systole lasts 0.33 seconds. After ventricular systole comes ventricular diastole. In this case, the semilunar valves slam shut, as the blood pressure in the aorta and pulmonary artery becomes higher than in the ventricles. At the same time, the leaflet valves open, and blood flows by gravity from the atria into the ventricles again. Ventricular diastole lasts 0.47 seconds. The physiological essence of ventricular diastole is the same as atrial diastole.
In a beating heart, atrial diastole partially coincides with ventricular diastole (Scheme 1). That's what it is third phase cardiac cycle - pause. During the pause period, blood flows freely from the superior and inferior vena cava into the right atrium, and from the pulmonary veins into the left atrium. Since the leaflet valves are open, some of the blood enters the ventricles. The pause lasts 0.4 seconds. Then a new cardiac cycle begins. Each cardiac cycle lasts approximately 0.8 seconds.
Scheme 1. Systole and diastole
Atria
Ventricles
The heart rate can be calculated from the pulse. In a healthy person, the heart beats an average of 70 times per minute. This heart rate is called normotension Your heart rate may change throughout the day. Heart rate is affected by body position. During physical activity, emotional arousal, and inhalation, heart rate increases. Heart rate depends on age: in children under 1 year old it is 100-140 beats per minute, in 10 years old - 90, in 20 years and older 60 - 80, and in old people it increases to 90-95 beats per minute. If the heart rate decreases to 40-60 beats per minute, then this rhythm is called bradycardia. If it rises to 90-100 and reaches 150 beats per minute, then this rhythm is called tachycardia. Pulse different frequencies called sinus arrhythmia.
Heart sounds. The work of the heart is accompanied by characteristic sounds, which are called heart sounds. When listening with a stethoscope, two heart sounds are distinguished: first tone called systolic, since it occurs during ventricular systole. It is drawn-out, dull and low. The nature of this tone depends on the trembling of the leaflet valves and tendon threads and on the contraction of the muscles of the ventricles. Second tone, diastolic, corresponds to ventricular diastole. It is short, tall and occurs when the semilunar valves close, which occurs as follows. After systole, blood pressure in the ventricles drops sharply. In the aorta and pulmonary artery at this time it is high, blood from the vessels rushes back to the side of lower pressure, that is, to the ventricles, and under the pressure of this blood the semilunar valves slam shut. The first sound, heard at the apex of the heart - in the fifth intercostal space, corresponds to the activity of the left ventricle and bicuspid valve. The same tone, heard on the sternum between the attachment of the IV and V ribs, will give an idea of the activity of the right ventricle and tricuspid valve. The second sound, heard in the second intercostal space to the right of the sternum, is determined by the slamming aortic valves. The same tone, heard in the same intercostal space, but to the left of the sternum, reflects the slamming of the pulmonary valves. The technique for recording heart sounds is called phonocardiography.
Heart beat. If you put your hand to the left fifth intercostal space, you can feel heartbeat . This impulse depends on the change in the position of the heart during systole. When contracting, the heart becomes almost solid, turns slightly from left to right, the left ventricle presses against the chest, pressing on it. This pressure is felt as a push.
Amount of blood ejected by the heart. When contracting, each ventricle releases an average of 70-80 ml of blood. The amount of blood ejected by each ventricle during systole is called percussion, or systolic, volume. The amount of blood ejected by the right and left ventricles is the same. If the amount of blood ejected by the ventricle during systole and the heart rate are known, then the amount of blood ejected by the heart per minute can be calculated, or minute volume(SVK∙HR=MIK). If blood flow to the heart increases, then the force of heart contraction increases accordingly. The increase in the force of contraction of the heart muscle depends on its stretching, or, in other words, on the initial length of the fibers. It has been established that the more a muscle is stretched, the stronger it contracts. This property of the heart muscle is called law of the heart(Starling's law). This "law" has limited value. The activity of the heart is regulated by the nervous system, and not by mechanical stretching of the muscle, since it characterizes only one particular dependence in the work of the heart. However, these relationships also depend on functional state heart, which is ultimately determined by the regulatory influence of the nervous system.
Electrical phenomena in the heart. The activity of the heart is accompanied by electrical phenomena. All excitable tissues at rest have a positive charge. When excitation occurs, the charge of the excited area changes to negative. The myocardium also obeys this pattern. When excitation occurs, that is, when electronegativity appears, a potential difference arises between the excited area and the unexcited one. As the wave of electronegativity spreads, more and more new areas become electronegative, and, consequently, a potential difference arises in new areas. That is, a current of action appears in them. A method for studying the heart, based on recording and analyzing the total electrical potential (action currents) that arises during the excitation of various parts of the heart, is called electrocardiography. Electrocardiogram(ECG) is a periodically repeating curve reflecting the course of the process of cardiac excitation over time. Using ECG data, you can evaluate the heart rhythm and diagnose its disorders, identify various types of disorders and damage to the myocardium (including the conduction system), monitor the effect of cardiotropic drugs. medicines. Electrocardiogram for everyone healthy people is always constant and has five teeth, which are designated by the letters P, Q, R, S, T. The P wave corresponds to the excitation of the atria, and teeth Q,R,S,T- excitation of the ventricles.
The spread of excitation throughout the heart and its subsequent repolarization has a complex geometry.
Atrial depolarization. The excitation wave normally propagates from top to bottom from the region of the sinus node to the atrioventricular node. First, the right and then the left atrium are excited. Atrial depolarization is recorded on the ECG as a P wave.
Atrial repolarization has no reflection on the ECG, since it is layered in time with the process of ventricular depolarization (QRS complex).
Atrioventricular delay. From the atria, excitation is directed to the atrioventricular junction, where its spread is slowed down. After a certain delay, the His bundle, its legs, branches and Purkinje fibers are excited. The potential difference is very small, since only the conductive atrioventricular system is excited. Therefore, the isoelectric segment P-Q is recorded on the ECG.
Ventricular depolarization On the ECG it is recorded in the form of a QRS complex, in which three successive phases are distinguished. Ventricular excitation begins with depolarization of the interventricular septum (Q wave). Then the apical region of the right and left ventricles (R wave) is excited. The wave of depolarization is directed down to the right and then down to the left, after which, “reflected” from the apex of the heart, it is directed retrograde - upward towards the base of the ventricles. The last to be excited are the basal sections of the interventricular septum and the myocardium of the right and left ventricles (S wave).
Full coverage of excitation and repolarization of the ventricles. During complete coverage of the ventricles by excitation, there is no potential difference between any of its points, therefore an isoelectric line is recorded on the ECG - segment S - T. The process of rapid final repolarization of the ventricles corresponds to the T wave.
Automaticity of the heartConduction system of the heart. The ability of the heart to contract rhythmically regardless of any external stimulation is called automatic. The reason for automation is a change in metabolism in the nodes and their cells. The occurrence of periodic waves of excitation also depends on the reaction of the blood: a shift in the reaction to the alkaline side causes an increase in heart rate, and to the acidic side - a slowdown. Great importance has a ratio of sodium, potassium and calcium ions. With a relative increase in the concentration of sodium and potassium ions, the activity of the heart slows down and weakens. With a relative increase in the concentration of calcium ions, the heart gradually ceases to relax. The conduction system of the heart is represented by nodes that are formed by clusters of atypical cardiomyocytes and a bundle extending from these nodes.
First cluster atypical cardiomyocytes are located in the right atrium between the mouths of the superior and inferior vena cava. This cluster was named Keith-Flack node, or sinoatrial node. Second cluster is also located in the right atrium, but at the atrioventricular septum, therefore called atrioventricular node, or Ashof-Tawara junction. A bundle departs from the Ashof-Tavara node, which is directed into the ventricles along the interventricular septum. This bundle is called His bundle. The bundle of His is divided into two legs, one of which goes to the right ventricle, and the other to the left, accordingly what these legs are called right and left bundle branches. Between the sinoatrial and atrioventricular nodes are located internodal tracts: anterior internodal and interatrial (Bachmann's bundle); middle internodal (Wenckebach's bundle); posterior internodal and interatrial (Torel's bundle).
The main center of automation is the Keith-Flack node. From it, along the conductive fibers of the atria, excitation reaches the atrioventricular node (Ashof-Tavara), where there is some delay in the conduction of excitation, necessary for the coordinated work of the ventricles and atria. Then excitation along the conducting cardiomyocytes (atypical) of the His bundle, its branches and Purkinje fibers, into which both bundle branches are divided, spreads to the myocardium (contractile cardiomyocytes - typical) of both ventricles, causing their contraction.
Normally, the pacemaker of the heart is the sinoatrial node. If the automaticity of this node is disrupted, the rhythmic contractions of the heart can continue due to impulses arising in the atrioventricular node, but the frequency and strength of contractions will be approximately half as much. In principle, all parts of the myocardial conduction system are capable of automatism. The decrease in the ability of automaticity from the base of the heart to its apex is called the gradient of automaticity and obeys W. Gaskell's law:
· The degree of automaticity is higher, the closer the area of the conduction system is located to the sinoatrial node;
· The sinoatrial node is capable of generating electrical potential with a frequency of 60-80 impulses/min;
· The atrioventricular node is capable of generating electrical potential with a frequency of 40-50 impulses/min;
· His bundle – 30-40 imp/min;
· Purkinje fibers – 20 imp/min.
Automatic disorder is called heart block. There are incomplete and complete heart blocks. With incomplete heart block The excitability of the atrioventricular node is reduced, so all impulses arising in the Keith-Flack node do not pass through it. Typically, every second or third impulse passes to the ventricles, therefore, with incomplete block, the ventricles contract 2-3 times slower than the atria. At full block, which most often occurs when the His bundle is damaged, impulses arising in the sinoatrial node do not enter the ventricles. At the same time, the own automatism of the ventricles awakens, which begin to contract at a slower rhythm, regardless of the rhythm of the atria. In this case, there is no coordination between the rhythm of contractions of the atria and ventricles.
Extrasystole and refractory period. One of the most important physiological characteristics cardiac muscle are:
a) the duration of the excitation process in contractile cardiomyocytes and
b) the associated long refractory period.
If you irritate any muscle, including the heart, with a weak electric current, gradually increasing its value, then a moment will come when the muscle responds with contraction. The force of stimulation that causes the first muscle contraction is called irritation threshold. A stimulus that does not cause contraction is called subliminal, and exceeding the threshold value – super-refractory. When the cardiac muscle is stimulated by threshold stimulation, it responds with a maximum contraction. The period of inexcitability that occurs after arousal is called refractory period. Important feature cardiac muscle is the presence of a long period of absolute refractoriness (0.27 s), which occupies almost the entire time of ventricular systole (0.33 s). Long-term refractoriness of the heart muscle is an essential functional adaptation that ensures the intermittent nature of the occurrence of excitation, and, consequently, contraction, in response to continuous stimulation. The long duration of the refractory period makes it impossible for the occurrence of tetanus in the myocardium and guarantees a regime of single rhythmic contractions. If the heart is irritated when systole has ended, that is, the refractory period has ended, and the next impulse from the Keith-Flack node has not yet arrived, then the heart will respond with an extraordinary contraction. This extraordinary contraction is called extrasystole. Following the extrasystole, a longer pause occurs, called a compensatory pause. The compensatory pause is explained by the fact that the next impulse from the sinoatrial node enters the refractory period of the ventricular extrasystole and disappears. Some people experience heart failure when two successive contractions are followed by a long pause. This pathological phenomenon is caused by disturbances in the conduction system of the heart.
Regulation of cardiac activityCardiac activity changes dynamically in accordance with the needs of the body. There are several pathways of regulation - hemodynamic, nervous and humoral, working cooperatively and in concert. According to the law of hemodynamic regulation, the force of heart contraction is directly proportional to the stretching of the heart during diastole. The Frank-Starling law is relative, since stretching of the cardiac fibers leads to an increase in their subsequent contractions only at certain average degrees of stretching. Intracardiac regulation is carried out by intracardial peripheral reflexes, extracardiac regulation is carried out by the centrifugal autonomic nerves of the heart. A significant role in the reflex regulation of the activity of the heart is played by the receptor formations of the reflexogenic zones of blood vessels - the aortic arch, carotid sinus, superior vena cava, right atrium, as well as internal organs - mesentery, stomach, intestines. Humoral regulation is mediated by substances found in the blood and myocardial tissue.
Innervation of the heart. Despite the fact that the periodic activity of the heart is due to automaticity, its work is also under the constant influence of extracardiac (extracardiac) factors. One of the most important among them is the action of the autonomic nervous system - its sympathetic and parasympathetic departments. The sympathetic nerves arise from the cervical sympathetic ganglion, and the vagus nerves (parasympathetic division of the ANS) begin in the medulla oblongata, where their center lies. Irritation of the sympathetic and vagus nerves leads to changes in excitability (batmotropic effect), conductivity (dromotropic effect), heart rate (chronotropic effect), contraction amplitude (inotropic effect) and changes in the tone of muscle fibers (tonotropic effect). The sympathetic and vagus nerves have the opposite effect on the heart: the sympathetic ones cause positive effects - they speed up and intensify heart contractions, increase the excitability and tone of the myocardium, improve conductivity, and the vagus nerves cause similar negative effects.
Reflex influences on the activity of the heart. Extracardiac nervous regulation of the heart is of a reflex nature. A significant role in this is played by influences from the reflexogenic zones of blood vessels - the aortic arch, carotid sinus, superior vena cava and right atrium. In addition, reflex changes in heart function occur when mechanoreceptors located in the stomach, intestines, mesentery, lungs are stimulated, when pressure is applied to the eyeballs, etc. Therefore, irritation of these organs can have both an exciting and inhibitory effect on cardiac activity. Thus, when the mesentery is irritated, excitation from its receptors reaches the spinal cord along the centripetal fibers of the splanchnic nerve and then rises to the medulla oblongata. Here, in the region of the nuclei of the vagus nerves, the reflex arc closes, and excitation along the centrifugal fibers of the vagus nerves is directed to the heart and inhibits its activity (Goltz reflex).
Humoral regulation of heart activity. Most blood components, including hormones, electrolytes, and other biological active substances influence the functioning of the heart in the most ancient – humoral way. Have a positive effect hormones– adrenaline (hormone of the adrenal medulla), glucagon (hormone of the pancreas), corticosteroids (hormones of the adrenal cortex), thyroxine, triiodothyronine (hormones thyroid gland), as well as kinins and prostaglandins. Sodium ions necessary for normal contractile function of the myocardium. With a decrease in their intracellular concentration, the release from the tanks also decreases. endoplasmic reticulum and intercellular fluid of calcium ions. Calcium ions necessary for electromechanical coupling. Under the influence of excitation, they leave the endoplasmic reticulum and connect with the calcium-reactive regulatory protein troponin, which ensures the formation of the actomyosin complex and muscle contraction. Therefore, an increase in the concentration of calcium in the blood causes an increase in the strength and frequency of heart contractions. Excess potassium leads to a weakening of cardiac activity up to cardiac arrest in the diastole stage. This is due to the fact that excess potassium in the environment surrounding the cell causes a decrease or even disappearance of the concentration gradient. The latter leads to a decrease or cessation of potassium outflow from the cell and a decrease in the magnitude of MP and excitability up to complete refractoriness. The pacemaker cells of the sinoatrial node are especially sensitive to an increase in the content of potassium ions. The activity of the heart is also inhibited hydrogen ions, an excess of which is formed in all cases associated with oxygen starvation(hypoxia).
Structure of the heart
In humans and other mammals, as well as in birds, the heart is four-chambered and cone-shaped. The heart is located in the left half of the chest cavity, in the lower part of the anterior mediastinum on the tendon center of the diaphragm, between the right and left pleural cavity, fixed on large blood vessels and enclosed in a pericardial sac made of connective tissue, where fluid is constantly present, moisturizing the surface of the heart and ensuring its free contraction. A solid septum divides the heart into right and left halves and consists of the right and left atria and the right and left ventricles. In this way they distinguish right heart and left heart.
Each atrium communicates with the corresponding ventricle through the atrioventricular orifice. At each orifice there is a valve that regulates the direction of blood flow from the atrium to the ventricle. The leaflet valve is a connective tissue petal, which with one edge is attached to the walls of the opening connecting the ventricle and the atrium, and with the other hangs freely into the cavity of the ventricle. Tendon filaments are attached to the free edge of the valves, and the other end grows into the walls of the ventricle.
When the atria contract, blood flows freely into the ventricles. And when the ventricles contract, the blood, with its pressure, lifts the free edges of the valves, they come into contact with each other and close the hole. Tendon threads prevent the valves from turning away from the atria. When the ventricles contract, blood does not enter the atria, but is sent to arterial vessels.
In the atrioventricular ostium of the right heart there is a tricuspid (tricuspid) valve, in the left - a bicuspid (mitral) valve.
In addition, at the places where the aorta and pulmonary artery exit from the ventricles of the heart, semilunar, or pocket (in the form of pockets), valves are located on the inner surface of these vessels. Each flap consists of three pockets. Blood moving from the ventricle presses the pockets against the walls of the vessels and passes freely through the valve. During the relaxation of the ventricles, blood from the aorta and pulmonary artery begins to flow into the ventricles and, with its reverse movement, closes the pocket valves. Thanks to the valves, blood in the heart moves only in one direction: from the atria to the ventricles, from the ventricles to the arteries.
Blood enters the right atrium from the superior and inferior vena cava and the coronary veins of the heart itself (coronary sinus); four pulmonary veins flow into the left atrium. The ventricles give rise to vessels: the right one - the pulmonary artery, which is divided into two branches and carries venous blood to the right and left lungs, i.e. into the pulmonary circulation; The left ventricle gives rise to the aortic arch, through which arterial blood enters the systemic circulation.
The heart wall consists of three layers:
- internal - endocardium, covered with endothelial cells
- middle - myocardium - muscular
- outer - epicardium, consisting of connective tissue and covered with serous epithelium
Outside, the heart is covered with a connective tissue membrane - the pericardial sac, or pericardium, also lined with inside serous epithelium. Between the epicardium and the heart sac there is a cavity filled with fluid.
Thickness muscle wall the greatest in the left ventricle (10-15 mm) and the smallest in the atria (2-3 mm). The thickness of the wall of the right ventricle is 5-8 mm. This is due to the unequal intensity of work different departments the heart to pump out blood. The left ventricle pumps blood into the systemic ventricle under high pressure and therefore has thick, muscular walls.
Properties of the heart muscle
The cardiac muscle, the myocardium, differs both in structure and properties from other muscles of the body. It consists of striated fibers, but unlike fibers skeletal muscles, which are also striated, the fibers of the cardiac muscle are interconnected by processes, so excitation from any part of the heart can spread to all muscle fibers. This structure is called a syncytium.
Contractions of the heart muscle are involuntary. A person cannot at will stop the heart or change its rate.
A heart removed from an animal's body and placed under certain conditions may long time contract rhythmically. This property of it is called automaticity. The automaticity of the heart is caused by the periodic occurrence of excitation in special cells of the heart, a cluster of which is located in the wall of the right atrium and is called the center of cardiac automaticity. Excitation arising in the cells of the center is transmitted to all muscle cells hearts and causes them to contract. Sometimes the center of automation fails, then the heart stops. Currently, in such cases, a miniature electronic stimulator is implanted on the heart, which periodically sends electrical impulses to the heart, and it contracts each time.
Work of the heart
The heart muscle, the size of a fist and weighing about 300 g, works continuously throughout life, contracts about 100 thousand times a day and pumps more than 10 thousand liters of blood. Such high performance is due to increased blood supply to the heart, high level the metabolic processes occurring in it and the rhythmic nature of its contractions.
The human heart beats rhythmically at a frequency of 60-70 times per minute. After each contraction (systole), relaxation occurs (diastole), and then a pause during which the heart rests, and contraction again. The cardiac cycle lasts 0.8 s and consists of three phases:
- atrial contraction (0.1 s)
- ventricular contraction (0.3 s)
- relaxation of the heart with a pause (0.4 s).
If the heart rate increases, the time of each cycle decreases. This occurs mainly due to a shortening of the overall cardiac pause.
In addition, through coronary vessels, the cardiac muscle during normal heart function receives about 200 ml of blood per minute, and at maximum load, coronary blood flow can reach 1.5-2 l/min. In terms of 100 g of tissue mass, this is much more than for any other organ except the brain. It also enhances the efficiency and fatigue of the heart.
During contraction of the atria, blood is ejected from them into the ventricles, and then, under the influence of ventricular contraction, is pushed into the aorta and pulmonary artery. At this time, the atria are relaxed and filled with blood flowing to them through the veins. After the ventricles relax during the pause, they fill with blood.
Each half of an adult's heart pumps approximately 70 ml of blood into the arteries in one contraction, which is called stroke volume. In 1 minute, the heart pumps out about 5 liters of blood. The work performed by the heart can be calculated by multiplying the volume of blood ejected by the heart by the pressure under which the blood is ejected into the arterial vessels (this is 15,000 - 20,000 kgm/day). And if a person performs very strenuous physical work, then the minute volume of blood increases to 30 liters, and the work of the heart increases accordingly.
The work of the heart is accompanied by various manifestations. So, if you put your ear or phonendoscope to a person’s chest, you can hear rhythmic sounds - heart sounds. There are three of them:
- the first sound occurs during ventricular systole and is caused by vibrations of the tendon threads and the closure of the leaflet valves;
- the second sound occurs at the beginning of diastole as a result of valve closure;
- the third tone - very weak, it can only be detected with the help of a sensitive microphone - occurs during the filling of the ventricles with blood.
Heart contractions are also accompanied by electrical processes, which can be detected as an alternating potential difference between symmetrical points on the surface of the body (for example, on the hands) and recorded with special devices. Recording heart sounds - phonocardiogram and electrical potentials- the electrocardiogram is shown in Fig. These indicators are used clinically to diagnose heart diseases.
Regulation of the heart
The work of the heart is regulated by the nervous system depending on the influence of internal and external environment: concentrations of potassium and calcium ions, thyroid hormone, state of rest or physical work, emotional stress.
Nervous and humoral regulation the activity of the heart coordinates its work with the needs of the body at each this moment regardless of our will.
- The autonomic nervous system innervates the heart, like everyone else internal organs. Nerves sympathetic division increase the frequency and strength of contractions of the heart muscle (for example, with physical work). Under resting conditions (during sleep), heart contractions become weaker under the influence of parasympathetic (vagus) nerves.
- Humoral regulation of the activity of the heart is carried out with the help of special chemoreceptors present in large vessels, which are excited under the influence of changes in blood composition. An increase in the concentration of carbon dioxide in the blood irritates these receptors and reflexively increases the work of the heart.
Especially important in this sense, adrenaline enters the blood from the adrenal glands and causes effects, similar topics, which are observed when the sympathetic nervous system is irritated. Adrenaline causes an increase in heart rate and amplitude of heart contractions.
Electrolytes play an important role in the normal functioning of the heart. Changes in the concentration of potassium and calcium salts in the blood have a very significant effect on the automation and processes of excitation and contraction of the heart.
An excess of potassium ions inhibits all aspects of cardiac activity, acting negatively chronotropically (reduces the heart rate), inotropically (reduces the amplitude of heart contractions), dromotropically (impairs the conduction of excitation in the heart), bathotropically (reduces the excitability of the heart muscle). With an excess of K+ ions, the heart stops in diastole. Sharp disturbances in cardiac activity also occur with a decrease in the content of K + ions in the blood (with hypokalemia).
Excess calcium ions acts in the opposite direction: positively chronotropic, inotropic, dromotropic and bathmotropic. With an excess of Ca 2+ ions, the heart stops in systole. With a decrease in the content of Ca 2+ ions in the blood, heart contractions are weakened.
Table. Neurohumoral regulation of the cardiovascular system
| Factor | Heart | Vessels | Blood pressure level |
| Sympathetic nervous system | narrows | increases | |
| Parasympathetic nervous system | expands | lowers | |
| Adrenalin | increases rhythm and strengthens contractions | narrows (except for heart vessels) | increases |
| Acetylcholine | slows down the rhythm and weakens contractions | expands | lowers |
| Thyroxine | quickens the rhythm | narrows | increases |
| Calcium ions | increase the rhythm and weaken contractions | narrow | raise |
| Potassium ions | slow down the rhythm and weaken contractions | expand | lower |
The work of the heart is also connected with the activities of other organs. If excitation is transmitted to the central nervous system from working organs, then from the central nervous system it is transmitted to the nerves that enhance the function of the heart. So reflexively correspondence between activities is established various organs and the work of the heart.
1. The structure and work of the heart, regulation of its work.§19.
2. Reproduction in organic world. §52.
Answers:
1. Reveal the structural features and functions of the heart. Cardiac cycle, blood pressure.
The heart is a hollow four-chamber muscular organ that pumps blood into the arteries and receives venous blood, located in the chest cavity. The shape of the heart resembles a cone. It works throughout life. The right half of the heart (right atrium and right ventricle) is completely separate from the left half (left atrium and left ventricle).
The heart is four-chambered; two atria and two ventricles provide blood circulation. The septum divides the heart into right and left side, which prevents blood from mixing. Leaf valves allow blood to flow in one direction: from the atria to the ventricles. Semilunar valves ensure the movement of blood in one direction: from the ventricles to the systemic and pulmonary circulation. The walls of the stomachs are thicker than the walls of the atria because perform a heavy load, push blood into the systemic and pulmonary circulation. The walls of the left ventricle are thicker and more powerful because it carries out a greater load than the right one, pushing blood into the systemic circulation.
The atria and ventricles are connected by valves. Between the left atrium and the left ventricle, the valve has two leaflets and is called bivalve, between the right atrium and the right ventricle is tricuspid valve.
The heart is covered with a thin and dense membrane, forming a closed sac - pericardial sac. Between the heart and the pericardial sac there is a fluid that moisturizes the heart and reduces friction during its contractions.
The average heart weight is about 300 grams. Trained people have larger heart sizes than untrained people.
The activity of the heart is a rhythmic change of three phases of the cardiac cycle: contraction of the atria (0.1 s.), contraction of the ventricles (0.3 s.) and general relaxation of the heart (0.4 s.), the entire cardiac cycle is (0.8 s.)
The pressure of blood on the walls of blood vessels is called blood pressure, it is created by the force of contraction of the ventricles of the heart.
The heart works automatically throughout your life.
The structure of heart cells is determined by the function they perform.
Regulation and coordination The contractile functions of the heart are carried out by its conduction system.
Sensitive fibers from the receptors of the walls of the heart and its vessels go as part of the cardiac nerves and cardiac branches to the corresponding centers of the spinal cord and brain.
Nervous regulation of the heart. The central nervous system constantly controls the functioning of the heart through nerve impulses. Inside the cavities of the heart itself and in the walls of large vessels there are nerve endings - receptors that perceive pressure fluctuations in the heart and in the vessels. Impulses from the receptors cause reflexes that affect the functioning of the heart. There are two types of nervous influences on the heart: some are inhibitory, which reduce the heart rate, others are accelerating.
Humoral regulation. Along with with nervous control the activity of the heart is regulated chemicals, constantly entering the blood.
2. R reproduction in the organic world.
Types of reproduction of organisms. Maintaining a constant number of different plants and animals is ensured by the reproduction of similar organisms. Reproduction is the process of reproduction to constantly replace those individuals that have died from old age, disease, or destroyed by predators. Without reproduction, it is impossible to imagine the appearance of man on Earth. Without reproduction it is impossible to imagine the evolution of an animal and flora. There are many forms of reproduction of animals and plants. However, all the diversity of reproduction processes fits into two main types - asexual and sexual.
In asexual reproduction, a new organism develops from one cell or group of cells of the mother's body. This type of reproduction is found in bacteria, yeast and most plants, and among animals - in protozoa, coelenterates, and flatworms.
Features of sexual reproduction.Sexual reproduction characteristic of most animal organisms. Sexual reproduction involves two individuals - male and female. Sex cells arise in each individual. Sex cells are called special cells: eggs, or eggs, in females and seed, or spermatozoa, in males. An egg is a small cell that contains nutrients necessary for the development of the embryo. The nucleus of the egg contains half the set of chromosomes characteristic of a given species.
Spermatozoa, unlike immobile eggs, are capable of movement and are equipped with a long flagellum. In the sperm of various animals, many similarities can be found with human sperm.
The emergence of new organisms occurs as a result of the fusion of an egg and a sperm. This process is called fertilization. During sexual reproduction, the hereditary characteristics of both parents are combined in a new organism. This means that their offspring may be more viable. In addition, having retained these characteristics, it can pass them on to its descendants, etc. This process occurs continuously. Thanks to natural selection more advanced living organisms appear that are better adapted to constantly changing conditions environment.
During the development of a fertilized egg, a series of successive divisions occurs. Various groups embryonic cells turn into tissues and organs. On early stages development in the embryos of various animals there are many common features: gill slits, tails, etc. All this speaks of the origin of man from his distant animal ancestors. Sexual reproduction is more advanced than other types of reproduction.
Human sex glands. Sex cells are produced in special gonads. Male gonads - testes located in the outer skin sac - the scrotum. From the testes come the vas deferens, which flow into urethra. Male reproductive cells - sperm and male sex hormones - are formed in the testes. These hormones influence the appearance of secondary sexual characteristics characteristic of male body. These include facial hair growth, deep voice, specific body shapes, etc.
Female gonads - ovaries located in abdominal cavity. In the ovaries, female sex cells (eggs) develop and mature, and female sex hormones enter the blood and lymph, which contribute to the formation of secondary sexual characteristics characteristic of female body. These include the development and enlargement of the mammary glands, the distribution of fat in certain areas of the body, creating specific shapes female body, and etc.
Suitable for ovaries the fallopian tubes. Along them, with the help of special cells equipped with ciliated cilia, a mature egg moves from the ovary to the uterus. Uterus- a sac-like unpaired hollow muscular organ in which the embryo develops and the fetus is born. The uterus is located in the middle part of the pelvic cavity, lies behind Bladder and in front of the rectum. The uterus is pear-shaped. It distinguishes between the bottom, body and neck. The fruit grows in it, protected from various external influences. The inside of the uterus is covered with a mucous membrane rich in blood vessels. The entrance to the uterus is called the vagina.
Fertilization. The process of fusion of germ cells is called fertilization. Out of hundreds of millions of sperm, only one fertilizes the egg. After a single sperm penetrates the egg, its surface membrane becomes impermeable to other sperm. Then the nuclei of both germ cells merge into one. From this moment the egg is considered fertilized.
The main importance of reproduction is the preservation and continuation of the human race
Biology lesson in 8th grade.
Subject:Heart function and its regulation.
Target: systematize knowledge about the structure of the heart; form the concept of the cardiac cycle and the automaticity of the heart; reveal the features of the regulation of heart contractions,intensify cognitive activity students by solving problematic issues; nurturing kindness, sensitivity, mutual respect for others.
Equipment: “Heart Function” table, computer, multimedia, “Heart Function Regulation” diagram.
During the classes:
Updating knowledge
We continue to get acquainted with the circulatory organs. Let's remember what we already know:
A) Blitz survey
The circulatory system consists of... (heart and blood vessels)
There are three types of vessels: ... (arteries, veins and capillaries)
The vessels that carry blood from the heart are called... (arteries)
The largest artery is called ... (aorta), located in ... the circulatory system.
The vessels that carry blood to the heart are called... (veins)
The vessels in which gas exchange occurs are called... (capillaries)
Which vessels have the thickest walls? (arteries)
Which vessels have semilunar valves? (veins)
How many circles of blood circulation are there in the human body? Which?
What is the name of scarlet-colored blood saturated with oxygen? (arterial)
What is the name of burgundy-colored blood saturated with carbon dioxide? (venous)
Does arterial blood always flow through arteries?
When does arterial blood flow through the veins?
What is the sequence of blood movement through the circulation? (ventricle – artery – capillary – vein – atrium)
Where is the heart located? What is it protected by?
What is its size? Form?
(excerpt from the poem “Heart” by E. Mezhelaitis)
What is a heart?
Is the stone hard?
An apple with purple-red skin?
Maybe between the ribs and the aorta,
Is there a beating ball that looks like a globe on Earth?
One way or another, everything earthly
Fits within its boundaries
Because he has no peace
There's something to do with everything.
Many works are dedicated to the “heart”:
M. Gorky - “Danko’s brave heart.”
Wilhem Hauff - “Frozen”.
What kind of epithets is not awarded to the heart in literary works: hot and cold, selfless and greedy, smart and stupid, sympathetic, kind and cruel, brave, proud and evil, stony, sensitive and generous, open and callous, deaf, black heart and golden, wounded, broken, mother’s heart and heart friend.
What kind of heart is it?
B) work with the drawing “Structure of the Heart” - r/t p. 82 exercise 124
( Self-test: 1 – veins, 2 – aorta, 3 – pulmonary artery, 4 – pulmonary veins, 5 – left atrium, 6 – leaflet valves, 7 – left ventricle, 8 – right ventricle, 9 – semilunar valves, 10 – right atrium)
Motivational stage
What work does the heart do, static or dynamic?
In what type of work does fatigue develop faster? Over what period of time?
Why, performing static? can the heart work for an average of 70-80 years?
The heart is capable of contracting rhythmically and at rest contracts 100,000 times per day, while expending as much energy as would be enough to lift a load of 900 kg to a height of 14 m.
(Additionally - p. 152)
Formation of new knowledge
So why does the heart have such efficiency?
The performance function falls on itselfheart muscle.
What is its structure? (fabric - p. 37 figure; p. 38 text, top)
The heart wall has three layers:
*epicardium – outer serous layer, covers the heart (fused with the pericardium);
*myocardium – medium muscle layer formed by striated cardiac muscle (each muscle fiber contains 1-2 nuclei, many mitochondria);
*endocardium – inner layer(from epithelium).
In order for a muscle to work for a long time and actively, it must systematically receive nutrition, how does this happen? (intracardiac circulation). INpericardial sac contains a serous fluid that moisturizes the heart and reduces friction during its contractions.
(nerve nodes – p. 151 fig.)
IN nerve nodes of the heart, excitation occurs, which is transmitted to all chambers of the heart, first to the atria, then to the ventricles, thereforeare reduced sequentially.
The ability of the heart to contract rhythmically, under the influence of impulses arising in the heart muscle itself, is called automaticity of the heart.
If you cut the nerves and blood vessels and remove the heart from the body, then the heart will contract rhythmically for some time;
An isolated frog heart “drives” a 6% solution of table salt;
The human heart can be revived by passing Ringer's solution (body temperature, glucose with oxygen) through it;
The experiment of reviving an isolated heart was first carried out in 1903 by the Russian scientist A.A. Kulyabko (the heart of a child after 20 hours of death, who died of pneumonia).
This is how it arises - cardiac cycle -70-75 times per minute
Phases of the cardiac cycle:
Atrial contraction (0.1 sec) – blood into the ventricles
Ventricular contraction (0.3 sec) - blood is ejected into the aorta and pulmonary artery
Pause general relaxation (0.4 sec)
The period covering 1 contraction and relaxation of the heart is called cardiac cycle.
Abbreviation - systole
Relaxation - diastole
Watching video clips
Thus, one cardiac cycle lasts 0.8 seconds.
So what kind of work does the heart do, static or dynamic?
How long does the heart rest? (half of a person's life)
Regulation of the heart
Does the heart always work the same? Give examples.
It’s not for nothing that when they depict love, they draw a heart. Why does the heart, a symbol of love, look different? This is an image of the symbol of kissing swans.
(working with the “Regulation of the Heart” schemes)
Nervous regulation – p.56 of the textbook
Humoral regulation – p.47 of the textbook
View video clips 343, 344, 348, 346 of the electronic application.
Application of new knowledge
A) Execution laboratory work- 345 video fragments
B) Performing tests 349 “Phases of the cardiac cycle”, 350 “Tests with missing terms”
Lesson summary. Reflection
Analyze: Do you need the knowledge you learned today in your future life? For what?
Among numerous environmental factors, nicotine and alcohol are very bad for the heart.
Not only do these substances negatively affect the heart, but harsh words, evil, and injustice hurt the heart. And how does it have a positive effect on the heart? kind word, smile, good mood, sensitive Attentive attitude, i.e. positive emotions.
The heart is a special organ. In all centuries it has been held in high esteem by poets; so many poems and songs have been written about it. And the mother’s heart is on a very special pedestal - infinitely kind and loving, all-forgiving, as in Dmitry Kedrin’s poem “Heart”.
A girl is being tortured by a Cossack at the fence:
“When will you, Oksana, love me?
I'll get it with my saber for stealing
And light sequins, and ringing rubles!”
The girl responded, braiding her hair:
“The fortune teller told me fortunes about this in the forest.
She prophesies: I will love the one
Who will bring my hearts to my mother as a gift,
No need for sequins, no need for rubles,
Give me the heart of your old mother.
I will infuse its ashes into hops,
I’ll get drunk and I’ll love you!”
From that day on, the Cossack became silent, frowned,
I didn’t slurp borscht, I didn’t eat salamata.
He cut his mother's chest with a blade
And with the treasured burden he set off:
He puts her heart on a colored towel
Kohanoi brings it in his shaggy hand.
On the way, his vision grew dim,
As he was going up the porch, the Cossack tripped.
And the mother’s heart, falling on the threshold,
She asked him: “Are you hurt, son?”
After such words, I would like to urge everyone to take care of their hearts, each other’s hearts, be sensitive to others, spare their hearts from unnecessary stress, take care of each other.
D/z
