DEVELOPMENT. The source of development of cardiac muscle tissue is myoepicardial plate- part of the visceral fluid in cervical spine embryo. Its cells turn into myoblasts, which actively divide by mitosis and differentiate. Myofilaments are synthesized in the cytoplasm of myoblasts, forming myofibrils. Initially, myofibrils do not have striations and a specific orientation in the cytoplasm. In the process of further differentiation, they take on a longitudinal orientation and are attached by thin myofilaments to the developing sarcolemma seals (Z-substance).
As a result of the ever-increasing ordering of myofilaments, myofibrils acquire transverse striations. Cardiomyocytes are formed. In their cytoplasm, the content of organelles increases: mitochondria, granular EPS, free ribosomes. During the process of differentiation, cardiomyocytes do not immediately lose their ability to divide and continue to multiply. Some cells may lack cytotomy, leading to the appearance of binucleated cardiomyocytes. Developing cardiomyocytes have a strictly defined spatial orientation, lining up in the form of chains and forming intercellular contacts with each other - intercalary discs. As a result of divergent differentiation, cardiomyocytes turn into three types of cells: 1) working, or typical, contractile; 2) conductive, or atypical; 3) secretory (endocrine). As a result of terminal differentiation, cardiomyocytes lose the ability to divide by the time of birth or in the first months of postnatal ontogenesis. In a mature heart muscle tissue cambial cells are absent.
STRUCTURE. Cardiac muscle tissue is formed by cardiomyocyte cells. Cardiomyocytes are the only tissue element of cardiac muscle tissue. They connect to each other with the help of intercalary discs and form functional muscle fibers, or functional symplast, which is not a symplast in the morphological concept. Functional fibers branch and anastomose with lateral surfaces, resulting in the formation of a complex three-dimensional network (Fig. 12.15).
Cardiomyocytes have an elongated rectangular, weakly branched shape. They consist of a nucleus and cytoplasm. Many cells (more than half in an adult individual) are binucleate and polyploid. The degree of polyploidization varies and reflects adaptive capabilities myocardium. The nuclei are large, light, located in the center of cardiomyocytes.
The cytoplasm (sarcoplasm) of cardiomyocytes has pronounced oxyphilia. It contains a large number of organelles and inclusions. The peripheral part of the sarcoplasm is occupied by longitudinally striated myofibrils, built in the same way as in skeletal muscle tissue (Fig. 12.16). Unlike the myofibrils of skeletal muscle tissue, which lie strictly isolated, in cardiomyocytes the myofibrils often merge with each other to form a single structure and contain contractile proteins that are chemically different from the contractile proteins of skeletal muscle myofibrils.
SIR and T-tubules are less developed than in skeletal muscle tissue, which is associated with the automaticity of the heart muscle and less influence of the nervous system. Unlike skeletal muscle tissue, the SPR and T-tubules form not triads, but dyads (one SPR tank is adjacent to the T-tubule). There are no typical terminal tanks. SPR accumulates calcium less intensively. On the outside, cardiocytes are covered with a sarcolemma, consisting of the plasma membrane of the cardiopulmonary cell and the basal membrane on the outside. The vasal membrane is closely connected with the intercellular substance; collagen and elastic fibers are woven into it. The basement membrane is absent at the sites of intercalated discs. Associated with the intercalary discs are cytoskeletal components. They are also connected to the intercellular substance through cytolemma integrins. Intercalated discs are the site of contact between two cardiomyocytes, complexes of intercellular contacts. They provide both mechanical and chemical functional communication of cardiomyocytes. In a light microscope they look like dark transverse stripes (Fig. 12.14 b). In an electron microscope, intercalated disks have a zigzag, stepped, or jagged line appearance. They can be divided into horizontal and vertical sections and three zones (Fig. 12.1, 12.15 6).
1. Zones of desmosomes and stripes of adhesion. They are located on the vertical (transverse) sections of the disks. Provide mechanical connection of cardiomyocytes.
2. Nexus zones (gap junctions) - places where excitation is transferred from one cell to another, ensure chemical communication of cardiomyocytes. They are found on the longitudinal sections of the intercalary discs. 3. Myofibril attachment zones. They are located on the transverse sections of the insertion disks. They serve as sites for attachment of actin filaments to the sarcolemma of the cardiomyocyte. This attachment occurs to the Z-bands found on the inner surface of the sarcolemma and similar Z-lines. Found in large numbers in the area of intercalated discs cadherins(adhesive molecules that carry out calcium-dependent adhesion of cardiomyocytes to each other).
Types of cardiomyocytes. Cardiomyocytes have different properties in different parts of the heart. So, in the atria they can divide by mitosis, but in the ventricles they never divide. There are three types of cardiomyocytes, which differ significantly from each other in both structure and function: workers, secretory, conductive.
1. Working cardiomyocytes have the structure described above.
2. Among the atrial myocytes there are secretory cardiomyocytes, which produce natriuretic factor (NUF), enhancing sodium secretion by the kidneys. In addition, NUF relaxes smooth myocytes of the arterial wall and suppresses the secretion of hormones that cause hypertension (aldosterone And vasopressin). All this leads to an increase in diuresis and arterial lumen, a decrease in the volume of circulating fluid and, as a result, a decrease in blood pressure. Secretory cardiomyocytes are localized mainly in the right atrium. It should be noted that in embryogenesis all cardiomyocytes have the ability to synthesize, but during the process of differentiation, ventricular cardiomyocytes reversibly lose this ability, which can be restored here when the cardiac muscle is overstrained.
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3. Significantly different from working cardiomyocytes conducting (atypical) cardiomyocytes. They form the conduction system of the heart (see " cardiovascular system"). They are twice as large as working cardiomyocytes. These cells contain few myofibrils, the volume of sarcoplasm is increased, in which a significant amount of glycogen is detected. Due to the content of the latter, the cytoplasm of atypical cardiomyocytes does not perceive color well. The cells contain many lysosomes and lack T-tubules. The function of atypical cardiomyocytes is to generate electrical impulses and transmit them to working cells. Despite the automaticity, the work of cardiac muscle tissue is strictly regulated by autonomic tissue. nervous system. The sympathetic nervous system speeds up and strengthens, while the parasympathetic nervous system reduces and weakens heart contractions.
REGENERATION OF CARDIAC MUSCLE TISSUE. Physiological regeneration. It is realized at the intracellular level and occurs with high intensity and speed, since the heart muscle bears a huge load. It increases even more with severe physical work and in pathological conditions (hypertension, etc.). In this case, there is constant wear and tear of the components of the cytoplasm of cardiomyocytes and their replacement with newly formed ones. With increased stress on the heart, it occurs hypertrophy(increase in size) and hyperplasia(increase in the number) of organelles, including myofibrils with an increase in the number of sarcomeres in the latter. IN at a young age Polyploidization of cardiomyocytes and the appearance of binucleate cells are also noted. Working hypertrophy of the myocardium is characterized by adequate adaptive growth of it vascular bed. In pathology (for example, heart defects, which also cause hypertrophy of cardiomyocytes), this does not happen, and after some time, due to malnutrition, some cardiomyocytes die and are replaced by scar tissue (cardiosclerosis).
Reparative regeneration. Occurs with injuries to the heart muscle, myocardial infarction and other situations. Since there are no cambial cells in the cardiac muscle tissue, when the ventricular myocardium is damaged, regenerative and adaptive processes occur at the intracellular level in neighboring cardiomyocytes: they increase in size and take over the function of dead cells. A connective tissue scar forms in place of dead cardiomyocytes. IN Lately It has been established that necrosis of cardiomyocytes during myocardial infarction affects only cardiomyocytes of a relatively small area of the infarction zone and the adjacent zone. A larger number of cardiomyocytes surrounding the infarction zone die by aptosis, and this process is the leading one in the death of cardiac muscle cells. Therefore, treatment of myocardial infarction should primarily be aimed at suppressing cardiomyocyte apoptosis in the first day after the onset of a heart attack.
If the atrial myocardium is damaged in a small volume, regeneration can occur at the cellular level.
Stimulation of reparative regeneration of cardiac muscle tissue. 1) Prevention of apoptosis of cardiomyocytes by prescribing drugs that improve myocardial microcirculation, reduce blood coagulation, its viscosity and improve the rheological properties of blood. Successful fight against post-infarction apoptosis of cardiomyocytes is an important condition for further successful myocardial regeneration; 2) Prescription of anabolic drugs ( vitamin complex, RNA and DNA preparations, ATP, etc.); 3) Early use of dosed physical activity, a set of physical therapy exercises.
IN last years Under experimental conditions, transplantation of myosatellite cells from skeletal muscle tissue began to be used to stimulate the regeneration of cardiac muscle tissue. It has been established that myosatellite cells introduced into the myocardium form skeletal muscle fibers that establish a close not only structural but also functional connection with cardiomyocytes. Since replacing the myocardial defect not with inert connective tissue, but with skeletal muscle tissue exhibiting contractile activity is more functionally and even mechanically advantageous, further development of this method may be promising in the treatment of myocardial infarctions in humans.
The heart is a hollow organ. It is approximately the size of a human fist. The heart muscle forms the walls of the organ. It has a partition dividing it into left and right halves. Each of them contains a network of ventricle and atrium. The direction of blood flow in the organ is controlled by valves. Next, let's take a closer look at the properties of the heart muscle.
General information
The heart muscle - the myocardium - makes up the bulk of the organ's mass. It consists of three types of fabric. In particular, they distinguish: atypical myocardium of the conduction system, fibers of the atrium and ventricles. Measured and coordinated contraction of the heart muscle is ensured by the conduction system.
Structure
The heart muscle has a mesh structure. It is formed from fibers woven into a network. Connections between fibers are established due to the presence of lateral jumpers. Thus, the network is presented in the form of a narrow-loop syncytium. Connective tissue is present between the fibers of the heart muscle. It has a loose structure. In addition, the fibers are entwined with a dense network of capillaries.
Properties of the heart muscle
The structure contains intercalary disks, presented in the form of membranes, separating fiber cells from each other. It should be noted here important features heart muscle. Individual cardiomyocytes, present in the structure in large numbers, are connected to each other in parallel and in series. Cell membranes merge so that they form gap junctions of high permeability. Ions diffuse through them unhindered. Thus, one of the features of the myocardium is the free movement of ions through the intracellular fluid along the entire myocardial fiber. This ensures unimpeded distribution of action potentials from one cell to another through the intercalary discs. It follows from this that the heart muscle is a functional unit huge amount cells that have a close relationship with each other. It is so strong that when only one cell is excited, it provokes the potential to spread to all other elements.
Myocardial syncytia
There are two of them in the heart: atrial and ventricular. All parts of the heart are separated from each other by fibrous septa with openings equipped with valves. Excitation from the atrium to the ventricle cannot pass directly through the tissue of the walls. Transmission is carried out through a special atrioventricular bundle. Its diameter is several millimeters. The bundle consists of fibers of the conducting structure of the organ. The presence of two syncytia in the heart causes the atria to contract before the ventricles. This, in turn, has vital importance to ensure effective pumping activity of the organ.
Myocardial diseases
The functioning of the heart muscle can be impaired due to various pathologies. Depending on the provoking factor, specific and idiopathic cardiomyopathies are distinguished. Heart disease can also be congenital or acquired. There is another classification, according to which restrictive, dilated, congestive and hypertrophic cardiomyopathies are distinguished. Let's look at them briefly.
Hypertrophic cardiomyopathy
To date, experts have identified gene mutations that provoke this form of pathology. Hypertrophic cardiomyopathy is characterized by thickening of the myocardium and changes in its structure. Against the background of pathology, muscle fibers increase in size, “twist”, acquiring strange shapes. The first symptoms of the disease are observed in childhood. The main signs of hypertrophic cardiomyopathy are chest tenderness and shortness of breath. There is also unevenness heart rate, the ECG reveals changes in the heart muscle.
Congestive form
This is a fairly common type of cardiomyopathy. As a rule, the disease occurs in men. Pathology can be recognized by signs of heart failure and disturbances in heart rhythm. Some patients experience hemoptysis. The pathology is also accompanied by pain in the heart area.
Dilated cardiomyopathy
This form of the disease manifests itself as a sharp expansion in all chambers of the heart and is accompanied by a decrease in contractility left ventricle. As a rule, dilated cardiomyopathy occurs in combination with hypertension, IHD, stenosis in the aortic orifice.
Restrictive form
Cardiomyopathy of this type is diagnosed extremely rarely. The cause of the pathology is inflammatory process in the heart muscle and complications after valve surgery. Against the background of the disease, the myocardium and its membranes degenerate into connective tissue, and slow filling of the ventricles is noted. The patient has shortness of breath, fast fatiguability, valve defects and heart failure. The restrictive form is considered extremely dangerous for children.
How to strengthen the heart muscle?
Exist various ways do it. Activities include correction of the daily routine and nutrition, exercises. As a preventative measure, after consulting with your doctor, you can start taking a number of medications. Besides this, there is also traditional methods strengthening the myocardium.
Physical activity
It should be moderate. Physical activity should become an integral element of the life of any person. In this case, the load must be adequate. Do not overload the heart and exhaust the body. The best options are race walking, swimming, and cycling. Exercises are recommended to be done in the fresh air.
Walking
It is excellent not only for strengthening the heart, but also for healing the entire body. When walking, almost all human muscles are involved. In this case, the heart additionally receives a moderate load. If possible, especially at a young age, it is worth giving up the elevator and walking over heights.
Lifestyle
Strengthening the heart muscle is impossible without adjusting your daily routine. To improve myocardial activity, it is necessary to stop smoking, which destabilizes blood pressure and causes narrowing of the lumen in the blood vessels. Cardiologists also do not recommend getting carried away with baths and saunas, since staying in a steam room significantly increases cardiac stress. It is also necessary to take care of normal sleep. You should go to bed on time and get enough rest.
Diet
Rational nutrition is considered one of the most important measures in strengthening the myocardium. You should limit the amount of salty and fatty foods. Products must contain:
- Magnesium (legumes, watermelons, nuts, buckwheat).
- Potassium (cocoa, raisins, grapes, apricots, zucchini).
- Vitamins P and C (strawberries, black currants, peppers (sweet), apples, oranges).
- Iodine (cabbage, cottage cheese, beets, seafood).
Cholesterol in high concentrations has a negative effect on myocardial activity.
Psycho-emotional state
Strengthening the heart muscle can be complicated by various unresolved problems of a personal or work nature. They can cause pressure changes and rhythm disturbances. Stressful situations should be avoided whenever possible.
Drugs
There are several means that help strengthen the myocardium. These include, in particular, drugs such as:
- "Riboxin". Its action is aimed at stabilizing the rhythm, enhancing nutrition of the muscles and coronary vessels.
- "Asparkam". This drug is a magnesium-potassium complex. Thanks to taking the drug, it normalizes electrolyte metabolism, signs of arrhythmia are eliminated.
- Rhodiola rosea. This remedy improves the contractile function of the myocardium. Caution should be exercised when taking this drug as it has the ability to excite the nervous system.
The body of all animals, including humans, consists of four nervous, connective and muscular. About the last one we'll talk in this article.
Types of muscle tissue
It comes in three types:
- striated;
- smooth;
- cardiac.
Functions of muscle tissue different types somewhat different. And the building too.
Where are muscle tissues located in the human body?
Muscle tissues of different types occupy different locations in the body of animals and humans. So, as the name implies, the heart is built from cardiac muscles.
Skeletal muscles are formed from striated muscle tissue.
Smooth muscles line the inside of the cavities of organs that need to contract. This is, for example, the intestines, bladder, uterus, stomach, etc.
The structure of muscle tissue varies between species. Let's talk about it in more detail later.
How is muscle tissue structured?
It consists of large cells - myocytes. They are also called fibers. Muscle tissue cells have several nuclei and a large number of mitochondria - organelles responsible for energy production.
In addition, the structure of muscle and animals provides for the presence of a small amount intercellular substance, containing collagen, which gives muscles elasticity.
Let's look at the different types separately.
Structure and role of smooth muscle tissue
This tissue is controlled by the autonomic nervous system. Therefore, a person cannot consciously contract muscles made of smooth tissue.
It is formed from mesenchyme. This is a type of embryonic connective tissue.
Reduced this fabric much less active and fast than striated.
Smooth tissue is built from spindle-shaped myocytes with pointed ends. The length of these cells can range from 100 to 500 micrometers, and the thickness is about 10 micrometers. The cells of this tissue are mononuclear. The nucleus is located in the center of the myocyte. In addition, organelles such as the agranular ER and mitochondria are well developed. Also in the cells of smooth muscle tissue there are a large number of inclusions from glycogen, which represent reserves of nutrients.
The element that ensures the contraction of this type of muscle tissue is myofilaments. They can be built from two actin and myosin. The diameter of myofilaments that are composed of myosin is 17 nanometers, and those that are built of actin are 7 nanometers. There are also intermediate myofilaments, the diameter of which is 10 nanometers. The orientation of myofibrils is longitudinal.
The composition of muscle tissue of this type also includes collagen, which provides communication between individual myocytes.
Functions of muscle tissue of this type:
- Sphincteric. It consists in the fact that smooth tissues are made of circular muscles that regulate the transition of contents from one organ to another or from one part of an organ to another.
- Tow truck. The point is that smooth muscles help the body remove unnecessary substances and also take part in the process of childbirth.
- Creation of vascular lumen.
- Formation of the ligamentous apparatus. Thanks to it, many organs, such as the kidneys, are kept in place.
Now let's look at the next type of muscle tissue.
Cross-striped
It is regulated. Therefore, a person can consciously regulate the work of muscles of this type. Skeletal muscles are formed from striated tissue.
This fabric consists of fibers. These are cells that have many nuclei located closer to plasma membrane. In addition, they contain a large number of glycogen inclusions. Organelles such as mitochondria are well developed. They are located near the contractile elements of the cell. All other organelles are localized near the nuclei and are poorly developed.
The structures through which striated tissue contracts are myofibrils. Their diameter ranges from one to two micrometers. Myofibrils occupy most of the cell and are located in its center. The orientation of myofibrils is longitudinal. They consist of light and dark discs that alternate, which creates the transverse “striation” of the tissue.
Functions of muscle tissue of this type:
- Provide movement of the body in space.
- Responsible for the movement of body parts relative to each other.
- Capable of maintaining body posture.
- They participate in the process of temperature regulation: the more actively the muscles contract, the higher the temperature. When frozen, striated muscles may begin to contract involuntarily. This explains the trembling in the body.
- Execute protective function. This is especially true for the abdominal muscles, which protect many internal organs from mechanical damage.
- Act as a depot of water and salts.
Cardiac muscle tissue
This fabric looks like both cross-striped and smooth. Like smooth, it is regulated by the autonomic nervous system. However, it contracts just as actively as the striated one.
It consists of cells called cardiomyocytes.
Functions of this type of muscle tissue:
- There is only one: ensuring the movement of blood throughout the body.
The structural units of cardiac muscle tissue are cells - cardiomyocytes, covered with a basement membrane.
There are 5 types of cardiomyocytes: contractile (working), or typical, and atypical: sinus (pacemaker), transitional, conductive and secretory.
Working cardiomyocytes have the shape of an elongated cylinder with a length of about 100-150 microns and a diameter of up to 20 microns. They contain one, or less often two, nuclei located in the center of the cell, and myofibrils (Conheim's fields) are localized in groups around the nuclei. The structure of myofibrils is the same as in skeletal muscle tissue, but they lack triads. Cardiomyocytes connect end to end to form functional muscle fibers. In the area of cardiomyocyte junctions, intercalated discs are clearly visible at the light-optical level.
In Insert discs distinguish between longitudinal and transverse sections:
IN Transverse sections there are many intercellular contacts - Desmos , they ensure the strength of the connection of cardiomyocytes; V Longitudinal Plots there are many intercellular contacts like Nexus , which form narrow channels between neighboring cells, water and ions are able to pass through these channels, which creates conditions for the free passage of electric current from one cardiomyocyte to another; Thus, the presence of nexuses ensures the electrical coupling of cardiomyocytes necessary for rapid spread excitation throughout the myocardium and for its synchronous contraction
Pacemaker cardiomyocytes (P-cells) are located in the sinus region. They are able to contract rhythmically and transmit control signals through transitional and conductive cardiomyocytes to workers, which contract with a given rhythm.
Transitional and Conductive cardiomyocytes They transmit excitation of the heart rhythm from β-cells to contractile cardiomyocytes.
Secretory cardiomyocytes They produce atrial natriuretic factor, which regulates urine formation and is a renin antagonist (increases diuresis and reduces blood pressure).
Common to the morphology of skeletal and cardiac muscle tissue is the presence of striations, detected at the light-optical level, and the so-called T-tubules, detected by ultramicroscopic examination.
T-tubules are tube-shaped invaginations of the cytomembrane that go inside the muscle fiber and cardiomyocyte, that is, they are located transversely relative to their length. Approximately at the level of the Z-lines, they come close to the endoplasmic reticulum.
Smooth muscle tissue
In smooth muscle tissue of mesenchymal origin structural unit is a myocyte that has a spindle-shaped shape, its nucleus is elongated, and is localized in the center of the cell. The length of myocytes ranges from 20-500 microns, and the width in the abdominal region is only 5-8 microns. The contractile apparatus is represented by actin filaments, forming a three-dimensional network, next to which myosin monomers are located.
In smooth muscle tissue there is no troponin-tropomyosin complex; the myosin head has light chains that must first be phosphorylated in order for it to cleave and attach ATP and interact with actin.
The structural unit of smooth muscles of ectodermal origin is the myoepitheliocyte of the exocrine glands, and the structural unit of neural origin is the myoneural cells m. m. sphincter et dilatator pupille.
17. Muscle tissue. Cardiac and smooth muscle tissue
Cardiac muscle tissue
The structural and functional unit of cardiac striated muscle tissue is the cardiomyocyte. Based on their structure and functions, cardiomyocytes are divided into two groups:
1) typical, or contractile, cardiomyocytes, which together form the myocardium;
2) atypical cardiomyocytes that make up the conduction system of the heart.
A contractile cardiomyocyte is an almost rectangular cell in the center of which one nucleus is usually localized.
Atypical cardiomyocytes form the cardiac conduction system, which includes the following structural components:
1) sinus-atrial node;
2) atrioventricular node;
3) atrioventricular bundle (bundle of His) – trunk, right and left legs;
4) terminal branches of the legs (Purkinje fibers). Atypical cardiomyocytes ensure the generation of biopotentials, their conduction and transmission to contractile cardiomyocytes.
The sources of development of cardiomyocytes are myoepicardial plates, which are certain areas of visceral splanchiotomes.
Smooth muscle tissue of mesenchymal origin
Localized in the walls of hollow organs (stomach, intestines, respiratory tract, organs genitourinary system) and in the walls of blood vessels and lymphatic vessels. The structural and functional unit is the myocyte: a spindle-shaped cell 30-100 µm long (in the pregnant uterus - up to 500 µm), 8 µm in diameter, covered with a basal lamina.
Myosin and actin filaments make up the contractile apparatus of the myocyte.
Efferent innervation of smooth muscle tissue is carried out by the autonomic nervous system.
The contraction of smooth muscle tissue is usually long-lasting, which ensures the maintenance of the tone of hollow internal organs and blood vessels.
Smooth muscle tissue does not form muscles in the anatomical sense of the word. However, in hollow internal organs and in the wall of blood vessels between the bundles of myocytes there are layers of loose fibrous connective tissue, forming a kind of endomysium, and between the layers of smooth muscle tissue - perimysium.
Regeneration of smooth muscle tissue is carried out in several ways:
1) through intracellular regeneration (hypertrophy with increased functional load);
2) through mitotic division of myocytes (proliferation);
3) through differentiation from cambial elements (from adventitial cells and myofibroblasts).
From the book Dermatovenerology author E. V. Sitkalieva From the book Histology author From the book Histology author Tatyana Dmitrievna Selezneva From the book Histology author Tatyana Dmitrievna Selezneva From the book Histology author V. Yu. Barsukov From the book Histology author V. Yu. Barsukov From the book Histology author V. Yu. Barsukov From the book Histology author V. Yu. Barsukov From the book Histology author V. Yu. Barsukov author Evgeniy Ivanovich Gusev From the book Neurology and Neurosurgery author Evgeniy Ivanovich Gusev From the book Chinese Art of Healing. History and practice of healing from antiquity to the present day by Stefan Palos From the book Golden Mustache and other natural healers author Alexey Vladimirovich Ivanov From the book Osteochondrosis author Andrey Viktorovich Dolzhenkov From the book Iplicator Kuznetsov. Relief from back and neck pain author Dmitry Koval From the book Therapeutic self-massage. Basic techniques by Loy-So
