There are 3 groups of smooth muscle tissues:
mesenchyme
epidermal
neural
Muscle tissue of mesenchyme origin
Its structural-functional unit is smooth muscle cell smooth myocyte.
It is spindle-shaped cell with dimension 20-500 mcm.
Stick-shaped nucleus is located at the central part.
Smooth myocyte contains non-striated myofibrils.
In structure of myofibrils thin actin and thick myosin myofilaments are present.
This smooth muscle tissue is localized in the walls of internal organs, and also in blood and lymphatic vessels.
Th e contraction cycle consists of four steps:
1. ATP hydrolysis.
2. Attachment of myosin to actin to form cross-bridges.
3. Power stroke.
4. Detachment of myosin from actin.
Classification of muscle fibers
Muscle fibers are classified into three main categories:
1.slow oxidative fibers (type I),
2.fast glycolytic fibers (type IIa) and
3.intermediate fast oxidative-glycolytic fibers (type IIb).
Regeneration of skeletal muscle
The source of regeneration of skeletal muscle is myosatellite.
While organism grows myosatellites are divided and daughter cells are built into ends of symplasts.
After finishing of growth division of myosatellites is stopped.
Regeneration of skeletal muscle is realized at the expense of 2 mechanisms: compensative hypertrophy of myosymplast and proliferation of myosatellites.
Age-related changes of skeletal muscle
With aging, humans undergo a slow, progressive loss of skeletal muscle mass that is replaced largely by fibrous connective tissue and adipose tissue.
In fibers regularity of arrangement of mitochondria is damaged, mitochondria can hypertrophy and are degenerated or giant forms appear.
Volume of sarcoplasmic net is increased.
Some myofibrils loose transversal striation, are fragmented and myofilaments are disorganized.
In myofibres brown pigment lipofuscin is accumulated.
As a result of growth of connective tissue resiliency and elasticity are decreased.
All these changes make muscles quickly tired.
Muscle tissue.
plan:
1. The development of muscle tissue in evolution.
2. Classification MT.
3. Brief morphological and functional characteristics of the MT.
4. Regeneration MT.
MT perform the function of reduction and provide various types of motor response. During the evolution of specialization MT took place on the basis of the primary mechanisms of reduction, universal for all cells of a multicellular organism.
In this connection, the MT originated from different sources, and the variety in the structure acquired.
The oldest among MT - a somatic MT. Somatic MT originated from the surface epithelium (hypothetical ancestor). Then, in the course of evolution from the wall of the coelomic cavity of the heart cells appeared in MT I and II-but rotyh.
Reduces tissue also appeared from the tissues of the internal environment - the so-called visceral (splanchnic) muscles.
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In addition MT may develop from bookmarks nervous system. These include muscles extending the pupil narrows. And there are also muscle elements that make up the gland epithelium - the so-called myoepithelial cells of the salivary glands.
Reduction function is achieved by muscle elements is extended, accumulate in the cytoplasm of contractile proteins (actin and myosin), and finally formed a special contractile apparatus.
Due to mnogoobra.ziya MT and muscular elements proposed several classifications. At the same time, most researchers adhere to the classification proposed by Nikolai Grigoryevich Khlopin:
1. Smooth MT.
2. Striated MT.
1) Striated MT somatic type.
2). Striated MT coelomic (heart) type.
3. Mioneyralnye MT.
4. Myoepithelial cells or cell complexes mioidnie.
Consider the histological structure, function and regeneration of certain types of MT.
Smooth MT (HMT) is a part of the muscle membranes of blood vessels, intestines, urinary, ejaculatory tract; detected in spleen, skin and other organs. Structural and functional unit of HMT is smooth muscle cells or leomiotsit. This fusiform cell cytoplasm contains thin (? 5.8 nm), medium (up to 10 nm) thick (13-18 nm) myofilaments. Thin myofilaments, or actin, in close cooperation with the thick (myosin) myofilaments. And the thin myofilaments about 15 times more than fat. Myocyte Length ranges from 20 to 500 microns and a diameter of 10-20 microns. The nucleus is situated in the central part of the expanded cells. Shape of the nucleus elongated, rod-shaped. Chromatin is packed tightly, often visible deep wrinkles kariolemmy. With the cell surface cell is surrounded by a shell - miolemmoy (corresponding tsitolemmy). In addition there is a further miolemmy outside the basement membrane, which is attached to the collagen fibers and argyrophilic. Leomiotsity collected in beams having longitudinal and circular direction in the body. These beams are innervated by one nerve and are called effector contractile unit of HMT.
Trophic component leomiotsita presented mitochondria, complex plate, EPS, glycogen inclusions.
Smooth MT innervated autonomic nervous system, ie is not subject to the will of man. Reducing GMT slow - tonic, but maloutomlyaema GMT.
HMT in the embryonic period develops from the mesenchyme. Initially, the mesenchymal cells are stellate, otroschatuyu shape and during differentiation in GM cells become spindle-shaped; cytoplasmic organelles accumulate Specialty - myofibrils of actin and myosin.
Regeneration HMT:
1. Mitosis myocytes after dedifferentiation: myocytes lose their contractile proteins, mitochondria disappear and turn into myoblasts. Myoblasts begin to multiply and then re-differentiate into mature leomiotsity.
2. Probably the formation of new GM undifferentiated cells from stem cells of fibroblastic differon loose s.d.t.
Striated MT somatic type (skeletal muscle) - is the oldest histological system "in embryogenesis PP MT somatic type develops from the myotome. Structural and functional unit of muscle fiber is or CASE. Muscle fiber in the form of organization of living matter is symplasts (a huge mass of cytoplasm, where scattered hundreds of thousands of cores).
Muscle fiber contains a large number of cores, sarcoplasm. In the sarcoplasm are:
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- Organelles Specialty - myofibrils
- mitochondria
- T-system (T-tubules, L-tubes, tanks;)
- Included (especially glycogen);
Muscle fiber is surrounded by a special shell sarcolemma, and on top of it yet and the basement membrane. Myofibrils arranged in a strictly logical in length, with the formation of light (I-drives, isotropic) of the protein actin thin filaments and dark (A-ROMs, anisotropic) of the protein myosin thick filaments. And in the center of dark-ROM runs transverse line - mezofragma, and the center of light and drive passes transverse line - telofragma.
In addition to the contractile proteins actin and myosin in the sarcoplasm are still accessory proteins - troponin and trpomiozin - they are involved in providing (delivery) of contractile proteins by calcium ions, is the catalyst in the interaction of actin and myosin.
Strukturnofunktsionalnoy unit myofibrils sarcomere is - is the area between two adjacent telofragmami. With the reduction of between actin and myosin protofibrils in the presence of a catalyst - calcium ions form bridges or acto-myosin complex and it provides a sliding filaments toward each other and the shortening of the sarcomeres.
Tubules of sarcoplasmic reticulum arranged longitudinally to form L-tube (longentidunalis = longitudinal); they are connected by tubes going in the transverse direction in muscle fibers - the T-tubules (transversus = cross). L- and T-tube connected to the tank - it svoebrazny capacity for calcium ions. In the walls of the tanks are calcium pumps, bilge Ca ++ from the sarcoplasmic in the tank. Nerve impulses in motor plaques goes on the sarcolemma of the muscle fiber, down the T-tubule depolarization wave penetrates the fiber distributed L-tubules and finally depolarization wave passes through the wall of the tank. At the time of passage through the membrane depolarization wave tank in the latter increases permeability to Ca ++ ions, and calcium is released into the sarcoplasm and picked up by accessory proteins troponin and tropomyosin and is brought to the acto-myosin complexes in the presence of ATP is a reduction of the sarcomere. Calcium pump rapidly pumps the calcium back into the tank - the actomyosin complex decomposes, so there is a relaxation muscles. Receipt of a new pulse leads to a repetition of the cycle.
According to the structure and functional characteristics of isolated muscle fibers of type I (red MV), which contain many mitochondria, myoglobin (gives red color), high activity of the enzyme succinate dehydrogenase, but few myofibrils. Red MV mined to reduce energy by aerobic oxidation of glycogen, ie need to go. MV Type II (white M.W.) contain more relatively larger myofibrils and glycogen, but less mitochondria and have low activity of succinate dehydrogenase. White MV Abbreviations for energy produced by anaerobic oxidation glycogen i.e. breathing is not needed.
Of particular note is the so-called miosatellitotsity cells (MSC). MSC were observed with an electron microscope in 1961. Since histogenesis and regeneration of skeletal MT is considered in this connection and MSC. MSC localization feature is that they are located between the basal lamina and the sarcolemma m.volokna. Under normal conditions, these cells have neolshie size (20-30 mm in length), rod-shaped core with a high content of heterochromatin narrow cytoplasm surrounding the nucleus; organelles are presented very poorly. Actin and myosin protofibrils in the MSC can not be detected. Physiological and reparative regeneration PP MT somatic type at the expense of poorly differentiated elements - MSC. In case of injury or great exertion MSC cells are gradually emerging from the m.volokna, begin to divide by mitosis and form a population of myoblasts. Subsequently, myoblasts are arranged in "chain" and begin merging to form miotubuly - symplast. Miotubuly accumulate in the cytoplasm of myofibrils, mitochondria and turn into new myschechnye fibers that comprise its membership and simplastichesky component and reserve cells - MSC.
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Age-related changes striated MT somatic type accompanied by atrophy of the MV, ie decrease in the number and thickness of the myofibrils, lipofuscin accumulation and fat inclusions in sarcoplasm, significant thickening of the basement membrane around the sarcolemma.
PP MT heart (coelomic) type - develops from a visceral leaf splanhnatomov called mioepikardialnoy plate. In histogenesis PP MT type of heart distinguish the following stages:
1. Stage cardiomyoblasts.
2. Stage kardiopromiotsitov.
Step 3. cardiomyocytes.
Morphofunctional unit PP MT cardiac type is cardiomyocyte (CMC). CMC contacting each other end-to-end form functional muscle fibers. In doing so, CMC demarcated from each other by intercalated disks as special cell-cell contacts. Morphologically CMC - a highly specialized cell localized in the center of one core, myofibrils occupy the bulk of the cytoplasm between the large number of mitochondria; there EPS and inclusion of glycogen. Sarcolemma (respectively, a tsitolemmy) consists of plasmolemma and basement membrane, less pronounced compared with the PP MT skeletal type. Unlike skeletal cardiac MT MT cambial elements does not matter. In histogenesis cardiomyoblasts able mitotically dividing and at the same time to synthesize myofibrillar proteins. Considering the features of CMC should be pointed out that in early childhood, these cells after disassembly (t, e, extinction) can start the cycle of proliferation with subsequent assembly of acto-myosin structures. This is a characteristic of heart muscle cells. Subsequently, however, the ability to mitosis in CMC decreases sharply with adults practically zero. In addition to the histogenesis with age in CMC is an accumulation of lipofuscin inclusions. Dimensions CMC decreases. There are 3 kinds of CMC:
1. Contractile CMC (typical) - see description above.
2. Atypical (conductive) CMC - form the conducting system of the heart.
3. Secretory CMC.
Atypical (conductive CMC - they are characterized by:
- Poorly developed myofibrillar apparatus;
- Few mitochondria;
- Sarcoplasm contains more with a large amount of inclusions glycogen.
Atypical CMC provides automata heart, as part of them, located in the sinus node of the heart of P-cells or pacemakers, are able to produce rhythmic nerve impulses that cause contraction of typical CMC; so even after transection nerves appropriate to heart, myocardium continues to decrease its rhythm. Another part of the atypical CMC conduct nerve impulses from the pacemaker and impulses from the sympathetic and parasympathetic nerve fibers to the contractile CMC.
Secretory CMC - are located in the atria; under the electron microscope in the cytoplasm are EPS granular, lamellar complex and secretory granules, which contain natriuretic factor or atriopeptin - regulates blood pressure. In addition CMC produce secretory glycoproteins, which are connected to prevent the formation of blood lipoproteins, blood clots in the blood vessels.
Cardiac regeneration MT PP type. Reparative regeneration (after injury) - very badly expressed, so after injury (etc.: infarction) heart MT replaced by connective scar. Physiological regeneration (replenishment of normal wear and tear) is carried out by intracellular regeneration - ie CMC is not able to share, but is constantly updating their worn-out organelles, especially mitochondria and myofibrils.
Mioneyralnaya fabric - is part of the muscles extend and narrows the pupil, as well as part of the ciliary muscle of the eye. Mioneyralnaya iris tissue develops from the optic cup, ie rudiment of the nervous tissue - the neural tube. Some authors consider the source mioneyralnoy neural crest tissue (ganglion plate). Mioneyralnaya tissue is only in vertebrates and is their evolutionary acquisition. In fishes, amphibians and mammals mioneyralnaya smooth muscle tissue is presented, whereas in reptiles and birds - myosymplasts.
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Myoepithelial Beams - located around the end of salivary secretory departments, sweat and mammary glands. Source of development - the ectoderm. Otroschaty myoepithelial cells in the cytoplasm are contractile proteins actin and myosin. Spikes myoepitheliocytes cover adenomere and reduction contribute to the removal of secretions from the secretory to the hatching way.
Also listed in the body of the contractile structures exist a large number of cells containing cytoplasmic contractile proteins and consequently with significant motility - so-called mioidnye cells. So, mioidnye cells are found in the pineal gland, cerebellum, arachnoid brain and even in the brain. The nature of these cells is largely unclear, their morphology and function has been insufficiently studied.
