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Main page | Structure | Departments | Department of Histology and Embryology | Materials for students | Modul 1 | MUSCLE TISSUE.

MUSCLE TISSUE. (=MT). It includes 5 types.
  1. STRIATed SKELETAL MT (is developed from MYOTOME of SOMITE),
  2. STRIATed  CARDIAC MT (is developed from mesoderm portion, named MYOEPICARDIAL PLATE). It locates in MYOCARDIUM.,
  3. SMOOTH MT of mesenchymal type, developing from MESENCHYME.
  4. SMOOTH MT of ectodermal type, developing from SURFACE ECTODERM.
  5. SMOOTH MT of neural type, developing from NEURAL TUBE.
STRIATED MT means - because organelles MYOFIBRILLS contain visible in microscope alternating DARK bands (or A-bands) and LIGHT bands (or I-bands).
SMOOTH MT means -  because  microscopically dark and light bands in cells are absent.
It is composed of striated skeletal mucle FIBRes (=SSMF). One SSMF is composed of  2 components: A) Multinucleated MYOSYNCYTIUM, with funct.. of contraction, B) mononucleated SATELLITE cells, as origin of REGENERATION for syncytium after its rupture. Skeletal MT well regenerates due to proliferation of SATELLITE cs. Structure of MYOSYNCYTIUM (=MC): It has a) 10, 000 nuclei in SARCOplasm periphery (below SARCOlemma), b) abundance of MYOFIBRILLs occupy center of SARCOplasm.(SARCOplasm – is CYTOplasm of MC; SARCOlemma – is plasma membrane of MC). MYOFIBRILLs  contain CROSS STRIATION, locating in SARCOMEREs. MYOFIBRILL is composed of structural units-  SARCOMERs. SARCOMERE is composed of ½ I-band+1 A-band+1/2 I-band. I-band contains ONLY thin (or ACTIN) myofilaments.  A-band  contains  ACTIN (or thin) myofilaments and   MYOSIN (or thick) myofilaments.
It is composed of cardiac muscle fibres (=CMF). One CMF – is chain of MONOnucleated  cardiac muscle CELLS, attached each to other by intercalated disks. (NO syncytium  and   NO   satellite cs  in   myocardium).
1) CONTRACTILE CMC. It is: a) CYLINDRICAL-shaped, b) contains 1-2 nuclei in centre, c)abundance of MYOFIBRILLs in cytoplasm periphery, d) lives ALWAYS in Go-phase(NEVER divides by mitosis), e) is placed in miocardium  of    VENTRICLes.   Funct.:  proyide  heart  CONTRACTION.
2) SECRETORY CMC.  It is: a) STAR-(STELLATE)-shaped, b) abundance of rER  and secretory GRANULES in cytoplasm, c) are placed in myocardium of ATRIA. Funct.: secretion of cardiac hormone “NATRIURETIC  PEPTIDE”. 3) Conducting CMC, including P-cells (pace-maker) and Purkinje fibres. Funct.: P-cell generates 60-80 potentials of  action per min.
Regeneration of CMCs: After necrosis NEW CMCs are NOT developed (because live in Go-phase). But FIBROBLASTS, locating in ENDOMISIUM, form collagen SCAR, replacing xone of necrosis.
  1. SMOOTH MT of mesenchymal type:
It locates in wall of stomach, intestine, blood vessels, urinary bladder, myometrium. This tissue is composed of  bundles of SMOOTH MUSCLE CELLS (=SMC).
One SMC is: a) SPINDLE-shaped, b) in cytoplasm abundance of THICK and THIN myofilaments WITHOUT cross striation; c) myofilaments attach to plasma membrane by DENSE BODIES. Funct.: if SMCs are in intestine, it provide peristalsis; If SMCs are in arterioles wall, it regulate level of blood pressure.
  1. SMOOTH MT of ectodermal type
It is composed of MYOEPITHELAL cells (=MECs).
One MEC is a) BASKET-shaped with long cytoplasmic PROCESSES, surrounding secretory portions of exocrine glands, b) in cytoplasm abundance of THICK and THIN myofilaments.
Funct.: MEC contracts and compresses secretory portion, providing  releasing of secretory products  (saliva, milk) into ducts.
  1. SMOOTH MT of neural type.
It locates in eye IRIS and form muscles, DILATING and CONSTRICTING of PUPIL.
It is composed of smooth muscle cells with one long process.
Skeletal muscle and myocardium BETWEEN muscle fibres  contain layers of loose irregular connective tissue, named ENDOMISIUM and PERIMISIUM. Main cell type in its – is differentiated FIBROBLAST. Funct.: Fibroblasts  form collagen SCAR in:a) MYOCARDIUM after its NECROSIS
(or INFARCT) and in 2) MYOMETRIUM after operation CESARIAN section.. Usually endomisium provide TROPHIC function and INNERVATES muscle fibres.
Составитель – доцент В.В. Бондаренко.
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