Types of Tissue and Muscle

Types of Tissue and MuscleMuscleMuscle is genius of the four fundamental types of create from raw stuff present in animals. It is a gentle wind primarily responsible to produce rangement of a dust part. Its electric cellular phones convert the chemical energy of adenosine tri orthophosphate into the mechanical energy of feat and exert a useful snap on a nonher tissue. much specialized everyy, vim contraction serves the following imbrication functions take upment and contractile move of body contents in the course of respiration, circulation, digestion, defecation, urination, and childbirth. Stability by resisting the pull of gravity. Communication. As well as the control of body openings and passages. And fin wholey, producing around 85% of our body heat, which is vital for the metabolism (C atomic number 18y Carpenter, 2007).ClassificationThere ar trine histological types of heftinesscardiac, smooth and pinchedwhich disaccord in fashion, physiology, and funct ion.The cardiac vigour is essentially limited to the heart, though it extends slightly into the nearby rail line vessels. It is involuntary and striated because of the regular arrangement of their actin and myosin filaments. Its cells ar much shorter, so they are commonly called myocytes, and are mononuclated (Saladin, 2003). The myocytes assemble branches of adjoining cells and form a meshwork by arrogateing to distri besidesively former(a) in attachment points called intercalated discs that provide warm mechanical adhesions surrounded by adjacent cells. Smooth si immature lacks striations and is involuntary. Smooth vigor cells are ordinarily long and spindle-shaped, and each fusiform cell has a wholeness and centered nucleus (Purves et al., 2004). Small amounts of smooth muscle are found in the iris of the eye and in the skin, but roughly of it, called visceral muscle, forms layers in the walls of the digestive, respiratory, and urinary tracts, blood vessels, the u terus, and other viscersa (Alberts et al., 2008). The skeletal muscle type is of special interest of this thesis and will be elevate studied in the following sections.Skeletal muscleSkeletal muscles are, as the see implies, are bound to the skeleton by manner of tendons, which means that they are volitional. It is composed of some(prenominal) stringy tissue and connective. A skeletal muscle cell (muscle fiber) is ab bring out 10 to 100m in diameter and 30 cm long. It is surrounded by a sparse layer of areolate connective tissue called the endomysium, which allows room for blood capillaries and nerve fibers to reach each muscle fiber. Muscle fibers are rooted in bundles called fascicles, which are visual to the naked eye as parallel strands. each fascicle is dislocated from neighboring ones by a connective tissue sheath called the perimysium, normally somewhat thicker than the endomysium. The muscle as a whole is surrounded by still another connective tissue layer, the epimy sium. The epimysium grades imperceptibly into connective tissue sheets called fasciae, deep fasciae between adjacent muscles and a superficial fascia (hypodermis) between the muscles and skin. It is described as striated and voluntary (Saladin, 2003).StructureThe skeletal muscle tissue consists of long and cylindrical cells called muscle fibers, which are actually huge single cells that form during festering by the fusion of many separate cells, called myoblasts. Each cell contains multiple nuclei adjacent to the plasma membrane, and they are about 10 to 100m in diameter and 30 cm long. The bulk of the cytoplasm privileged is made up of myofibrils, which is the name given to the basic contractile elements of the muscle cell. Wi curve each myofibril are thin actin filaments and thick specific muscle isoforms of myosin II filaments (Alberts et al., 2008). Myosin filaments are bundles of molecules with globular heads and polypeptide tails. Actin filaments consist of dickens durance of actin monomers twisted together. They are wrapped by chains of the polypeptide tropomyosin and studded at intervals with another protein, troponin.In most regions of the myofibril, each thick myosin filament is surrounded by six thin actin filaments, and conversely, each thin actin filament sits at bottom a triangle of three thick myosin filaments. The myofibril consists of repeating units, called sarcomeres, which are the units of contraction, built up of approximately 2.2 microns in length. Each sarcomere is made of overlapping filaments of actin and myosin, which create a distinct band pattern. As the muscle contracts, the sarcomeres shorten, and the appearance of the band pattern changes. Each sarcomere is bounded by Z-lines, which are structures that ground the thin actin filaments. Centered in the sarcomere is the A-band, which contains all the myosin filaments. The H-zone and the I-band, are regions where actin and myosin filaments do not overlap in the relaxed muscle. The dark stripe within the H-zone is called the M-band it contains proteins that serve up adapt the myosin filaments in their regular arrangement. The bundles of myosin filaments are held in a centered specify within the sarcomere by a protein called titin. Cardiac muscle and smooth muscle alike contain sarcomeres, although the organization is not as regular as that in skeletal muscle (Alberts et al., 2008 Purves et al., 2004.).The plasma membrane, called the sarcolemma has tunnel-like infoldings called transverse (T) tubules that penetrate through and through and through the fiber and emerge on the other side. The function of a T tubule is to carry an electrical current from the surface of the cell to the interior when the cell is stimulated. Most other organelles of the cell, such as mitochondria and smooth endoplasmic reticulum (ER), are located between adjacent myofibrils. The sarcoplasm to a fault contains an abundance of glycogen, which provides stored energy for the muscl e to use during exercise, and a red pigment called myoglobin, which binds oxygen until it is needed for muscular activity. The smooth ER of a muscle fiber is called sarcoplasmic reticulum (SR). It forms a network around each myofibril, and alongside the T tubules it exhibits dilated sacs called termination cisternae. The SR is a reservoir for calcium ions it has gated channels in its membrane that wad release a flood of calcium into the cytosol, where the calcium activates the muscle contraction process (Saladin, 2003).Muscle contractionFor contraction to occur, an action potentials spreads from the end crustal plate and when it reaches the T tubules, it continues down them into the sarcoplasm. Action potentials open voltage- mildewd ion gates in the T tubules. These are physically linked to calcium channels in the remainder cisternae of the sarcoplasmic reticulum (SR), so gates in the SR open as well and calcium ions diffuse out of the SR, down their concentration incline and into the cytosol. The calcium ions bind to the troponin of the thin filaments. The troponin-tropomyosin complex changes shape and shifts to a new position. This exposes the active sites on the actin filaments and makes them available for binding to myosin heads the myosin heads must have an ATP molecule bound to it to initiate the contraction process. Myosin ATPase, an enzyme in the head, hydrolyzes this ATP. The energy released by this process activates the head, which cocks into an extended, high-energy position. The head temporarily keeps the ADP and phosphate group bound to it. The cocked myosin binds to an active site on the thin filament. Myosin releases the ADP and phosphate and flexes into a bent, low-energy position, tugging the thin filament along with it. This is called the power stroke. The head remain bound to actin until it binds a new ATP. Upon binding more ATP, myosin releases the actin. It is now fain to repeat the whole processit will hydrolyze the ATP, recock (t he recovery stroke), attach to a new active site farther down thethin filament, and produce another power stroke (Saladin, 2003).Classes of muscle fibersNot all muscle fibers are metabolically alike or able to make the same task. Some respond slackly but are comparatively resistant to wear thin, while others respond more quickly but as well as fatigue quickly. Indeed, skeletal muscles layabout be divided into fast and decompress twitch fibers and its myosin heavy chain (MHC) isoform expression.Type I (MHC-I) overly called slow oxidative (SO) or slow-twitch. These fibers have relatively abundant mitochondria, myoglobin, and blood capillaries, and thusly a relatively deep red color. They are well adapted to aerobic respiration, which does not generate lactic sour. Thus, these fibers do not fatigue easily. However, in response to a single stimulus, they exhibit a relatively long twitch, lasting about 100 milliseconds (msec).Type II (MHC-II) too called fast glycolytic (FG) or fast-twitch. They are well adapted for quick responses but not for fatigue resistance. They are rich in enzymes of the phosphagen and glycogenlactic acid sy kiboshs. Their sarcoplasmic reticulum releases and reabsorbs Ca2 quickly, which partially accounts for their quick, forceful contractions. They are relatively pale (white fibers). These fibers produce twitches as short as 7.5 msec, but because of the lactic acid they generate, they fatigue more easily than SO fibers.Some authorities know two subtypes of FG fibers called types MHC-IIA and MHC-IIB. Type IIB is the common type just described, while IIA, or intermediate fibers, combine fast-twitch responses with aerobic fatigue-resistant metabolism. Type IIA fibers, however, are relatively archaic except in some endurance-trained athletes (Saladin, 2003). Notably, human skeletal muscle does not contain MHCIIb (Spangenburg and Booth, 2003 Schiaffino and Reggiani, 1994 Smerdu et al., 1994). In addition, hybrid fibers containing tw o MHC isoforms (i.e., type I/IIA, IIAX, IIXB) open fire also be present in muscle (Schiaffino and Reggiani, 1994 Staron and Pette, 1993).The fiber types goat be differentiated histologically by using stains for received mitochondrial enzymes and other cellular components, like using immunohistochemical procedures with antibodies against the specific MHC isoforms (Schiaffino et al., 1989 Lucas et al., 2000). All muscle fibers of one motor unit belong to the same physiological type. Nearly all muscles are composed of both SO and FG fibers, but the proportions of these fiber types differ from one muscle to another.Muscle myogenesisVertebrate skeletal myogenesis proceeds through three stages finish of the muscle progenitor cells, called myoblasts proliferation and in some cases migration of myoblasts and their terminal eminence into mature muscle by fusing to form multinucleated myotubes (Buckingham et al., 2003 Shi and Garry, 2006).Muscle developmentMuscle tissuesare derived from the mesoblastallayer of embryonicgerm cellsin a process known asmyogenesis. All muscles are derived fromparaxial mesoderm 8.The paraxial mesoderm is divided along the embryos length intosomites, corresponding to thesegmentationof the body.Muscle cells come from two cell lineages in the myotome somite, the epimere and hypomere, which formepaxialandhypaxialmuscles, respectively. Most muscles are hypaxial. During development,myoblasts either remain in the somite to form muscles associated with the vertebral column or migrate out into the body to form all other muscles. Myoblast migration is preceded by the formation ofconnective tissueframeworks, usually formed from the somaticlateral plate mesoderm.Myoblasts follow chemical signals to the appropriate locations, where they fuse into defer skeletal muscle cells (Sweeney, 1997).Muscle specialisationMuscle fibersform from the fusion ofmyoblastsinto multi-nucleated fibers calledmyotubes. In the early development of an embryothese myoblas ts will proliferate if enoughfibroblast growth figure(FGF) is present, without differentiating. When these factors are depleted, the myoblasts forfeit division and secretefibronectinonto theirextracellular matrix and bind to it through _51 integrin, their major fibronectin sensory sensory receptor (Menko and Boettiger 1987 Boettiger et al. 1995).The second stage involves the alignment of the myoblasts together into chains and subsequently into myotubes. This meter is mediated by cell membrane glycoproteins, including several cadherins and CAMs (Knudsen 1985 Knudsen et al. 1990). Recognition and alignment between cells takes place only if the two cells are myoblasts. However, identity of the species is not critical (Yaffe and Feldman, 1965).The third stage is the actual cell fusion itself. In this stage,calciumions are critical for development (Shainberg et al. 1969 David et al. 1981). Fusion is mediated by a set of metalloproteinasescalledmeltrins (e.g., c-Met).Myocyte enhance r factors(MEFs) promote myogenesis.Serum response factor(SRF) plays a central federal agency during myogenesis, being required for the expression of striated alpha-actin genes (Wei et al., 1998).Expression of skeletalalpha-actinis also regulated by theandrogen receptor steroids can thereby regulate myogenesis (Vlahopoulos et al., 2005).The specific extracellular signals that induce determination of each group of myoblasts are expressed only transiently. These signals trigger outturn of intracellular factors that maintain the myogenic program after the inducing signals are gone. We reason the identification and functions of these myogenic proteins, and their interactions, in the next several sections.Muscle-specific transcription factorsPax family transmit cells and proliferating myoblasts is characterized by the expression of Pax-genes, more specifically Pax7 and Pax3, which are transcription factors that regulate proliferation. Back to the developmental stage, in the lateral por tion of the somite, which forms the hypaxial muscles, factors from the surrounding environs induce the Pax3 transcription factor. In the absence of other inhibitory transcription, Pax3 thusly activates the genes encoding two muscle-specific transcription factors, Myf5 and MyoD. In the medial region of the somite, which forms the epaxial muscles, MyoD is bring forth through a slightly different pathway1.Pax7 residing satellite cells proliferating stage and Pax7 steady mice completely lack satellite cells (Seale et al., 2000). Cells expressing Pax7 is believed to be important for the regeneration of myoblasts. Also the expression of Pax3 has negative effect on the specialisation and it has been shown that this transcription factor is down-regulated in muscle by ubiquitination and proteasomal degradation before specialisation can proceed (Boutet et al., 2007). Pax genes have been shown to regulate the proliferation and survival even of certain cancers such as melanoma (Muratovska et al., 2003). Pax transcription factors are downregulated upon bring forward specialisation and other proteins predominate.Meanwhile Pax3 _____, Pax7 appears only in muscle stem cells (___).MyoD familyMuscle cells come from two cell lineages in the somite. In both instances, paracrine factors instruct the myotome cells to become muscles by inducing them to synthesize the MyoD proteins (Maroto et al. 1997 Tajbakhsh et al. 1997). Or also called the myogenic bHLH (basic helix-loop-helix) proteins. The proteins of this family all bind to similar sites on the DNA and activate muscle-specific genes (e.g. the muscle-specific creatine phosphokinase gene by binding to the DNA immediately upstream from it, or the chicken muscle acetylcholine receptor) (Lassar et al. 1989 Piette et al. 1990). MyoD and Myf5 belong to this family and are particularly important for muscle differentiation 2.Their important office staff during differentiation is supported by the MyoD-/-/Myf-5-/- mice miss fu lly developed skeletal muscle (Rudnicki et al., 1993). Myf-5 promotes myoblasts proliferation and is required for the cells to initiate differentiation (Ustanina et al., 2007). Absence of MyoD inhibits differentiation in cell culture and the protein is therefore considered to be a positive regulator of the process (Sabourin et al., 1999). While Pax3 is found in several other cell types, the myogenic bHLH proteins are specific for muscle cells. either cell making a myogenic bHLH transcription factor such as MyoD or Myf5 is committed to becoming a muscle cell.Myogenic regulatory factors (proper name?)Later than the MyoD proteins expression during differentiation, the myogenin and the myogenic regulatory factor 4 (MRF4) are present. Mice with deleted myogenin in developing myoblasts can start the differentiation process but they cannot move and die soon after birth (Hasty et al., 1993). Among other things, this suggests that myogenin is required at a later stage of the process. Simila rly, MRF4 is important for the growth of muscle tissue (Rhodes and Konieczny, 1989). It is noted that the MEF2 family of transcription factors also regulate differentiation (Olson et al., 1995), but their functions are not described in this context.In summary, Pax transcription factors help to sustain it from the stem cell stage of satellite cells, MyoD and Myf-5 act as myogenic determinants in the myoblasts diet, and myogenin and MRF4 are known as regulators of the later differentiation and muscle fiber formation (Pallari, 2011).Other factorsAlthough some factors that induce differentiation remain unknown, some growth factors and signaling molecules have been shown to regulate the process. dent signaling is important in animal embryonic development, in that it participates in the cell fate determination (Alberts et al., 2008). Notch has a dual role of myoblasts in that the protein has an inhibitory effect on myoblasts differentiation (Shawber et al., 1996) and simultaneously stimu lates their proliferation (Conboy and Rando, 2002). The chemoattractant SDF-1 also has an inhibitory effect on myoblasts differentiation and stimulates their proliferation by activation of the PKC (demi et al., 2007). Moreover, differentiation requires the expression and activity of cyclindependent kinase (Cdk) inhibitors, such as p21 and p27, critical for the withdrawal of myoblasts from the cell cycle (Kitzmann and Fernandez, 2001). To fully understand the factors that regulate, activate and inhibit satellite cells and their differentiation requires even much research (Kuang and Rudnicki, 2007 Shi and Garry, 2006.).1 developmental biology Scott gilbert2 developmental biology Scott gilbert