Muscle atrophy refers to a decrease in the size of skeletal muscle, which occurs in a variety of settings. Atrophy may or may not be distinct from "sarcopenia", which is the loss of muscle seen in the aged. Sarcopenia (from the Greek meaning "poverty of flesh" is the degenerative loss of Skeletal muscle mass and strength associated with Senescence.
When a muscle atrophies, it necessarily becomes weaker, since the ability to exert force is related to mass.
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Clinical settings of atrophy
There are many diseases and conditions which cause a decrease in muscle mass, known as atrophy, including: inactivity, as seen when a cast is put on a limb, or upon extended bedrest (which can occur during a prolonged illness); cachexia - which is a "body-wasting" syndrome that is a co-morbidity of cancer and Congestive Heart Failure; Chronic Obstructive Pulmonary Disease; burns, liver failure, etc. Muscle (from Latin musculus, diminutive of mus "mouse" is contractile tissue of the body and is derived from the Atrophy is the partial or complete Wasting away of a part of the Body. Cachexia (kəˈkɛksiə is loss of weight, Muscle atrophy, fatigue weakness and significant loss of appetite in someone who is not actively trying to Cancer (medical term Malignant Neoplasm) is a class of Diseases in which a group of cells display uncontrolled Heart failure is a Cardiac condition that occurs when a problem with the structure or function of the Heart impairs its ability to supply Chronic obstructive pulmonary disease ( COPD) is a Disease of the lungs in which the Airways become narrowed Other syndromes or conditions which can induce skeletal muscle atrophy are congestive heart disease, liver disease, and starvation.
Other muscles diseases, distinct from atrophy
During aging, there is a gradual decrease in the ability to maintain skeletal muscle function and mass. This condition is called "sarcopenia". Sarcopenia (from the Greek meaning "poverty of flesh" is the degenerative loss of Skeletal muscle mass and strength associated with Senescence. The exact cause of sarcopenia is unknown, but it may be due to a combination of the gradual failure in the "satellite cells" which help to regenerate skeletal muscle fibers, and a decrease in sensitivity to or the availability of critical secreted growth factors which are necessary to maintain muscle mass and satellite cell survival. Sarcopenia (from the Greek meaning "poverty of flesh" is the degenerative loss of Skeletal muscle mass and strength associated with Senescence. Satellite cells are small mononuclear Progenitor cells with virtually no Cytoplasm found in mature Muscle. The term growth factor refers to a naturally occurring Protein capable of stimulating cellular growth proliferation and Cellular differentiation.
In addition to the simple loss of muscle mass (atrophy), or the age-related decrease in muscle function (sarcopenia), there are other diseases which may be caused by structural defects in the muscle (muscular dystrophy), or by inflammatory reactions in the body directed against muscle (the myopathies). Atrophy is the partial or complete Wasting away of a part of the Body. Sarcopenia (from the Greek meaning "poverty of flesh" is the degenerative loss of Skeletal muscle mass and strength associated with Senescence. Muscular dystrophy (MD refers to a group of genetic, Hereditary Muscle diseases that cause progressive muscle weakness
Pathophysiology
Muscle atrophy occurs by a change in the normal balance between protein synthesis and protein degradation. During atrophy, there is a down-regulation of protein synthesis pathways, and an activation of protein breakdown pathways. The particular protein degradation pathway which seems to be responsible for much of the muscle loss seen in a muscle undergoing atrophy is the "ATP-dependent, ubiquitin/proteasome pathway. Ubiquitin is a highly-conserved regulatory Protein that is ''ubiquitously'' expressed in Eukaryotes. Proteasomes are large Protein complexes inside all Eukaryotes and Archaea, as well as in some Bacteria. In this system, particular proteins are targeted for destruction by the ligation of at least four copies of a small peptide called ubiquitin onto a substrate protein. Ubiquitin is a highly-conserved regulatory Protein that is ''ubiquitously'' expressed in Eukaryotes. When a substrate is thus "poly-ubiquitinated", it is targeted for destruction by the proteasome. Proteasomes are large Protein complexes inside all Eukaryotes and Archaea, as well as in some Bacteria. Particular enzymes in the ubiquitin/proteasome pathway allow ubiquitination to be directed to some proteins but not others - specificity is gained by coupling targeted proteins to an "E3 ubiquitin ligase". A ubiquitin ligase (also called an E3 ubiquitin ligase is a Protein that covalently attaches Ubiquitin to a Lysine on a target protein via an Isopeptide Each E3 ubiquitin ligase binds to a particular set of substrates, causing their ubiquitination. A ubiquitin ligase (also called an E3 ubiquitin ligase is a Protein that covalently attaches Ubiquitin to a Lysine on a target protein via an Isopeptide
Potential treatment
Muscle atrophy can be opposed by the signaling pathways which induce muscle hypertrophy, or an increase in muscle size. Therefore one way in which exercise induces an increase in muscle mass is to downregulate the pathways which have the opposite effect.
See also
External links
Muscle weakness (or "lack of strength" is a direct term for the inability to exert force with one's Muscles to the degree that would be expected given the individual's Muscular dystrophy (MD refers to a group of genetic, Hereditary Muscle diseases that cause progressive muscle weakness Myotonic dystrophy (DM is a chronic, slowly progressing highly variable inherited multisystemic Disease that can manifest at any age from birth to old age Medical Subject Headings ( MeSH) is a huge Controlled vocabulary (or metadata system for the purpose of indexing journal articles and booksDapyx Software network: MP3 Explorer | Ebook Manager | Zenithic