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Satellite cells in skeletal muscle proliferate and regeneration

A 5-year-old boy sustains a tear in his gastrocnemius muscle when he is involved in a bicycle accident. Regeneration of the muscle will occur through which of the following?
a.Differentiation of satellite cells
b.Dedifferentiation of myocytes into myoblasts
c.Fusion of damaged myofibers to form new myotubes
d.Hyperplasia of existing myofibers
e.Differentiation of fibroblasts to form myocytes

 The answer is a.
Satellite cells in skeletal muscle proliferate and reconstitute the damaged part of the myofibers. They are supportive cells for maintenance of muscle and a source of new myofibers after injury or after increased load. There is no dedifferentiation of myocytes into myoblasts (answer b), or fusion of damaged myofibers to form new myotubes (answer c). Hypertrophy, not hyperplasia
(answer d),occurs in existing myofibers in response to increased load.

Proliferation of fibroblasts may occur in the damaged area but leads to fibrosis, not repair of skeletal muscle. Fibroblasts do not differentiate into myocytes (answer e). The multinucleate organization of skeletal muscle is derived developmentally by fusion and not by amitosis (failure of cytokinesis after DNA synthesis). Mitotic activity is terminated after fusion occurs. In the
development of skeletal muscle, myoblasts of mesodermal origin undergo cell proliferation. Myocyte cell division ceases soon after birth. Myoblasts, which are mononucleate cells, fuse with each other end to end to form myotubes. This process requires cell recognition between myoblasts, alignment, and subsequent fusion.

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