Figure 1012

Photomicrograph of developing skeletal muscle myotubes. This photomicrograph shows a cross section (on the left) and a longitudinal section (on the right) of developing skeletal muscle fibers in the stage of secondary myotubes. These myotubes are formed by sequential fusion of myoblasts forming elongated tubular structures. Note that the myotubes have a small diameter and widely spaced, centrally positioned nuclei that gradually become displaced into the cell periphery by the increased number of newly synthesized myofilaments. In the mature multinucleated muscle fiber (upper left), all nuclei are positioned in the peripheral sarcoplasm, just inside the plasma cell membrane. x220.

blends in with the muscle cell sarcoplasm when viewed in the light microscope, thus making them difficult to identify. Each satellite cell has a single nucleus with a chromatin network denser and coarser than that of muscle cell nuclei. The regenerative capacity of skeletal muscle is limited. Satellite cells function as stem cells that, after injury, proliferate to give rise to new myoblasts. As long as the external lamina remains intact, the myoblasts fuse within the external lamina to form myotubes, which then mature into a new fiber. In contrast, if the external lamina is disrupted, fibroblasts repair the injured site, with subsequent scar tissue formation.

Muscular dystrophies are characterized by progressive degeneration of skeletal muscle fibers, which places a constant demand on the satellite cells to replace the degenerated fibers. Ultimately, the satellite cell pool is exhausted. New experimental data indicate that during this process, additional myogenic cells are recruited from the bone marrow and supplement the available satellite cells. The rate of degeneration exceeds the rate of regeneration, however, resulting in loss of muscle function. A future treatment strategy for muscular dystrophies may include the transplantation of satellite cells or their myogenic bone marrow counterparts into damaged muscle.

How To Reduce Acne Scarring

How To Reduce Acne Scarring

Acne is a name that is famous in its own right, but for all of the wrong reasons. Most teenagers know, and dread, the very word, as it so prevalently wrecks havoc on their faces throughout their adolescent years.

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