Features of capillarization and mitochondria from gastrocnemius and pectoral muscle fibers in chickens of various age

: Using light and electron microscopy, more rapid morphological development of m. gastrocnemius as compared to m. pectoralis was demonstrated in chicken by the 10th day. In m. pectoralis some immature fibers with centrally located nuclei are found, its muscle fibers are generally thinner, contain smaller mitochondria which occupy lesser relative volume, and are surrounded by capillaries, the density of which is half of that in m. gastrocnemius. In both muscles the mitochondria were found to be evenly distributed over the section area of the fibers. In adult birds as well as in chicken capillary density in both oxidative m. gastrocnemius and glycolytic m. pectoralis corresponds to the mitochondrial content in their fibers. In both muscles there exists a distinct concentration of oxygen-absorbing structures within a narrow peripheral zone of the fibers irrespective of the location and number of the surrounding capillaries. This phenomenon is more expressed in m. gastrocnemius. In m. pectoralis mitochondria are smaller at fibers' periphery and larger in their center.