As stated above, myocyte diameter increases during the transitional and hypertrophic phases of development, from 4-6 um in the newborn to 15-20 um in the adult. Myocyte length is usually close to 5.5 times the diameter (Figure 2.10).
Adult myocytes are now simple cylinders, however. They show complex surface features, which has made it difficult to determine volume accurately. The constancy of myocyte size and volume is maintained over the body weight range from rats to man. It probably also holds for elephants and whales. Thus, larger animal's hearts don't have larger myocytes, just more of them. One exception my be very tiny shrews, which appear to have smaller myocytes, possibly this is related to their very high metabolic rate.
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