Page 14, O2 Uptake, Exercise & Cor. Circ., Dr. D. Penney
Coronary Circulation (continued..):
The adult human heart is composed of approximately 2 billion cardiomyocytes, which are relatively large cells 15-18 um in diameter and 75-90 um in length. Cardiomyocytes contain 0.4 g/100 g of myoglobin, which binds enough oxygen (plus that dissolved is tissue fluid) for about 8 seconds of activity. On average, each cardiomyocyte is served by a single capillary running parallel to it, each of which is approximately 4 um in diameter and 1 mm in length. At resting levels of oxygen consumption, mean intercapillary distance is about 17 um, providing a mean maximum diffusion distance of 8.5 um.
The approximately 2,500 myocytes per sq. mm of heart tissue are served by an equal number of capillaries (fiber: capillary ratio = 1), making the capillary density about 2,500 per sq. mm. Because each capillary is very small, actually near the limit of deformability of the erythrocyte, only 5% of the tissue volume is occupied by the capillaries.
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