Summary
Electron microscopy of the S-A and A-V nodes in the 15 human embryonic hearts revealed specific morphological characteristics of the tissue. In the embryonic S-A node muscle, a diffuse distribution of abundant mitochondria and ribosomes as well as of slim myofibrils was noted, while in the adjacent atrial myocardium glycogen occupied a vast area of the cytoplasm so as to leave myofibrils and scanty mitochondria in the peripheral part of the cell. Intrasarcoplasmic smooth-surfaced membrane system appeared in the S-A node muscle first at the 4 months stage. Embryonic A-V node muscle was characterized by its enormously rich content of fat droplets, which were in close association with glycogen. Extremely scanty nerve supply in the embryonic A-V node region examined was in a peculiar contrast to an earlier, abundant invasion of nerves into the S-A node.
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This research was suggested and consulted by Dr. I. Asami, Department of Anatomy, University of Tokyo.
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Yamauchi, A. Electron microscopic observations on the development of S-A and A-V nodal tissues in the human embryonic heart. Z. Anat. Entwickl. Gesch. 124, 562–587 (1965). https://doi.org/10.1007/BF00520847
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DOI: https://doi.org/10.1007/BF00520847