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CARDIOVASCULAR
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Volume 10, 2005, No 1 |
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Cytoarchitecture of the Cardiac
Conduction System, with Special Reference to Tawara’s Sketches Tawara (1906) described at the light microscope level the cytoarchitecture and structure of every part of the cardiac conduction system, except the sinoatrial node. In the present study, the cytoarchitecture and ultrastructure of the conduction system of sheep and goat hearts were investigated at high resolution using scanning and transmission electron microscopy and the data were compared to Tawara’s findings. Atrial cardiac myocytes were continuous with atrioventricular (AV) nodal cells. At the center of the AV node, densely packed nodal cells were arranged in a reticular pattern. Some nodal cells were combined with large, oval cells of the AV bundle. The AV bundle, bundle branches, moderator band and false tendon were composed of muscular strands of large oval or cuboidal cells, which met both end-to-end and side-to-side and ran in a linear pattern. Purkinje strands consisting of large, oval cells formed a relatively large network. Purkinje fibers were connected with ventricular cardiac myocytes via transitional cells, or were connected directly with ventricular myocytes. Specialized cardiac myocytes were connected to each other at the intercalated disks, which showed characteristic configurations in each part of the conduction system. As a whole, specialized cardiac myocytes, except the AV node, had small numbers of desmosomes, fasciae adherentes and large gap junctions for mechanical and electrical coupling. Our studies confirmed as well as expanded the careful findings of Tawara and reveal that the cytoarchitecture reflects the physiology of the cardiac conduction system. (CVE. 2005; 10 (1): 34-42) Key words: cytoarchitecture, cardiac conduction
system, mammalian heart, scanning electron microscopy, transmission
electron microscopy, Sunao Tawara Tatsuo Shimada,?Prof. Ph.D. |
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