DEVELOPMENT OF THE CONDUCTION SYSTEM OF THE HEART

The muscle cells forming the myocardium and the muscle cells forming t he intestinal smooth muscle layers, are both derived from the visceral mesoderm. All cardiomyocytes display autorhythmicity, intercellular c onduction via gap junctions, and contraction, irrespective whether the y are derived from atrium, ventricle, node, or bundles. It is the anat omical arrangement of the distinct components that is responsible for the coordinate contraction wave over the heart. These very basic princ iples have been insufficiently appreciated in most studies on the deve lopment of the conduction sytem, by which it got unnoticed that the pr oper anatomical arrangement is, in essence, layed down very early in d evelopment in the cardiac tube. In this review we will summarize recen t immunohistochemical studies that have permitted this appreciation.