Some morphological aspects of the atrioventricular junction in the rat heart.

The interrelationships of different components of atrioventricular junction of the rat heart were examined on serial sections. The results are the following: 1) The atrioventricular node of the rat is situated at the level of membraneous septum separating left ventricular cavity from the right atrium. This particular localization may be of functional significance since at this level both the state of systemic arterial circulation and venous return, can be integrated. 2) Apart from the node of Aschoff-Tawara adjacent to the upper edge of muscular septum, an accessory atrioventricular node is regularly present close to the aortic root. 3) In the proximity of both atrioventricular nodes we found vascular lacunae containing abundant mastocytes and chromaffin cells. These pictures seem to suggest the existence of local chemoregulation and transmitter liberation. 4) His bundle is apposed to subendocardial fibrous lamina running from mitral valve to the cartilaginous ring of the aortic root. This association of specialized cells with their connective environment reminds the organization of different mechanoreceptors described in literature.