Morphology of the atrioventricular junction in Iguana iguana (Reptilia-Iguanidae)

Abstract

The atrioventricular junctional area (AVJA), including atrioventricular (AV) node and bundle was investigated in seven hearts of common or green iguana (Iguana iguana) using the light microscopy. Adult animals, both sexes, were captured in the Pantanal, Brazil. All hearts were fixed in buffered formaldehyde 10% (pH 7.2) for 24 hours, embedded in paraplast according to routine methods, and serially cut at 5 µm thickness. In the Iguana iguana, the AVJA consists of a mass of the fibers intermingled with variable amount of connective tissue and blood vessels surrounded by adjacent myocardium and the attachment of the right atrioventricular valve in the fibrous skeleton. By light microscopy, conducting cells of the AV node and bundle can be distinguished from working cells by their much smaller size, paler staining reaction and the presence of a sheath of connective tissue. The AV node and bundle and its branches were found to constitute a continuous tract. Histochemically, we found elastic fibers between cells of the conduction, mainly in the AV node. The PAS method reveals absence of glycogen in specialized cells. The fibrous skeleton, mainly the right trigone, showed a well-developed chondroid tissue, made by hyaline like cartilage (binucleated condrocytes included in the big lacunas and extracellular matrix with fibrillar collagen). In conclusion, the nodal and Purkinje cells in heart iguana presented poorly morphological differentiation comparing mammals and birds, however the skeleton fibrous has a different cartilage kind.