Morfologia do coração durante o desenvolvimeto embrionário de Podocnemis unifilis Troschel 1848, (Testudines: Podocnemididae)

Abstract

The present study aimed to describe the morphology of the heart during the embryonic development of Podocnemis unifilis under controlled temperature. We collected 100 eggs and incubated in an artificial incubator during the 4th to the 60th day of incubation, with an average temperature of 31,8ºC. The hearts were collected after euthanasia of the embryos and submitted to processing for light microscopy. The main structures analyzed for description were: cardiac tube, interatrial septum, mesenchymal tissue, myocardium, trabeculations, endocardial cushions, partial ventricular septa, ventricular subcompartments, outflow tract and cardiac valves. The development of the cardiac tube was visualized from the 4th day of incubation. On the 5th day the cardiac tube torsion process was visualized as well as the expansion of the atrial, ventricular and outflow pathway compartments. The atrial septation process began on the 8th day and completed on the 17th day, when the first interatrial septum containing the mesenchymal cover fused to the atrioventricular cushion forming the interatrial septum, dividing the atrial compartments, but small perforations appeared in the cranial region of the septum. The development of the meat trabeculae of the ventricle was visualized on the 6th day, and continued to grow, becoming thick throughout development. The meat trabeculae to the right of the ventricle clustered, forming the horizontal septum, and the bulbolamelar septum on the 15th day, while the vertical septum was observed on the 19th day. The outflow route has a single lumen, which is divided by the fusion of the dorsal and ventral endocardic crests forming two septa, the aoticopulmonary septum and interaortic septum visualized on the 16th day. The pairs of bicuspid valves at the base of the large vessels were formed by remodeling of the aoticopulmonary septum and endocardial cushions present at the base of the exit pathway on the 26th day. Between the 30th and 35th day, hyaline cartilage was formed at the base of the exit pathway near the bicuspid valves. In the first 20 days of heart development in P. unifilis, the main cardiac processes such as cardiac tube folding, trabeculation and septation of the atrial and ventricular compartments and the outflow tract occurred, making the morphology of the heart very similar to the heart of an adult individual. After this period the heart continued to develop and growth of intracardiac structures such as spongy myocardium and meat trabeculae, and the differentiation of mesenchymal tissue into hyaline cartilage at the base of the outflow tract were observed throughout cardiac development.