RESUMEN
Previous work showed that in the adult sturgeon an intrapericardial, nonmyocardial segment is interposed between the conus arteriosus of the heart and the ventral aorta. The present report illustrates the ontogeny of this intermediate segment in Acipenser naccarii. The sample studied consisted of 178 alevins between 1 and 24 days posthatching. They were examined using light and electron microscopy. Our observations indicate that the entire cardiac outflow tract displays a myocardial character during early development. Between the fourth and sixth days posthatching, the distal portion of the cardiac outflow tract undergoes a phenotypical transition, from a myocardial to a smooth muscle-like phenotype. The length of this region with regard to the whole outflow tract increases only moderately during subsequent developmental stages, becoming more and more cellularized. The cells soon organize into a pattern that resembles that of the arterial wall. Elastin appears at this site by the seventh day posthatching. Therefore, two distinct components, proximal and distal, can be recognized from the fourth day posthatching in the cardiac outflow tract of A. naccarii. The proximal component is the conus arteriosus, characterized by its myocardial nature and the presence of endocardial cushions. The distal component transforms into the intrapericardial, nonmyocardial segment mentioned above, which is unequivocally of cardiac origin. We propose to designate this segment the "bulbus arteriosus" because it is morphogenetically equivalent to the bulbus arteriosus of teleosts. The present findings, together with data from the literature, point to the possibility that cells from the cardiac neural crest are involved in the phenotypical transition that takes place at the distal portion of the cardiac outflow tract, resulting in the appearance of the bulbus arteriosus. Moreover, they suggest that the cardiac outflow tract came to be formed by a bulbus arteriosus and a conus arteriosus from an early period of the vertebrate evolutionary story. Finally, we hypothesize that the embryonic truncus of birds and mammals is homologous to the bulbus arteriosus of fish.
Asunto(s)
Evolución Biológica , Peces/embriología , Tronco Arterial/embriología , Animales , Peces/anatomía & histología , Microscopía Electrónica de Rastreo , Tronco Arterial/ultraestructuraRESUMEN
The developmental anatomy of the ventricular outlets and intrapericardial arterial trunks is a source of considerable confusion. First, major problems exist because of the multiple names and definitions used to describe this region of the heart as it develops. Second, there is no agreement on the boundaries of the described components, nor on the number of ridges or cushions to be found dividing the outflow tract, and the pattern of their fusion. Evidence is also lacking concerning the role of the fused cushions relative to that of the so-called aortopulmonary septum in separating the intrapericardial components of the great arterial trunks. In this review, we discuss the existing problems, as we see them, in the context of developmental and postnatal morphology. We concentrate, in particular, on the changes in the nature of the wall of the outflow tract, which is initially myocardial throughout its length. Key features that, thus far, do not seem to have received appropriate attention are the origin, and mode of separation, of the intrapericardial portions of the arterial trunks, and the formation of the walls of the aortic and pulmonary valvar sinuses. Also as yet undetermined is the formation of the free-standing muscular subpulmonary infundibulum, the mechanism of its separation from the aortic valvar sinuses, and its differentiation, if any, from the muscular ventricular outlet septum.
Asunto(s)
Corazón/embriología , Conducto Arterial/ultraestructura , Corazón/anatomía & histología , Tabiques Cardíacos/anatomía & histología , Tabiques Cardíacos/embriología , Humanos , Microscopía Electrónica de Rastreo , Morfogénesis/fisiología , Terminología como Asunto , Tronco Arterial/ultraestructuraRESUMEN
Sturgeons constitute a family of living "fossil" fish whose heart is related to that of other ancient fish and the elasmobranches. We have undertaken a systematic study of the structure of the sturgeon heart aimed at unraveling the relationship between the heart structure and the adaptive evolutionary changes. In a related paper, data were presented on the conus valves and the subendocardium. Here, the structure of the conus myocardium, the subepicardial tissue, and the conus-aorta transition were studied by conventional light, transmission, and scanning electron microscopy. In addition, actin localization by fluorescent phalloidin was used. The conus myocardium is organized into bundles whose spatial organization changes along the conus length. The variable orientation of the myocardial cell bundles may be effective in emptying the conus lumen during contraction and in preventing reflux of blood. Myocardial cell bundles are separated by loose connective tissue that contains collagen and elastin fibers, vessels, and extremely flat cells separating the cell bundles and enclosing blood vessels and collagen fibers. The ultrastructure of the myocardial cells was found to be very similar to that of other fish groups, suggesting that it is largely conservative. The subepicardium is characterized by the presence of nodular structures that contain lympho-hemopoietic (thymus-like) tissue in the young sturgeons and a large number of lymphocytes after the sturgeons reach sexual maturity. This tissue is likely implicated in the establishment and maintenance of the immune responses. The intrapericardial ventral aorta shows a middle layer of circumferentially oriented cells and internal and external layers with cells oriented longitudinally. Elastin fibers completely surround each smooth muscle cell, and the spaces between the different layers are occupied by randomly arranged collagen bundles. The intrapericardial segment of the ventral aorta is a true transitional segment whose structural characteristics are different from those of both the conus subendocardium and the rest of the ventral aorta.
Asunto(s)
Aorta/ultraestructura , Peces/anatomía & histología , Miocardio/ultraestructura , Pericardio/ultraestructura , Tronco Arterial/ultraestructura , Animales , Tejido Linfoide/ultraestructura , Microscopía ElectrónicaRESUMEN
BACKGROUND: Marsupials are born at an early stage of development after a short period of gestation. In this study the nature and timing of closure of the central cardiovascular shunts was investigated. METHODS: Light and scanning electron microscopy were used to determine changes in central cardiovascular shunts in eight marsupial species with gestation periods of between 12.5 and 36.5 days and birth weights ranging from 12.5 mg to 740 mg. Laboratory mice with a birth weight of about 1,000 mg and a gestation period of 21 days were included for comparison. RESULTS: Marsupials have a ductus arteriosus and an interatrial communication. The former closes rapidly after birth in the marsupial; however the interatrial communication is in the form of a fenestrated septum, which closes as a result of tissue proliferation over a period of days after birth. An additional central shunt, an interventricular foramen, was found to persist in three species for a short time after birth. In one species, the eastern native cat, Dasyurus viverrinus, which has a gestation period of about 19 days and low birth weight of about 12.5 mg, in addition to the two common shunts there was a large interventricular communication and septation of the outflow tract was incomplete. CONCLUSION: In adapting from intra-uterine life, it seems that marsupials have adopted different, but equally effective strategies, with regard to the circulatory system.
Asunto(s)
Corazón Fetal/anatomía & histología , Corazón/anatomía & histología , Marsupiales/anatomía & histología , Marsupiales/embriología , Animales , Animales Recién Nacidos , Aorta/anatomía & histología , Aorta/ultraestructura , Conducto Arterial/anatomía & histología , Conducto Arterial/embriología , Conducto Arterial/ultraestructura , Femenino , Corazón Fetal/embriología , Corazón Fetal/ultraestructura , Corazón/embriología , Corazón/crecimiento & desarrollo , Atrios Cardíacos/anatomía & histología , Atrios Cardíacos/ultraestructura , Tabiques Cardíacos/anatomía & histología , Tabiques Cardíacos/embriología , Tabiques Cardíacos/ultraestructura , Ventrículos Cardíacos/anatomía & histología , Ventrículos Cardíacos/embriología , Ventrículos Cardíacos/ultraestructura , Masculino , Ratones , Embarazo , Arteria Pulmonar/anatomía & histología , Tronco Arterial/anatomía & histología , Tronco Arterial/embriología , Tronco Arterial/ultraestructuraRESUMEN
The presence of cell death in the walls of the truncus and conus of the developing chick heart was investigated by a variety of light and electron microscopic techniques. Necrotic areas were observed in the myocardial layer of the truncus and conus and within the mesenchymal cells of the truncoconal ridges and aortopulmonary septum. These necrotic zones appeared first at Stage 25-26 and reached their maximum extent at Stages 29-32 undergoing later progressive disappearance. The morphological changes of the degenerating cells detectable under both transmission and scanning electron microscopy are also reported. The possible role of cell death in the morphogenesis of the truncus and conus is discussed.