Septation and separation within the outflow tract of the developing heart

Abstract

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.

Mechanisms of tissue fusion during development

“…Thus, of the three organs highlighted in this review, we know the least about what drives fusion in the heart. By E9.5 in the mouse, the unseptated tubular heart has already looped to the right (Webb et al, 2003). Between E9.5 and E10.5, two sets of endocardial cushions (ECs) begin to grow towards each other across the open internal space of the tube (Fig.…”

Apoptosis in the developing mouse heart

“…It is a tubular structure lined by cardiac muscle on the outside surface of the heart and a single sheet of epithelial cells, the endocardial epithelium, on the luminal side, with a layer of connective tissue in between termed "cardiac jelly" that is populated at later stages by mesenchymal cells. In avian and mammalian species with four-chambered hearts, this simple tubular structure undergoes complex morphogenesis during the last stages of cardiac septation (reviewed in Webb et al, 2003). The events include septation of the OFT lumen, shortening, realignment of the roots of the pulmonary and aortic vessels, and differentiation of the valves of the aortic and pulmonary artery.…”

Functional Disruption of the Netrin-1 Guidance Gue Leads to Disruption in Mammary Gland Development and Increased Tumor Incidence

“…Take, for example, the formation of the outflow tract which is disrupted in Sema3c, Nrpl[end°-] , Plxndl, and Vegf 165 single homozygous null animals and in Nrpl [sma] ;Nrp2 double null homozygotes. By a number of developmental events that are still poorly understood, this bilayered tubular structure is transformed into two spiraling tubes that are capped by valves (Webb et al, 2003).…”