Developmental changes in the myocardial architecture of the chick

Abstract

Background: Numerous studies describing myocardial architecture have been performed on the adult heart but considerably fewer have been made during embryonic or fetal development. To serve as a basis for interspecies comparison of ventricular morphology, and as a reference for studying the effects of experimental perturbations, we examined the development of chick throughout the entire incubation period.Methods: Chick hearts from stage 14 (day 2) to stage 46 (day 21) were perfusion-fixed, and sectioned in transverse, frontal and sagittal planes. The ventricular myocardial architecture was examined and photographed in the scanning electron microscope.Results: At embryonic stage 16 and earlier, the smooth-walled heart loop had an outer myocardial mantle, cardiac jelly, and endocardium. From stage 18, there was an outer compact and inner trabeculated myocardium. Trabeculated myocardium could be subdivided into the outer (basal) portion adjacent to the compact layer and the central (luminal) part. The outer basal layer could be distinguished from the inner luminal by shorter and finer trabeculae with small, round intertrabecular spaces. From stage 24, the patterns of trabeculae and intertrabecular spaces were ventriclespecific. Between stages 24 to 31, abundant trabeculations were present throughout both ventricular cavities. The trabeculae were initially radially arranged, but later adopted a spiral course, which persisted in a simplified form into adulthood.Conclusions: The ventricular myocardium undergoes distinctive morphogenesis, characterized by changes in trabecular patterning and orientation. We speculate that the embryonic trabecular architecture reflects the directions of the main stresses. Unlike fetal and adult hearts, which rely mostly on the compact myocardial layer, the trabeculae play a crucial role in the contractile function of the embryonic heart. Anat. Rec. 248:421-432, 1997. r 1997 Wiley-Liss, Inc.

Valvulogenesis: the moving target

“…The mural/lateral cushions form the mural leaflets. The right mural cushion of the chick becomes muscularized (like the conus region of the OT) forming a large muscular flap, while the right AV septal leaflet is only a 'micro-leaflet' (Sedmera et al 1997). The right AV valves in the mouse, however, are similar in structure and morphogenesis to the tricuspid valve of the human (Wessels & Sedmera 2003).…”

Mechanisms of heart valve development and disease

“…A small number of cells in AV and SL valves are not derived from endothelial or neural crest cells. In avians, but not mammals, one leaflet of the tricuspid valve is highly muscularized, suggesting some contribution from myocardial cells (Lincoln et al, 2004;Sedmera et al, 1997). In line with this, a lineage tracing study using a cardiomyocyte-specific Tnnt2Cre in mice revealed that a small number of myocardial Isl1 + cells also contribute to the SL valves.…”

Quantifying blood flow dynamics during cardiac development: demystifying computational methods

“…Meanwhile, by the end of week 4 in human gestation, the primitive ventricle starts developing trabecular structures, which resemble a sponge-like porous structure [25,26]. These trabecular structures aid ventricular contraction, and their architecture is influenced by blood flow conditions [26 -29].…”