In the young embryo epiblast cells wander via the primitive streak between epi- and hypoblast and form the mesoderm layer out of which various structures arise. Cells, which are destined for cardiogenesis, take up a position that is cranial to the forming neural tube. Cardiogenesis takes place via a complex series of steps:
- Determination of mesoderm- and neural crest cells for heart formation
- Growth and differentiation processes to become cardiomyocytes
- Migration and transformation processes in order to form the heart
First signs of cardiac development
The cardiogenic plate is formed by a collection of mesoderm cells in the most anterior part of the embryo.
In the, please observe how the position of the pericardial cavity changes in relation to the cardiogenic plate due to the bending of the cranial end of the embryo.
Up to the early stage 9 (at roughly 25 - 27 days), this cardiac anlage is still located in the visceral part of the splanchnic mesoderm (splanchnopleura) above the umbilical vesicle. Out of this mainly develops the myocardium, which is responsible for the very early contractile ability (stages 9-10) of the embryonic heart. Through the rotation following the cranial folding of the embryo the pericardial cavity comes to lie ventrally from the cardiac anlage and, as things progress, will surround it.
The blood from the supplying vessels, the umbilical and omphalomesenteric veins, flows caudally over the inflow tract into the cardiac anlage and leaves it via the outflow tract and the aortic arches at the cranial end.
The cardiac tube itself consists of three layers: epicardium, myocardium and endocardium.
The outermost layer and boundary of the pericardial cavity is the epicardium. The myocardial mantle follows as the next inner layer. Together they form the myoepicardium. The considerable distance from the myocardial mantle to the endocardial tube is filled with cardiac jelly and the cardiac lumen is coated with endocardial cells.