Advanced - Heart Fields
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The heart primordium arises predominantly from splanchnic mesoderm in the cardiogenic region of the trilaminar embryo. Blastodermal cardiogenic precursors have been located in the rostral epiblast either side of the primitive streak in multiple animal models. Cardiogenic precursors have also been located in the rostral primitive streak. After ingression through the primitive streak, mesodermal cells rapidly move laterally and cranially until they reach the cardiogenic fields. Studies in chicks define these cardiogenic areas as distinct bilateral fields in the cranial portion of the embryonic disc. However, studies using mice models repeatedly describe the cardiogenic area as a continuous horseshoe. The most likely explanation for this discrepancy is in the timing of mesodermal migration which occurs rapidly in mice such that distinct cardiogenic fields are indistinguishable. Thus the cardiogenic region can be thought of as bilateral fields that later merge cranially so that independent fields are no longer identifiable.
The following animation shows the location of cardiogenic precursors in the epiblast that proceed to migrate through the primitive streak to form the mesodermal cardiogenic fields. The cells in the primitive streak are organised rostrocaudally, while after migration to form the cardiogenic fields they are organised mediolaterally. The most cranial end of the cardiogenic field becomes the ventral midline of the later heart tube which becomes the right border during looping. (Click image to play on current page or Play video on new page)
<html5media height="720" width="550">File:Heart fields 001.mp4</html5media>
Anterior and Secondary Heart Fields
The anterior heart field has been described and defined differently within different species and by different labs as:
- In mice - the splanchnic mesoderm and mesodermal core of the pharyngeal arches which migrates to form the distal portion of the right ventricle and conus
- In chicks - the mesenchyme surrounding the outflow tract and contributing to the addition of conotruncal myocardium.
The secondary heart field has been described as pharyngeal mesenchyme that contributes myocardium and smooth muscle to the arterial pole.
The cells from this field have been located medial to the originally defined cardiogenic fields. However, the existence of multiple heart fields has not been proven, as these cells may form a complex part of the original cardiogenic fields and there may be several cell populations in the cardiogenic fields with complex determination and development.
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