The endocardial tubes are paired regions in the
embryo
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
that appear in its ventral pole by the middle of the third week of gestation and consist of precursor cells for the development of the
embryonic heart. The endocardial heart tubes derive from the
visceral mesoderm and initially are formed by a confluence of
angioblastic blood vessels on either side of the embryonic midline. The endocardial tubes have an intimate proximity to the foregut or pharyngeal
endoderm
Endoderm is the innermost of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gast ...
.
As folding of the embryo in the horizontal plane initiates in the 4th week of gestation, the endocardial tubes meet in the midline to form the
primitive heart tube, which will eventually develop into the histologically definitive
endocardium. The
myocardium
Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that ...
forms from mesoderm cells surrounding the heart tube, while the
epicardium develops from other cells, most likely from
neural crest cells.
References
External links
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{{Development of circulatory system
Embryology of cardiovascular system