The endocardial tubes are paired regions in the
embryo
An embryo ( ) is the initial stage of development for 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 sp ...
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 gastr ...
.
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 endocardium (: endocardia) is the innermost layer of tissue that lines the chambers of the heart. Its cells are embryologically and biologically similar to the endothelial cells that line blood vessels. The endocardium also provides prot ...
. The
myocardium
Cardiac muscle (also called heart muscle or myocardium) is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that constitutes the main tissue of the wall o ...
forms from mesoderm cells surrounding the heart tube, while the
epicardium develops from other cells, most likely from
neural crest
The neural crest is a ridge-like structure that is formed transiently between the epidermal ectoderm and neural plate during vertebrate development. Neural crest cells originate from this structure through the epithelial-mesenchymal transition, ...
cells.
References
External links
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{{Development of circulatory system
Embryology of cardiovascular system