Heart Wall - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 271

blastocyst

inner cell mass trophoblast

hypoblast epiblast cytotrophoblast

syncythiotrophoblast

embryonic part of placenta

ectoderm

endoderm heart

mesoderm

amnionic ectoderm

hemangioblast

angioblast blood cell lineages

extraembryonic endoderm

endothelial cell

Fig. 6.1 The cardiovascular organs develop from the mesoderm. The blood vessels form indepen-
dently from the heart. The heart is the first functional body's organ.

After heart looping, the cardiac jelly that overlies the future atrioventricular
canal and outflow tract expands into cardiac cushions. The formation of the cardiac
cushions is characterized by endothelial-mesenchymal transformation of a subset
of endothelial cells. During heart valve formation, a subset of endothelial cells that
corresponds to future valve sites delaminates, differentiates, and migrates into the
cardiac jelly [ 485 ].

6.1.1 First and Second Heart Fields

Soon after gastrulation, heart formation starts in the precardiac anterior mesoderm
(first and second heart fields) under the coordinated action of inductive and
repressive signals from neighboring endoderm and ectoderm (Table 6.2 ). On the
other hand, posterior mesoderm is a blood-forming region.
Mesodermal cells that differentiate into cardiac cells during cardiogenesis
segregate into 2 distinct populations of cardiac progenitors: the primary heart and