G7
An overview of blood flow through the embryo of
oxygenated blood. Note the umbilical artery and
veins anastomose within the chorion of the
placenta, there is no direct connection of maternal
and fetal blood.
Maternal Blood
umbilical vein
liver
anastomosis
ductus venosus
sinus venosus
atria ventricles
truncus arteriosus
aortic sac
aortic arches
dorsal aorta
pair of umbilical arteries
Maternal Blood
|
|
B1: Large veins lateral to dorsal aortae. These are the superior or anterior cardinal veins. Their function is to drain the head region. |
|
D6: Large veins lateral to dorsal aortae. These are the inferior or posterior cardinal veins. Their function is to drain the lower part of the embryo. |
|
Follow alternately, the course of the superior cardinal veins caudally, and the course of the inferior cardinal veins cranially until they emerge about Dl -C5 into the common cardinal veins. |
|
|
|
|
|
C7: Left common cardinal entering sinus venosus. |
C5: Right common cardinal entering sinus venosus. |
Next page for embryonic blood flow: Human Embryo sections (Stage 22)
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In human embryos the heart begins to beat at about 22-23 days, with blood flow beginning in the 4th week.
The heart is therefore one of the earliest differentiating and functioning organs. (More? see recent review article). Most texts will separate heart development from vascular development in order to simplify their descriptions of cardiovascular development, though the 2 are functionally and embryologically connected.
The heart develops from cardiogenic mesoderm that originally lies above the cranial end of the developing neural tube. Enlargement of the cranial neural fold brings this region ventrally to its correct anatomical position. The original paired cardiac tubes fuse, with the "ventricular" primordia initially lying above the "atria". Growth of the cardiac tube flexes it into an "S-shape" tube, rotating the "ventricles" downward and pushing the "atria" upward. This is then followed by septation, a complex process which converts this simple tube into a four chambered heart. A key part of this process is the separation of cardiac outflow (truncus arteriosus) into a separate pulmonary and aortic arch outflow. During embryonic development there is extensive remodelling of the initially r/l symetrical cardiovascular system and a contribution from the neural crest to some vessels.
Please email Dr Mark Hill if you wish to make a comment about this current project.
