Biomedical Engineering Reference
In-Depth Information
LV
LV
SV
BC
BC
LA
CC
CC
TA
TA
RA
AS
AS
FIGURE 4.5
Mid-phase development of the fetal heart showing the developed atria
and left ventricle. AS = aortic sac, BC = bulbus cordis, CC = conus cordis,
LA = left atrium, LV = left ventricle, RA = right atrium, SV = sinus venosus,
TA = truncus arteriosus. (Modified from McNulty, J. and Wellman, C., Heart
Development. Original image at http://www.meddean.luc)
right auricle, whereas the left sinus horn forms the veins of the left ventricle;
at the same time, the left atrium develops and pulmonary veins start to grow.
At the end of the seventh week, the human heart has reached its final
stage of development. Because the fetus does not use its lungs, most of the
blood is diverted to the systemic circulation, which is accomplished by a right
to left shunting of blood between the two atria. At this stage, the bulbous
cordis forms the left ventricle, whereas the proximal bulbous cordis forms
the right ventricle, finally, the ventricles separate completely and the heart
is almost fully developed. The final morphological change to the heart is the
partitioning of the outflow tract. At this stage, the truncus arteriosus morphs
into the aorta and the conus cordis becomes the pulmonary trunk. This is
done by the development of a septum, which forms in the outflow tract, and
the emergence of the two major blood vessels.
In the fetal heart's developmental stages, the heart resembles several other
animal hearts. The initial tubelike heart is reminiscent of a fish heart, whereas
the two-chambered heart resembles a frog heart. In the third phase, the three-
chambered structure is similar to that of a snake or turtle. Only the final
four-chambered heart structure uniquely distinguishes the human heart. The
heart's rate of pumping oxygen-rich blood is fastest in infancy, that is, about
120 beats/min. As the child grows, the heart rate slows. A 7-year-old child's
Search WWH ::
Custom Search