Compare and contrast the fetal and adult hearts and their circulations.
The fetal and adult cardiovascular systems exhibit significant differences, reflecting different sources of respiratory and nutritional support. Most strikingly, the embryonic lungs are collapsed and nonfunctional, and the digestive tract has nothing to digest. The nutritional and respiratory needs of the fetus are provided by the diffusion across the placenta. Although the interatrial and interventricular septa develop early in fetal life, the interatrial partition remains functionally incomplete until birth. The foramen ovale, or interatrial opeing, is associated with a long flap that acts as a valve. Blood can flow freely from the right atrium to the left atrium, but any backflow will close the valve and isolate the two chambers from one another. Thus, blood entering the heart at the right atrium can bypass the pulmonary circuit. A second short-circuit exists between the pulmonary and aortic trunks. This connection, the ductus arteriosus, consists of a short, muscular vessel. With the lungs collapses, the capillaries are compressed and little blood flows through the lungs. During diastole, blood enteres the right atrium and flows into the right ventricle, but it also passes into the left atrium through the foramen ovale. Avout 25 percent of the blood arriving at the risght atrium bypasses the pulmonary circuit in thie way. In addition, more than 90 prcent of the blood leaving the right ventricle passes through the ducus arteriosus and enters the systemic circuit rather than continuing to the lungs.