Structure and Function: The Heart Before and After Birth

In the fetus, only a little blood passes through the lungs because the task of adding oxygen to the blood and filtering out waste gases is done by the mother’s placenta. Before birth, most blood bypasses the lungs by flowing through two openings in the heart. With a baby’s first breath the lungs expand, triggering changes so that all blood flows through the lungs to be oxygenated.

Changes in the heart’s circulation

An opening in the fetal heart, the foramen ovale, diverts blood from the right atrium (chamber) to the left, and a duct, the ductus arteriosus, diverts blood into the aorta. The openings close soon after birth.

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

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