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MCAT Question A Day - 8/8/14 - Answer!

In the congenital heart defect known as patent ductus arteriosus, the ductus arteriosus, which connects the aorta and the pulmonary arteries during fetal development, fails to close at birth. This will likely lead to all of the following EXCEPT:

A.  equal, or increased, oxygen concentration in the blood that reaches the systemic tissues.
B.  increased oxygen concentration in the blood that reaches the lungs.
C.  increased work load imposed on the left ventricle.
D.  increased work load imposed on the right ventricle.

A is correct. Less oxygenated blood will reach the systemic system because some oxygenated blood will be shunted from the aorta to the lower pressure pulmonary arteries. The pulmonary circulation will carry blood that is more oxygenated than normal. since highly oxygenated blood from the aorta is mixing with deoxygenated blood on its way to the lungs. The entire heart will pump harder in order to compensate by with more blood to the tissues.

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