Fetal circulation includes which of the following unique shunts that DIRECTLY bypasses the pulmonary circulation?

• A Ductus venosus — connects umbilical vein to inferior vena cava
• B Foramen ovale — connects right atrium to left atrium
• C Umbilical arteries — carry oxygenated blood from placenta to fetus
• D Ductus arteriosus — connects pulmonary artery to descending aorta, bypassing the lungs ✓

Explanation

The ductus arteriosus connects the main pulmonary artery to the descending aorta, shunting ~90% of right ventricular output away from the high-resistance pulmonary vascular bed and directly into the systemic circulation. Patency is maintained by high PGE2 and low PaO2. At birth, oxygen triggers vasoconstriction of the ductus arteriosus muscle wall, and it functionally closes within hours. The foramen ovale bypasses pulmonary circulation at the atrial level; the ductus venosus bypasses the liver but does not directly bypass the lungs.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.