Final answer:
The patency of the ductus arteriosus during fetal life is maintained by low oxygen tension and high prostaglandins, elements crucial for fetal circulation.
Step-by-step explanation:
The two factors that sustain the patency (opening) of the ductus arteriosus during fetal life are B. Low oxygen tension and high prostaglandins. The ductus arteriosus is a critical component of fetal circulation, forming a shunt that allows blood to bypass the non-functioning fetal lungs and proceed directly from the pulmonary artery to the aorta. This shunt remains open primarily due to the low oxygen tension found in fetal blood and the high levels of prostaglandins, especially prostaglandin E2. Together, these conditions prevent the constriction of the ductus arteriosus that would normally occur upon exposure to higher oxygen levels after birth. Nonsteroidal anti-inflammatory drugs (NSAIDs) can block the synthesis of prostaglandins, which can encourage the closure of the ductus arteriosus.