Final answer:
The ductus arteriosus typically closes within the first 1-2 days after birth. This process occurs as the newborn's lungs expand and oxygen levels rise, causing the vessel to constrict. If it remains open, it is known as a patent ductus arteriosus, which requires medical intervention.
Step-by-step explanation:
The ductus arteriosus usually closes within the first 1-2 days of life, which corresponds to option (a). This blood vessel plays a crucial role in fetal circulation by shunting blood away from the lungs and into the aorta. After birth, the first breath a newborn takes causes a drop in pressure within the lungs and pulmonary vessels to expand, which increases the oxygen levels and prompts the smooth muscles in the wall of the ductus arteriosus to constrict, leading to its closure. In some cases, the ductus arteriosus may not close as it should, resulting in a condition known as patent ductus arteriosus (PDA). PDA can lead to significant health issues if not treated with interventions such as surgical closure, manual closure using devices, or medication to encourage natural closure.