In full-term neonates, the ductus aeriosus closure is due to
**Core Concept**
The ductus arteriosus is a vital fetal shunt that connects the pulmonary artery to the aortic arch, allowing blood to bypass the lungs and flow directly to the systemic circulation. Its closure is a critical physiological event that occurs shortly after birth.
**Why the Correct Answer is Right**
In full-term neonates, the ductus arteriosus closure is primarily due to the increase in oxygen tension in the blood. As the neonate takes its first breath, the oxygen levels in the blood rise, causing a significant increase in the production of prostaglandin I2 (PGI2). However, this is not the primary mechanism of ductus arteriosus closure. Instead, the increase in oxygen tension inhibits the production of prostaglandin E2 (PGE2) and increases the production of thromboxane A2 (TXA2). PGE2 is a potent vasodilator that keeps the ductus arteriosus open, while TXA2 is a potent vasoconstrictor that promotes ductal closure. The increased levels of TXA2 and decreased levels of PGE2 lead to ductal constriction and eventual closure.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the closure of the ductus arteriosus.
**Option B:** While prostaglandin E2 (PGE2) plays a role in maintaining the patency of the ductus arteriosus, its decrease is not the primary mechanism of ductal closure.
**Option C:** This option is not directly related to the closure of the ductus arteriosus.
**Clinical Pearl / High-Yield Fact**
The ductus arteriosus typically closes within 10-15 hours of birth in full-term neonates, but this timing can be influenced by various factors, including the level of oxygenation and the presence of certain medical conditions.
**Correct Answer: D. Increased production of thromboxane A2 (TXA2) and decreased production of prostaglandin E2 (PGE2).**