28. Before birth in the mammalian fetal heart, the ductus arteriosus joins the pulmonary artery andthe aorta and the foramen ovale joins the two atria. Why do these modifications disappear hoursafter birth?A. The fetal heart is not yet strong enough to sustain a normal circulation.B. Development of the beating heart is one of the last steps in the maturation of the fetus.C. The pulmonary circulation is bypassed because the fetus is not breathing in the womb.D. Maternal hormones suppress the competing infant circulation via the placenta.E. They act as safety valves to relieve the pressure of the viscous amniotic fluid on the fetal heart.
Question
- Before birth in the mammalian fetal heart, the ductus arteriosus joins the pulmonary artery andthe aorta and the foramen ovale joins the two atria. Why do these modifications disappear hoursafter birth?A. The fetal heart is not yet strong enough to sustain a normal circulation.B. Development of the beating heart is one of the last steps in the maturation of the fetus.C. The pulmonary circulation is bypassed because the fetus is not breathing in the womb.D. Maternal hormones suppress the competing infant circulation via the placenta.E. They act as safety valves to relieve the pressure of the viscous amniotic fluid on the fetal heart.
Solution
The modifications in the fetal heart, specifically the ductus arteriosus and the foramen ovale, disappear after birth due to the change in the circulatory needs of the newborn.
In the womb, the fetus is not breathing and therefore does not need to send blood to the lungs to be oxygenated. The ductus arteriosus allows blood that would go to the lungs to be redirected to the aorta, and the foramen ovale allows blood to pass from the right atrium to the left atrium, bypassing the lungs.
After birth, the baby begins to breathe and the lungs fill with air. This causes a change in pressure that closes the foramen ovale, and within a few hours or days, the ductus arteriosus also closes. This allows the blood to flow to the lungs to be oxygenated and then distributed to the rest of the body.
So, the correct answer is C. The pulmonary circulation is bypassed because the fetus is not breathing in the womb.
Similar Questions
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