Final answer:
Right to left shunting of blood in pulmonary blood vessels is typically seen in fetal circulation, where shunts like the ductus arteriosus bypass the nonfunctioning fetal lungs, directing blood to the systemic circuit for gas exchange. These shunts close after birth as the newborn begins to breathe and the lungs become functional.
Step-by-step explanation:
Right to Left Shunting in Pulmonary Blood Vessels
Right to left shunting of blood in pulmonary blood vessels is typically observed in fetal circulation. The fetal heart contains three major shunts to divert blood from the pulmonary circuit, which are nonfunctional at birth, to the systemic circuit. These are the ductus arteriosus, the foramen ovale, and the ductus venosus. In the fetus, the lungs are nonfunctional and filled with amniotic fluid, therefore, these shunts are critical for bypassing the nonfunctioning lungs and directing the blood to the placenta for gas exchange.
The ductus arteriosus is one of these shunts and it connects the pulmonary trunk to the aorta, allowing most of the blood from the right ventricle to bypass the nonfunctioning fetal lungs. After birth, as the baby takes its first breath, the resistance in the lungs decreases significantly, allowing the shunts to close and the blood to now flow to the now functional lungs for oxygenation. The ductus arteriosus constricts over time, and eventually becomes a ligament, ceasing its function as a shunt.