Only $35.99/year

Neonatal Review (Week 9 CCT Acadian)

Terms in this set (7)

Your Answer:
The blood returning to right atrium from the placenta passes through the foremen ovals to the left atrium. It mixes with the small pulmonary return and is pumped by the left ventricle and aorta to the coronary arteries and the brain. Of the ejected RV output, most flows to the aorta via the ductus arteriosus, mixing with the LV output. Blood carried by the descending aorta perfuses organs and the lower body umbilical arteries lead to the placenta for oxygenation. Clamping the cord removes the low-resistance placenta, creating a sudden rise in systemic vascular resistance and increasing pulmonary blood flow, and resulting in physiologic closure of the fetal shunts (the foremen ovals and the ductus areterriosus). Increased pulmonary venous return to the LA raises LA pressure over RA pressure, closing the foremen ovale. With this, a decrease or reversal of flow through the ductus arteriosus takes place. An anatomic closure is as early as 6hrs after birth, but full closure can take up to 6 weeks.

Oxygenated blood from the placenta reached the fetus through the umbilical vein. It enters the fetal liver at the ductus venosus and enters the inferior vena cava, mixing with some deoxygenated blood from the fetal systemic circulation. The mixed blood enters the RA, then RV, then PA, where some perfuses the immature fetal lungs and some enters the ductus arteriosus, entering the aorta. Some of the oxygen rich blood from the RA also passes though the foramen ovale, entering the LA and mixing with now deoxygenated blood from the fetal lungs. This mixed blood enters the LV then aorta, then enters the systemic circulation. Some mixed blood is siphoned off into the umbilical arteries from the iliac arteries and returned to the placenta.

At transition, the lungs expand, pulmonary pressure decreases, the foramen ovale closes with rising LA pressure, the ductus arteriosus closes with rising aortic pressure, and placental circulation ceases.