Walsh: Perinatal and Pediatric Respiratory Care, 3rd Edition

Chapter 02: Fetal Gas Exchange and Circulation

Answers to Assessment Questions and Clinical Scenarios

1.	B
Rationale: Angiogenic clusters are the primitive vascular pools and heart development is complete after the valves form. See Table 2-1.
2.	B
Rationale: Recognizable structures: bulbus cordis, ventricular bulge, atrial bulge, sinus venosus, and truncus arteriosus.
3.	B
Rationale: See Figure 2-6, the diagram of fetal circulation.
4.	C
Rationale: See Figure 2-6, the diagram of fetal circulation.
5.	B
Rationale: See Figure 2-6, the diagram of fetal circulation.
6.	C
Rationale: Clamping the umbilical vessels removes the low-pressure system of the placenta from the fetal circulation. During the first breath, several factors drastically improve pulmonary blood flow and reduce the pulmonary vascular resistance (PVR). Inflating the lungs initiates gas exchange, which increases and directly dilates pulmonary arterioles. Rising arterial oxygen pressure (Pao2) also stimulates the release of endogenous pulmonary vasodilating factors. Stretching of the pulmonary units also physically stretches open vascular units as well as stimulates the release of other vasodilating compounds. Besides vasodilation, lung inflation results in the inhibition of vasoconstricting agents produced by the lung to facilitate fetal circulation.
Once the PVR decreases, the cord is clamped, preventing flow to the placenta; pressures in the right side of the heart decrease and pressures in the left side increase. 
7.	A
Rationale: In the right atrium (RA) most of the blood flow from the inferior vena cava (IVC) crosses through the foramen ovale into the left atrium (LA). The foramen ovale acts as a one-way valve.
8.	E
Rationale: Blood from the pulmonary veins empties into the LA and then flows into the left ventricle (LV), out the aortic valve, and into the ascending aorta, where it supplies blood with the highest oxygen content to the head, right arm, and coronary circulation.
9.	C
Rationale: Clamping the cord prevents flow to the placenta, causing pressures on the left (systemic) side to increase.
10.	A
Rationale: Anatomic closure of the ductus arteriosus begins in the last trimester as endothelial tissue begins to proliferate into the lumen of the ductus, forming bulges known as intimal mounds.