Describe variations in fetal circulation and outline what each structure does in terms of hemodynamics of blood flow in the fetal heart. Pg. 147 ○ Blood leaves the placenta and enters the fetus through the umbilical vein. ○ The ductus venosus, the foramen ovale, and the ductus arteriosus allow the blood to bypass the fetal liver and lungs ○ Most blood flows through the ductus venosus directly into the fetal inferior vena cava, bypassing the liver ○ This blood then enters the right atrium, passes through the foramen ovale into the left atrium, and pours into the left ventricle into the aorta ■ Some blood from head and upper extremities returns by way of the superior vena cava, is emptied through into the right atrium and passes through the tricuspid valve into the right ventricle ■ This blood is pumped into the pulmonary artery, and a small amount passes to the lungs for nourishment only ○ The larger portion of blood passes from the pulmonary artery through the ductus arteriosus into the descending aorta, bypassing the lungs ○ Blood returns to the placenta through the two umbilical arteries, and the process is repeated ● What events occur to cause changes in fetal circulation to postnatal circulation? Describe how these events change flow in the heart of the newborn. Starts at pg. 470 ○ Neonate’s first breaths of air initiate a sequence of events that empties the airways of fluid, establishes volume and function of the newborn’s lungs, and causes fetal circulation to convert to neonatal circulation ○ Two most important things to help the change in cardiopulmonary adaptation: ■ When the baby’s chest pops out, the first breath happens when atmospheric pressure is exerted on the chest once it leaves the birth canal ● Empties the airways of fluid, establishes volume and function of the newborn’s lungs, and causes fetal circulation to convert to neonatal circulation ■ Clamping of the umbilical cord: placenta is excluded from circulation, cessation of blood flow through the umbilical vein facilitates collapse of the ductus venosus. Systemic pressure becomes greater than the pulmonary pressure, causing the blood to flow in the opposite direction, and the foramen ovale closes. The shunt across the ductus arteriosus reverses from L to R as pressure increases and causes it to constrict, leading to closure in the first days of life. ● Describe closure of these structures by time frame. What interventions are taken if the structures