Fetal Transitions (Segar)

Question 1

the primary functions of this organ are respiration and pathway exchange of nutrients and waste products between mother and fetus

Answer 1

placenta

Question 2

what fetal vessel carries the most concentrated oxygenated blood, and where does this blood flow?

Answer 2

the umbilical vein; oxygen rich blood in this vein combines with poorly oxygenated blood from the fetal tissues and passes preferentially across ductus venosus and foramen ovale to the left side of the heart, where it passes thru vessels that lead straight to the brain (and the general circulation)

Question 3

why does nearly 45% of cardiac output flow to the placenta, while a much smaller percentage travels to the lungs?

Answer 3

because of vascular resistance and pressure gradients. while the lungs have high vascular resistance, the placenta has much lower vascular resistance so bood preferentially flows here.

Question 4

where does poorly oxygenated blood from the fetal brain flow?

Answer 4

to the superior vena cava and into the right ventricle, where it is pumped via ductus arteriosis to the dorsal aorta

Question 5

what are the 3 shunts that allow oxygenated blood to bypass the right ventricle and pulmonary circulation to deliver blood directly to the left ventricle, aorta and brain?

Answer 5

ductus venosus
ductus arteriosis
foramen ovale

Question 6

what are the 2 routes of blood flowing through ductus venosus?

Answer 6

the ductus venosus carries mixed blood from the umbilical vein and the inferior vena cava to the right side of the heart, where it can flow 2 ways:

1. it can be pumped into the pulmonary artery for delivery to the lungs and ductus arteriosis
2. it can flow across foramen ovale directly to the left side of the heart where it is pumped to the brain and the aorta

Question 7

what percentage of the right ventricle output is diverted from the lungs thru the ductus arteriosis, where it flows into the aorta and on to the fetal trunk and limbs?

Answer 7

85%

Question 8

Which of the following statements regarding fetal circulation is INCORRECT?

A. ventricles of the fetal heart work in parallel
B. fetal caridac output per unit weight is 3 times higher than that of an adult at rest
C. as the ductus arteriosis closes, the left ventricle becomes responsible for increasing cardiac output to the body
D. In the neonate, the systemic vascular resistance increases exerting mechanical load onto the left ventricle, thereby causing hypertrophy
E. the left ventricle is the dominant ventricle in utero, because it contributes the most to general circulation

Answer 8

E. The RV contributes about 65% of the total cardiac output in utero.

Question 9

Which of these statements regarding fetal respiration is INCORRECT?

A. Most of the right ventricular ouptut is diverted away from the lungs into ductus arteriosis
B. The pulmonary vasculature is exposed to a low oxygen tension environment that promotes high intrinsic myogenic tone and high vasocontractility
C. Slight overexpansion of potential lung spaces increases pulmonary vascular resistance (PVR)
D. Lung fluid and Na+ are actively secreted from pulmonary epithelial cells
E. Maternal hyperoxygenation increases pulmonary blood flow (PBF) and decreases PVR late in gestation

Answer 9

D. Epithelial cells in the fetal lung actively secrete Cl- rich fluid, not Na+. The rate an volume secreted is calibrated to maintain the fetal lung volume at functional residual capacity (FRC) or greater, and is the major determinant of lung growth.

Question 10

Which of these statements regarding fetal renal function is CORRECT?

A. Most of the excretory function in a fetus is handled by the placenta.
B. Fetal kidneys are in a state of low renal blood flow with high K+ secretion
C. Fetal kidneys display finely tuned autoregulation that keeps GFR relatively stable with fluctuations in blood pressure.
D. Fetuses have a high urine flow rate that is hyperosmotic
E. Fetal GFR indirectly correlates with kidney weight and tends to decrease as the fetus grows

Answer 10

A.

Fetal kidneys are in a state of low renal blood flow (only 5% of total cardiac output) and high Na+ secretion, as well as a state of high urine flow that is hypoosmotic. The fetal GFR is directly proportionate to the weight of the kidneys and increases as the kidneys grow.

Question 11

Why does total body water decline in newborns, though intracellular water continues to increase?

Answer 11

Because the baby is excreting extracellular water from the lungs

Question 12

Which of these statements regarding fetal blood is CORRECT?

A. Fetoplacental blood volume at term is ~125 ml/kg of fetus, with the placenta containing about 65% of the volume
B. Fetal erythrocytes contain mostly Hgb A, which has a higher affinity for O2 than Hgb F
C. The oxygen saturation curve for fetal hemoglobin is left-shifted when compared to adults
D. Hgb A binds 2,3 DPG more tightly than Hgb F, which raises the affinity of Hgb for O2
E. Fetal hemoglobin’s affinity for oxygen is substantially greater than that of adult hemoglobin, which is explained by its increased interaction with 2,3 DPG

Answer 12

C. The fetal oxygen saturation curve is left-shifted compared to adults because its main Hgb (F) has a higher affinity for oxygen and lower affinity for 2,3 DPG, which would decrease hegmoglobin’s affinity for oxygen.

D is incorrect because although Hgb A does bind more tightly to 2,3 DPG, this actually lowers the affinity of Hgb for O2.

A is incorrect because the majority of the fetoplacental blood volume is in the fetus. Only about 35% is in the placenta right after the cord is clamped.

Question 13

What hormones are secreted during labor?

Answer 13

stress hormones (chatecolamines, cortisol) 
endorphins
oxytocin

Question 14

What is the major mechanism by which the fetal lungs clear fluid in preparation for birth?

Answer 14

changes in ENaC channels cause the cells to absorb Na+ to deal with all the extra fluid that was secreted during lung development

Question 15

What 2 circulatory changes happen when the placenta is lost?

Answer 15

increased SVR

decreased PVR –> increased PBF

Question 16

Which of these is NOT a mechanism involved in decreasing fetal pulmonary vascular resistance?

A. mechanical distension
B. oxygenation
C. shear stress
D. release of vasoactive agents
E. decreased SVR

Answer 16

E

Question 17

True or false: extra alveolar vessels have high resistance at low lung volumes, and are generally contributing most to the total PVR in ventilated newborns.

Answer 17

False. In ventilated newborns, it is alveolar vessels compressed by an overexpanded lung that contribute most to the total PVR. Extra alveolar vessels have high resistance at low lung volumes and are the greatest contributers to PVR in conditions like RDS, where lung volume is greatly decreased.

Question 18

a collection of phospholipoproteins lining the alveoli that lower surface tension and increase pulmonary compliance

Answer 18

surfactant

Question 19

cells that make up 10% of the lung parenchyma and produce surfactant

Answer 19

type II alveolar cells

Question 20

this is the predominant phospholipid in surfactant, making up about 80% of the total, whose production is enhanced by cortisol and exogenous glucocorticoids and delayed in gestational diabetes

Answer 20

phosphotidylcholine (lecithin)

Question 21

name 2 important changes in renal hemodynamics at birth that help a fetus transition to life outside of the uterus.

Answer 21

1. increase in renal blood flow
2. increase in Na+ reabsorption
3. increase GFR

Question 22

what percentage of newborns require some assistance to begin breathing at birth? What percent require extensive resuscitation measures?

Answer 22

10% require assistance at birth; <1% require extensive resuscitation efforts

Question 23

why is resuscitation with 100% oxygen toxic to newborns?

Answer 23

can cause lung, eye and brain damage because of excessive production of reactive oxygen species

Question 24

this condition is more common in c-section with no labor and results in the retention of fetal lung fluid (ie, “wet lung”)

Answer 24

transient tachypnea of the newborn (TTN)

Question 25

condition that may occur in the newborn when PVR does not decrease as it should (ie, infection, pneumonia, meconium aspiration, etc), and leads to a cycle of hypoxia, acidosis, and continued right to left shunting

Answer 25

persistent pulmonary hypertension (PPH)