VASCULAR: FETAL CIRCULATION

Question 1

When does fetal heart begin to beat?

Answer 1

week 4

Question 2

What does placental fulfill the role of?

Answer 2

Lungs
gastrointestinal tract
liver (waste removal)
kidneys (waste removal and electrolyte balance)

Question 3

What are the 4 circulatory shunts

Answer 3

Placenta
ductus venosus
foramen ovale
ductus arteriosus

Question 4

Where does fetal and maternal blood mix

Answer 4

placenta - across the placental membrane

Question 5

What is the role of the ductus venosus

Answer 5

connects umbilical vein bringing blood from the placenta to the IVC

Question 6

What is the role of the foramen ovale

Answer 6

connects RA to LA like a shunt

allows fetal ventricles to pump in parallel

Question 7

What is the role of the ductus arteriosus

Answer 7

connects pulmonary artery to aorta

flow to pulmonary vessels is low due to hypoxic vasoconstriction

Question 8

How does fetal hemoglobin (HbF) differ from regular hemoglobin

Answer 8

higher O2 affinity

Question 9

How much of the combined cardiac output does the placenta receive? via what artery

Answer 9

50%

umbilical arteries

Question 10

trophoblast

Answer 10

Trophoblast: thin layer of cells that separate maternal and fetal circulation

Question 11

Describe the cardiopulmonary adjustments at birth

Answer 11

1. Infant takes first breath (requires huge inspiratory pressure)
2. Umbilical arteries and veins vasoconstrict due to first breath
3. Ductus venosus closes (< 3 hours)
4. Increased pressure in LA (and ↓ RA pressure) causes foramen ovale to close
5. Direction of flow in ductus arteriosus changes (immediately)

Question 12

What causes a baby to take its first breath

Answer 12

temporary hypoxia and hypercapnia and decreased temperature

Question 13

What triggers the umbilical arteries and veins vasoconstriction

Answer 13

• stretch during delivery
• sudden in crease in PaO2

Question 14

why does the ductus venosus close

Answer 14

cessation of flow through umbilical vein

Question 15

Describe a patent foramen ovale defect

Answer 15

Foramen ovale doesn’t close completely; “Hole in the heart”; occurs in ~20% of the population

Question 16

What are the consequences of a patent foramen ovale

Answer 16

Consequences:
- coughing, sneezing, straining can cause mixing and briefly decrease oxygen saturation
- permits clots that are normally removed in lungs to enter systemic circulation → increased risk stroke
- if severe, can cause increased pressures in right heart → shortness of breath, arrhythmia

Question 17

What is a patent ductus arteriosus? Who is more likely to have it?

Answer 17

extra blood vessel found in babies before birth and just after birth

usually closes eventually more common in premature babies, girls, hypoxia

Question 18

What is the consequence of patent ductus arteriosus

Answer 18

increased pressure in pulmonary circulation

Question 19

What is the treatment of patent ductus arteriosus

Answer 19

Indomethacin - blocks prostaglandin synthesis