Foetal Circulation

Question 1

What blood vessels supply the placenta?

Answer 1

Maternal uterine veins & arteries

Question 2

What is the role of the foetal umbilical arteries?

Answer 2

Delivers deoxygenated blood to the placenta

Question 3

How does the foetus receive blood?

Answer 3

Receives oxygenated blood from the umbilical vein

Question 4

How does foetal blood bypass the liver?

Answer 4

Via the ductus venosus

Question 5

Why does blood bypass the foetal liver?

Answer 5

Delivers more richly oxygenated blood to the IVC

Question 6

How does oxygenated blood pass through the heart?

Answer 6

1) Oxygenated blood from the IVC is shunted through the foramen ovale
2) Goes into LA
3) LA to LV & ascending aorta
4) Provides blood to heart, brain, upper circulation

Question 7

How does deoxygenated blood move through the heart?

Answer 7

1) Returns to RA via SVC & coronary sinus
2) Ra to RV
3) Into pulmonary artery
4) Through ductus arteriosus
5) Down descending aorta

Question 8

Does blood go through the pulmonary circulation in a foetus?

Answer 8

10% only due to high pulmonary vascular resistance

Question 9

What is the paO2 and sats at different areas of the foetal circulation?

Answer 9

• Umbilical vein: 5kPa/90%
  -Ascending aorta: 3.5kPa/65%
• RA: 2.5kPa/40%
  -Lower circulation: 3kPa/50%

Question 10

What happens to the pulmonary circulation when a baby takes it first breath?

Answer 10

• Pulmonary vessels exposed to O2
• Causes VasoD = rapid decrease in PVR
• Inc blood flow in pulmonary circulation
• Inc flow to LA & atrial pressure
• Closes foramen ovale

Question 11

How does the ductus arteriosus close?

Answer 11

1) Cord clamped = no placental flow
2) Inc in SVR
3) Inc SVR & dec PVR = reversal of flow through arteriosus
4) Exposure of high O2 tension & reduced prostaglandin E2 causes contraction of arteriosus

Question 12

How long does it take for the ductus arteriosus to close?

Answer 12

24 hours post-delivery

Question 13

What happens if normal circulatory transition doesn’t occur at birth?

Answer 13

Pulmonary hypertension of the newborn

Question 14

What can trigger a newborns circulation to revert back to foetal circulation from adult?

Answer 14

• Hypoxia
• Hypothermia
• Hypovolemia
• Acidosis

Question 15

What does High pulmonary vascular resistance in the newborn give rise to?

Answer 15

Right to left shunting across FO/DA/both

Question 16

What factors can cause a patent ductus arteriosus (PDA)?

Answer 16

• Prematurity
• Maternal exposure to Rubella
• Maternal phenytoin
• Maternal ETOH use

Question 17

What is an adverse effect of PDA?

Answer 17

• Chronic exposure to high blood vol
• Causes CCF due to inc LV load

Question 18

How does Eisenmenger syndrome occur?

Answer 18

Effect of PDA
Inc pulmonary artery flow leads to pulmonary HTN
Reverses Left to right shunt

Question 19

What is the treatment for congenital cyanotic heart disease?

Answer 19

Prostaglandins- maintains PDA, allows some continuation into pulmonary circulation & descending aorta