Thorax 5 - Foetal Circulation

Question 1

Since there is no mixing of blood between mother and foetus, how are nutrients transferred from mother to baby and waste products vice versa?

Answer 1

Via the placenta

Question 2

How many umbilical vessels are there?

Answer 2

1 vein, 2 arteries

Question 3

What do the umbilical arteries become upon birth?

Answer 3

Medial umbilical ligaments

Question 4

What does the umbilical vein become upon birth?

Answer 4

Ligamentum teres

Question 5

List the flow of blood in the foetal heart from the inferior vena cava.

Answer 5

IVC —> Right Atrium —> Foramen ovale —> Left Atrium —> Left Ventricle —> Aorta

Question 6

How does the foramen ovale close?

Answer 6

Pressure in the left atrium rises at birth, forcing the septum premum into the septum secundum and closing the foramen ovale

Question 7

What is the name given to the vessel that allows blood coming from the SVC to bypass the pulmonary circulation?

Answer 7

Ductus arteriosus

Question 8

What is the name given to the vessel that allows blood to bypass the hepatic system?

Answer 8

Ductos venosus

Question 9

How does ductus arteriosus close?

Answer 9

Oxygen - potent constrictor

Prostaglandin levels fall

Question 10

If closure of the ductus arteriosus doesn’t ensue, what must be administered?

Answer 10

Prostaglandin inhibitors

Question 11

An overview: describe in relative detail the path blood takes from entering the foetus from the mother to emptying back to the placenta.

Answer 11

Oxygenated blood enters the foetus through the umbilical vein. It bypasses the liver via the ductus venosus and moves into the IVC where it combines with deoxygenated blood. Joined by deoxygenated blood from the SVC, it enters the RA and the majority of blood is shunted through the foramen ovale (due to the pressure in the RA being greater than the pressure in the LA). The minority that passes into the RV makes its way into the aorta via the ductus arteriosus, connecting the PT to the aorta. Deoxygenated blood returns to the placenta via the umbilical arteries, originating from the internal iliac near the bladder.

Question 12

How long after birth does it take for the ductus arteriosus to constrict and transform into the ligamentum arteriosus?

Answer 12

10-15 hours

Question 13

What is the first thing that happens to the CVS upon taking a first breath?

Answer 13

Increased alveolar O2 pressure causes vasodilation of the pulmonary vessels

Question 14

How do the umbilical arteries and vein constrict?

Answer 14

Obstetrical clamping

Question 15

What type of tissue does the placenta consist of?

Answer 15

Foetal tissue

Question 16

The membrane between the maternal and foetal circulations is very thin endothelium of the foetal capillaries. What are they solely covered by?

Answer 16

Syncytiotrophoblast

Question 17

How is a very low pressure system, which allows vast diffusion of material into the foetal villi, achieved?

Answer 17

Maternal capillaries break down and maternal blood bathes the foetal microvilli directly

Question 18

Is there any mixing of maternal and foetal blood?

Answer 18

NO

Question 19

Why is hepatic circulation to the liver restricted in the foetus?

Answer 19

Nutrients are already modified by the maternal liver before reaching the foetus via the placenta

Question 20

What produces prostaglandins?

Answer 20

The placenta

Question 21

What are some associated issues with patent foramen ovale?

Answer 21

Asymptomatic, however if a thrombus passes into the RA, it is unlikely to end up as a PE in the pulmonary circulation and instead will pass into the LA and later, the systemic circulation through the patent foramen ovale

Question 22

What are some associated issues with patent ductus arteriosus?

Answer 22

Aortic pressure > PT pressure –> left to right shunt (blood will flow back into the PT –> pulmonary hypertension or congestive cardiac failure

Question 23

What is a classic sign of patent ductus arteriosus?

Answer 23

Continuous ‘machinery’ murmur