Fetal circulation

Question 1

What are the 3 shunts in petal circulation?

Answer 1

• By pass of pulmonary circulation via Ductus arteriosus
• By pass of pulmonary circulation via Forman ovale
• By pass of the hepatic circulation (ductus venosus)

Question 2

What is the function of the placenta?

Answer 2

• Diffusion of O2 and nutrients across the placental barrier from mother to foetus, removal of CO2 and metabolic waste

Question 3

Where is the placenta usually located?

Answer 3

• In the fundus of the uterus

Question 4

What surrounds the umbilical cord?

Answer 4

• Fetal membrane
• Amnion
• It contains whartons jelly

Question 5

What is embedded in Wharton’s jelly?

Answer 5

• 2 umbilical arteries

* Single umbilical vein

Question 6

What is the function of the umbilical vein?

Answer 6

• Carries oxygen rich and nutrient rich blood from the placenta

Question 7

What are the branches of the umbilical vein?

Answer 7

• Smaller branch to the liver
• Ductus venosus - by passes the liver and drains into the inferior vena cava where the arterial blood mixes with venous blood from the lower limbs

Question 8

Foramen ovale

Answer 8

• most of the blood coming through the inferior vena cava passes from the right atrium to the left atrium through the foramen ovale (–> LV –> Aorta)

Question 9

Describe the flow of blood that comes from the superior vena cava

Answer 9

• Most will go into the right ventricle (gravity)
• Then most:
–> Pulmonary trunk –> Ductus Arteriosus –> Aorta
• 10%:
–> Pulmonary trunk –> Pulmonary arteries –> Lungs –> Pulmonary veins –> LA –> LV –> Aorta

Question 10

Where does the blood in the aorta go?

Answer 10

• 1/3 to lower limbs, pelvis and abdomen

* 2/3 to the placenta via the internal iliac artery –> umbilical artery

Question 11

Draw diagram of foetal circulation

Answer 11

look at diagram

Question 12

What happens to the circulation postnatally?

Answer 12

• Shunts obliterated
• Umbilical cord is cut and tied (2cm left in case of intestine)
- loss of blood via the placenta, has to go other way
- increased systemic vascular resistance
- increased aortic, left ventricular, left arterial pressure
• First breath:
- Expansion of the lungs
- Decreased pulmonary vascular resistance
- Reduced pulmonary arterial, right ventricular, right atrial pressure

Question 13

Describe the closure of foramen Ovale

Answer 13

• Blood from the pulmonary circulation is returned to the left atrium
• Pressure rises in the left atrium
• Valve of foramen ovale is pushed rightwards and closes the foramen
• Becomes structurally closed by 4 months –> fossa ovalis –> fall septi

Question 14

Patent foramen ovale

Answer 14

• Usually asymptomatic

* May cause paradoxical emboli

Question 15

Obliteration of Ductus arteriosus

Answer 15

• Functional closure (1 hour)
• constriction of smooth muscle on the wall of ductus arteriosus due to:
- increased oxygen
- fall in prostaglandins (vasodilator) and rise in bradykinin
• Structural closure (1-4 months)
- anatomical closure by thickening of tunica intima and becomes ligamentum arteriosum

Question 16

Patent ductus arteriosus

Answer 16

• Postnatally, aortic pressure is higher than the pressure in the pulmonary trunk
• Blood will flow back into the pulmonary circulation
- left to right shunt
- increased pulmonary blood flow –> pulmonary hypertension
- Congestive heart failure

Question 17

Obliteration of Ductus venosus

Answer 17

• Blood through the umbilical vein ceases
• Muscle wall of ductus venosus contracts
• Portal venous blood flows through hepatic sinuses
• Functionally closes within 1-3 hours of birth
• Obliterates and becomes ligamentum venosum

Question 18

Obliteration of the umbilical vessels

Answer 18

• Umbilical vein obliterates and forms the round ligament of the liver (ligamentum teres heaptis)
• Distal parts of the umbilical arteries atrophy around 2-3 months to become the medial umbilical ligament (within medial umbilical folds)