Fetal circulation Flashcards

1
Q

What are the 3 shunts in petal circulation?

A
  • By pass of pulmonary circulation via Ductus arteriosus
  • By pass of pulmonary circulation via Forman ovale
  • By pass of the hepatic circulation (ductus venosus)
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2
Q

What is the function of the placenta?

A

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

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3
Q

Where is the placenta usually located?

A

• In the fundus of the uterus

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4
Q

What surrounds the umbilical cord?

A
  • Fetal membrane
  • Amnion
  • It contains whartons jelly
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5
Q

What is embedded in Wharton’s jelly?

A
  • 2 umbilical arteries

* Single umbilical vein

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6
Q

What is the function of the umbilical vein?

A

• Carries oxygen rich and nutrient rich blood from the placenta

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7
Q

What are the branches of the umbilical vein?

A
  • 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
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8
Q

Foramen ovale

A

• 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)

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9
Q

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

A

• 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

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10
Q

Where does the blood in the aorta go?

A
  • 1/3 to lower limbs, pelvis and abdomen

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

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11
Q

Draw diagram of foetal circulation

A

look at diagram

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12
Q

What happens to the circulation postnatally?

A

• 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

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13
Q

Describe the closure of foramen Ovale

A
  • 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
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14
Q

Patent foramen ovale

A
  • Usually asymptomatic

* May cause paradoxical emboli

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15
Q

Obliteration of Ductus arteriosus

A

• 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

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16
Q

Patent ductus arteriosus

A

• 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

17
Q

Obliteration of Ductus venosus

A
  • 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
18
Q

Obliteration of the umbilical vessels

A
  • 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)