Fetal Circulation

Here are flashcard-style notes from the Fetal Circulation presentation—organized by topic for easy studying:

🩸 Fetal Blood & Hemoglobin

Q: What is fetal hemoglobin (HbF)?
A: A special form of hemoglobin (2 alpha, 2 gamma chains) with a higher oxygen affinity than adult hemoglobin (HbA).

Q: Why does fetal hemoglobin have higher oxygen affinity?
A: To "steal" oxygen from maternal blood at the placenta.

Q: What’s the P50 value difference between HbF and HbA?
A: HbF: 20 mmHg (higher affinity), HbA: 27 mmHg.

Q: Where does hematopoiesis begin in a fetus?
A: Liver and spleen (early); bone marrow and lymph nodes take over later.

Q: What causes infant jaundice?
A: Rapid breakdown of HbF after birth → excess bilirubin buildup.

👶 Fetal to Adult Hemoglobin Transition

Q: What percent of hemoglobin is HbF at birth?
A: About 80%.

Q: By 6–12 months, what percent is HbA?
A: Around 90%.

Q: What happens to the oxygen dissociation curve after birth?
A: It shifts right (HbA releases oxygen more easily to tissues).

❤ Fetal Heart Development

Q: When does the fetal heart start to pump blood?
A: Around 3.5 weeks.

Q: When does the heart have 4 chambers?
A: By 7 weeks gestation.

Q: Why does fetal circulation use shunts?
A: To bypass the lungs, which are not yet used for oxygen exchange.

🫀 Fetal Circulation Shunts

Q: What is the foramen ovale?
A: A hole between the right and left atria—lets blood bypass the lungs.

Q: What is the ductus arteriosus?
A: A vessel that connects the pulmonary artery to the aorta.

Q: What is the ductus venosus?
A: A vessel that bypasses the liver, sending blood directly to the heart.

🌱 Placenta & Gas Exchange

Q: What is the placenta’s function?
A: Acts as lungs, kidneys, and digestive system for the fetus—gas exchange, waste removal, and nutrient delivery.

Q: What is the transplacental barrier?
A: A semi-permeable membrane that separates fetal and maternal blood.

Q: What can cross the placental barrier?
A: Gases (O₂, CO₂), small nutrients, antibodies, some medications/drugs.

Q: Why is the placenta efficient despite smaller surface area than lungs?
A: HbF holds oxygen tightly, fetal blood has more hemoglobin, and there's a strong oxygen gradient from mom to baby.

👶 Postnatal Circulatory Changes

Q: What triggers circulatory change after birth?
A: Baby’s first breath → lungs inflate → pulmonary resistance drops.

Q: What happens to fetal shunts after birth?
A:

• Foramen ovale: closes functionally at birth, anatomically within months.

• Ductus arteriosus: functionally closes in hours, anatomically in days.

Q: What causes the foramen ovale to close?
A: Increased pressure in the left atrium due to lung use and loss of placenta.

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