FETAL CIRCULATION

What are the stages of human development in utero (3)

• ZYGOTE: Fertilization → implantation

• EMBRYO: Implantation → 8 weeks

• FETUS: 8 weeks → birth

Why does fetal circulation differ from the norm (2)

• Underdeveloped lungs

  • No air in utero

• Lungs are only used after birth

What is the placenta (1) [2]

• Network of intertwining but separate capillary beds

  • One from uterus (mother) + one from umbilical cord (baby)

    • Never join but are close enough for material exchange

What are the 4 differences in fetal circulation (3) (2) (2) (3)

DUCTUS VENOSUS:

• Passes through liver

• Umbilical vein (O₂) → VC

• Returns blood to heart

DUCTUS ARTERIOSUS:

• Connects aorta + pulmonary artery

• Bypasses lungs via aorta

  • Less blood to lungs cuz it doesn’t need it

FORAMEN OVULE:

• One-way opening from right atrium → left

• Bypasses lungs + recirculates the body

UMBILICAL ARTERIES + VEINS:

• Vessels that go enter/exit placenta

• Oxygenated blood = placenta → U. vein → vena cava

• Deoxygenated blood = iliac arteries → U. arteries → placenta

Path of blood through fetus (7) (4)

OXYGENATED

• O₂ + nutrients from mother → placenta

• Placenta → umbilical cord → fetus

• Enriched blood → umbilical vein towards liver

• Gets redirected by ductus venosus → IVC → RA

  • Some goes to liver

  • Redirected cuz blood doesn’t need to be filtered

• Most blood = RA → LA via foramen ovule

• LA → LV → aorta

• Aorta → Brain, heart muscle, lower body

DEOXYGENATED

• Returning blood from upper body → SVC → RA

• RA → RV towards pulmonary trunk

• Gets bypassed by ductus arteriosus into descending aorta

• Goes into umbilical arteries → placenta

Where does blood mixing occur in the baby? [2] [2]

• IVC

  • Carries deoxygenated blood from lower body

  • Mixes with oxygenated blood from U. vein

• Right atrium

  • Partially oxygenated blood from IVC

  • Mixes with deoxygenated blood from SVC

What happens to the adaptations nearing/after birth (3)

• Disappears

• Foremen ovule closes few months BEFORE birth

  • Incomplete closure in 25% of people

    • Hole closes during atrial contractions → usually fine

• Ducts disintegrate ~8 days after