Fetal Circulation

Question 0

Umbilical cord

Answer 0

• umb. Arteries carry deoxygenated blood from fetus to placenta & remove waste
• umb. Vein carries oxygenated blood & nutrients from placenta to fetus

Question 1

4 modifications to circulation in fetus

Answer 1

1. Umbilical cord
2. Ductus venosus
3. Foramen ovale
4. Ductus arteriosus

Question 2

Ductus venosus

Answer 2

• umb vein blood has been processed by mom’s liver, so 1/2 of it bypasses fetal liver through ductus venosus & straight to inferior vena cava
• oxygenated blood mixes with deoxygenated blood from lower extremities
• blood moves into right atrium

Question 3

Foramen ovale

Answer 3

• btwn the two atria, allows most blood to bypass lungs
• fetal lungs are collapsed and nonfunctional, so vessels have high resistance to blood flow -> get just enough blood to sustain them
• blood entering r atrium oxygenated by mom -> goes into l atrium, l ventricle, aorta
• flap on l atrium side prevents backflow of blood
• if this opening doesn’t close -> “blue baby” (blueish skin due to lack of O2 in blood)

Question 4

Ductus arteriosus

Answer 4

• goes from pulmonary artery to aorta to bypass lungs & deliver mixed blood to body

Question 5

What happens at birth?

Answer 5

• lungs expand and cause blood to flow through pulmonary vessels
• pressure drops in right atrium & rises in left atrium and the flap btwn them is shut
• increased flow to pulmonary artery causes it to expand and close off arterial duct
• cutting umbilical cord seals off artery & vein -> they soon atrophy