Foetal circulation

Question 1

describe the circulatory system in the foetus

Answer 1

1. uterine vein carrying oxygenated blood from mother passes to the liver
2. liver decontaminates maternal blood & metabolises maternal steroids
3. blood then passes into posterior vena cava & travels to heart
4. blood from head travels to heart in anterior vena cava
5. anterior & posterior vena cava converge on right side of heart, but the 2 blood streams don’t mix
6. blood from posterior fired straight into left atrium via foramen ovarle
7. blood pumped into left ventricle & out in aorta
8. anterior enters right ventricle via right atrium & is pumped out in pulmonary artery
9. high vascular resistance means lungs are non-operational, blood diverted into vena cava via ductus arteriosus
10. ductus arteriosus joins aorta after blood has been taken off by carotid arteris to supply head & forequarters
11. deoxygenated blood returns to heart from rest of body via anterior vena cava to right atrium
12. this is diverted to the aorta & blood leaves foetus via umbilical vein to be oxygenated by mother before returning to foetus
    13.

Question 2

what changes occur to the foetal blood supply at birth?

Answer 2

1. pulmonary circulation develops
2. lungs expand, circulation via pulmonary arteries becomes available
3. blood flow to lungs begins
4. there is disruption of flow in umbilical artery & vein meaningless blood is returned to inferior vena cava
5. umbilical vessels cause increased resistance, causes massive increase in aortic BP
6. has knock on effect on L heart causing a greater pressure difference between R & L atrium - L side thickens
7. pressure difference closes the foramen ovarle
8. increased pressure in aorta causes temporary back flow into ductus arteriosus & the vessel closes
9. once placental circulation cut off ductus venosus also closes
10. changes cause adult blood flow & heart conformation

Question 3

why is it important for the umbilical artery to maintain good blood pressure?

Answer 3

so blood can perfuse placental tissue and to drive return of blood in umbilical vein back to foetus