fetal circulation

Question 1

what does a fetus use for its source of oxygen and nutrients

Answer 1

the placenta

Question 2

what is a fetus surrounded by

Answer 2

amniotic fluid

Question 3

why must the fetal circulation direct blood away from non-functional organs and ensure that growing tissues receive their oxygen requirement

Answer 3

• while lungs are developing, they are not functional and provide no oxygenation
• there are also high energy demands of developing tissue - especially the brain

Question 4

what does the umbilical vein do

Answer 4

delivers oxygenated blood from the placenta to the fetus, providing oxygen and nutrients

Question 5

what do umbilical arteries do

Answer 5

used to transport deoxygenated blood away from the fetal tissue and back towards the placenta for re-oxygenation

Question 6

what does the ductus venosus do

Answer 6

allows blood from the placenta to bypass the highly demanding, but relatively inactive liver

Question 7

what does the ductus arteriosus do

Answer 7

it is the fusion of the primitive pulmonary artery to the aorta, therefore allowing blood to pass straight from the right ventricle into the aorta and bypass the inactive lungs

Question 8

what does the foramen ovale do

Answer 8

creates a shunt between the right atrium and the left atrium so oxygenated blood from the placenta can move to the left atrium - allows for the oxygenated blood to pass through the left ventricle and into the ascending aorta, oxygenating the brain

Question 9

what is the highest partial pressure of oxygen in the feto-placental circulation

Answer 9

approximately 4kPa

compared to 13kPa in an adult

Question 10

how is the fetus able to maintain adequate oxygen delivery to tissues

Answer 10

through the use of shunts assisted by a relative polycythaemia and the properties of fetal haemoglobin.

Question 11

how is fetal haemoglobin different to adult haemoglobin

Answer 11

has a different quaternary structure

contains 2 alpha subunits and 2 gamma subunits whereas adult contains 2 alpha subunits and 2 beta subunits

Question 12

what does the different fetal haemoglobin structure allow

Answer 12

• means that fetal haemoglobin can bind more readily to oxygen from maternal circulation
• allows for adequate oxygenation of tissues.

Question 13

what are the steps that take a fetal heart to a neonatal heart

Answer 13

1. first breath causes rise in partial pressure of oxygen
2. causes pulmonary vasodilation
3. leads to a drop in right heart pressure
4. simultaneously, placental circulation stops, causing left heart pressure to rise.
5. these factors combine to cause the foramen ovale to shut
6. the pulmonary and systemic circulations become separate, and the whole output of the right ventricle passes through the pulmonary circulation
7. the final step in the sequence is the closure of the ductus arteriosus, occurring 2 to 3 days after birth.
8. the structural remnants of the fetal circulatory structures are referred to as the fossa ovalis (foramen ovale), the ligamentum arteriosum (ductus arteriosus) and the ligamentum venosum (ductus venosus).