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Flashcards in 09 - Foetal Circulation Deck (11)

How does foetal blood differ from maternal blood?

HbF (70% saturated at 4pKa, higher oxygen affinity than maternal Hb)
More haemoglobin (18-20g/DL)
They don't have B globin chains so don't bind to 2,3BPG
Double Bohr effect as carbon dioxide moves in the opposite direction to oxygen - causing pH change


How do we maintain the partial pressure of oxygen gradient to ensure oxygen delivery to the foetus?

Maternal pO2 increases by progesterone driven hyperventilation
Foetal pO2 is lower (little blood over the whole system and little myoglobin)
There is only a small barrier - because the foetal villi are surrounded by maternal blood


Foetal oxygen stores are very low. Why is this a problem during labour?

Only have about two minutes worth of oxygen
Contracting myometrium impairs blood flow to the placenta
In response to low oxygen, foetal HR decreases
Needs monitoring in labour


Foetal kidneys are unable to counteract acid-base problems due to increased pCO2. How is this compensated for?

Maternal pCO2 needs to decrease for the pressure gradient
Due to progesterone driven hyperventilation


Why does the foramen ovale close at the first breath?

The volume of the lungs is increased and lowers the pulmonary pressure and lowers the pressure in the right atrium. The return of blood flow increases the pressure in the left atrium, causing closure.


What causes the closure of the ductus arteriosus?

Increases pO2 causes contraction of the smooth muscle and closes the shunt


Where, specifically, is the ductus arteriosus located?
And what does it prevent?

Pulmonary aorta to the aorta, distal to the carotid arteries (ensures delivery of oxygenated blood to the brain in utero)

Deoxygenated blood from the SVC mixing with oxygenated blood from the placenta in the left atrium


What is the function of the crista dividens?

It prevents the mixing of
1. Deoxygenated blood returning from the brain and body with
2. Oxygenated blood from the placenta
In the right atrium
It directs the oxygenated blood from the placenta to the foramen ovale


Why is heart rate variability a positive sign in a developing foetus?

It is a good index of developing control systems


Describe the foetal circulation and its in utero shunts

Oxygenated blood by-passes the liver and goes from the umbilical vein to the inferior vena cava by the ductus venosus.
The blood reaches the right atrium, where is it shunted into the left atrium by the foramen ovale. The blood is pumped from the left atrium around the body by the aorta.
The ductus arteriosus allows blood to pass from the pulmonary trunk to the aorta as not all of the blood goes through the foramen ovale. This is to by-pass the non-functional lungs.


What happens in the closure of the ductus venosus?

With the removal of the placental support, there is no blood entering through the umbilical vein. This causes the ductus venosus to close