Most deoxygenated blood in fetal circulation

[MudPhud20XX]

Hi all, so which one is more deoxygenated between ductus arteriousus and umbilical arteries?

I had a question that had both ductus arteriosus and umbilical artery as answer choices and the answer was DA without any good explanation.

Intuitively, I want to say umbilical artery. I also know that in fetal heart, there are two flows going through the heart, one the deoxygenated blood from SVC and oxygenated blood via IVC going through the heart, which joins with the deoxygenated blood from SVC to ductus arteriosus. So this may explain that ductus arteriosus can be more deoxygenated. But I am not completely convinced.... Shouldn't the umbilical artery still be more deoxygenated?

Can anyone help me? Many thanks in advance

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[ulikedaggers]

O2 in fetal circulation.

Umbilical vein -> IVC -> FO -> LA -> LV -> Aorta -> Umbilical Artery. The DA gets all its blood from the RV, which is not as oxygenated as the LV blood that goes into the umbilical artery.

 

[MudPhud20XX]

Thanks. I get that DA gets all its blood from the RV and then the blood gets mixed with more oxygenated blood coming from LV which goes to umbilical artery, but I would still think it is debatable that umbilical artery may still be more deoxygenated since it is really the last vessel collecting all the deoxygenated blood from the fetal body. I guess I will have to just take this as a fact. Thanks for the reply though. I appreciate it.

 

[ulikedaggers]

Thanks. I get that DA gets all its blood from the RV and then the blood gets mixed with more oxygenated blood coming from LV which goes to umbilical artery, but I would still think it is debatable that umbilical artery may still be more deoxygenated since it is really the last vessel collecting all the deoxygenated blood from the fetal body. I guess I will have to just take this as a fact. Thanks for the reply though. I appreciate it.

You're right that the umbilical arteries are the last vessels collecting the dO2 blood from the fetal body. But, a PDA is the last vessel collecting the dO2 blood from the fetal brain. There is virtually no exchange occurring in the RA between blood coming from the IVC and the SVC because of the laminar flow created by the valve of the IVC. So essentially the question can be asked like this. What is more likely to consume every last O2 molecule it gets access to; the brain, or barely-functioning trunk?

 

[MudPhud20XX]

Ah! That makes so much sense! Thanks so much man!

 

[ulikedaggers]

Ah! That makes so much sense! Thanks so much man!

Happy to help!