Clitus is back and he's going to help sort of get us in the mood to talk about fetal circulation.
It's important that we're oriented to what we're looking at on theses diagrams,
so I want to show you with Clitus.
So, here's our placenta. This is the maternal side.
Remember that we talked about the chorionic villi.
We talked about the amnion and chorion.
Now, let's look at the umbilical cord which is attached directly to the placenta
and also here at the umbilicus of the baby.
So I want you to understand that when we talk about fetal circulation
we're going to pick up at the point of the placenta as the blood moves through the cord
and into the baby.
So now were going to be magically transported back inside the fetus.
There are three very important concepts to keep in mind as we discuss fetal circulation.
First, in fetal circulation, the umbilical vein carries the oxygen rich blood
and the umbilical artery carries the deoxygenated blood back to the placenta.
This is the exact opposite of what happens in adult circulation.
Number two, because the placenta takes care of oxygenating the blood
and filtering out the waste products, the liver and the lungs
are not fully functional in fetal circulation.
And the third point, to preserve oxygen for fetal development and neurological functioning,
there are three shunts that alter the flow of blood away from certain organs.
Number one, the ductus venosus; number two, the foramen ovale;
number three, the ductus arteriosus.
You're going to hear these terms as we move through fetal circulation, so pay attention.
Now, we're ready to take a trip through fetal circulation.
Remember, you can listen to this recording as many times as you need to,
to help you understand this process.
Now, I will recommend that perhaps the first time you go through, put away your notes,
don't use any other thing except your ears and listen and see if you can capture the big picture.
Beginning at the placenta, oxygen-rich blood flows through the umbilical cord to the liver.
Here we encounter that very first shunt, the ductus venosus.
Most of this blood is sent through the ductus venosus to the inferior vena cava
and then to the right atrium of the heart.
Only a very minimal amount of blood actually oxygenates the liver,
just enough to keep those tissues going.
From the inferior vena cava the blood enters the right atrium.
When the blood enters the right atrium, most of that blood flows through the foramen ovale
into the left atrium, this is our second shunt
and it keeps the oxygen rich blood from going straight to the lungs.
Blood then passes the left ventricle and then to the aorta.
From the aorta, the blood oxygenates the heart itself and also the brain.
Blood then returns to the right atrium of the lungs through the superior vena cava.
The right atria is more like a complicated road way.
There is blood flowing in not one but two directions.
About two-thirds of the blood will pass through the foramen ovale just like it did on the first pass.
The remaining one-third however, will pass into the right ventricle toward the lungs.
This part should sound familiar.
Normally, the lungs are a low pressure system and it's this way
because this is how we receive the oxygen to breathe.
This is not the case however in fetal circulation.
The mighty placenta is actually the lungs, so the lungs only need enough oxygen
to make sure that tissue stays viable,
the lungs are not supporting respiratory function in the fetus.
This is where we encounter the third and final shunt, the ductus arteriosus.
The high pressure system in fetal circulation helps to shunt blood away
from the lungs and to the aorta.
At the same time, the blood, that does feed the lungs enters the pulmonary artery
and returns via the pulmonary vein and empties into the left atria.
From the aorta, circulation is supplied to the lower part of the fetal body.
The blood in circulation from the lower extremities enters the umbilical arteries
and makes its way back to the placenta for refueling so to speak.
In the placenta, carbon dioxide and waste products are released into the mother's circulatory system
and oxygen and nutrients from the mother's blood
are released into the fetal blood and the cycle begins again.
When we talk more about birth and the newborn assessment,
if you'll remember these elements of fetal circulation, the kinds of assessments
that we do will make so much more sense.
So let's review the points to remember.
There are two umbilical arteries and one umbilical vein.
Oxygen rich blood is carried from the placenta via the umbilical vein
and deoxygenated blood is carried back to the placenta via the umbilical artery.
The ductus venosus shunts blood away from the liver.
The foramen ovale and the ductus arteriosus shunt blood away from the lungs.
The pulmonary system in adult circulation is a relatively low pressure system,
but in fetal circulation, the pulmonary system is a high pressure system
to help shunt the blood away from the lungs.
So go back and review this a few times and even look in your textbook
and follow the graphic and I promise you'll have it.