Fetal Circulation | Cardiovascular system | Step 1 Simplified

Summary

This script explores fetal circulation, highlighting the role of the placenta for gas exchange instead of the lungs. It details key shunts like the ductus arteriosus, umbilical arteries, and the foramen ovale, which ensure efficient oxygen delivery to vital organs. Post-birth, the script explains how changes in pulmonary vascular resistance, atrial pressures, and prostaglandin levels lead to the closure of these shunts, transitioning the baby to adult circulation. It also briefly touches on congenital heart diseases.

Takeaways

• 🌟 The placenta is the organ for gas exchange in fetal circulation, not the lungs.
• 🚫 Fetal lungs have high pulmonary vascular resistance, preventing blood flow through them efficiently.
• 🔄 Deoxygenated blood from the veins is diverted from the pulmonary artery to the aorta through the ductus arteriosus.
• 🔄 Umbilical arteries carry deoxygenated blood to the placenta for oxygenation.
• 🌀 The umbilical vein returns oxygenated blood to the fetus, contrary to typical arterial function.
• 🚸 The ductus venosus shunts blood from the umbilical veins, bypassing the liver to increase oxygen delivery to the heart.
• 🕳️ The foramen ovale allows oxygenated blood to bypass the lungs by moving from the right to the left atrium.
• 🔄 The ductus arteriosus shunts deoxygenated blood from the superior vena cava to the aorta, bypassing the lungs and directing it to the placenta.
• 🌬️ At birth, the first breath decreases pulmonary vascular resistance, allowing blood to flow through the lungs.
• 🔧 After birth, the closure of the foramen ovale and ductus arteriosus occurs due to increased oxygen levels and decreased prostaglandins.

Q & A

What is the primary organ for gas exchange in fetal circulation?

The primary organ for gas exchange in fetal circulation is the placenta, not the lungs.

Why are the fetal lungs not capable of respiration until week 25?

The fetal lungs are not capable of respiration until week 25 because they are still developing and have very high pulmonary vascular resistance, making it difficult for blood to flow through them.

What is the role of the ductus arteriosus in fetal circulation?

The ductus arteriosus diverts deoxygenated blood from the pulmonary artery to the aorta, bypassing the lungs and directing it towards the placenta for gas exchange.

How do umbilical arteries and veins function differently in fetal circulation compared to adult circulation?

In fetal circulation, umbilical arteries carry deoxygenated blood to the placenta, while umbilical veins return oxygenated blood to the fetus. In adult circulation, arteries carry oxygenated blood and veins carry deoxygenated blood.

What is the purpose of the ductus venosus in fetal circulation?

The ductus venosus bypasses the hepatic circulation, allowing oxygenated blood from the umbilical veins to bypass the liver and directly enter the inferior vena cava, ensuring efficient delivery of oxygen to the heart.

Why does the foramen ovale allow blood to flow from the right atrium to the left atrium in fetal circulation?

The foramen ovale allows oxygenated blood from the right atrium to flow directly to the left atrium, ensuring that blood rich in oxygen is directed to vital organs like the brain and heart.

What changes occur in the circulatory system at birth to transition from fetal to adult circulation?

At birth, the baby takes its first breath, which increases lung volume and decreases pulmonary vascular resistance. This leads to closure of the foramen ovale and ductus arteriosus, and a decrease in prostaglandins causes closure of the ductus venosus.

How does the closure of the foramen ovale occur after birth?

The closure of the foramen ovale occurs after birth as the left atrial pressure exceeds the right atrial pressure due to increased blood flow to the lungs, causing the flap to close like a trapdoor.

What is the role of prostaglandins in maintaining the patency of the ductus arteriosus during fetal life?

Prostaglandins, specifically prostaglandin E1 and E2, keep the ductus arteriosus open during fetal life by preventing it from closing.

How can a patent ductus arteriosus be treated after birth if it fails to close naturally?

A patent ductus arteriosus can be treated with indomethacin, a non-steroidal anti-inflammatory drug that blocks prostaglandin production, leading to closure of the ductus arteriosus.

Outlines

00:00

👶 Fetal Circulation and Its Unique Characteristics

This paragraph explains the distinct features of fetal circulation compared to adult circulation. The placenta plays a crucial role as the organ for gas exchange since the fetal lungs are not yet functional for respiration. The fetal lungs have high pulmonary vascular resistance, causing deoxygenated blood to be diverted from the pulmonary artery to the aorta via the ductus arteriosus. This blood then flows through the umbilical arteries to the placenta for oxygenation. Unlike in adults, umbilical arteries carry deoxygenated blood, while umbilical veins carry oxygenated blood back to the fetus. The oxygenated blood bypasses the liver through the ductus venosus, which connects the umbilical veins to the inferior vena cava, avoiding the congested portal vein system. Another important shunt is the foramen ovale, which allows oxygenated blood to pass from the right atrium to the left atrium and then be pumped out through the aorta, ensuring oxygenated blood reaches the brain and heart. Lastly, the ductus arteriosus ensures deoxygenated blood from the superior vena cava is directed away from the brain and towards the placenta.

05:01

🌟 Transition from Fetal to Neonatal Circulation

The second paragraph discusses the changes that occur in circulation at birth. The baby's first breath leads to a decrease in pulmonary vascular resistance as the lungs expand and blood vessels stretch out. This allows blood to flow more easily through the lungs. With the lungs now responsible for oxygenation, blood from the right side of the heart goes to the lungs instead of the placenta. The increased left atrial pressure compared to the right atrial pressure causes the foramen ovale to close. Additionally, the decrease in prostaglandins due to placental separation and the increase in oxygenation lead to the closure of the ductus arteriosus and ductus venosus. The paragraph also mentions the use of indomethacin, a non-steroidal anti-inflammatory drug, to treat patent ductus arteriosus by blocking prostaglandin production, which is necessary to keep the ductus arteriosus open. The summary highlights the three main circulatory changes at birth: decreased pulmonary vascular resistance, closure of the foramen ovale, and closure of the ductus arteriosus and ductus venosus, marking the transition from fetal to neonatal life.

Keywords

💡Fetal Circulation

Fetal circulation refers to the unique blood flow pattern in a developing fetus. Unlike adult circulation, the fetus relies on the placenta for gas exchange rather than the lungs, which are not fully developed or functional until week 25. This circulation pattern ensures that oxygenated blood reaches vital organs such as the brain and heart. The script describes how blood is diverted away from the lungs through the ductus arteriosus and how oxygenated blood returns to the fetus via the umbilical vein.

💡Placenta

The placenta is an organ that plays a crucial role in fetal development by facilitating the exchange of nutrients, gases, and waste products between the mother and the fetus. In the script, it is highlighted as the primary site for gas exchange, taking over the function that the lungs perform in adults. The placenta is connected to the fetus via the umbilical cord.

💡Ductus Arteriosus

The ductus arteriosus is a blood vessel that connects the pulmonary artery to the aorta in the fetus. Its function, as explained in the script, is to shunt blood away from the non-functional lungs and direct it to the aorta, ensuring that oxygenated blood is circulated to the body. After birth, the ductus arteriosus usually closes as the lungs begin to function, and this is a critical change in the transition from fetal to neonatal circulation.

💡Umbilical Arteries

Umbilical arteries are blood vessels that carry deoxygenated blood from the fetus to the placenta. The script notes that these arteries carry blood with a lower oxygen content than what is typically found in adult arteries. This is because the blood is being sent to the placenta to pick up oxygen, which is then returned to the fetus via the umbilical vein.

💡Umbilical Vein

The umbilical vein returns oxygenated blood from the placenta to the fetus. Contrary to typical expectations where red-colored vessels are arteries, the umbilical vein is oxygen-rich and carries this blood to the fetus. The script emphasizes the importance of this vein in delivering oxygen to the developing fetus.

💡Ductus Venosus

The ductus venosus is a shunt that allows blood from the umbilical vein to bypass the liver and directly enter the inferior vena cava. This is significant as it provides a faster route for oxygenated blood to reach the heart, bypassing the congested portal vein system. The script uses the term 'carpool lane' to illustrate how this shunt facilitates efficient blood flow.

💡Foramen Ovale

The foramen ovale is a fetal shunt that allows blood to flow from the right atrium to the left atrium of the heart. This is crucial for ensuring that oxygenated blood is pumped to the brain and other vital organs. The script explains how the pressure changes after birth cause this shunt to close, which is a necessary step in the transition to adult circulation.

💡Pulmonary Vascular Resistance

Pulmonary vascular resistance refers to the resistance that blood encounters as it flows through the blood vessels in the lungs. In the fetus, this resistance is high, which is why blood is diverted away from the lungs. The script explains how the first breath a baby takes after birth decreases this resistance, allowing blood to flow through the lungs and facilitating the closure of the fetal shunts.

💡Prostaglandins

Prostaglandins are hormone-like substances that have various effects on the body, including the maintenance of the ductus arteriosus in the fetus. The script discusses how prostaglandins keep the ductus arteriosus open in the fetus, and after birth, a decrease in prostaglandins leads to the closure of this shunt. It also mentions the use of indomethacin, a drug that blocks prostaglandin production, to treat patent ductus arteriosus in some cases.

💡Indomethacin

Indomethacin is a non-steroidal anti-inflammatory drug (NSAID) mentioned in the script as a treatment for patent ductus arteriosus. It works by blocking the production of prostaglandins, which are responsible for keeping the ductus arteriosus open. By decreasing prostaglandins, indomethacin can help close a patent ductus arteriosus that has not closed naturally after birth.

💡Congenital Heart Diseases

Although not extensively covered in the provided script, congenital heart diseases refer to structural abnormalities of the heart or blood vessels present at birth. The script concludes by mentioning these diseases, indicating that they will be discussed further. These conditions can affect fetal circulation and the transition to neonatal circulation.

Highlights

Fetal circulation is the direct opposite of adult circulation.

The placenta is the organ for gas exchange in fetal circulation, not the lungs.

Fetal lungs are not capable of respiration until week 25 due to high pulmonary vascular resistance.

Deoxygenated blood is diverted from the pulmonary artery to the aorta through the ductus arteriosus.

Umbilical arteries carry deoxygenated blood to the placenta for gas exchange.

Umbilical vein returns oxygenated blood to the fetus.

The ductus venosus shunt bypasses the hepatic circulation to deliver oxygenated blood to the heart.

The foramen ovale shunt allows oxygenated blood to bypass the lungs and go directly to the left atrium.

The ductus arteriosus shunts deoxygenated blood from the SVC to the aorta to bypass the lungs.

At birth, the baby's first breath decreases pulmonary vascular resistance.

Blood from the right side of the heart goes to the lungs for oxygenation after birth.

The foramen ovale closes due to increased left atrial pressure after birth.

Decreased prostaglandins and increased oxygenation lead to closure of the ductus arteriosus and ductus venosus.

Indomethacin, a non-steroidal anti-inflammatory drug, can be used to decrease prostaglandins and close a patent ductus arteriosus.

Three main circulatory changes at birth: decreased pulmonary vascular resistance, closure of foramen ovale, and closure of ductus arteriosus and ductus venosus.

Congenital heart diseases will be discussed after understanding fetal circulation.

Transcripts

so let's turn our attention to the fetal

circulation which in some ways is the

direct opposite of the actual adult

circulation so in the fetal circulation

the key thing is the placenta this is

where this is the organ for gas exchange

for fetuses not the lungs and this is

the mother's placenta note this is a

mother's placenta and this is the

fetuses circulation okay and the reason

why the placenta is the location of gas

exchanges not the lungs is first the

fetal lungs are not capable of

respiration until week 25 they're still

developing and even after that the

fetuses have a very high pulmonary

vascular resistance there are other long

other blood vessels and the lungs are

all scrunched up and so it's very hard

for blood to flow through them so

deoxygenated blood coming from the veins

will be diverted from the poner artery

remember to go from the veins to the

right side of the heart to the pulmonary

artery they're gonna be diverted to the

aorta through the ductus arteriosus so

that's ductus arteriosus it makes total

sense cuz it sorry I'm gonna go back

because it connects the pulmonary artery

and the aorta then it's gonna go down

the aorta as you can see here so this is

our ductus arteriosus take it from the

pulmonary artery today order it's gonna

go down the aorta it's gonna split and

eventually it's gonna go to the

umbilical veins so that's two umbilical

I'm sorry umbilical arteries and there's

two umbilical arteries as you can see

because they come from the branches of

the aorta and the two umbilical arteries

will go into the placenta for gas

exchange to retrieve oxygen so umbilical

arteries I want to point out one key

thing is that in the fetus much the

mythical arteries carry a lot of low

oxygenated blood okay it's not super low

but it's not super high like you would

normally expect in humans where humans

have oxygenated blood in the arteries in

contrast at least the umbilical arteries

the oxygenated blood and umbilical veins

had the oxygenated blood because the

arteries to go to the placenta to get

get oxygen and see this big fat red

thing this is the vein umbilical vein

which is confusing because usually when

you see red a red vessel you think it's

an artery but this umbilical vein

returns it's oxygenated blood to the

fetus via the IVC it's gonna connect to

the IVC so there's three shunts to know

about on the fetal circulation the first

one is from the umbilical veins and it's

gonna bypass the hepatic circulation and

that is through what shunt us through

the ductus venosus again that make sense

because doctors venosus connects the

veins in the inferior vena cava and the

reason why we have this shunt is because

the liver the hepatic circulation with a

portal vein portal vein system that's

like it's like traffic is like sitting

in traffic is very congested and we want

to get as much higher oxygenated blood

to the circuit system as much as

possible and we want a fast pass so this

ductus venosus is our fast fast

it's our carpool lane that's gonna let

us skip the portal venous circulation

and go directly to the heart now what's

gonna happen when this oxygenated blood

goes to the right atrium is it's

actually going to go through another

shunt and this shot is called the

foramen ovale and this foramen connects

the left atrium and the right atrium and

the left atrium so as you can see here

this this one you can imagine that it

shoots through it it's gonna keep going

and visit hole there it's gonna go from

the right atrium to the left atrium okay

that's what it's gonna do it's gonna go

to the left side of the heart now and

it's go today or do-- and the reason why

we want to do this is because then it's

gonna shoot out the aorta as you wanna

see here now and then it can go up all

these branches and these branches are

gonna take your nice oxygenated blood up

into the brain as well as to the heart

your heart will also get this blood so

you wanted to get this oxygenated blood

to the brain and to the heart so that's

why we have this foramen ovale

finally we have the ductus arteriosus

which

we already talked about and the reason

why we need this because we have

deoxygenated blood coming from the SVC

okay deoxygenated blood coming from the

SVC and this is gonna go down and it's

gonna follow gravity it's gonna follow

the way that makes the most sense it's

not going to go through that formula

valley because that doesn't make sense

the how is it gonna just suddenly shift

direction it's gonna go down it's the

right ventricle it's gonna go through

the right ventricle into the pulmonary

artery but remember you can't get that

blood into the lungs because of that

high resistance so this deoxygenated

blood is gonna get shunted and it's

gonna get shunted you want to shunt it

to the placenta so how are you gonna

shine it you have to shine it remember

to do it to get to the person you have

to go to lay order so you're gonna shine

it through this ductus arteriosus goes

from the pulmonary arteries to through

the ductus arteriosus into the order so

you're getting this deoxygenated blood

to really order and you're also note

that you're gonna skip all these

branches and ruin these branches you

don't wanna go you don't want this

deoxygenated blood going up to the brain

so you're gonna skip all these branches

because this shine is gonna make you

skip it all and it's gonna go straight

down the descending order and again

remember through the umbilical arteries

to the placenta so this is a beautiful

thing

the shunts all make complete sense why

we need them and just fascinating how we

have these shunts that do exactly what

we need them to do so at birth we're

gonna have circulatory changes to make

us more normal so the first change

that's gonna happen is the baby's gonna

take a first breath and when it takes a

breath the oxygens gonna fill up the

lungs like a balloon everything's gonna

stretch out including all the blood

vessels of the lungs and what happens to

pulmonary vascular resistance if your

blood vessels stretch out well your

radius is going to increase and when

your radius increases your vascular

resistance will decrease it's gonna be a

lot easier for blood to go through those

vessels the second thing that happens is

blood from the right side right side

heart of the heart will go to the lungs

for oxygenation rather than the placenta

and because we have blood flowing

through the lungs and then the lungs is

then you're gonna drain into the left

atrium the left atrial pressure will now

exceed the right atrial pressure and now

another thing is the right atrial

pressure will decrease

museum decreased umbilical vein flow all

that all that Venus flows knowledge

diverted to the lungs instead of the

placenta so because of this you have

closure of the foramen ovale I'm gonna

show this to you okay

this is prenatal when there still have a

fetus when they still have that foramen

ovale

and because the right atrial pressure is

greater than the left atrial pressure so

blood wants to go this way blood wants

to go down and pressure goes down the

pressure gradient so it's gonna open and

this like this septum primum

opens like I don't know like a trapdoor

and that's blood go through but at birth

we talked about all these changes that

are gonna make the left atrium greater

than the right atrium and because of

that blood is gonna want to go the other

way it's gonna go down the pressure

gradient and when it does this it kind

of closes that trapdoor as we see in

this picture and that's how you're

framing ovalle closes finally the last

thing we're gonna have increases in

oxygenation through your lungs and

you're gonna have decreased

prostaglandins from the placenta and

this was caught this will cause closure

of the ductus arteriosus and the ductus

venosus and the reason why is i focus on

the prostaglandins because

prostaglandins will normally make a

prostaglandin e1 and e2 keep the ductus

arteriosus alive that's what they do

they keep it patent they keep it open

that's this what that's what this is

it's the key that stays open so if your

prostaglandins decreased due to that

placental separation then your ductus

arteriosus will die it will close off

now the opposite will hold true let's

say you have a you have someone not the

opposite but let's say you do have

someone now for some reason their

prostaglandins don't go down and they

have a patent ductus arteriosus which is

a problem we'll talk about in a second

we have a treatment for that all you

have to do is decrease prostaglandins

somehow and the way we do that is with

indomethacin

do you know what type of drug and what

mechanism of action this is this is the

end set it's a non-steroidal

anti-inflammatory drug what what this

does is it blocks prostaglandin

production because that's an

inflammatory molecule so you brach plus

design and production you decreased

prostaglandins and now you have nothing

keeping that ductus arteriosus alive so

you can close that patent ductus

arteriosus so again let me just

summarize three circuits on circulatory

changes at birth three main ones when

you think of a deep breath you get

decreased pulmonary vascular resistance

this in turn will lead to your closure

of the formation for a Manoa Valley by

changing the pressure in the left atrium

in the right atrium and finally because

of that decreased prostaglandin and that

increase in oxygenation your closure or

your ductus arteriosus and your ductus

venosus so now you see that all three of

our fronts all three of our fetal shunts

have now closed so again another very

beautiful thing of how we transition

from the fetal life to the non funeral

life now we're going to talk about

congenital heart diseases