Foetal (Fetal) Circulation

Summary

This video explains the complex process of fetal circulation, highlighting key differences from adult circulation. It covers the roles of the heart chambers, the foramen ovale, and the ductus arteriosus in allowing blood to bypass the lungs in a fetus. The placenta and umbilical cord are crucial for delivering oxygen and nutrients from the mother to the fetus, with fetal and maternal blood exchanging gases without mixing. The video concludes by describing how circulation changes after birth when the fetal structures close and adapt to adult circulation.

Takeaways

• 👶 Fetal circulation is different and more complicated than adult circulation, and relies on the placenta for oxygen instead of the lungs.
• ❤️ The fetal heart has four chambers, similar to an adult's heart, but blood bypasses the lungs through special openings.
• 🔄 Blood can flow from the right atrium to the left atrium through a hole called the foramen ovale, bypassing the lungs.
• 🩸 Another passage called the ductus arteriosus allows blood to bypass the lungs by moving from the pulmonary artery directly into the aorta.
• 🌬️ The fetal lungs have high pressure, which prevents blood from flowing into them, so the fetus depends on the placenta for oxygen.
• 👩‍🍼 Oxygen and nutrients are delivered to the fetus through the umbilical vein, which carries oxygenated blood from the placenta to the fetal liver.
• 🔗 The placenta is crucial as it allows maternal blood to transfer oxygen to fetal blood without mixing the two blood supplies.
• 🧬 Fetal hemoglobin has a higher affinity for oxygen than maternal hemoglobin, facilitating efficient oxygen transfer from mother to fetus.
• 🔄 Deoxygenated blood is returned to the placenta via two umbilical arteries, where it is reoxygenated by maternal blood.
• 👶 After birth, the fetal circulatory system transitions to adult circulation as the foramen ovale and ductus arteriosus close, and the umbilical vessels turn into ligaments.

Q & A

What is fetal circulation, and how does it differ from adult circulation?

Fetal circulation is the system of blood flow in a fetus, which differs from adult circulation because the fetus does not use its lungs for oxygen. Instead, it relies on the placenta for oxygen, and it has special structures like the foramen ovale and ductus arteriosus that allow blood to bypass the lungs.

What are the key structures in the fetal heart that enable blood to bypass the lungs?

The key structures in the fetal heart are the foramen ovale, an opening between the right and left atria, and the ductus arteriosus, which connects the pulmonary artery to the aorta. These allow blood to bypass the lungs since the fetus is not breathing air.

How does oxygenated blood from the placenta reach the fetus?

Oxygenated blood from the placenta reaches the fetus through the umbilical vein. This vein carries the oxygen-rich blood to the fetal liver and then to the inferior vena cava, mixing with deoxygenated blood before entering the heart.

What role does the placenta play in fetal circulation?

The placenta acts as the site of gas exchange between the maternal and fetal blood. It delivers oxygen and nutrients to the fetus via the umbilical cord and removes carbon dioxide and waste products.

How do the foramen ovale and ductus arteriosus facilitate the right-to-left shunt in fetal circulation?

The foramen ovale allows blood to flow directly from the right atrium to the left atrium, bypassing the right ventricle and lungs. The ductus arteriosus connects the pulmonary artery to the aorta, allowing blood to bypass the lungs and flow into the systemic circulation.

Why is there no need for blood to go to the lungs in fetal circulation?

There is no need for blood to go to the lungs in fetal circulation because the fetus does not breathe air. Oxygen is supplied through the placenta, so blood bypasses the lungs through the foramen ovale and ductus arteriosus.

How does the fetal body ensure it gets oxygen, and what makes fetal hemoglobin different from adult hemoglobin?

Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin, allowing it to efficiently extract oxygen from maternal blood. This enables the fetus to get sufficient oxygen even from the lower-oxygen environment of the placenta.

What happens to the foramen ovale and ductus arteriosus after birth?

After birth, the foramen ovale and ductus arteriosus close as the baby starts using its lungs for oxygen. The foramen ovale closes within hours to days, and the ductus arteriosus becomes a ligament, establishing the normal adult circulation pattern.

What is the function of the umbilical arteries in fetal circulation?

The umbilical arteries carry deoxygenated blood and waste products from the fetus back to the placenta for reoxygenation and disposal via the maternal blood circulation.

How does the exchange of oxygen and carbon dioxide occur between maternal and fetal blood?

Oxygen and carbon dioxide exchange between maternal and fetal blood in the placenta. Maternal blood delivers oxygen to fetal blood through diffusion, while fetal blood offloads carbon dioxide into the maternal circulation for elimination.

Outlines

00:00

👶 Introduction to Fetal Circulation

This paragraph introduces the concept of fetal circulation, explaining that it differs significantly from that of a baby or adult. The focus of the video is on fetal circulation, assuming the viewer already understands adult human circulation. It begins by explaining the heart’s anatomy—its four chambers and how, in fetal circulation, blood bypasses the lungs via anatomical openings like the foramen ovale and ductus arteriosus, which connect the right and left sides of the heart, allowing blood to bypass the lungs.

05:01

💡 The Role of the Placenta and Umbilical Cord

The placenta and umbilical cord play vital roles in delivering oxygen and nutrients to the fetus. The umbilical cord contains one umbilical vein, carrying oxygenated blood from the mother to the fetal liver. The oxygenated blood enters the fetal circulatory system, mixes with deoxygenated blood from the fetal body, and then proceeds to the heart. Through the right and left heart chambers, the blood can bypass the lungs, using openings like the foramen ovale and ductus arteriosus, to circulate oxygen-rich blood throughout the fetus’s body.

10:03

🔄 Blood Flow and Fetal Oxygenation

This section explains how blood travels through the fetal circulatory system, focusing on how partly oxygenated blood in the aorta supplies the fetal tissues with oxygen. Once the oxygen is used, deoxygenated blood returns to the heart. The umbilical arteries then carry this deoxygenated blood back to the placenta for reoxygenation via the maternal blood. Importantly, the fetal and maternal blood do not mix, but oxygen is transferred from the mother's blood cells to the fetal red blood cells.

🔬 Oxygen Exchange Between Fetal and Maternal Blood

Here, the oxygen transfer between maternal and fetal blood in the placenta is described. Maternal red blood cells deliver oxygen to fetal red blood cells, which have a higher affinity for oxygen due to their unique hemoglobin. In return, fetal red blood cells transfer carbon dioxide to maternal circulation for excretion. This exchange allows the fetus to receive oxygen and eliminate carbon dioxide, ensuring the continuation of the fetal circulatory process.

👶 Transition from Fetal to Adult Circulation

The final paragraph describes how fetal circulation transforms into adult circulation after birth. Once the baby is born, the umbilical vessels and ductus venosus close and become ligaments. The foramen ovale and ductus arteriosus also close, eliminating the right-to-left shunt that bypassed the lungs in fetal circulation. This marks the transition to the normal circulatory pattern of an adult.

Keywords

💡Fetal Circulation

Fetal circulation refers to the unique circulatory system of a fetus, which is different from that of a newborn or adult. In this system, blood bypasses the lungs because the fetus does not breathe air and receives oxygen through the placenta from the mother's circulation. This is a key focus of the video, explaining how blood is transported in the fetus before birth.

💡Foramen Ovale

The foramen ovale is an anatomical opening between the right and left atria of the fetal heart. It allows blood to bypass the lungs by flowing directly from the right atrium to the left atrium. In the context of the video, this opening is essential for fetal circulation, as the lungs are not used for oxygen exchange.

💡Ductus Arteriosus

The ductus arteriosus is a connection between the pulmonary artery and the aorta in the fetal heart. It allows blood to bypass the lungs and flow directly into the aorta, contributing to the right-to-left shunt. The video explains how this helps redirect blood away from the high-pressure fetal lungs and into systemic circulation.

💡Placenta

The placenta is the organ that connects the mother and fetus, facilitating the exchange of oxygen, nutrients, and waste. The fetus relies on the placenta for oxygen since it does not use its lungs. In the video, the placenta is described as essential for delivering oxygenated blood to the fetus via the umbilical vein.

💡Umbilical Cord

The umbilical cord is the physical connection between the fetus and the placenta. It contains veins and arteries that transport blood to and from the fetus. The video describes the umbilical vein, which carries oxygenated blood to the fetus, and the umbilical arteries, which return deoxygenated blood to the placenta.

💡Right-to-Left Shunt

A right-to-left shunt refers to the movement of blood from the right side of the heart to the left side, bypassing the lungs. In fetal circulation, this occurs through the foramen ovale and ductus arteriosus. The video emphasizes this shunting as a critical feature of fetal circulation, ensuring oxygenated blood is directed to the body.

💡Oxygenated Blood

Oxygenated blood is blood that has been enriched with oxygen, typically through the lungs or, in the case of a fetus, via the placenta. The video explains how oxygenated blood travels from the placenta to the fetus through the umbilical vein, supporting fetal growth and development.

💡Deoxygenated Blood

Deoxygenated blood is blood that has delivered its oxygen to tissues and carries carbon dioxide and other waste products. In fetal circulation, deoxygenated blood returns to the placenta via the umbilical arteries to be reoxygenated. The video details how this blood flows back to the placenta for oxygen exchange.

💡Ductus Venosus

The ductus venosus is a fetal blood vessel that connects the umbilical vein to the inferior vena cava, allowing oxygenated blood from the placenta to bypass the liver and flow directly to the heart. The video highlights the importance of this vessel in ensuring efficient oxygen delivery to the fetal heart and body.

💡Hemoglobin

Hemoglobin is the protein in red blood cells responsible for carrying oxygen. The video explains that fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin, which allows the fetus to effectively extract oxygen from the mother's blood in the placenta. This is crucial for the fetus’s survival and development.

Highlights

Introduction to fetal circulation and how it differs from adult circulation.

Fetal heart has four chambers: the right atrium, right ventricle, left atrium, and left ventricle.

The foramen ovale is an anatomical opening that connects the right atrium to the left atrium, allowing blood to bypass the lungs.

The patent ductus arteriosus connects the pulmonary artery to the aorta, further allowing blood to bypass the lungs.

The purpose of bypassing the lungs in fetal circulation is due to the fetus not breathing air and relying on the placenta for oxygen.

The placenta plays a crucial role in delivering oxygen and nutrients to the fetus via the umbilical cord.

The umbilical vein carries oxygenated blood from the placenta to the fetal liver and then joins the inferior vena cava.

Fetal circulation involves partially oxygenated blood mixing with deoxygenated blood before entering the heart.

The right-to-left shunt is a key feature of fetal circulation, allowing blood to bypass the lungs.

Fetal hemoglobin has a higher affinity for oxygen compared to maternal hemoglobin, facilitating oxygen transfer from mother to fetus.

The umbilical arteries return deoxygenated blood to the placenta for reoxygenation.

Fetal and maternal blood do not mix directly, but oxygen and carbon dioxide are exchanged in the placenta.

Once the fetus is delivered, the fetal circulation transitions to adult circulation, and structures like the foramen ovale and ductus arteriosus close.

The umbilical vein and arteries turn into ligaments post-birth as part of the transition to adult circulation.

Fetal circulation efficiently supports oxygen delivery and waste removal while bypassing the inactive fetal lungs.

Transcripts

hello in this video we're going to talk

about fetal circulation the fetus is you

when you were inside your mother's womb

uterus

now the fetal circulation is actually

very complicated and different to the

circulation of a baby which is

essentially the circulation of an adult

in this video it is assumed that the

viewer you will already have some

understanding of normal adult human

circulation so if you don't please

revise that now let us focus on fetal

circulation here is a fetus and it's

lungs and hot let's zoom in and focus on

the heart the heart has four chambers

the right consists of the right atrium

and right ventricle the right side of

the heart is responsible to pump blood

into the lungs blood returns to the

heart to the right side via veins here

in blue and will enter the right atrium

and then the right ventricle before

being pumped by the heart into the lungs

however in the fetal circulation there's

actually an anatomical opening a hole

called the foramen ovale which is the

connection between the right atrium and

the left atrium and so when the blood

flows from the right atrium to the right

ventricle blood will also flow from the

right atrium to the left atrium the left

side of the heart it consists of the

left atrium and left ventricle the left

side of the heart is responsible for

pumping blood to the rest of the fetal

body aside for the anatomical hole the

patent foramen ovale there is another

important connection or sort of hole

called the patent ductus arteriosus the

patent ductus arteriosus is the

connection between the pulmonary artery

and the aorta and so in the fetal

circulation blood traveling through the

pulmonary artery can bypass the lungs

and go straight to the aorta and be then

transported to the rest of the fetal

tissue the blood can bypass the lungs

because there is a lot of pressure in

the fetal lungs and so blood can't can

actually easily go in into the aorta the

patent foramen ovale and patent ductus

arteriosus allow a right-to-left shunt

which means blood normally entering the

right side of the heart can easily be

shunted to the left side of the heart

bypassing the lungs in fetal circulation

there is really no need for blood to go

into the lungs because the fetus is not

breathing air anyway rather the fetus

relies on the oxygen delivered by the

maternal circulation in the placenta see

the placenta is this important

connection between the mother and the

fetus the placenta delivers oxygen and

nutrients to the growing fetus via the

umbilical cord

the umbilical cord attaches the fetus to

the placenta the a miracle cord is not

just a cord it actually contains veins

and arteries the umbilical vein here

drawn in red travels from the placenta

to the fetal liver

there is one umbilical vein and it is

drawn here in red because it is

oxygenated

it contains oxygenated blood which was

delivered from the mum it's called a

umbilical vein because vein travels back

to the heart again the one umbilical

vein which is oxygenated travels to the

fetal liver and becomes the ductus

venosus which then will join with the

inferior vena cava here drawn in blue

the inferior vena cava in blue here is

blue because it contains deoxygenated

blood from the fetal circulation the

inferior

kaiba that is about to enter the right

side of the fetal heart now will contain

partly oxygenated blood and partly

deoxygenated blood and so this blood

will enter the right atrium and then

either go into the right ventricle or it

will go through the patent foramen ovale

into the left atrium bypassing the lungs

and then it will enter the left

ventricle which the which then will be

the blood will be pumped into the aorta

and into circulation the blood that is

pumped from the right ventricle can also

go through the pulmonary artery and

enter the lungs or mainly it can bypass

the lungs and just go straight into the

aorta via the patent ductus arteriosus

okay so now you have partly oxygenated

blood in the aorta where it will now be

delivered to the fetal tissue the fetus

needs oxygenated blood once the

oxygenated blood is used by the tissue

blood will then normally return back to

the heart via the veins

so here the veins are in blue which

indicates deoxygenated blood but in

fetal circulation there are actually

umbilical arteries which carry some of

this deoxygenated blood back towards the

placenta and there are two umbilical

arteries that do this and they again

contain deoxygenated blood and their aim

is to go to the placenta to reoxygenate

the blood via the maternal blood so

let's take a closer look at what happens

here so here we are looking at where the

fetal and maternal blood meet it is

really important to understand that

fetal and maternal blood do not actually

mix okay so here on the left you have

the maternal circulation and on the

right you have the fetal circulation

these things here are red blood cells

the cells that actually carry your

oxygen what happens in the placenta

is that the red blood cells from the

maternal circulation will transfer its

oxygen to the red blood cells in the

fetal circulation and the fetal red

blood cells will then offload their

carbon dioxide into the maternal

circulation and so the umbilical artery

is becoming essentially a reoxygenate

by the maternal circulation but how is

this possible why is the mum giving

oxygen to the fetus well it's because

the maternal red blood cell and the

fetal red blood cell are actually very

different you see the maternal red blood

cell like the fetal red blood cell

contain hemoglobin molecules the

molecules that actually carry the oxygen

but in the fetal red blood cells there

are actually more hemoglobin molecules

and the fetal hemoglobin has more

affinity for oxygen and this has to do

with the genes that are active early on

in in the fetus anyway this is the

reason why oxygen is usually taken from

the maternal red blood cells and into

fetal red blood cells so the umbilical

vein which is now oxygenated oxygenated

thanks to the maternal circulation will

travel back to the fetus via the

umbilical vein and it will go to the

heart and then it will be pumped by the

fetal heart to feed the fetal tissues so

what happens in the futile tissues well

let's take a look so here is the fetal

capillary here is a fetal cell let's

just say it's the skin cell and here is

the red blood cell of the fetus which

contains hemoglobin the molecule that

carries the oxygen now once once in the

fetal tissues so let's just say the skin

or what not

oxygen will detach from hemoglobin and

will go into the fetal tissue fetal cell

and it will and it will undergo a

reaction together with glucose to

produce energy for the cell and also

produce

dioxide and water h2o as well carbon

dioxide is a by-product and actually

needs to be excreted otherwise it can be

dangerous

one way that coverin dioxide is excreted

is that it can react with water in the

blood vessel or in the red blood cell

and here it will form bicarbonate ions

the bicarbonate ions can travel in

plasma this blood now is actually

deoxygenated blood because it contains

less oxygen carbon dioxide is largely

carried in blood in the form of

bicarbonate ions and so this

deoxygenated blood will now go back to

the placenta via the two umbilical

arteries we talked about in the placenta

this fetal circulation will again meet

the maternal circulation and so the

maternal red blood cell and feel red

blood cell will meet sort of and the

bicarbonate ions will react with

hydrogen again to form carbon dioxide

and water once this reaction takes place

carbon dioxide can then diffuse to the

maternal circulation now in the placenta

the fetal red blood cell needs to

receive oxygen like before and the whole

process continues I hope this story

actually made sense it's important to

know that once the fetus grows and is

delivered

so it's born the circulation changes

into the adult circulation after several

hours 2 days so what happens is that

after the fetus is delivered so it's a

baby

the umbilical artery and umbilical vein

and the ductus venosus will actually

disappear or change to become ligaments

and the patent foramen ovale and ductus

arteriosus will close up preventing the

right to left shunt

I hope this video I hope you enjoyed

this video thank you for watching