Foetal (Fetal) Circulation

hello in this video we're going to talk

about fetal circulation the fetus is you

when you were inside your mother's womb


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


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


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


dioxide and water h2o as well carbon

dioxide is a by-product and actually

needs to be excreted otherwise it can be


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


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


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