Foetal (Fetal) Circulation | Before and At Birth | Cardiac Physiology | Embryology
Summary
TLDRThis video from Bite Size Med explores fetal circulation, highlighting the unique differences from adult circulation due to the non-functional lungs and reliance on the placenta for gas exchange. It details the three key shunts in the fetal circulatory system: the ductus venosus, foramen ovale, and ductus arteriosus, which facilitate blood flow bypassing the lungs. The video also explains the physiological changes at birth that lead to the closure of these shunts, transitioning the baby's circulation to an adult pattern.
Takeaways
- 🌟 Fetal circulation is distinct from adult circulation due to the non-functional lungs and reliance on the placenta for gas exchange.
- 🔄 The umbilical cord has two arteries and one vein, with the arteries carrying deoxygenated blood and the vein carrying oxygenated blood.
- 🚦 Three shunts are crucial for fetal circulation: the ductus venosus, foramen ovale, and ductus arteriosus, allowing blood to bypass the liver, lungs, and directing it towards vital organs.
- 📍 The ductus venosus shunts blood from the umbilical vein to the inferior vena cava, bypassing the liver.
- 🫀 The foramen ovale allows oxygenated blood to pass from the right atrium to the left atrium, bypassing the lungs.
- 🩸 The ductus arteriosus channels blood from the pulmonary artery to the aorta, ensuring only a small portion goes to the lungs.
- 🌡️ High pulmonary vascular resistance in the fetus due to collapsed lungs and high blood flow to the placenta due to low systemic vascular resistance.
- 👶 At birth, the first breath decreases pulmonary vascular resistance, leading to closure of the shunts as the circulatory system adapts to lung breathing.
- ⏳ After birth, the functional closure of the ductus arteriosus occurs within hours to days, followed by anatomical closure over months.
- 🔗 The remnants of fetal circulatory structures persist into adulthood as ligaments and other anatomical markers.
Q & A
What is the primary difference between fetal and adult circulation?
-The primary difference is that in fetal circulation, the lungs are non-functional, and the placenta performs the gas exchange, whereas in adults, the lungs are fully functional.
Why does the umbilical vein carry oxygenated blood and the umbilical arteries carry deoxygenated blood?
-The umbilical vein carries oxygenated blood because it transports blood from the oxygenating placenta to the fetus. The umbilical arteries carry deoxygenated blood because they transport blood from the fetus to the placenta for oxygenation.
What are the three shunts in fetal circulation and their functions?
-The three shunts are the ductus venosus, the foramen ovale, and the ductus arteriosus. The ductus venosus allows blood from the placenta to bypass the liver. The foramen ovale allows blood to pass from the right atrium to the left atrium, bypassing the lungs. The ductus arteriosus allows blood to bypass the lungs by shunting from the pulmonary artery to the aorta.
How does the blood from the umbilical vein enter the fetal heart?
-The blood from the umbilical vein enters the inferior vena cava (IVC) and then bypasses the liver through the ductus venosus, entering the IVC and right atrium.
What directs the oxygenated blood towards the foramen ovale in the right atrium?
-The Eustachian valve at the junction of the IVC and the right atrium directs the more oxygenated blood towards the foramen ovale.
Why does the majority of oxygenated blood from the left ventricle go to the brain and coronary circulation?
-The majority of oxygenated blood from the left ventricle goes to the brain and coronary circulation because these are vital structures that require a good supply of oxygen.
What causes the right-to-left shunt in the fetal circulation?
-The right-to-left shunt in fetal circulation is caused by the high pulmonary vascular resistance due to the collapsed lungs and the lower systemic vascular resistance in the placenta, leading to higher pressures on the right side of the heart compared to the left.
What changes occur in the fetal circulation at birth?
-At birth, the baby takes a breath, the lungs expand, and the pulmonary vascular resistance falls. This causes the pressures in the left side of the heart to become higher than the right, reversing the shunts and closing them.
How do the shunts close after birth?
-The foramen ovale closes due to the left atrial pressure becoming higher than the right, causing a flap to close. The ductus arteriosus closes due to high oxygen tension and loss of prostaglandin E2, leading to constriction and eventual fibrous tissue growth. The ductus venosus closes as the umbilical vein flow stops and portal venous pressure rises.
What are the remnants of the fetal circulation structures in adults?
-In adults, the remnants are the ligamentum teres (from the umbilical veins), the ligamentum venosum (from the ductus venosus), the ligamentum arteriosum (from the ductus arteriosus), and the fossa ovalis (from the foramen ovale).
Outlines
🔬 Fetal Circulation and its Unique Characteristics
This paragraph introduces the concept of fetal circulation, highlighting the key differences from adult circulation due to the non-functional lungs and the role of the placenta in gas exchange. It explains the unique blood flow through the umbilical arteries and vein, with deoxygenated blood in the arteries and oxygenated blood in the vein. The circulatory pathway is detailed, emphasizing the role of three shunts: the ductus venosus, foramen ovale, and ductus arteriosus. These shunts allow blood to bypass the liver and lungs, directing oxygenated blood to vital organs and tissues. The paragraph concludes with an explanation of why these shunts occur, due to the high pulmonary vascular resistance in the fetus and the lower systemic vascular resistance in the placenta.
🌱 Changes in Circulation at Birth and Beyond
The second paragraph discusses the physiological changes that occur at birth, which alter the fetal circulatory system. It explains how the first breath of the baby reduces pulmonary vascular resistance and increases systemic vascular resistance, leading to the closure of the foramen ovale and ductus arteriosus. The paragraph also describes the functional and anatomical closure of these shunts and the reasons behind them, such as increased oxygen tension and the loss of prostaglandin E2. It concludes with the remnants of these fetal structures in adults, such as the ligamentum venosum, ligamentum arteriosum, and fossa ovalis, and the transformation of the umbilical arteries into the medial umbilical ligament.
Mindmap
Keywords
💡Fetal circulation
💡Placenta
💡Umbilical cord
💡Shunts
💡Ductus venosus
💡Foramen ovale
💡Ductus arteriosus
💡Pulmonary vascular resistance
💡Patent foramen ovale
💡Patent ductus arteriosus
Highlights
Fetal circulation differs from adult circulation due to non-functional lungs and reliance on the placenta for gas exchange.
The liver is partially functional, receiving less blood compared to the placenta, which receives a lot.
The umbilical cord has two arteries and one vein, with the artery carrying deoxygenated blood and the vein carrying oxygenated blood.
The placenta oxygenates blood, leading to oxygenated blood in the umbilical vein and deoxygenated blood in the arteries.
Fetal circulation is dependent on three shunts: one at the liver, one at the heart, and one at the great vessels.
The ductus venosus shunts oxygenated blood from the umbilical vein to the inferior vena cava, bypassing the liver.
The Eustachian valve directs oxygenated blood towards the foramen ovale, the second shunt.
The foramen ovale allows blood to bypass the lungs by directing it from the right atrium to the left atrium.
The ductus arteriosus, the third shunt, connects the pulmonary artery to the aorta, bypassing the lungs.
Only about 12% of blood from the right ventricle reaches the lungs, with the rest going through the ductus arteriosus.
The high pulmonary vascular resistance in the fetus causes right-to-left shunting at the foramen ovale and ductus arteriosus.
At birth, the baby's first breath reduces pulmonary vascular resistance, leading to closure of the shunts.
The foramen ovale closes due to increased left atrial pressure, preventing right-to-left shunting.
The ductus arteriosus closes due to increased oxygen tension and loss of prostaglandin E2, which relaxes vessels.
If the ductus remains open, it's called a patent ductus arteriosus, leading to a left-to-right shunt.
The ductus venosus closes as portal blood is redirected into the hepatic sinusoids after birth.
In adults, remnants of the fetal circulation structures remain as ligaments and the fossa ovalis.
Transcripts
hi everyone welcome to bite size med
where we talk about quick
bite size concepts in medicine for study
and rapid review
this video is on fetal circulation
the circulation in the fetus differs
from that of an adult for one main
reason
the lungs are non-functional and the
placenta does the job of gas exchange
the liver is partially functional so
neither the lung nor the liver need much
blood
versus the placenta which gets a lot
the umbilical cord from the placenta has
two umbilical arteries and one umbilical
vein
compared to the usual arteries and veins
the umbilical artery has deoxygenated
blood
and the umbilical vein oxygenated blood
why does that happen because the
placenta is the one that's oxygenating
blood
so the vein which carries blood from the
placenta to the heart
will be oxygenated and the arteries
which come from the heart to the
placenta
will bring deoxygenated blood for
oxygenation
now let's look at the circulatory
pathway so fetal circulation
is dependent on shunts there are three
bypass
shunts one at the liver one at the heart
and one at the great vessels
the umbilical vein carries oxygenated
blood
from the placenta to the inferior vena
cava
this is 70 to 80 percent saturated
the blood bypasses hepatic circulation
and enters the ivc
via the first shunt that's the ductus
venosus
so very little blood enters the hepatic
sinusoids
in the ivc the oxygenated blood from the
ductus venosus
tends to stay relatively separate from
the deoxygenated blood
coming from the rest of the lower half
of the body and portal circulation
the blood enters the right atrium from
the ivc
there is a valve of the ivc called the
eustachian valve at the junction with
the right atrium
and that directs the more oxygenated
blood towards the second shunt
the foramen ovale
this is an opening in the atrial septum
so that blood can reach the left atrium
the rest of the deoxygenated blood
coming from the head end of the fetus
through the superior vena cava
and from the lower half of the body and
portal circulation through the ivc
they go through the tricuspid valve into
the right ventricle
from the right ventricle blood enters
the pulmonary artery
the better oxygenated blood from the
left atrium whose saturation now would
be around 65 percent
enters the left ventricle from the left
ventricle the blood enters the aorta
majority of the oxygenated left
ventricular blood
goes to the brain and coronary
circulation so the vital structures are
getting good oxygen
to the origin of the left subclavian
artery is shunt
iii the ductus arteriosus it's a
connection between the pulmonary artery
and the aorta so blood from the
pulmonary artery
goes through the ductus arteriosus to
the aorta
thanks to this shunt only around 12
percent of blood that comes out of the
right ventricle
reaches the lungs the rest goes through
the ductus arteriosus to the aorta
from the aorta blood gets supplied to
the rest of the systems
it passes through the umbilical arteries
back to the placenta for oxygenation
so in both these shunts blood moves from
the right side
to the left side why does that happen so
the fetal lungs are collapsed
the alveoli are closed and the pulmonary
vessels are collapsed
if the vessels are closed the resistance
to blood flow
is high that's the pulmonary vascular
resistance
so that's high and thus the pulmonary
arterial pressure is high
as is the right atrial and the right
ventricular pressure
the placenta on the other hand has large
vessels
so the vascular resistance in systemic
circulation is
low because of the low systemic vascular
resistance
there's a low aortic pressure a low left
atrial and left ventricular pressure
so since the right atrial pressure is
higher than the left atrium
blood flows through the foramino valley
from the right atrium to the left
similarly the pulmonary arterial
pressure is higher than the aortic
so blood flows from the pulmonary artery
to the aorta
so right to left shunt and thus they
bypass the lungs
so blood gets immediately recirculated
through systemic arteries without the
lungs
so what happens at birth the baby takes
a breath and the lungs expand
the vessels are no longer compressed so
the resistance to flow is lesser
so the pulmonary vascular resistance
will fall
during fetal life there's some amount of
hypoxia that keeps the pulmonary vessels
constricted
but once there is aeration there is
vasodilation
so that also reduces the pulmonary
vascular resistance
that in turn causes a reduction of the
pulmonary artery pressure
the right atrial and the right
ventricular pressure loss of blood flow
to the placenta makes the systemic
vascular resistance rise
so high aortic pressure left atrial
pressure
and left ventricular pressure so now the
pressure of the left circulation is
higher than the right
with the left atrial pressure being
higher than the right atrium
blood will flow backwards through the
foramen ovale
there's a flap towards the left side of
the atrial septum
that will close backwards so the shunt
closes
and there's no more flow in most people
it'll close permanently
if it doesn't it's called a patent
foramen ovale
but because in general the left atrial
pressure is gonna stay higher than the
right
the flap stays closed and most of the
times it goes unnoticed
high aortic pressure and low pulmonary
artery pressure means blood flows
backwards through the ductus arteriosus
as well
in a few hours the muscles in the wall
will constrict
more so over the next one to eight days
the flow stops and this is a functional
closure over the next one to four months
once fibrous tissue grows into the lumen
that's when it anatomically closes so
what makes the ductus close
there are two possible reasons one is
high oxygen tension
the partial pressure of oxygen increases
from 15 to 20 millimeters of mercury
during fetal life
to 100 millimeters of mercury once
breathing starts
also there's a loss of prostaglandin e2
and that has vessel relaxing effects
so pg e2 keeps the ductus open
if the ductus remains open it's called a
patent ductus arteriosus
however contrary to fetal life the shunt
here is a left to right shunt
from the aorta to the pulmonary artery
because of the pressure changes
the last shunt the ductus venosus flow
through the
umbilical vein stops the portal blood
goes into the ductus phenosis
a small amount goes through the hepatic
channels in around one to two hours the
muscles in the wall of the ductus
venosus contract and it closes
so a rise in the portal venous pressure
pushes the portal venous blood into the
hepatic sinusoids
a patent ductus venosus is quite rare
in adults these structures they remain
as vestiges
the umbilical arteries become the medial
umbilical ligament
not to be confused with the median
umbilical ligament which is a remnant of
the arrakis
the umbilical veins become ligamentum
tears of the liver
the others are pretty easy the ductus
venosus becomes the ligamentum venosum
the ductus arteriosus becomes the
ligamentum arteriosum
and the foramen ovale it remains as the
fossa ovalis
so that's the fetal circulation and the
changes that happen at birth
thanks for watching and i hope you found
this video useful if you did give this
video a thumbs up and subscribe to my
channel
so i'll see you in the next one
تصفح المزيد من مقاطع الفيديو ذات الصلة
Sirkulasi Darah Fetus aka Janin
Embryology: Development of the Placenta and Fetal Circulation, Animation
胎児循環グランプリ ~酸素を届ける壮絶なレースを実況してみました~
Renal Circulation | Renal Blood Flow | Renal Autoregulation | Renal Physiology
IMAT Biology Lesson 6.4 | Anatomy and Physiology | Circulatory System I
Sistema Cardiovascular - Toda Matéria
5.0 / 5 (0 votes)