The presentation discusses fetal circulation, highlighting the unique pathways that allow the fetus to receive oxygen and nutrients from the placenta while bypassing the lungs. It outlines blood flow patterns in the fetus and the essential vessels involved, such as the umbilical vein, ductus venosus, foramen ovale, and ductus arteriosus. Following birth, significant changes occur in circulation as the foramen ovale and ductus arteriosus close, transitioning fetal circulation to adult circulation as the baby takes its first breath.

1. Presentation by group one
On
FETAL CIRCULATION AND CHANGES
AFTER BIRTH

2. FETAL CIRCULATION
• The fetal circulation supplies tissues of the
foetus with oxygen and nutrients from the
placenta. It bypasses the fetal lungs.
• Though the fetus does not perform any
vigorous metabolic activity for its survival, it
requires efficient circulation to keep the
development of its organs.

3. FETAL CIRCULATION CONT’
• During intra uterine life the fetus obtains
nourishment from the maternal blood
whether it has enough for her own use or not.
• The fetus receives oxygen and excretes carbon
dioxide through the placenta because its lungs
do not function as organs of gas exchange in
utero.

4. FETAL CIRCULATION CONT’
• To ensure this, the fetal circulation contains
certain vessels (bypasses) that shunt the blood
around the lungs, with only small amount
circulating through them for nutritional
purposes.

5. SPECIAL VESSELS OR BYPASSES
• Umbilical veins (carries oxygenated blood
from the placenta)
• Ductus venosus ( from vein to vein)
• Foramen ovale
• Ductus arteriosus (from an artery to artery)
• Hypogastrics arteries
• Umbilical arteries (carries deoxygenated blood
to the placenta)

6. BLOOD FLOW IN THE FETUS
• From the onset (placenta), oxygenated blood
flows to the umbilical cord through the
umbilical vein from the placenta and passes
into the inferior vena cava.
• However, on its way to the inferior vena cava,
as the umbilical vein passes undersurface of
the liver, it divides into two (a smaller and a
bigger part).

7. BLOOD FLOW IN THE FETUS CONT’
• The smaller part of the oxygenated blood goes
to the liver but most of it passes through the
Ductus venosus, a vessel that connects the
Umbilical vein and the inferior vena cava.
• From the inferior vena cava, the blood flows
into the right atrium then directly into the left
atrium through the Foramen ovale.

8. BLOOD FLOW IN THE FETUS CONT’
• Then from the left atrium the blood flows into
the left ventricle and out through the aorta to
supply the arms and the head after which it
returns to the right atrium through the
superior vena cava.

9. BLOOD FLOW IN THE FETUS CONT’
• However, from the right atrium, instead of
blood passing through the Foramen ovale, it is
pushed downwards into the right ventricle.
• It must be noted that 25% of mixing of both
deoxygenated and oxygenated occurs at this
time.

10. BLOOD FLOW IN THE FETUS CONT’
• Finally, from the right ventricle the blood flows
through the pulmonary arteries small
amounts of blood goes to the lungs to nourish
it as the great chunk join the descending
aorta through the Ductus arteriosus.
• The blood in the descending aorta supplies
the trunk and lower extremities.

11. BLOOD FLOW IN THE FETUS CONT’
• As the descending aorta reaches the pelvis
little amount goes to supply the structures of
the pelvis whiles bulk enters its way to the
through the Hypogastric arteries (internal
iliac) and back through the umbilical arteries
to the placenta to be oxygenated.

12. CHANGES THAT OCCUR AT BIRTH
• The umbilical vessels are obliterated when the cord
is clamped externally and becomes vesicle ligaments
on anterior abdominal wall. Note the umbilical vein
within the body becomes the round ligament of the
liver.
• There is a fall in blood flow through the inferior vena
cava and the ductus venosus, the latter subsequently
closes passively over the next 3 – 10 days. Lung
expansion occurs as the baby takes his first breath
resulting in increased blood flow into the lungs.

13. CHANGES THAT OCCUR AT BIRTH CONT’
• The increase in pulmonary blood flow leads to
a large rise in pulmonary venous return to the
left atrium.
• The left atrial pressure therefore exceeds the
right atrial pressure. This pressure gradient
across the atrium allows the flap of the
foramen ovale to push against the atrial
septum and the atrial shunt is effectively
closed.

14. CHANGES THAT OCCUR AT BIRTH CONT’
• Although the initial closure of the foramen
ovale occurs within minutes to hours after
birth, anatomical closure by tissue
proliferation takes several days.
• The instantaneous closure of the foramen
ovale changes the entire course of blood flow
and converts fetal circulation to into an adult
one.

15. CHANGES THAT OCCUR AT BIRTH CONT’
• As a result, all blood from the right atrium now
passes into the right ventricle. The ductus
arteriosus constricts due to high partial pressure
of oxygen and the process is usually completed
within 2days after birth.
• The ductus arteriosus and the ductus venosus
shrivel up, that is become dry and smaller and are
converted into ligamentum arteriosum and
ligamentum venosum in 2 – 3 months respectively.

16. CHANGES THAT OCCUR AT BIRTH CONT’
• After the umbilical cord is tied and separated,
the large amount of blood returned to the
heart and lungs causes equal pressures in both
atrium causing the foramen ovale to close and
eventually disappears.
•

17. THE END