Physiology chapter presentation Reference - Guyton and Hall By Swetha Rani Savala, MBBS 1st year (2017), Gandhi medical College, Hyderabad.

1. Fetal and Neonatal
circulation
- Swetha Rani

2. Basics to remember
Development of the heart -
between 20-44 days after
fertilization
The Heart starts beating during
the 4th week - Rate of 65
beats/min
Just before birth - 140 beats/min

3. Adult : The lungs oxygenate venous blood
and the liver handles the products of
digestion from portal vein to pass the
nutritional blood to the heart.
Fetus : The placenta handles both these
functions and so the lungs and liver need
less blood (almost non functional). Lungs
are compressed and filled with fluid here.
Shunts are present anatomically which
bypass instead of direct blood flow through
the liver and lungs. They have Valves.

4. PATHWAY TO THE UPPER
EXTREMITIES
Placenta → Umbilical vein →
Ductus venosus (shunt bypasses
liver) → Right atrium → Foramen
ovale → Left atrium → Ascending
Aorta
Blood flows to the arteries of
head and forelimbs
OXYGENATION OF THE
BLOOD
Head and forelimbs → Superior
vena cava → Right atrium→ Right
ventricle → Pulmonary artery →
Ductus Arteriosus (Shunt
bypasses lungs) → Descending
aorta → Umbilical arteries →
Placenta

5. Changes after Birth
Placental connection is lost: The
Umbilical cord is cut and clamped to the baby,
This constricts the umbilical vessels and the
Vascular resistance for the blood to return
from the descending aorta to the right atrium
INCREASES
Systemic Resistance ↑ (x2)
Aortic pressure ↑
Left Atrial and Ventricular pressure ↑

6. Onset of Breathing: The CNS reacts to the sudden
change in temperature and new environment. This
triggers it to take the first breath, within about 10
seconds after delivery. The Hypoxic baby this
eliminates lung fluid and expands the lungs.
Vasodilation of the compressed blood vessels takes
place and hypoxia is eliminated
Resistance to blood flow through lungs ↓
DECREASES (x5)
Pulmonary arterial pressure ↓
Right atrial and ventricular pressure ↓

7. Right atrium and ventricle - Low Pressure
Left atrium and ventricle - High Pressure
Blood travels from Left to Right side of the
heart now. The direction of blood flows
reverses over Ductus Arteriosus and
foramen ovale.
Closure of Foramen Ovale : A small valve
present on the left side of atrial septum closes
over the opening of the foramen to prevent
blood flow through it. The valve becomes
adherent over the foramen within a few
months.
Fossa Ovalis -Remnant

8. Patent Foramen Ovale : When permanent closure does
not occur. The Left atrial pressure is 2-3 mm of Hg >
Right atrial pressure through out life. This keeps the
valve closed and prevents mixing of blood.
Closure of Ductus Venosus : Most of the blood still
flows through Ductus Venosus even after the placental
connection is lost immediately after birth, however
within 3 Hours the muscle of Ductus Venosus contracts
strongly and closes the blood flow through it. Patent
Ductus Venosus is rare.
The Pressure increases in the portal vein to about 6-
10mm of Hg and forces blood to finally open into the
liver sinuses.

9. Closure of Ductus Arteriosus :
Aortic pressure ↑
Pulmonary arterial pressure↓
Backflow of blood from aorta to pulmonary artery
The muscle wall constricts within 8
days after birth due to the loss of
PGE2
Prostaglandin E2 - Vasodilator
Increased oxygenation through ductus is also a factor for
closure
Po2 increases from 20mmHg immediately after birth to 100
mmHg within a few hours
Patent Ductus Arteriosus : Failure to flow
hrough systemic circulation (bypasses)

10. Recirculation Through the lungs
Pulmonary Congestion and Pulmonary
Edema
Patent Ductus Arteriosus/ Left to right shunt
Atrium
Ventricle
Early death due to heart
disease between 20 to 40
years

11. Machinery Murmur : Abnormal Heart
sound
Not found when Immediately born
Age 1-3 years : Harsh Blowing Continous Murmur
Aortic pressure High - Systole - Intense murmur
Aortic pressure Low - Diastole - Less intense

12. Congenital Heart
defects
These cause abnormal circulatory
effects.
The 3 Major congenital anomalies
1. Stenosis of a major blood vessel
2. Left to right Shunt (Patent Ductus
Arteriosus)
3. Right to Left Shunt (Tetrology of
Fallot)

13. Tetrology of Fallot /Right to left Shunt
Most Common cause of Blue baby syndrome
• Ventricular Septal
Hole/Defect
• Pulmonary Artery
stenosis
• Overriding Aorta
• Right Ventricle
Hypertrophy
Four main abnormalities
* VPOR*

14. Diagnosis of a Blue baby
Boot shaped Heart Abnormal Angiogram

15. Is this the future?!

16. Thank you!
Not all Superheroes wear
Capes
Moms!