• Acts as fetal lung during gestation
• Less efficient than the lungs
• Less efficient blood flow pattern for gas exchange
• "hypoxic"(less oxygen) environment

Fetal hemoglobin has higher O₂ affinity than adult hemoglobin.

Fetal has lower lower P₅₀

↑RBC

↓P₅₀=↑Hb oxygen affinity

Fetal shunt(vessel) that brings oxygenated blood from placenta to heart, bypassing the liver.

Fetal opening that shunts blood from right to left atrium and through the left ventrical to the head.

• Less oxygenated blood from the brain comes to the right atrium through the superior vena cava.
• The blood goes from right atrium to right ventricle  and out the pulmonary artery.
• The blood bypasses the lungs through the ductus arteriosus and enters aorta.

They constrict... unlike systematic vessels

• right(venous) side converts to low pressure, left(aterial) side converts to high pressure.
• Clamping the umbilical cord increases arterial vascular resistance and decreases venous return.
• Shunts must close

Need huge negative and huge positive pressure to open the lung.

Less pressure is needed as time goes on.

Decreases surface tension of lungs so that it can expand properly.

Premature babies don't have it.

• Closure in 1-3 hours
• closure of smooth muscle.
• Mechanism not understood

• Decreased pulmonary vascular resistance lowers right atrial pressure.
• Blood returning from lungs raises right atrium pressure
• valve-like Foramen Ovale closes

• within 1-8 days.
• ↑O₂
• ↓Prostaglandin E

• Ductus arteriosus doesn't close.
• Blood goes from Left→ Right(Aorta to Pulmonary Artery) Acyanotic
• Enlargement of LA, LV, and Aorta
• If pressure gets to high in Pulmonary artery the direction of blood flow will reverse and become Cynotic. Eisenmenger's syndrome.

• Shunt between the Atrium. (Maybe foramen ovale doesn't close)
• Can be Acyanotic or Cyanotic(Eisenmenger's)
• Enlargement of the RA, RV, and PA

Most Common

• Shunt between Ventricals.
• Starts off Acyanotic but can become cyanotic.
• Enlargement of LA and LV