How does fetal circulation differ from adult circulation?

Fetal circulation is adapted for life in the womb, where oxygenation occurs in the placenta instead of the lungs. The fetal lungs are non-functional, leading to high pulmonary resistance, and the portal circulation plays a minimal role compared to postnatal life.

What is the pathway of oxygenated blood from the placenta in fetal circulation?

Oxygenated blood from the placenta travels via the left umbilical vein to the fetal liver. It mainly bypasses the liver through the ductus venosus to join the inferior vena cava (IVC), then enters the right atrium and is directed through the foramen ovale into the left atrium for distribution to the brain and upper body.

How does blood bypass the lungs in fetal circulation?

Most blood from the right ventricle flows into the pulmonary trunk but bypasses the collapsed lungs via the ductus arteriosus, which shunts it directly into the aortic arch. This ensures that oxygenated blood from the placenta is prioritized for vital organs like the brain and heart.

What happens to fetal circulatory structures after birth?

After birth, key fetal structures close and transform into ligaments or remnants. The foramen ovale closes to form the fossa ovalis, the ductus arteriosus constricts into the ligamentum arteriosum, and the umbilical vein becomes the ligamentum teres hepatis. These changes establish adult circulation.

What are the postnatal remnants of the umbilical arteries?

The umbilical arteries transform after birth. Proximal parts remain patent as the superior vesical arteries, while distal parts become the medial umbilical ligaments. This reflects the shift from placental to systemic circulation.

Why is the foramen ovale important in fetal circulation?

The foramen ovale is a crucial shunt that allows oxygenated blood from the inferior vena cava to bypass the right ventricle and lungs, directing it directly into the left atrium. This ensures that the most oxygen-rich blood reaches the brain and heart efficiently.

Fetal Circulation – Shunts & Postnatal Closure