What is fetal circulation and why is it different from adult circulation?

Fetal circulation is the unique circulatory pathway in a fetus, distinct from adults because the lungs are non-functional and collapsed in utero. Instead, the placenta acts as the organ for oxygenation, nutrient exchange, and waste elimination, bypassing the underdeveloped systems.

What are the key shunts in fetal circulation and what do they do?

The fetal circulatory system has three main shunts that bypass non-functional organs: the ductus venosus shunts blood from the umbilical vein to the inferior vena cava, bypassing the liver; the foramen ovale directs oxygen-rich blood from the right atrium to the left atrium, bypassing the lungs; and the ductus arteriosus connects the pulmonary trunk to the descending aorta, diverting blood away from the lungs.

How does oxygenated blood flow from the placenta to the fetus?

Oxygenated blood from the placenta travels via the left umbilical vein through the umbilical cord. Most of this blood bypasses the liver via the ductus venosus to reach the inferior vena cava, then enters the right atrium and is directed through the foramen ovale into the left atrium for distribution to the upper body.

What happens to deoxygenated blood in fetal circulation?

Deoxygenated blood from the upper body returns via the superior vena cava to the right atrium, then into the right ventricle. It enters the pulmonary trunk and is diverted via the ductus arteriosus into the descending aorta, eventually traveling through umbilical arteries back to the placenta for oxygenation.

What do fetal circulatory structures become after birth?

After birth, fetal shunts and vessels close and form adult remnants: the ductus venosus becomes the ligamentum venosum, the foramen ovale becomes the fossa ovalis, the ductus arteriosus becomes the ligamentum arteriosum, the left umbilical vein becomes the ligamentum teres hepatis, and the umbilical arteries become the medial umbilical ligaments.

Why is the placenta important in fetal circulation?

The placenta is crucial because it compensates for the underdeveloped fetal organs by acting as the functional equivalent for respiration, nutrition, and excretion. It serves as the organ for oxygenation, nutrient exchange, and waste elimination, replacing the non-functional lungs and insignificant portal circulation.

Fetal Circulation – Shunts & Postnatal Remnants