Lecture 3.2 - Fetal circulation

Study Notes

In-utero, the lung is not functional, and the fetus receives nutrients from the placenta.
Hypoxic vasoconstriction of pulmonary arteries occurs due to lack of oxygen.
Pressure is higher in the right side of the heart compared to the left side.

Oxygenated blood from the placenta is carried by the umbilical vein to the hepatic portion of the inferior vena cava (IVC).
The ductus venosus shunts blood from the umbilical vein into the IVC.
Blood passes from the IVC to the right atrium, then through the foramen ovale to the left atrium.
Blood flows from the right to left atrium due to higher pressure in the right side, allowing for more oxygenated blood.
Blood then passes from the left atrium to the left ventricle, aorta, and body.
Some blood passes into the right ventricle, pulmonary trunk, and arteries, and then through the ductus arteriosus shunt into the aorta.

Deoxygenated blood is carried by the superior vena cava (SVC) to the right atrium.
Oxygenated and deoxygenated blood mixes in the right atrium.
Blood passes from the right atrium to the right ventricle, pulmonary arteries, and then through the ductus arteriosus shunt into the aorta.
Blood then flows from the descending aorta to the internal iliac artery, and then through the two umbilical arteries to the placenta.

After birth, the lung becomes functional, and hypoxic vasoconstriction of pulmonary arteries ceases.
Pressure is lower in the right side of the heart compared to the left side.
The blood level in pulmonary arteries increases, and pulmonary veins empty blood into the left atrium, establishing the adult system.