Placenta → umbilical vein → ductus venosus → inferior vena cava → right atrium → foramen ovale → left atrium → left ventricle → aorta → hypogastric arteries → umbilical arteries → placenta.
Blood that passes from the right atrium to the right ventricle travels:
Right ventricle → pulmonary trunk → ductus arteriosus → aorta
Oxygenated blood returns from the placenta through the umbilical vein
enters the portal venous system
enters the inferior vena cava by way of the ductus venosus.
partly deflected across the foramen ovale into the left atrium.
Because of a streaming effect, almost all superior vena caval blood passes directly through the tricuspid valve, entering the right ventricle.
Most of the blood bypasses the high-resistance, unexpanded lungs and passes through the ductus arteriosus into the descending aorta.
The major portion of blood ejected from the left ventricle supplies the brain and upper body to the descending aorta, where it joins with the large stream from the ductus arteriosus before flowing to the lower body and back to the placenta.
Foetal cardiovascular physiology
pulmonary arteries and arterioles =thick walls and a small lumen, similar to arteries in the systemic circulation.
low pulmonary blood flow (7% to 10% of the total cardiac output) = due to high pulmonary vascular resistance.
pulmonary vessels are highly reactive to changes in oxygen tension or in the pH of blood perfusing them .
3 shunts exist in utero which allow blood to bypass the lungs, liver and kidneys, whose functions are performed by the placenta
foramen ovale - blood travels from the right atrium to the left atrium
ductus venosus - blood from the umbilical vein bypasses the liver to enter the inferior vena cava
ductus arteriosus - blood passes from the pulmonary trunk into the aorta
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