Fetal Circulation
Umbilical vein carrying oxygenated blood from placenta (80%), enters fetus at umbilicus.
In liver oxygenated blood mixed with some portal venous blood, through ductus venousus (from portal vein in left lobe; which receive deoxygenated blood), blood enter inferior vena cava (IVC), little mixing.
Then blood reaches right atrium of heart.
Through foramen ovale (PFO) blood directed into left atrium (75% oxygenated blood).
Left atrial blood is passed on through mitral opening into left ventricle.
Left ventricular blood pumped into ascending and arch of aorta and distributed to heart, neck, brain, arms.
(25%) deoxygenated blood, after reaching right atrium via superior and inferior venacava, passes through tricuspid opening into right ventricle.
Right ventricular blood (deoxygenated blood), enter into pulmonary artery, where through ductus arteriosus blood enter into descending aorta (bypassing lung).
After aorta deoxygenated blood leaves by way of two umbilical arteries to reach placenta, where blood gets oxygenated and get ready for recirculation.
Changes of the Fetal Circulation at Birth
Changes soon after birth due to;
1. Cessation of placental blood flow
2. Initiation of respiration
Following changes occurs;
1. Closure of umbilical arteries
Functional closure; preventing blood drain out
2. Closure of umbilical vein
Umbilical vein forms ligamentum teres and ductus venosus become ligamentum venosum.
3. Closure of ductus arteriosus
Functional closure; 1-3 months and become ligamentum arteriosum (no useful function).
4. Closure of foramen ovale
Functional closure soon after birth, but anatomical closure about 1 year.
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