Lecture 3.2 - Fetal circulation.pdf

Fetal circulation: in-utero: ◦Pressures on left and right side of the foetal heart in-utero ‣ Lung is not functional -as foetus is gaining nutrients from placenta, and so isn't breathing in or out any air ‣ Hypoxic vasoconstriction of pulmonary arteries - since there is...

Fetal circulation: in-utero: ◦Pressures on left and right side of the foetal heart in-utero ‣ Lung is not functional -as foetus is gaining nutrients from placenta, and so isn't breathing in or out any air ‣ Hypoxic vasoconstriction of pulmonary arteries - since there is no oxygen for the arteries to travel towards ‣ Pressure higher in the right side of the heart compared to the left side Fetal circulation: oxygenated blood: ◦The umbilical vein carries oxygenated blood from placenta-> hepatic portion of inferior vena cava (IVC) ◦Ductus venosus - shunts blood from umbilical vein into the IVC ◦Blood passes from IVC to right atrium -> foramen ovale -> left atrium ‣ Blood passes from right to left as there is higher pressure in right side - to get more oxygenated blood ◦Blood passes from left atrium -> left ventricle -> aorta -> body ◦Some blood passes into right ventricle -> pulmonary trunk and arteries -> Ductus arteriosus (shunt)-> aorta Fetal circulation: deoxygenated blood: ◦Deoxygenated blood carried by superior vena cava (SVC) -> right atrium ‣ Oxygenated and deoxygenated blood mixes in the right atrium ◦Blood passes from right atrium -> right ventricle -> pulmonary arteries -> Ductus arteriosus -> Aorta ◦Descending aorta -> internal iliac artery -> 2x umbilical arteries -> placenta Fetal circulation - after birth: ◦Pressures on left and right side of the foetal heart after birth: ‣ Lung is functional ‣ No hypoxic vasoconstriction of pulmonary arteries - so arteries get filled with blood ‣ Pressure lower in the right side of the heart compared to the left side ‣ Blood level in pulmonary arteries increases ‣ Pulmonary veins empty blood into left atrium - adult system is established Fate of fetal shunts: ◦Umbilical vein disintegrates-> becomes Ligamentum Teres ◦Umbilical arteries disintegrates -> becomes medial umbilical ligament ◦Ductus venosus closes -> becomes Ligamentum venosum ◦Foramen ovale closes -> becomes Fossa Ovalis ◦Ductus arteriosus closes -> becomes Ligamentum arteriosum.