Sirkulasi Fetus (Fetus Circulation)

7/15/2019 Sirkulasi Fetus (Fetus Circulation)

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Rahmatina B Herman

Bagian FisiologiFak Kedokteran Univ Andalas


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Fetal Circulation

Differs from the postnatal (after birth)circulation, because

Lungs, kidneys, and gastrointestinaltract are nonfunctional

O2 and nutrients are derived from

maternal blood

CO2 and wastes are eliminated intomaternal blood


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Placenta

Is the fetal lungHowever cellular layers covering the

villi are thicker and less permeable thanthe alveolar membranes in the lungsand exchange is much less efficient

Is also the route by which all nutritivematerials enter the fetus and wastesare discharged to the maternal blood


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Arrangement of Fetal Circulation

55 % of fetal COP goes through placenta

Blood in umbilical vein 80 % saturatedwith O2 (in arterial circulation of adult:

98 % )

Ductus venosus diverts some of the blooddirectly to IVC (Inferior Vena Cava) and

remainders mixes with portal blood- IVC blood is 67 % saturated with O2

- Portal and systemic venous blood isonly 26 % saturated with O2


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Most of the blood entering heart throughIVC is diverted directly to left atrium viaforamen ovale left ventricleMost of blood from SVC enters rightventricle and is expelled into pulmonaryartery

Resistance of collapsed lungs is very highPressure in pulmonary artery > aorta

Most of the blood from pulmonary arterypasses into aorta via ductus arteriosus


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In this fashion:

Relatively unsaturated blood from rightventricle is diverted into trunk and lower

bodyThe head of fetus receives the better-oxygenated blood from the left ventricle

From aorta, some of blood is pumped into

the umbilical arteries and back to placentaO2 saturation of the blood in lower aortaand umbilical arteries is 60 % saturatedwith O2


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Fetal Respiration

Tissues of fetal and newborn mammalshave a remarkable but poorly understoodresistance to hypoxia

O2 saturation of maternal blood inplacenta is so low that the fetus mightsuffer hypoxic damage if fetal red cells didnot have a greater O2 affinity than adult

Fetal red cells contain fetal Hb (Hb F)while adult red cells contain adult Hb (HbA)


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Changes in Fetal Circulation

& Respiration at BirthAt birth, placental circulation is cut off andperipheral resistance suddenly rises

Pressure in aorta rises until > than in

pulmonary arteryBecause of placental circulation has been cutoff, the infant becomes increasingly asphyxial

Finally, infant gasps several times and the

lungs expand

Markedly negative intrapleural pressure (-30to -50 mmHg) during the gasps contributes tothe expansion of the lungs


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Changes in Fetal Circulation.& Respiration at BirthThe sucking action of the first breath plusconstriction umbilical veins squeezes 100 mlof blood from placenta (the placentaltransfusion)

Once the lungs are expanded, the pulmonaryvascular resistance falls to < 20% of uterovalue and pulmonary blood flow increasesmarkedly

Blood returning from the lungs raises thepressure in the left atrium, closing foramenovale by pushing the valve that guards itagainst the interatrial septum


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Changes in Fetal Circulation.& Respiration at Birth

Ductus arteriosus constricts within a fewhours after birth, producing functional

closure, and permanent anatomic closurefollows in the next 24-48 hours due toextensive intimal thickening

Mechanism producing the initial

constriction is not completely understood,but the increase in arterial O2 tensionplays an important role


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Changes in Fetal Circulation.& Respiration at Birth

Relatively high concentrations ofvasodilators (especially prostaglandin) arepresent in the ductus arteriosus

Synthesis of the prostaglandin is inhibitedby inhibition of cyclooxygenase at birth

In many premature infants the ductus failsto close spontaneously, but closure can beproduced by infusion of drugs that inhibitcyclooxygenase


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Sirkulasi Fetus (Fetus Circulation)