Fetal & Adult Circulation

8/14/2019 Fetal & Adult Circulation

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FETAL & ADULT

CIRCULATION


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Fetal CirculationBlood from placenta (80% saturation) returnsto fetus via umbilical veinMain portion of blood flows through theductus venosus directly into IVCSmaller portion enters the liver sinusoids(mixes with blood from portal circulation)

Sphincter mechanism in ductus venosus


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In IVC mixes blood from lower limbsEnters right atrium

Guided by the valve of IVC toward foramenovale and passes to left atriumA small portion remains & mixes with blood

from head & upper limbs (SVC)In left atrium (mixes with blood from lungs) left ventricle & ascending aortaHeart muscle & brain receive well-oxygenatedbloodFrom SVC into right ventricle pulmonarytrunk


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Resistance in pulmonary vessels ishigh, most of the blood passes intodescending aorta via ductus arteriosus(mixes with blood from proximal aorta)Descending aorta umbilical arteries(oxygen saturation ~ 58%) placenta


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Mixing with desaturated blood mayoccur in the following places:

2. liver 3. inferior vena cava4. right atrium5. left atrium6. at the entrance of the ductus

arteriosus into the aorta


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Changes At BirthChanges are caused by cessation of placental blood flow & beginning of respiration

As the alveoli expand, constricted pulmonaryvessels open (response to O 2) & the of thepulmonary vasculature drop

Spontaneous constriction of the umbilicalvessels cuts off blood flow from placenta


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Create changes in pressure & flow thatcause ductus ateriosus to constrict &foramen ovale to closePressure in pulmonary trunk slightreversal of flow through the ductusarteriosus

in O 2 tension ductus arteriosusconstrict


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Closure of foramen ovale due toreversal in pressure between the 2 atria

Cessation of umbilical flow & opening of the pulmonary vasculature pressure in right atriumSudden in pulmonary venous return pressure in left atriumSeptum primum pressed againstseptum secundum

First few days, reversibleFusion in about 1 year Probe patent foramen ovale 20% of

individuals


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1. Closure of the umbilical arteriescontraction of smooth musclethermal & mechanical stimuli & change in

O 2 tensionactual obliteration, 2 3 monthsdistal parts medial umbilcal ligaments

proximal parts superior vesical arteries


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2. Closure of the umbilical vein & ductusvenosusoccurs shortly after that of umbilical

arteriesumbilical vein ligamentum tereshepatis

ductus venosus ligamentumvenosum


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3. Closure of ductus arteriosuscontraction of smooth musclemediated by bradykinincomplete anatomical closure, 1 3

months ligamentum arteriosum

4. Closure of foramen ovale

Fetal & Adult Circulation

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