Fetal & Adult Circulation

FETAL & ADULT CIRCULATION

Fetal Circulation Blood from placenta (80% saturation) returns to fetus via umbilical vein  Main portion of blood flows through the ductus venosus directly into IVC  Smaller portion enters the liver sinusoids (mixes with blood from portal circulation)  Sphincter mechanism in ductus venosus 

In IVC mixes blood from lower limbs  Enters right atrium  Guided by the valve of IVC toward foramen ovale and passes to left atrium  A small portion remains & mixes with blood from head & upper limbs (SVC)  In left atrium (mixes with blood from lungs) → left ventricle & ascending aorta  Heart muscle & brain receive well-oxygenated blood  From SVC into right ventricle → pulmonary trunk 

 Resistance

in pulmonary vessels is high, most of the blood passes into descending aorta via ductus arteriosus (mixes with blood from proximal aorta)  Descending aorta → umbilical arteries (oxygen saturation ~ 58%) → placenta

 2. 3. 4. 5. 6.

Mixing with desaturated blood may occur in the following places: liver inferior vena cava right atrium left atrium at the entrance of the ductus arteriosus into the aorta

Changes At Birth Changes are caused by cessation of placental blood flow & beginning of respiration  As the alveoli expand, constricted pulmonary vessels open (response to O2) & the Ω of the pulmonary vasculature drop  Spontaneous constriction of the umbilical vessels cuts off blood flow from placenta 

 Create

changes in pressure & flow that cause ductus ateriosus to constrict & foramen ovale to close  Pressure ↓ in pulmonary trunk → slight reversal of flow through the ductus arteriosus  ↑ in O2 tension → ductus arteriosus constrict

 Closure

of foramen ovale due to reversal in pressure between the 2 atria  Cessation of umbilical flow & opening of the pulmonary vasculature → ↓ pressure in right atrium  Sudden ↑ in pulmonary venous return → ↑ pressure in left atrium  Septum primum pressed against septum secundum  First few days, reversible  Fusion in about 1 year  Probe patent foramen ovale – 20% of individuals

1.

Closure of the umbilical arteries contraction of smooth muscle thermal & mechanical stimuli & change in O2 tension actual obliteration, 2 – 3 months distal parts → medial umbilcal ligaments proximal parts → superior vesical arteries

2. Closure of the umbilical vein & ductus venosus occurs shortly after that of umbilical arteries umbilical vein → ligamentum teres hepatis ductus venosus → ligamentum venosum

3. Closure of ductus arteriosus contraction of smooth muscle mediated by bradykinin complete anatomical closure, 1 – 3 months → ligamentum arteriosum 4. Closure of foramen ovale