Fetal circulation Flashcards
3 fetal vascular communications
ductus venosus
ductus arteriosus
foramen ovale
Role of fetal vascular communications
DA and FO: bypass lungs
DV: bypass liver (50% of blood)
Pulm blood flow in fetal circ and why
5-10%
SpO2 50%
Low O2 tension of this fluid => constriction of pulmonary vessels => high PVR => facilitates shunting of blood => ductus arteriosus => systemic circulation
Role of crista terminalis in fetal circ
guide blood into FO
Highest SpO2
85% in UMBILICAL VEIN
Defects resulting from inappropriate closure
ASD or PDA
Changes after birth
- Ductus arteriosus:
* Aeration of lungs => fluid surrounding pulmonary vasculature replaced by air => decr PVR → ↓ R sided P
* Allows collapsed vessels to open
* Vasodilation 2nd to incr in O2 tension
* ↑ pulmonary blood flow → ↑ LAP → functional closure of PFO
* Removal of placental circulation => incr SVR => ↑ L sided P → prevents R to L shunt through ductus arteriosus
* Contraction of ductus musculature 2nd to O2 exposure + ↓ PGE (by 6-8day/old)
* Sensitive to O2 tension
* Mediated by local prostaglandins/bradykinins
o During gestation = incr PGE2 secondary to hypoxia maintain relaxation of smooth muscles in the ductus - Foramen ovale:
* Ductus arteriosus closure + decr PVR => incr volume to LA (incr blood flow to lungs) => incr LA and decr RA pressures => septum primum flap against secundum - Ductus venosus: constriction 2nd to decr pressure in CaVC and RA
Anatomical closure
Fibrosis
Circulation in primitive heart
peristaltism waves from sinus venosus => truncus arteriosus
1. Bidirectional for 4w, then unidirectional flow
2. Venous blood => sinoatrial orifice (sinoatrial valve + septum spurium) => sinus venosus => AV canal =>bulbus cordis => truncus arteriosus => aortic arches + dorsal aorta => umbilical/vitellin arteries
Circulation after partitioning
double // circuit w crossover prox. and distal to ventricles
1. Placenta => umbilical veins => ductus venosus (50%)/hepatic sinusoid (50%) => CaVC => RA => fossa ovalis => LA => LV => Ao => head/heart
* Lower edge of septum primum acting as a flap: allows shunt from R to L only. Pressure is in RA vs LA.
2. Blood from CrVC (SpO2 50%) => RA => crista dividens => RV => PA => ductus arteriosus => Ao => lower body (50-60%)/umbilical arteries (40-50%) => placenta
* Pulmonary circulation = high resistance => 5-10% of RV blood flow
* Pulmonary alveoli filled w amniotic fluid
Fetal echo
- Foramen ovale: RA => LA
- Continuous flow through in LPA => PDA
Embryologic venous systems
3 bilateral symmetric venous drainage => enter sinus venosus of primitive heart tube
* Vitelline: drains embryonic GI and gut derivatives
* Umbilical: bring O2 blood from placenta heart
o No derivative of embryonic umbilical venous drainage
o Left umbilical vein will anastomose w ductus venosus
* Cardinal: return blood from embryonic head, neck and body wall
Vitelline
drains embryonic GI and gut derivatives
o Yolk sac → sinus venosus
o Forms hepatic veins + part of CaVC
Umbilical
- Umbilical: bring O2 blood from placenta => sinus venosus → heart
o No derivative of embryonic umbilical venous drainage
o Left umbilical vein will anastomose w ductus venosus
Extraembryonic venous sytems
Vitelline
Umbilical
