Fetal Circulation Flashcards
Where does nutrient and waste exchange between the mother and fetus occur?
Placenta
Fetal organs not functional until birth
Lungs
Kidneys
GI tract
Carries blood away from fetus to placenta
Umbilical artery
-low O2 content, carries waste and CO2
Carries blood from placenta to fetus
Umbilical vein
-carries nutrient and O2, high O2 content
Umbilical arteries and veins branch into these that are located in the intervillous space in the placenta
Fetal capillaries
Spaces filled with maternal blood from uterine arterioles, drained by uterine veins
Intervillous spaces
How much higher is the concentration if hemoglobin in fetal blood compared to adult?
50% higher
Can carry 30-35% more oxygen
Exchange of gases in the placenta
Exchange of CO2, O2, CO (via diffusion)
- 20-30ml/min O2 extracted
- short interruption of blood flow can be fatal to fetus
- depends on delivery not diffusion
Exchange of nutrients in placenta
Amino acids, free fatty acids, carbohydrates, vitamins
Exchange is rapid and increases throughout pregnancy
Transfer of maternal antibodies in placenta
Late first trimester: fetus makes component of complement, start of immunologic competence
IgG can cross placenta, passive immunity
Hormone production in the placenta
4th month: placenta produces enough progesterone to maintain pregnancy if corpus luteum should fail
Continues to produce estrogenic hormones (estriol, rises until end of pregnancy)
Umbilical arteries
From fetus to placenta
Have 2
Branch from internal iliac arteries
Saturation about 58%
Umbilical vein
Have 1
Saturation about 80%
Goes to liver of fetus and divides into hepatic portal vein (to liver, 1/3) and ductus venous (to IVC, 2/3)
Blood in the IVC
Oxygenated blood via ductus venosus meets deoxygenated blood from lower body
Saturation drops to 67%
Blood path that enters IVC
IVC–>RA–>Foramen ovale–>LA–>LV–>Aorta–>perfused brain and myocardium
Blood path that enters SVC
SVC–>RA–>RV–>PA–>ductus arteriosus–>descending aorta–>perfused fetal tissue
Only fetal vessel to carry fully oxygenated blood
Umbilical vein
3 shunts present in fetal circulation that usually close after birth
Ductus arteriosus
Foramen ovale
Ductus venosus
Umbilical arteries after birth
Get contraction in smooth muscle walls caused by thermal and mechanical stimuli and change in oxygen tension
Functionally close after birth and fill with connective tissue
Distal portion becomes fibrous cords (medical umbilical ligaments)
Complete closure takes 2-3 months
Umbilical vein after birth
Collapses shorty after umbilical arteries
Blood from placenta may enter newborn for some time after birth
Remains as the ligamentum teres hepatis (lower margin of falciform ligament that attaches umbilicus to liver)
Ductus venosus after birth
Collapses
Remains as ligamentum venosum (fibrous cord on inferior surface of liver)
Patent ductus venosus extremely rare
Foramen ovale after birth
Closes after birth becoming fossa ovalis:
- First breath causes lungs to expand, increases BF to lungs
- XBlood returning to LA increases pressure in LA (pressure in RA falls)
- Septum primum gets pushed against septum secundum, closing formamen ovale (can be reversible first days of birth because crying baby can create a right to left shunt causing cyanosis)
- Constant apposition leads to fusion of septa
- Permanent closure within first year of life
Patent foramen ovale
Foramen ovale that has not closed after a year
27% prevalence
Most patients asymptomatic
Ductus arteriosus after birth
Closes via contraction of muscular wall after birth (mediated by bradykinin)
After first breath, lungs fill with air instead of fluid, pulmonary BF increases
Ductus protects pulmonary vasculature from overload, closes via vasoconstriction (1-2 days after birth)
Becomes ligamentum arteriosum
Complete obliteration takes 1-3 months
