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Fetal DevelopmentFetal Development
RC 290
The PlacentaThe Placenta
Placental StructurePlacental Structure
Purple and pancake shaped
6 inch diameter, 1 inch thick
13-16 square meter surface area
Attaches to upper 1/3 of uterus
Maternal side: Decidua Basalis
Fetal side: Chorion (attaches to amniotic membrane)
Placental FunctionsPlacental Functions
Primary function is to act as organ of respiration and to be the pathway for exchange of nutrients and waste products between mother and fetus
Physical protection Hormone synthesis Iron and Glycogen storage Some metabolic functions Antibodies
Maternal-Fetal CirculationMaternal-Fetal Circulation
Note: Maternal and fetal blood do not come into direct contact!
Maternal-Fetal CirculationMaternal-Fetal Circulation
Blood comes to IV spaces (maternal side) from uterine arteries
Blood in villi (fetal side) comes from umbilical arteries
After exchange of O2 and CO2, the “fresh blood” returns to the fetus via the umbilical vein
Umbilical CordUmbilical Cord
2 arteries 1 vein Surrounded by
Wharton’s jelly
Amniotic SacAmniotic Sac
The outer layer of the umbilical cord forms the amniotic sac around the fetus
Fetus is in amniotic sac containing amniotic fluid– Amniotic fluid made up of maternal serum and fetal
urine and fetal lung fluid
3 Functions of amniotic fluid:– Shock absorption, temperature stability, sterile
environment
Blood Gas ValuesBlood Gas Values
Hence, fetal PO2 is 25-30 mmhg!
Why is fetal PO2 low?Why is fetal PO2 low?
Placental O2 consumption Admixture and shunting
– Like the lung, the IV space and the villi are not perfectly matched
Fetal hemoglobin (HbF)– More of it (when compared to adult blood) and has greater
affinity for O2– Concentration is 17-18 grams%– Made up of alpha and gamma chains of amino acids– HbF is present for up to two months after birth
Fetal O2 consumption is about twice what an adults is
Fetal CirculationFetal Circulation
OOOPS! This is fecal circulation!
Fetal CirculationFetal Circulation
Fetal CirculationFetal Circulation UV goes into liver and portal
circulation Most of blood shunts across
the Ductus Venosus into the inferior vena cava
As inferior vena cava empties into right atrium, most blood shunts across the Foramen Ovale into the left atrium where it enters the systemic circulation from the left ventricle
– The heart and brain get the best blood first!
Blood from superior vena cava goes into right ventricle and then to pulmonary artery
Most of this blood flow shunts across the Ductus Arteriosus into the aorta
– DA is in the descending aorta after the arch
Pre-ductal blood may have a higher PO2!
– Hence, only 3-10% of fetal cardiac out put perfuses the fetal lings
Summary: Fetal CirculationSummary: Fetal Circulation
3 Shunts: Ductus Venosus, Foramen Ovale, and Ductus Arteriosus
Placental CirculationOnly 3-10% of fetal cardiac output actually
perfuses the fetal lungs
Fetal Lung DevelopmentFetal Lung Development
Lung buds appear at 3.5 weeksTracheo-bronchial tree formed by 16 weeksAlveoli start forming at 20-24 weeks
– Surfactant also starts to formCapillary networks starts forming and
approaching alveoli at 26-28 weeksLungs and surfactant mature at 35 weeksNormal term is 40 weeks
SurfactantSurfactant
Reduces surface tension so alveoli don’t collapse with each exhalation
Is a phospolipid made up of dipalmityl-lecithin and sphingomyelin
Produced through two enzymatic pathways:– Methyl transferase– Phosphocholine
transferase This is the major
pathway and has a longer half-life
Matures last
Respiratory Problems at Birth!Respiratory Problems at Birth!
Immature lung architecture if born premature
And/or:Surfactant levels may not be adequate if:
– Premature birth– Production inhibited if significant hypoxia,
hypothermia, or hypoglycemia