1. Fetal Development
RC 290

2. The Placenta

3. Placental 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)

4. Placental 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

5. Maternal-Fetal Circulation
Note: Maternal and fetal blood do not come into direct contact!

6. Maternal-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

7. Umbilical Cord
2 arteries
1 vein
Surrounded by Wharton’s jelly

8. Amniotic 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

9. Blood Gas Values
Hence, fetal PO2 is mmhg!

10. 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 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

11. Fetal Circulation
OOOPS! This is fecal circulation!

12. Fetal Circulation

13. Fetal 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

14. Summary: Fetal Circulation
3 Shunts: Ductus Venosus, Foramen Ovale, and Ductus Arteriosus
Placental Circulation
Only 3-10% of fetal cardiac output actually perfuses the fetal lungs

15. Fetal Lung Development
Lung buds appear at 3.5 weeks
Tracheo-bronchial tree formed by 16 weeks
Alveoli start forming at weeks
Surfactant also starts to form
Capillary networks starts forming and approaching alveoli at weeks
Lungs and surfactant mature at 35 weeks
Normal term is 40 weeks

16. Surfactant
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

17. 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