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Fetal Development. RC 290. The Placenta. 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 Structure. Placental Functions.

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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)

Placental Structure
placental functions
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
maternal fetal circulation
Maternal-Fetal Circulation

Note: Maternal and fetal blood do not come into direct contact!

maternal fetal circulation6
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
umbilical cord
Umbilical Cord
  • 2 arteries
  • 1 vein
  • Surrounded by Wharton’s jelly
amniotic sac
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
blood gas values
Blood 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 circulation
Fetal Circulation

OOOPS! This is fecal circulation!

fetal circulation13
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

Fetal Circulation
summary fetal circulation
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
fetal lung development
Fetal Lung Development
  • Lung buds appear at 3.5 weeks
  • Tracheo-bronchial tree formed by 16 weeks
  • Alveoli start forming at 20-24 weeks
    • Surfactant also starts to form
  • Capillary networks starts forming and approaching alveoli at 26-28 weeks
  • Lungs and surfactant mature at 35 weeks
  • Normal term is 40 weeks
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

Surfactant
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