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Placenta

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  • 1. The Placenta
    • Early gestation (10-12 weeks) is the period of placentiation
      • Fetus is nourished by secretions of uterine endometrial glands in early gestation
    • Placenta is a metabolically active tissue
      • Responsible for exchange of nutrients, gases & metabolic waste products between maternal and fetal circulation
      • Glucose is predominant energy source for both placenta and fetus
  • 2. Placental Architecture
    • Maternal and fetal blood do not mix: “placental barrier”
      • Fetal blood flows through capillary networks within highly branched terminal chorionic villi
      • Maternal blood flows through intervillous space
        • Uterine arteriols bring blood in
        • Uterine venules drain blood
  • 3. Figure 29.6 A Three-Dimensional View of Placental Structure Figure 29.6a
  • 4.
    • Chorionic villi extend into maternal tissue
      • Forms intricate branching network for maternal blood
    • Umbilical cord connects fetus to placenta
    Placentation
  • 5. Placental Capacity Increases During Gestation
    • Expression of transporters increases
    • The “brush border” microvilli develop to:
      • increase surface area
      • impede maternal blood flow
    • Flow through the placenta at term is 500 ml/minute
  • 6. Mechanisms of Nutrient Transfer Across the Placenta
  • 7. Maternal to Infant Nutrient Transportation Across The Placenta
  • 8. Fetal to Maternal Transport
    • Carbon dioxide
    • Water & urea
    • Hormones
  • 9.  
  • 10. Factors Affecting Placental Transfer
    • Placental size
    • Diffusion distance –
      • diabetes and infection cause edema of the villi
      • distance decreases as pregnancy progresses and fetal needs increase
    • Maternal-placental blood flow
    • Blood saturation with gases and nutrients
  • 11. Factors Affecting Placental Transfer (cont)
    • Maternal-placental metabolism of the substance
    • Disorders in expression or activity of nutrient transporters
    • Maternal use of tobacco, cocaine, alcohol
  • 12.
    • Trophoblast secretes hormones to maintain pregnancy
      • HCG
      • Estrogens
      • Progesterone
      • hPL
      • Placental prolactin
      • relaxin
    Hormones of the placenta