Placental Circulation and Membrane
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Questions and Answers

What is the primary function of syncytiotrophoblast nuclei during the third trimester?

  • They transport nutrients directly to the fetus.
  • They facilitate gas exchange between maternal and fetal blood.
  • They form syncytial knots that enter maternal circulation. (correct)
  • They synthesize hormones for fetal development.

    • Which substance does NOT easily cross the placenta?

  • Thyroxine
  • Glucose
  • Electrolytes
  • Insulin (correct)

    • What can result from a compromised maternal blood supply to the placenta?

  • Normal fetal growth
  • Enhanced nutrient transfer
  • Fetal hypoxia (correct)
  • Increased fetal metabolism

    • Which nutrient is transferred from mother to fetus more rapidly?

    <p>Water-soluble vitamins</p> Signup and view all the answers

    What is the role of transferrin during pregnancy?

    <p>To transfer iron to the fetus.</p> Signup and view all the answers

    What mechanism primarily allows gas exchange between mother and fetus?

    <p>Simple diffusion</p> Signup and view all the answers

    Which of the following substances cannot be considered an effective waste product for fetal excretion through the placenta?

    <p>Glucose</p> Signup and view all the answers

    Which function is NOT associated with the placenta?

    <p>Storage of maternal blood</p> Signup and view all the answers

    What is the primary function of chorionic villi?

    <p>To facilitate gas and nutrient exchange</p> Signup and view all the answers

    How does maternal blood enter the placenta?

    <p>Through spiral arteries into intervillous spaces</p> Signup and view all the answers

    What happens to the placental membrane after 20 weeks of pregnancy?

    <p>It reduces to three layers in some regions</p> Signup and view all the answers

    Which statement best explains the blood flow in the intervillous spaces?

    <p>Maternal blood forms a 'lake' around chorionic villi</p> Signup and view all the answers

    Which component is NOT part of the placental membrane during early pregnancy?

    <p>Amniotic membrane</p> Signup and view all the answers

    What role do microvilli on syncytiotrophoblasts play?

    <p>Increase surface area for material exchange</p> Signup and view all the answers

    Which characteristic of maternal blood flow aids in nutrient exchange?

    <p>High pressure forcing blood deep into the space</p> Signup and view all the answers

    At what point in pregnancy does the cytotrophoblast begin to thin and disappear in many villi?

    <p>At 20 weeks</p> Signup and view all the answers

    What characterizes dizygotic (DZ) twins?

    <p>They may be of the same or different sexes.</p> Signup and view all the answers

    How are monozygotic (MZ) twins formed?

    <p>From a single zygote splitting into two embryos.</p> Signup and view all the answers

    What is superfecundation?

    <p>Fertilization of multiple oocytes at different times.</p> Signup and view all the answers

    Which statement regarding conjoined twins is true?

    <p>They are named based on the region of attachment.</p> Signup and view all the answers

    Which of the following is true about the placental structure of MZ twins?

    <p>They typically share a chorionic sac and placenta.</p> Signup and view all the answers

    What role does oxytocin play during labor?

    <p>It triggers uterine contractions.</p> Signup and view all the answers

    What is the typical diameter of the placenta?

    <p>15-20 cm</p> Signup and view all the answers

    Which condition is characterized by abnormal adherence of chorionic villi to the myometrium?

    <p>Placenta accreta</p> Signup and view all the answers

    Which hormone is stimulated by corticotropin-releasing hormone during labor?

    <p>Adrenocorticotropin</p> Signup and view all the answers

    What is the average length of the umbilical cord?

    <p>30-90 cm</p> Signup and view all the answers

    What complication can arise from placenta previa?

    <p>Late pregnancy bleeding</p> Signup and view all the answers

    The maternal surface of the placenta has what kind of appearance?

    <p>Cobblestone appearance</p> Signup and view all the answers

    Which condition is associated with chorionic villi penetrating through the perimetrium?

    <p>Placenta percreta</p> Signup and view all the answers

    What is the primary function of human chorionic gonadotropin (hCG) during early pregnancy?

    <p>Maintaining the corpus luteum</p> Signup and view all the answers

    Which steroid hormone is produced by the placenta and is essential for maintaining pregnancy?

    <p>Progesterone</p> Signup and view all the answers

    Which infectious agent is known to cross the placental membrane and can lead to fetal infection?

    <p>Toxoplasma gondii</p> Signup and view all the answers

    During which week of pregnancy does human chorionic gonadotropin (hCG) peak?

    <p>8th week</p> Signup and view all the answers

    What is the primary physiological change that occurs in the uterus during pregnancy?

    <p>Hypertrophy of smooth muscle fibers</p> Signup and view all the answers

    How does human chorionic somatomammotropin affect maternal metabolism during pregnancy?

    <p>Supports fetal growth and modifies maternal metabolism</p> Signup and view all the answers

    What role does progesterone play during the first trimester of pregnancy?

    <p>Maintains pregnancy and prevents menstruation</p> Signup and view all the answers

    What is the term for the process of childbirth where the fetus, placenta, and fetal membranes are expelled?

    <p>Parturition</p> Signup and view all the answers

    Study Notes

    Placental Circulation

    • Fetal blood enters the placenta through umbilical arteries, forming capillary networks in the terminal villi, where gas and nutrient exchange occurs.
    • Oxygenated fetal blood returns to the fetus through the umbilical vein.
    • Maternal blood enters the placenta through spiral arteries, flowing freely into the intervillous spaces - a "lake" that bathes the chorionic villi.
    • This high-pressure flow ensures a slow, maximizing exchange of oxygen and nutrients with the fetal blood.
    • Maternal blood returns to maternal circulation through endometrial veins.

    Placental Membrane

    • The placental membrane is composed of extrafetal tissues that separate maternal and fetal blood.
    • It initially comprises four layers: syncytiotrophoblast, cytotrophoblast, connective tissue of the villi, and endothelium of fetal capillaries.
    • After 20 weeks, the cytotrophoblast thins and disappears in some areas, reducing the membrane to three layers.
    • The syncytiotrophoblast directly contacts fetal capillary endothelium in some regions, forming a vasculosyncytial placental membrane.
    • The placental membrane allows many substances to pass freely, but its effectiveness is critical for fetal health.
    • Compromised maternal blood supply can lead to fetal hypoxia, IUGR, or even fetal death.

    Placental Functions

    • Synthesizes glycogen, cholesterol, and fatty acids for fetal growth and development.
    • Facilitates gas transfer (oxygen, carbon dioxide, carbon monoxide) via simple diffusion.
    • Transports nutrients (glucose, cholesterol, fatty acids, vitamins) from mother to fetus.
    • Allows for transfer of maternal antibodies (IgG) to fetus, providing passive immunity.
    • Facilitates excretion of fetal waste products (urea, uric acid, bilirubin).

    Placental Hormones

    • Produces various protein and steroid hormones, including:
      • Human chorionic gonadotropin (hCG): Maintains corpus luteum and prevents menstruation. Peaks at 8 weeks, then declines.
      • Human chorionic somatomammotropin: Supports fetal growth and maternal metabolism.
      • Progesterone: Maintains pregnancy and is produced throughout gestation.
      • Estrogens: Important for fetal development and maternal adaptations during pregnancy.

    Uterine Growth during Pregnancy

    • The uterus increases in size and weight to accommodate the growing fetus.
    • Its walls become thinner, and the uterus moves out of the pelvis during the first trimester.
    • By 20 weeks, it reaches the level of the umbilicus, and by 28-30 weeks, it extends to the epigastric region.

    Parturition

    • The process of childbirth involving labor, a sequence of involuntary uterine contractions leading to the dilation of the cervix and expulsion of the fetus and placenta.
    • Hormones involved:
      • Fetal hypothalamus secretes corticotropin-releasing hormone, which stimulates the anterior pituitary to release adrenocorticotropin, leading to cortisol secretion.
      • Oxytocin triggers uterine contractions and stimulates prostaglandin release, increasing uterine contractility.
      • Estrogens enhance uterine contractile activity and promote oxytocin and prostaglandin release.

    Placenta after Birth

    • The placenta is discoid, 15-20 cm in diameter, 2-3 cm thick, weighing 500-600 grams.
    • Maternal surface: Cobblestone appearance with cotyledons separated by grooves.
    • Fetal surface: Umbilical cord attaches, covered by epithelium continuous with the amnion.

    Placental Abnormalities

    • Placenta accreta: Abnormal adherence of chorionic villi to the myometrium, leading to complications during detachment.
    • Placenta percreta: Villi penetrate the myometrium, causing complications and hemorrhage.
    • Placenta previa: Placenta implants near or over the internal os, causing late pregnancy bleeding and necessitating cesarean delivery.

    Umbilical Cord

    • Typically attaches near the center of the placenta, but may attach at other locations.
    • Contains two arteries and one vein surrounded by Wharton's jelly.

    Twin Births

    • Dizygotic (DZ) Twins: Fraternal twins, originate from two zygotes, resulting in two distinct individuals.
      • Always have two amnions and two chorions, but their placentas may fuse.
    • Monozygotic (MZ) Twins: Identical twins, originate from a single zygote splitting into two embryos.
      • Typically have two amniotic sacs but one shared chorionic sac and placenta.
      • Rare early blastomere separation can lead to separate placentas, indistinguishable from DZ twins based on placental structure.

    Other Multiple Births

    • Triplets and higher multiples can arise from one to three zygotes, involving both identical and non-identical individuals.
    • Conjoined twins result from incomplete embryonic disc fusion.
      • Rare (1 in 50,000 - 100,000 births).
    • Superfecundation: Fertilization of two or more oocytes at different times, resulting in twins with different fathers.
    • Superfetation: Fetuses conceived at different times, extremely rare in humans.

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    Description

    This quiz covers the processes of placental circulation and the structure of the placental membrane. It examines how fetal and maternal blood interact within the placenta for nutrient and gas exchange, as well as the changes in the placental membrane as pregnancy progresses. Test your knowledge on these crucial topics in fetal development.

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