Prenatal Development and Fertilization
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Questions and Answers

What is the cavity formed in the blastocyst stage?

  • Trophectoderm
  • Endoderm
  • Amniotic cavity
  • Blastocele (correct)

    • What is the function of proteolytic enzymes secreted by syncytiotrophoblasts?

  • To prevent menstruation
  • To stimulate uterine contractions
  • To produce human chorionic gonadotropin
  • To implant the embryo in the uterus (correct)

    • During which phase of the menstrual cycle does the uterine endometrium prepare for implantation?

  • Proliferative phase
  • Menstrual phase
  • Secretory phase (correct)
  • Ovulation phase

    • What is the function of human chorionic gonadotropin (hCG) secreted by syncytiotrophoblasts?

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

    What is the term for the outer cell mass that forms the epithelial wall of the blastocyst?

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

    During which day of pregnancy do the trophoblastic cells begin to penetrate the uterine mucosa?

    <p>Sixth day</p> Signup and view all the answers

    During which stage of development does fertilization occur?

    <p>Zygotic Stage</p> Signup and view all the answers

    Where does fertilization typically occur?

    <p>Uterine tube</p> Signup and view all the answers

    What is the purpose of the acrosome reaction?

    <p>To release enzymes needed to penetrate the zona pellucida</p> Signup and view all the answers

    What is the result of ovulation?

    <p>Mature oocyte is expelled from the ovary</p> Signup and view all the answers

    What is the function of capacitation?

    <p>To allow only capacitated sperm to pass through the corona cells</p> Signup and view all the answers

    During which day of a regular 28-day menstrual cycle does ovulation occur?

    <p>14th day</p> Signup and view all the answers

    What is the correct order of the phases of fertilization?

    <p>Penetration of the corona radiata, penetration of the zona pellucida, fusion of the oocyte and sperm cell membranes</p> Signup and view all the answers

    What is the term for the period from 0-2 weeks of development?

    <p>Zygotic Stage</p> Signup and view all the answers

    What is the role of the enzymes in the acrosome?

    <p>To break down the zona pellucida of the oocyte</p> Signup and view all the answers

    What happens to the oocyte if it is not fertilized within 24 hours of ovulation?

    <p>It degenerates</p> Signup and view all the answers

    What is the result of the cortical and zona reactions?

    <p>The sperm is prevented from entering the oocyte</p> Signup and view all the answers

    What is the significance of the diploid number of chromosomes being restored?

    <p>It restores the normal number of chromosomes in the zygote</p> Signup and view all the answers

    What is the result of the resumption of the second meiotic division?

    <p>The oocyte finishes its second meiotic division</p> Signup and view all the answers

    What is the term for the series of mitotic divisions that occur after fertilization?

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

    What is the term for the cells that result from cleavage?

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

    What is the stage of development that occurs approximately 3 days after fertilization?

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

    What is the process called when syncytiotrophoblasts erode the endometrium and the blastocyst burrows into the compact layer of endometrium?

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

    What is the structure that forms from the hypoblast?

    <p>Primary yolk sac</p> Signup and view all the answers

    What is the most common type of ectopic pregnancy?

    <p>Tubal pregnancy</p> Signup and view all the answers

    What is the layer of the endometrium that the blastocyst burrows into during implantation?

    <p>Compact layer</p> Signup and view all the answers

    What is the membrane that forms from the epiblast?

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

    When does the completion of implantation occur?

    <p>Between the 5th and 10th day</p> Signup and view all the answers

    What is the most common type of ectopic pregnancy?

    <p>Tubal pregnancy</p> Signup and view all the answers

    What is the role of Early Pregnancy Factor (EPF)?

    <p>As an immunosuppressant protein</p> Signup and view all the answers

    During In Vitro Fertilization, what is the purpose of hormonal stimulation?

    <p>To form several mature follicles</p> Signup and view all the answers

    What is the result of dispermy?

    <p>Fertilization of a secondary oocyte by two sperms</p> Signup and view all the answers

    What is the stage of development after fertilization?

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

    What is the purpose of an assay of HCG and Progesterone?

    <p>To detect pregnancy by the end of the second week</p> Signup and view all the answers

    What is the term for a pregnancy that attaches to the mesenteric blood vessels?

    <p>Abdominal pregnancy</p> Signup and view all the answers

    What is the stage of development where the zygote is transferred to the uterine cavity?

    <p>4-8 cell stage</p> Signup and view all the answers

    Study Notes

    Stages of Prenatal Development

    • Zygotic (or Germinal) Stage: 0-2 weeks
    • Embryonic Stage: 2-8 weeks
    • Fetal Stage: 9-40 weeks

    Ovulation

    • Event in which a mature oocyte is expelled from the ovary
    • Occurs on the 14th day of a regular 28-day menstrual cycle

    Fertilization

    • Process by which male and female gametes fuse
    • Occurs in the ampullary region of the uterine tube
    • Phases of fertilization:
      • Phase 1: Penetration of the corona radiata
      • Phase 2: Penetration of the zona pellucida
      • Phase 3: Fusion of the oocyte and sperm cell membranes

    Capacitation

    • Only capacitated sperm can pass through the corona cells and undergo the acrosome reaction
    • Acrosome reaction: Release of enzymes needed to penetrate the zona pellucida, including acrosin and trypsin-like substances

    Results of Fertilization

    • Restoration of the diploid number of chromosomes
    • Determination of the sex of the new individual
    • Initiation of cleavage

    Cleavage

    • Series of mitotic divisions, increasing the number of cells
    • Cells, known as blastomeres, become smaller with each cleavage division
    • Approximately 3 days after fertilization, cells divide again to form a 16-cell morula

    Blastocyst Formation

    • Fluid penetrates the zona pellucida, forming a single cavity, the blastocele
    • Embryoblast and outer cell mass, or trophoblast, flatten and form the epithelial wall of the blastocyst
    • Zona pellucida disappears, allowing implantation to begin

    Implantation

    • Trophoblastic cells over the embryoblast pole begin to penetrate between the epithelial cells of the uterine mucosa
    • Approximately 6th day after fertilization

    Syncytiotrophoblasts

    • Show villous projections and lacunar spaces
    • Secrete:
      • Proteolytic enzymes, which erode the endometrium to implant
      • HCG, which sustains the corpus luteum

    Uterus at Time of Implantation

    • Uterine endometrium passes through three stages:
      1. Menstrual phase
      2. Proliferative phase (influenced by estrogen)
      3. Secretory phase (influenced by progesterone produced by the corpus luteum)

    Ectopic Pregnancy

    • Most common type: Tubal pregnancy
    • May secondarily attach itself to mesenteric blood vessels and continue as abdominal pregnancy
    • Rarely: Falls into the pouch of Douglas

    Pregnancy Tests

    • Early Pregnancy Factor (EPF): appears in maternal serum by 24 to 48 hours
    • Assay of HCG and Progesterone by the end of the second week
    • Confirmation of pregnancy: by ultrasonogram by the end of the 5th week

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    Learn about the stages of development from conception to birth, including ovulation, fertilization, cleavage, and implantation. Test your knowledge of prenatal development.

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