Prenatal Development: First Week Pregnancy
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Prenatal Development: First Week Pregnancy

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Questions and Answers

What is the duration of the Zygotic Stage of prenatal development?

  • 0-4 weeks
  • 4-8 weeks
  • 2-6 weeks
  • 0-2 weeks (correct)

    • Where does fertilization occur?

  • In the vagina
  • In the ovary
  • In the ampullary region of the uterine tube (correct)
  • In the cervix

    • What is the term for the event in which a mature oocyte is expelled from the ovary?

  • Ovulation (correct)
  • Fertilization
  • Cleavage
  • Implantation

    • What is the function of the acrosome reaction?

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

    How many stages of prenatal development are there?

    <p>3</p> Signup and view all the answers

    What is the term for the process of fusion of the oocyte and sperm cell membranes?

    <p>Fusion of the oocyte and sperm cell membranes</p> Signup and view all the answers

    What is the purpose of capacitation?

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

    At what day of a regular 28-day menstrual cycle does ovulation occur?

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

    At which stage do cells become arranged in a hollow sphere?

    <p>Blastocyst stage</p> Signup and view all the answers

    What is the outer layer of cells in a morula called?

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

    How many cells are present in a morula?

    <p>12-16 cells</p> Signup and view all the answers

    At which stage do cells start to lose totipotency?

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

    What is the function of the zona pellucida?

    <p>Protects the blastocyst during implantation</p> Signup and view all the answers

    When does implantation of the blastocyst begin?

    <p>By day 5-6</p> Signup and view all the answers

    How many cells are present after 72 hours of fertilization?

    <p>32 cells</p> Signup and view all the answers

    What happens to the zona pellucida by day 5-6?

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

    What happens to the zona pellucida during blastocyst formation?

    <p>It disappears allowing implantation to begin</p> Signup and view all the answers

    What is the function of the proteolytic enzymes secreted by the syncytiotrophoblast?

    <p>To erode the endometrium for implantation</p> Signup and view all the answers

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

    <p>The secretory phase</p> Signup and view all the answers

    What is the main function of the HCG secreted by the syncytiotrophoblast?

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

    What is the purpose of the lacunar spaces in the syncytiotrophoblast?

    <p>To facilitate the exchange of nutrients and waste</p> Signup and view all the answers

    How many days after ovulation does the secretory phase of the menstrual cycle begin?

    <p>2-3 days</p> Signup and view all the answers

    What is the primary function of syncytiotrophoblasts during implantation?

    <p>To erode the endometrium and allow the blastocyst to burrow into the compact layer</p> Signup and view all the answers

    During which days does the process of implantation take place?

    <p>5th to 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 name of the membrane that forms around the exocoelomic cavity?

    <p>Hueser's membrane</p> Signup and view all the answers

    What is the name of the layer of endometrium that the blastocyst burrows into?

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

    What is the structure that forms from the epiblast?

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

    What is the main function of the enzymes in the acrosome of a sperm?

    <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>Prevention of polyspermy</p> Signup and view all the answers

    What is the term for the process by which the zygote undergoes a series of mitotic divisions?

    <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 result of the metabolic activation of the egg?

    <p>Initiation of cleavage</p> Signup and view all the answers

    How many cells are present in a morula?

    <p>16</p> Signup and view all the answers

    When does the oocyte finish its second meiotic division?

    <p>Immediately after entry of the spermatozoon</p> Signup and view all the answers

    Study Notes

    Prenatal Development

    • The three stages of prenatal development from conception to birth are:
    • Zygotic (or Germinal) Stage (0-2 weeks)
    • Embryonic Stage (2-8 weeks)
    • Fetal Stage (9-40 weeks)

    Ovulation

    • A mature oocyte is expelled from the ovary around the 14th day of a regular 28-day menstrual cycle.

    Fertilization

    • Fertilization occurs in the ampullary region of the uterine tube.
    • The three phases of fertilization are:
    • Penetration of the corona radiata
    • Penetration of the zona pellucida
    • Fusion of the oocyte and sperm cell membranes
    • Capacitation is necessary for sperm to penetrate the corona radiata and undergo the acrosome reaction.
    • The acrosome reaction releases enzymes needed to penetrate the zona pellucida, including acrosin and trypsin-like substances.

    Results of Fertilization

    • The main results of fertilization are:
    • Restoration of the diploid number of chromosomes
    • Determination of the sex of the new individual
    • Initiation of cleavage

    Cleavage

    • Cleavage is a series of mitotic divisions that increase the number of cells, known as blastomeres.
    • The cells divide every 12-24 hours, resulting in:
    • 2-cell stage (36 hours)
    • 4-cell stage (48 hours)
    • 8-cell stage (72 hours)
    • Morula (12-16 cells) or Blastula
    • Until the 8-cell stage, the cells are totipotent.

    Blastocyst Formation

    • The blastocyst forms around the 5th day.
    • Fluid penetrates the zona pellucida into the intercellular spaces of the inner cell mass, forming a single cavity, the blastocele.
    • The embryoblast is at one pole, and the outer cell mass, or trophoblast, flattens and forms the epithelial wall of the blastocyst.

    Implantation

    • Implantation begins around the 6th day.
    • The trophoblastic cells over the embryoblast pole penetrate between the epithelial cells of the uterine mucosa.
    • Syncytiotrophoblasts secrete proteolytic enzymes to erode the endometrium and human chorionic gonadotropin (hCG) to sustain the corpus luteum.

    Uterus at Time of Implantation

    • The uterine endometrium passes through three stages during the menstrual cycle:
    • Menstrual phase
    • Proliferative phase (influenced by estrogen)
    • Secretory phase (influenced by progesterone produced by the corpus luteum)

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    Description

    Learn about the stages of prenatal development from ovulation to implantation, including fertilization, cleavage, and implantation. Understand the normal site of fertilization and results.

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