EMBRYOLOGY-3
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Questions and Answers

What role does hyaluronidase play during the fertilization process?

  • It breaks down the sticky matrix of the corona radiata. (correct)
  • It facilitates the fusion of the sperm with the oocyte.
  • It increases the calcium concentration in the sperm.
  • It assists in the penetration of the zona pellucida.

    • During which phase of fertilization does the sperm attach to and penetrate the zona pellucida?

  • Pre-fertilization phase
  • Phase 2 (correct)
  • Phase 3
  • Phase 1

    • Which component of the spermatozoon aids its attachment to the oocyte's plasma membrane?

  • Zonal proteins
  • Antigens on its head (correct)
  • Acrosin enzymes
  • Granulosa cells

    • What is the result of spermatozoa penetrating the zona pellucida?

    <p>Only one spermatozoon attaches to the plasma membrane of the oocyte.</p> Signup and view all the answers

    Which phase of fertilization involves the spermatozoa swimming through the granulosa cells?

    <p>Phase 1</p> Signup and view all the answers

    What type of proteins do spermatozoa bind to when they reach the zona pellucida?

    <p>ZP3 proteins</p> Signup and view all the answers

    What happens to the components of the spermatozoon during fusion with the oocyte's plasma membrane?

    <p>The head, midpiece, and tail sink into the cytoplasm.</p> Signup and view all the answers

    Why is the ampullary region of the Fallopian tube significant for fertilization?

    <p>It provides an optimal environment for sperm and oocyte interaction.</p> Signup and view all the answers

    What is the primary function of the syncytiotrophoblast during implantation?

    <p>To erode the endometrium and create a passage for the blastocyst</p> Signup and view all the answers

    What role does hCG play in early pregnancy maintenance?

    <p>It maintains the functional activity of the corpus luteum</p> Signup and view all the answers

    What is a function of decidual cells in the endometrium?

    <p>They produce substances that can either support or inhibit implantation</p> Signup and view all the answers

    What does the term 'decidual reaction' refer to?

    <p>Changes in the lamina propria of the endometrium</p> Signup and view all the answers

    Which of the following best describes the cytotrophoblast?

    <p>It is the internal part of the trophoblast</p> Signup and view all the answers

    What impact does progesterone have during early pregnancy?

    <p>It regulates endometrial functions and trophoblast activity</p> Signup and view all the answers

    What process occurs when the syncytiotrophoblast contacts maternal blood vessels?

    <p>Establishment of nutrient supply through lacunae</p> Signup and view all the answers

    During implantation, which structure is primarily responsible for providing nutrients to the embryo?

    <p>Lacunae filled with maternal blood</p> Signup and view all the answers

    What major change occurs in the male nucleus during the formation of the male pronucleus?

    <p>Decondensation of genetic material</p> Signup and view all the answers

    Which of the following is NOT a role of the zona pellucida?

    <p>Facilitates differentiation of inner blastomeres</p> Signup and view all the answers

    What is the outcome of fertilisation regarding the genetic composition of the zygote?

    <p>Zygote is restored to a diploid number with 23 maternal and 23 paternal chromosomes</p> Signup and view all the answers

    Which stage follows cleavage in early embryonic development?

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

    How long after fertilisation does cleavage typically begin?

    <p>30 hours</p> Signup and view all the answers

    What differentiates outer blastomeres from inner blastomeres during compaction?

    <p>Outer blastomeres are in contact with the zona pellucida</p> Signup and view all the answers

    What triggers the acrosomal reaction during fertilisation?

    <p>Contact with the zona pellucida</p> Signup and view all the answers

    What is the primary function of the blastomeres during cleavage?

    <p>Increase the number of cells within the same cytoplasm</p> Signup and view all the answers

    What is the primary role of the trophoblast in early embryonic development?

    <p>Creation of the placenta</p> Signup and view all the answers

    Which type of junctions primarily hold the outer blastomeres together?

    <p>Tight junctions</p> Signup and view all the answers

    What initiates the formation of the blastocoele in the morula?

    <p>Flow of fluids mediated by the zona pellucida</p> Signup and view all the answers

    What is the primary function of the Early Pregnancy Factor produced by the trophoblast?

    <p>Immunosuppression to avoid maternal immune attack</p> Signup and view all the answers

    During which phase does the embryo begin to depend on its own genetic material?

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

    Which term describes the phenomenon where the subdivision of chromosomes during cleavage does not occur correctly?

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

    What is the significance of the polarized structure of the blastocyst?

    <p>Establishment of embryonic and abembryonic poles</p> Signup and view all the answers

    Where does the cleavage stage of embryo development predominantly take place?

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

    What role do JUNO receptors play during the process of fertilization?

    <p>They are removed from the egg membrane to prevent additional sperm attachment.</p> Signup and view all the answers

    What is one way the paternal mitochondria are eliminated after fertilization?

    <p>Through degradation by macrophages.</p> Signup and view all the answers

    What is the purpose of the fast block to polyspermy?

    <p>To cause membrane depolarization and temporarily prevent further sperm adhesion.</p> Signup and view all the answers

    What triggers the permanent block to polyspermy?

    <p>Release of JUNO and the secretion of contents from cortical granules.</p> Signup and view all the answers

    What is the significance of calcium changes during fertilization?

    <p>They are involved in the activation of egg metabolism and prevention of polyspermy.</p> Signup and view all the answers

    What occurs to the oocyte once it is fertilized?

    <p>It becomes a fertilized oocyte with two pronuclei.</p> Signup and view all the answers

    How many viable cells result from female meiosis?

    <p>One viable cell and three polar bodies.</p> Signup and view all the answers

    What happens to mRNA after the fertilization process begins?

    <p>It gets actively recruited to facilitate egg metabolism.</p> Signup and view all the answers

    What describes the relationship between the epiblast and the amniotic cavity?

    <p>The epiblast is dorsal and forms the amniotic cavity.</p> Signup and view all the answers

    What does the hypoblast contribute to in early development?

    <p>Development of the parietal endoderm (Heuser's membrane).</p> Signup and view all the answers

    Which statement is correct regarding the yolk sac?

    <p>The yolk sac is beneficial in oviparous animals but not in humans.</p> Signup and view all the answers

    What structure surrounds the amniotic cavity as development progresses?

    <p>Chorion.</p> Signup and view all the answers

    What role does the body stalk play in embryo development?

    <p>It is the first site of blood vessel formation.</p> Signup and view all the answers

    What does the extraembryonic coelom develop into during embryonic development?

    <p>Chorionic cavity.</p> Signup and view all the answers

    At what stage does the vitelline sac significantly decrease in size?

    <p>By the 13th day of development.</p> Signup and view all the answers

    Which structure is primarily formed from the growth of hypoblast cells?

    <p>Yolk sac.</p> Signup and view all the answers

    Study Notes

    Fertilization

    • The egg is significantly larger than the sperm cell, approximately 10 million times larger in volume.
    • Fertilization occurs in the ampullary region of the fallopian tube due to the folds which slow the oocyte. Optimal conditions are created for sperm to meet the oocyte.
    • Several changes need to occur for fertilization to take place.

    Phase 1 of Fertilization

    • Sperm travel among the granulosa cells of the corona radiata.
    • Hyaluronidase is released, breaking down the hyaluronic acid, allowing the sperm to move.
    • Spermatozoa then rapidly swim to the zona pellucida.
    • Sometimes, enzymes from the uterine tube aid the process.

    Phase 2 of Fertilization

    • Sperm reach the zona pellucida and attach.
    • Sperm bind to zona proteins (mainly ZP3), which are species-specific.
    • Acrosome enzymes (like acrosin) digest the membrane.
    • Calcium concentration increases, causing the sperm head to fuse with the zona pellucida.
    • Spermatozoa penetrate the zona pellucida, entering the perivitelline space.
    • Only one sperm will attach to the oocyte's plasma membrane.

    Phase 3 of Fertilization

    • One sperm attaches to the oocyte's microvilli via antigens (IZUMO) on the sperm head that bind to receptors (JUNO) on the egg membrane.
    • The sperm head, midpiece, and tail enter the cytoplasm.
    • Mitochondria from the sperm remain outside.
    • Juno receptors are ejected to prevent polyspermy.

    Phase 4 of Fertilization

    • Prevention of polyspermy:
      • Fast block: membrane depolarizes within seconds.
      • Permanent Block: Calcium waves trigger cortical granule release, causing swelling and hardening of the zona pellucida.

    Phase 5 of Fertilization

    • The female nucleus completes meiosis II.
    • A second polar body is formed.
    • Two pronuclei fuse.

    Cleavage

    • Cleavage increases cell number within the zona pellucida without increasing the size of the zygote.
    • Cleavage begins around 30 hours after fertilization.
    • Mammalian cleavage takes several days.
    • Cleavage leads to blastomeres and a morula, which forms a blastocyst in around 3 days.

    Compaction

    • Blastomeres become tightly compacted, increasing cell-to-cell contact.

    Blastocyst formation

    • Blastomeres move towards one side of the embryo.
    • A cavity called the blastocoele forms within the blastocyst.
    • The embryo is composed of an outer trophoblast layer and an inner cell mass (embryoblast), and the zona pellucida is still present.

    Early Pregnancy Factor (EPF)

    • EPF is produced by the trophoblast.
    • It is believed to help avoid a mother's immune responses.

    Blastocyst Polarity

    • Blastocysts have a polar side (the inner cell mass) and an opposite (mural), abembryonic side, where the trophoblast covers the surface..

    Implantation

    • The blastocyst implants in a prepared uterine environment at the end of the previous menstrual cycle.
    • Three stages:
      • Apposition (approaches the endometrium)
      • Adhesion (close contact with adhesion molecules)
      • Invasion (trophoblasts erode the endometrium)

    Zygote, embryonic cells and chromosomal issues

    • The zygote initially depends on maternal genetic material.
    • The embryo generates its own genetic material during blastula.
    • Mishap in chromosomal division during cleavage can lead to mosaicism.

    Implantation Window

    • A specific timeframe when the endometrium is receptive to embryo implantation.
    • Implantation begins 4-6 days after the LH surge.

    Invasive Trophoblast

    • Syncytiotrophoblast: erosive and invasive.
    • It digests endometrium for implantation passageway

    Maintenance of Pregnancy

    • Corpus luteum: produces progesterone, regulating endometrial function and trophoblastic activity.
    • hCG (human chorionic gonadotropin): maintains the corpus luteum.
    • Decidual reaction in the endometrial stroma protects the embryo.

    Ectopic Pregnancy

    • Implantation occurs outside of the uterine cavity.
    • Commonly in the uterine tubes.

    Second Week

    • The embryo rearranges and forms an epiblast and hypoblast layers.
    • Amniotic and yolk sac development.

    Implantation Sites

    • The typical implantation site is the uterine posterior wall.
    • This is not the only implantation site; other locations are possible, but they can lead to complications.

    Pregnancy Loss (Miscarriage)

    • Spontaneous abortions frequently occur during the first 12 weeks of pregnancy.
    • Reasons for miscarriage are multiple, including chromosomal abnormalities or maternal and placental or fetal causes.

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    Embryology 3 - Fertilisation and Implantation PDF

    Description

    Explore the fascinating stages of fertilization, focusing on the intricate interactions between sperm and egg. This quiz covers the critical phases, including the journey of sperm through the female reproductive tract and the biochemical changes essential for successful fertilization.

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