Fertilization & Cleavage in Human Development
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Questions and Answers

What is the function of the syncytiotrophoblast during implantation?

  • To facilitate oxygen exchange with maternal blood
  • To initiate the development of the primary follicle
  • To produce enzymes that erode maternal tissues (correct)
  • To provide a protective barrier for the embryo

    • At what stage does the oocyte get fertilized?

  • At the two-cell stage
  • During the early blastocyst stage
  • Immediately after ovulation
  • Approximately 12 to 24 hours after ovulation (correct)

    • Which of the following best describes the condition of the blastocyst before implantation?

  • It is deeply embedded within the uterine tissue.
  • It has developed into an advanced morula.
  • It is floating freely in the uterus. (correct)
  • It has formed a complete chorion.

    • Which layer of the endometrium is referred to as the 'decidua' after implantation?

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

    What occurs during the advanced morula stage of development?

    <p>The morula reaches the uterine lumen.</p> Signup and view all the answers

    What initiates the penetration of the blastocyst into the uterine endometrium?

    <p>Formation of finger-like processes by the trophoblast</p> Signup and view all the answers

    What is the primary function of the umbilical arteries in fetal circulation?

    <p>Carry fetal blood containing CO2 and waste products to the placenta</p> Signup and view all the answers

    What is the typical timeline for the completion of implantation after fertilization?

    <p>Starts by the 6th day and completes by the 11th day</p> Signup and view all the answers

    Which layer is NOT part of the placental membrane structure?

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

    At what stage of pregnancy does the placental membrane begin to thin?

    <p>From the fourth month onwards</p> Signup and view all the answers

    What is the primary purpose of the placental barrier?

    <p>To separate fetal blood from maternal blood while allowing selective exchange</p> Signup and view all the answers

    What is contained within the primitive umbilical cord?

    <p>Allantois and umbilical blood vessels</p> Signup and view all the answers

    What is the significance of the trophoblast differentiating into cytotrophoblast and syncytiotrophoblast?

    <p>They facilitate implantation and erode maternal tissues.</p> Signup and view all the answers

    What happens to maternal blood during the second week of development?

    <p>It enters the lacunar network formed by the syncytiotrophoblast.</p> Signup and view all the answers

    At the end of the second week of development, which structures does the inner cell mass differentiate into?

    <p>Epiblast and hypoblast.</p> Signup and view all the answers

    What is the primary function of the primary villi formed by the cytotrophoblast?

    <p>They contribute to the maternal-fetal exchange via the placenta.</p> Signup and view all the answers

    Which of the following correctly describes the changes occurring during the second week of development?

    <p>The surface defect in the uterine mucosa heals by the end of the second week.</p> Signup and view all the answers

    How does gastrulation relate to teratogenesis during fetal development?

    <p>Errors during gastrulation can lead to embryonic development abnormalities.</p> Signup and view all the answers

    What is formed as a result of the development of vacuoles in extraembryonic mesoderm?

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

    Which of the following statements is false regarding the development of the amniotic cavity?

    <p>The amniotic cavity forms prior to the completion of the bilaminar disc.</p> Signup and view all the answers

    What is the result of placenta previa during delivery?

    <p>The placenta covers the cervix, which can complicate birth.</p> Signup and view all the answers

    What distinguishes the somatopleuric primary mesoderm from the splanchnopleuric primary mesoderm?

    <p>Somatopleuric mesoderm forms structures associated with the body wall.</p> Signup and view all the answers

    During the second week of development, which of the following pairs of layers are formed from the inner cell mass?

    <p>Epiblast and hypoblast</p> Signup and view all the answers

    What is a defining characteristic of embryonic stem cells?

    <p>They are totipotent and can differentiate into any other cell type.</p> Signup and view all the answers

    What is the role of stem cells in regenerative medicine?

    <p>They regenerate damaged cells through transplantation.</p> Signup and view all the answers

    Which structure is lined by extraembryonic splanchnopleuric mesoderm?

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

    At which stage of development is the hypoblast formed and spreading beneath the cytotrophoblast?

    <p>Implanted blastocyst at 6 days</p> Signup and view all the answers

    What does self-renewal in stem cells refer to?

    <p>The capacity for unlimited cell division while maintaining an undifferentiated state.</p> Signup and view all the answers

    Which terms are used to describe the two layers formed by the trophoblast?

    <p>Syncytiotrophoblast and cytotrophoblast</p> Signup and view all the answers

    Which of the following best describes the bilaminar disc?

    <p>It consists of a layer of columnar epiblast cells and a layer of cuboidal hypoblast cells.</p> Signup and view all the answers

    What is the ethical concern associated with the use of embryonic stem cells?

    <p>They are derived from embryos, raising moral questions.</p> Signup and view all the answers

    What defines multipotent stem cells in relation to embryonic stem cells?

    <p>They can only differentiate into a limited number of cell types.</p> Signup and view all the answers

    What initiates the process of gastrulation in embryonic development?

    <p>Formation of the primitive streak.</p> Signup and view all the answers

    Which of the following accurately describes the fate of the ectoderm during gastrulation?

    <p>It migrates inward to create the mesoderm.</p> Signup and view all the answers

    What is the role of the notochord in embryonic development?

    <p>It stimulates ectoderm to develop the central nervous system.</p> Signup and view all the answers

    During the development of the embryonic disc, the mesoderm is primarily formed from which of the following cells?

    <p>Invaginated epiblastic cells.</p> Signup and view all the answers

    What is the significance of the primitive node during gastrulation?

    <p>It acts as a signaling center for cell differentiation.</p> Signup and view all the answers

    What remains of the notochord after it degenerates?

    <p>Nucleus pulposus of the intervertebral discs.</p> Signup and view all the answers

    Which of the following statements about the formation of the germ layers is true?

    <p>The endodermal layer arises from epiblast cells.</p> Signup and view all the answers

    What forms the basis for the axial skeleton during development?

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

    What occurs at the area of the oral membrane and the cloacal membrane during embryonic development?

    <p>Layers of ectoderm and endoderm are untouched by mesoderm.</p> Signup and view all the answers

    What does the presence of placenta previa indicate regarding the position of the placenta at delivery?

    <p>The placenta completely covers the internal cervical os.</p> Signup and view all the answers

    What is the role of the syncytiotrophoblast during the second week of development?

    <p>To erode maternal tissues and establish maternal blood flow.</p> Signup and view all the answers

    During the second week of development, which process is primarily responsible for the formation of the primitive uteroplacental circulation?

    <p>Development of vacuoles in the extraembryonic mesoderm.</p> Signup and view all the answers

    What two layers are formed from the inner cell mass in the second week of development?

    <p>Epiblast and hypoblast.</p> Signup and view all the answers

    What structure is formed by the trophoblast during the second week of development to penetrate the uterine tissue?

    <p>Primary villi.</p> Signup and view all the answers

    At the end of the second week of development, what fills the space between the trophoblast and the amnion?

    <p>Extraembryonic mesoderm.</p> Signup and view all the answers

    What is the significance of the development of lacunae in the syncytiotrophoblast during pregnancy?

    <p>They are critical for maternal-fetal exchange.</p> Signup and view all the answers

    What is the primary consequence of polyhydramnios during pregnancy?

    <p>It may indicate underlying fetal or maternal health issues.</p> Signup and view all the answers

    Which structure is primarily responsible for forming the lining of the definitive yolk sac?

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

    What complication arises from the persistence of the yolk sac?

    <p>Fecal umbilical hernia</p> Signup and view all the answers

    How does the yolk sac contribute to the development of the gastrointestinal tract?

    <p>Its endoderm forms the mucous membrane of the tract.</p> Signup and view all the answers

    What is a clinical outcome observed in cases of oligohydramnios?

    <p>Higher risk of renal agenesis in the fetus.</p> Signup and view all the answers

    What structure is formed as a result of the differentiation of the lateral plate of mesoderm?

    <p>Intraembryonic coelom</p> Signup and view all the answers

    Which mesodermal structure is responsible for forming the axial skeleton?

    <p>Paraxial mesoderm</p> Signup and view all the answers

    What is the primary derivative of the endodermal germ layer?

    <p>Epithelial lining of the respiratory tract</p> Signup and view all the answers

    Which type of mesoderm gives rise to the urinary and genital systems?

    <p>Intermediate cell mass</p> Signup and view all the answers

    What is the correct order of differentiation in the mesodermal germ layers?

    <p>Paraxial, intermediate, lateral plate</p> Signup and view all the answers

    Which of the following structures is derived from the ectodermal germ layer?

    <p>Nervous system</p> Signup and view all the answers

    What happens to the allantois during embryonic development?

    <p>It shifts to a ventral position</p> Signup and view all the answers

    What distinguishes multipotent stem cells from embryonic stem cells?

    <p>Multipotent stem cells can only differentiate into a limited number of cell types.</p> Signup and view all the answers

    Which structures do the somites contribute to during development?

    <p>Skeletal muscles and axial skeleton</p> Signup and view all the answers

    During gastrulation, which of the following processes occurs first?

    <p>Establishment of the primitive pit.</p> Signup and view all the answers

    What causes the neural plate to appear during embryonic development?

    <p>Thickening of ectoderm due to the notochord</p> Signup and view all the answers

    Which germ layer is primarily formed from the invaginating epiblast cells during gastrulation?

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

    What is the primary consequence of insufficient mesoderm in the embryo during caudal dysgenesis?

    <p>Defects in the lower limbs and lumbosacral vertebrae</p> Signup and view all the answers

    During embryonic folding, what significant change occurs in the structure of the embryo?

    <p>Conversion from a flat trilaminar disc to a cylindrical structure</p> Signup and view all the answers

    What structure is formed by mesenchymal cells migrating cranially from the primitive node?

    <p>The notochord.</p> Signup and view all the answers

    Which developmental stage is most sensitive to teratogenic effects?

    <p>Embryonic period</p> Signup and view all the answers

    Which of the following statements about the notochord is false?

    <p>It persists throughout a person's life.</p> Signup and view all the answers

    What defines the function of the primitive streak during the third week of development?

    <p>It is the origin of mesoderm and endoderm layers.</p> Signup and view all the answers

    What type of tumor can form if remnants of the primitive streak persist?

    <p>Sacrococcygeal teratoma</p> Signup and view all the answers

    What causes cephalocaudal folding during embryogenesis?

    <p>Rapid longitudinal growth of the central nervous system</p> Signup and view all the answers

    Which function is NOT attributed to the notochord in embryonic development?

    <p>Complete absorption of nutrients.</p> Signup and view all the answers

    What is the role of ectoderm during the formation of germ layers?

    <p>To serve as a signaling center for mesoderm formation.</p> Signup and view all the answers

    Which of the following structures are primarily associated with caudal dysgenesis?

    <p>Lower limb fusion and vertebral defects</p> Signup and view all the answers

    At what point during development does the definitive endoderm first become established?

    <p>After epiblast cells have fully migrated through the primitive streak.</p> Signup and view all the answers

    What significant events occur at the end of the fourth week of embryonic development?

    <p>Disappearance of the primitive streak</p> Signup and view all the answers

    What are the derivatives formed from the ectoderm during embryonic development?

    <p>Nervous system and skin</p> Signup and view all the answers

    Which of the following describes a potential consequence of maternal diabetes during pregnancy?

    <p>Higher incidence of caudal dysgenesis</p> Signup and view all the answers

    What defines the embryonic period within human development?

    <p>Third to eighth weeks of development</p> Signup and view all the answers

    At which stage does the male and female pronuclei form during human development?

    <p>Approximately 12 to 24 hours after fertilization</p> Signup and view all the answers

    What occurs to the blastocyst immediately after the disappearance of the zona pellucida?

    <p>It gets embedded into the decidua</p> Signup and view all the answers

    Which correctly describes the transformed state of the endometrium after implantation?

    <p>It becomes the decidua</p> Signup and view all the answers

    What is the main role of enzymes produced by the syncytiotrophoblast during implantation?

    <p>To erode maternal uterine tissues</p> Signup and view all the answers

    What distinguishes the cytotrophoblast from the syncytiotrophoblast in the context of implantation?

    <p>Cytotrophoblast comprises fewer cells with defined boundaries</p> Signup and view all the answers

    When does the advanced morula stage reach the uterine lumen during human development?

    <p>About 4 days of age</p> Signup and view all the answers

    What is the first structure formed as a result of cellular differentiation from the trophoblast?

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

    Identify the two layers into which the trophoblast differentiates.

    <p>Cytotrophoblast and Syncytiotrophoblast</p> Signup and view all the answers

    What are the two distinct layers formed from the inner cell mass during the second week of development?

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

    Which type of stem cells are described as capable of differentiating into any cell type?

    <p>Totipotent Stem Cells</p> Signup and view all the answers

    What does the term 'potency' refer to in the context of stem cells?

    <p>The capacity to differentiate into multiple specialized cell types</p> Signup and view all the answers

    Which of the following structures is covered by the extraembryonic splanchnopleuric mesoderm?

    <p>Yolk Sac</p> Signup and view all the answers

    What key event occurs during the late blastocyst stage within the second week of development?

    <p>Development of lacunae in syncytiotrophoblast</p> Signup and view all the answers

    What is one major ethical concern regarding embryonic stem cell research?

    <p>The destruction of human embryos during cell extraction</p> Signup and view all the answers

    What is the function of the hypoblast during embryonic development?

    <p>To act as a source of endodermal cells</p> Signup and view all the answers

    What key structural development occurs by the end of the second week of embryonic development?

    <p>Development of the bilaminar disc</p> Signup and view all the answers

    Which layer of the placental membrane is not normally involved in nutrient and gas exchange?

    <p>Primary mesoderm</p> Signup and view all the answers

    What is the main role of the umbilical vein in fetal circulation?

    <p>Delivers oxygen and nutrients from the mother to the fetus</p> Signup and view all the answers

    What happens to the placental membrane as pregnancy progresses beyond four months?

    <p>It thins to increase the exchange rate of materials</p> Signup and view all the answers

    Which function is not attributed to the placenta?

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

    At the end of pregnancy, what change occurs to the placental barrier?

    <p>Fibrinoid material is deposited to decrease permeability</p> Signup and view all the answers

    What is the primary cause of caudal dysgenesis or sirenomelia?

    <p>Insufficient mesoderm formation</p> Signup and view all the answers

    What commonly associated factor can lead to the occurrence of caudal dysgenesis?

    <p>Maternal diabetes</p> Signup and view all the answers

    During which weeks does the embryonic period, or period of organogenesis, primarily occur?

    <p>Third to eighth weeks</p> Signup and view all the answers

    What process describes the conversion of the flat trilaminar embryonic disc into a cylindrical embryo?

    <p>Embryonic folding</p> Signup and view all the answers

    What are the two main types of folding that occur during the embryonic period?

    <p>Cephalocaudal and transverse folding</p> Signup and view all the answers

    What occurs to the primitive streak by the end of the fourth week of development?

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

    What is a potential result of remnants of the primitive streak persisting in the sacrococcygeal region?

    <p>Formation of teratomas</p> Signup and view all the answers

    What is one of the primary derivatives of the mesoderm layer during development?

    <p>Muscle tissue</p> Signup and view all the answers

    Which of the following describes a range of defects commonly associated with sirenomelia?

    <p>Lower limb defects and renal agenesis</p> Signup and view all the answers

    What is the significance of the embryonic period in relation to teratogens?

    <p>It is the most sensitive period for structural defects caused by teratogens.</p> Signup and view all the answers

    What is the length of Meckel’s diverticulum?

    <p>2 inches</p> Signup and view all the answers

    What potential complication can arise from the persistence of the yolk stalk?

    <p>Intestinal obstruction</p> Signup and view all the answers

    Which of the following represents a developmental remnant of the allantois?

    <p>Median umbilical ligament</p> Signup and view all the answers

    What is a possible outcome of an abnormality in the allantois?

    <p>Urachal fistula</p> Signup and view all the answers

    How far is Meckel’s diverticulum typically located from the ileocaecal junction?

    <p>2 feet</p> Signup and view all the answers

    Which structure forms the umbilical blood vessels derived from the allantois?

    <p>Connecting stalk</p> Signup and view all the answers

    Which of the following congenital anomalies is not associated with the allantois?

    <p>Meckel’s diverticulum</p> Signup and view all the answers

    What stage of embryonic development is the allantois primarily involved in?

    <p>Cephalocaudal folding</p> Signup and view all the answers

    What is the fate of the intraembryonic part of the allantois after birth?

    <p>Transforms into the urachus</p> Signup and view all the answers

    How frequently does Meckel’s diverticulum occur in the population?

    <p>2%</p> Signup and view all the answers

    Study Notes

    Fertilization, Cleavage & Implantation

    • Fertilization is the fusion of mature sperm and ovum
    • The fertilization site is the ampullary part of the uterine tube
    • Spermatozoa require capacitation and the acrosome reaction to fertilize the oocyte
    • Spermatozoa have a head, containing the nucleus and acrosome, and a tail (flagellum) with mitochondria
    • The acrosome contains enzymes (e.g., acrosin) to penetrate the zona pellucida
    • The acrosome reaction occurs after sperm binds to the zona pellucida
    • Fertilization normally restores the diploid number of chromosomes
    • Fertilization determines the sex of the embryo
    • Ovulation and fertilization occur approximately 24 hours apart
    • Fertilization initiates cleavage
    • Cleavage is a series of mitotic cell divisions
    • The cleavage site is the uterine tube, medial to the ampulla
    • Cleavage leads to the formation of a morula, then a blastocyst

    Blastocyst Formation

    • The morula enters the uterus and forms a cavity (blastocele)
    • Blastomeres divide into inner cell mass and outer cell mass
    • The inner cell mass forms the embryo
    • The outer cell mass forms the trophoblast, which develops into the placenta
    • The zona pellucida disappears before implantation
    • The blastocyst implants approximately 6 days after fertilization

    Implantation

    • Implantation is the embedding of the blastocyst into the uterine wall
    • Normal implantation occurs in the endometrium of the anterior or posterior wall of the uterus, typically in the middle of the uterine wall
    • A layer proliferates around the blastocyst and becomes differentiated into inner layer of cytotrophoblasts and outer layer of syncytiotrophoblast
    • The syncytiotrophoblast produces enzymes to erode the uterine tissue
    • The endometrium is called the decidua after implantation

    Decidua

    • Decidua basalis is the part of the endometrium lying between the blastocyst and the myometrium
    • Decidua capsularis is the part of the endometrium that covers the surface of the implanted blastocyst
    • Decidua parietalis is the endometrium lining the rest of the uterine cavity
    • Decidua marginalis is the part of the endometrium at the junction between the decidua capsularis and parietalis

    Clinical Correlation

    • Abnormal implantation (ectopic pregnancy) occurs outside the uterus
    • Common ectopic pregnancy site is in the fallopian tube
    • Placenta previa is implantation of the blastocyst in the lower segment of the uterus

    The Second and Third Weeks of Development

    • The blastocyst becomes partially embedded in the endometrial stroma (during the second week)
    • The trophoblast differentiates into two layers (cytotrophoblast and syncytiotrophoblast)
    • Lacunae (cavities) develop in the syncytiotrophoblast
    • The inner cell mass differentiates into epiblast and hypoblast
    • The epiblast and hypoblast together form a bilaminar embryonic disc
    • The extraembryonic mesoderm forms the extraembryonic coelom

    Gastrulation

    • It happens when the bilaminar disc converts into a trilaminar germ disc
    • A midline primitive streak forms on the epiblast
    • Epiblast cells migrate into the primitive streak, forming the endoderm and mesoderm
    • The cells form the notochord, a structure that runs along the midline that guides the development of the body axis

    Neuralation

    • The neural plate forms in the dorsal ectoderm over the notochord
    • Neural folds develop, which fuse to form the neural tube
    • The neural crest cells form between the neural tube and ectoderm

    The Fetal Membranes

    • The membranes are the chorion, amnion, yolk sac, allantois
    • Chorion forms the fetal part of the placenta
    • Amnion surrounds the developing embryo/fetus
    • Yolk sac provides nutrition during early development
    • Allantois is involved in the formation of the umbilical cord and urinary bladder
    • The formation of the villous structure depends on the formation of tertiary villi
    • The placenta exchanges nutrients and waste products from the fetal and maternal circulation
    • The structure of the placental barrier consists of three layers comprising the syncytiotrophoblast, cytotrophoblast and mesoderm (intervillous spaces)

    The Umbilical Cord

    • Consists of blood vessels (2 arteries and 1 vein) surrounded by Wharton's jelly
    • Develops between the chorionic and decidual plates

    The 2nd and 3rd Trimester

    • The fetal period occurs from the 9th week until birth
    • Rapid growth and maturation of tissues and organs are the main events during the fetal period
    • The size of the head is relatively smaller compared to the body during the fetal period
    • Several milestones occur during the development of the fetal period, including the appearance of taste buds, swallowing, respiratory and sucking movements, and the development of hearing and light sensitivity
    • The fetus gains weight throughout the fetal period, especially in the last trimester
    • Congenital anomalies can occur during development

    Low Birth Weight

    • Variations in fetal length and weight occur; they are influenced by both genetic and environmental factors.
    • Several medical conditions can affect the fetus's development, resulting in low birth weight

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    Description

    This quiz covers the processes of fertilization, cleavage, and implantation in human development. You will learn about the roles of sperm and ovum, as well as the stages leading to blastocyst formation. Test your knowledge on the biological mechanisms involved in these essential reproductive processes.

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