Embryonic Development Week 3
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Questions and Answers

What is the primary role of the inner cell mass during development?

  • To form the future embryo (correct)
  • To organize the notochord
  • To create the oral membrane
  • To contribute to the placenta

    • What is the significance of the primitive node in embryonic development?

  • It acts as an organizing center for axial structure formation (correct)
  • It assists in the development of the morula
  • It contributes to the formation of the trophoblast
  • It helps form the oropharyngeal membrane

    • Which structure will the oropharyngeal membrane develop into?

  • The future mouth opening (correct)
  • The primitive streak
  • The inner cell mass
  • The trophoblast layer

    • What occurs during the process of compaction in the morula stage?

    <p>Blastomeres become restructured to maximize contact with each other (B)</p> Signup and view all the answers

    In which stage is the structure known as the morula formed?

    <p>At the 16-cell stage (C)</p> Signup and view all the answers

    What is a characteristic of the outer cell mass in the developing embryo?

    <p>It contributes to the placenta (D)</p> Signup and view all the answers

    What defines the region at the cranial end of the embryonic disc?

    <p>The absence of mesoderm (C)</p> Signup and view all the answers

    What happens to the blastomeres during the morula stage?

    <p>They maximize contact and form tight junctions (D)</p> Signup and view all the answers

    What are blastomeres characterized by during mitotic divisions?

    <p>They become progressively smaller. (C)</p> Signup and view all the answers

    What type of structures will the mesoblast formation contribute to?

    <p>Mesodermal structures. (C)</p> Signup and view all the answers

    What is the significance of the area located at the caudal end of the embryonic disc?

    <p>It will form the future anal membrane. (B)</p> Signup and view all the answers

    What defines the totipotent nature of blastomeres?

    <p>They have the potential to form an entire organism. (D)</p> Signup and view all the answers

    Which of the following statements about mesoblast formation is correct?

    <p>It happens through a series of mitotic divisions. (B)</p> Signup and view all the answers

    Which process occurs first in the development of the mesodermal structures?

    <p>Mitotic cell divisions. (C)</p> Signup and view all the answers

    Which best describes the molecular characteristics of the embryonic cells involved in mesoblast formation?

    <p>They are capable of forming multiple types of tissues. (D)</p> Signup and view all the answers

    What distinguishes the cells at the caudal end of the embryonic disc?

    <p>They lack mesoderm and will create the cloacal membrane. (A)</p> Signup and view all the answers

    Why is the concept of totipotency important in early embryonic development?

    <p>It allows for the potential development of a full organism from a single cell. (A)</p> Signup and view all the answers

    What effect occurs to the size of cells during the cleavage stage of embryonic development?

    <p>Cells decrease progressively in size. (A)</p> Signup and view all the answers

    Which structure is a derivative of the para-axial mesoderm?

    <p>Somites (D)</p> Signup and view all the answers

    What do lacunar spaces precede in the embryonic development?

    <p>Uteroplacental circulation (B)</p> Signup and view all the answers

    Which of the following best describes what the hypoblast differentiates into?

    <p>Endoderm and yolk sac (A)</p> Signup and view all the answers

    The amnion and amniotic cavity are formed during which part of embryonic development?

    <p>Second week (D)</p> Signup and view all the answers

    Which structure is associated with the formation of early kidney structures?

    <p>Nephrogenic Cord (C)</p> Signup and view all the answers

    What do the lacunar spaces eventually contribute to in the embryo?

    <p>Establishment of uteroplacental circulation (A)</p> Signup and view all the answers

    The intraembryonic coelom is primarily responsible for the formation of which cavities?

    <p>Pericardial, pleural, and peritoneal cavities (C)</p> Signup and view all the answers

    Which of the following structures forms from the ectoderm?

    <p>Amnion (B)</p> Signup and view all the answers

    What is considered the primary component during the development of the bilaminar embryonic disc?

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

    The secondary yolk sac is developed by the end of which week?

    <p>End of the second week (C)</p> Signup and view all the answers

    What is the primary function of the syncytiotrophoblast during early development?

    <p>Secretes enzymes for maternal tissue erosion (B), Establishes blood supply via hCG secretion (D)</p> Signup and view all the answers

    Which layer is responsible for forming the gastrointestinal system?

    <p>Endoderm (D)</p> Signup and view all the answers

    From which structure does the neural plate arise?

    <p>Ectoderm (A)</p> Signup and view all the answers

    What is formed as the neural plate invaginates?

    <p>Neural groove (C)</p> Signup and view all the answers

    Which of the following accurately describes the role of trophoblast cells?

    <p>To invade maternal tissues for connection (D)</p> Signup and view all the answers

    What does the ectoderm differentiate into during early embryonic development?

    <p>Neuroectoderm (B)</p> Signup and view all the answers

    Which structure is specifically created to secure anchorage in the uterus?

    <p>Syncytiotrophoblast (A)</p> Signup and view all the answers

    What is the outcome of the formation of the amniotic cavity?

    <p>Support for embryonic development (A)</p> Signup and view all the answers

    What triggers the differentiation of the trophoblast into syncytiotrophoblast?

    <p>Contact with maternal blood (D)</p> Signup and view all the answers

    Which layer is directly involved in erosion of the uterine wall?

    <p>Syncytiotrophoblast (C)</p> Signup and view all the answers

    What is the primary role of the primitive streak during gastrulation?

    <p>To establish the embryo's craniocaudal axis and symmetry (A)</p> Signup and view all the answers

    Which germ layer is formed through the migration of epiblast cells during gastrulation?

    <p>Definitive endoderm (A)</p> Signup and view all the answers

    What process occurs as the zygote travels through the fallopian tube toward the uterus?

    <p>Cleavage (D)</p> Signup and view all the answers

    What structure forms as a result of the thickening of the ectoderm during embryonic development?

    <p>Neural plate (D)</p> Signup and view all the answers

    Which two structures are involved in the formation of the intraembryonic mesoderm?

    <p>Epiblast and endoderm (B)</p> Signup and view all the answers

    What is the consequence of epiblast cells migrating through the primitive line?

    <p>Creation of the definitive endoderm (A)</p> Signup and view all the answers

    During which phase does the neural groove begin to form?

    <p>When the neural plate folds inward (B)</p> Signup and view all the answers

    What prevents premature implantation of the zygote?

    <p>Zona pellucida (D)</p> Signup and view all the answers

    What occurs approximately 24 hours post-fertilization?

    <p>Cleavage of the zygote (A)</p> Signup and view all the answers

    Mesoblast cells differentiate into which of the following structures?

    <p>Muscles, bones, and blood vessels (B)</p> Signup and view all the answers

    What is the name of the process that involves merging of male and female pronuclei?

    <p>Syngamy (D)</p> Signup and view all the answers

    What significance does the primitive line have in embryonic development?

    <p>It marks the beginning of mesoderm formation (A)</p> Signup and view all the answers

    Which structure provides the lining for the gastrointestinal and respiratory systems during embryonic development?

    <p>Definitive endoderm (B)</p> Signup and view all the answers

    What role does the hypoblast play during the formation of the definitive endoderm?

    <p>It is replaced by migrating epiblast cells (A)</p> Signup and view all the answers

    What key purpose does the primary yolk sac serve during early development?

    <p>Facilitates nutrient exchange (C)</p> Signup and view all the answers

    Which type of mesoderm is responsible for the formation of the heart and blood vessels?

    <p>Lateral mesoderm (B)</p> Signup and view all the answers

    What is the result of the split in extraembryonic mesoderm?

    <p>Creation of the chorionic cavity (B)</p> Signup and view all the answers

    During neural tube formation, which direction does the closure begin?

    <p>Caudal to cranial (C)</p> Signup and view all the answers

    What forms the exocoelomic membrane?

    <p>Hypoblast layer (C)</p> Signup and view all the answers

    What do the para-axial mesoderm cells give rise to?

    <p>Vertebrae and dermis (C)</p> Signup and view all the answers

    Which cells are involved in the formation of peripheral nerves and parts of the craniofacial skeleton?

    <p>Neural crest cells (D)</p> Signup and view all the answers

    What does the secondary yolk sac replace during development?

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

    Which mesodermal type is responsible for forming the urogenital system?

    <p>Intermediate mesoderm (A)</p> Signup and view all the answers

    What fills the lacunae formed by the syncytiotrophoblast?

    <p>Maternal blood (C)</p> Signup and view all the answers

    What is the main role of the neural tube in development?

    <p>Precursor to the central nervous system (B)</p> Signup and view all the answers

    Which structure acts as a protective layer during early embryonic development?

    <p>Amnion (B)</p> Signup and view all the answers

    The term 'Week of Twos' refers to which developmental stage?

    <p>Second week of development (A)</p> Signup and view all the answers

    What initiates the differentiation of mesoderm into three regions?

    <p>Gastrulation (B)</p> Signup and view all the answers

    Flashcards

    Morula

    The initial stage of embryonic development characterized by a solid ball of cells.

    Primitive Node

    A small, elevated region at the cranial end of the primitive streak that serves as an organizing center for notochord and axial structure formation.

    Trophoblast

    The outer layer of cells in the morula that contributes to the placenta.

    Inner Cell Mass (Embryoblast)

    The inner layer of cells in the morula that forms the embryo itself.

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    Compaction

    The process where blastomeres maximize contact with each other, forming tight junctions in the outer layer of the morula.

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    Oropharyngeal Membrane

    A membrane located at the cranial end of the embryonic disc that marks the future mouth opening.

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    16-cell stage

    A stage in early embryonic development where the zygote undergoes multiple cell divisions to form a ball of cells.

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    Notochord

    A structure that serves as a primitive backbone during embryonic development.

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    Cleavage

    Cell divisions that happen without an increase in cell size. The cells get smaller with each division.

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    Mesoblast Formation

    The process of creating the mesoderm, which forms connective tissues and the cardiovascular system.

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    Totipotent

    Cells that can develop into any type of cell in the body.

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    Cloacal Membrane

    The area at the tail end of the embryonic disc that lacks mesoderm and will eventually form the anal membrane.

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    Blastocyst

    A hollow ball of cells formed during embryonic development. It is surrounded by a fluid-filled cavity called the blastocoel.

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    Inner Cell Mass

    A specific cell layer inside the blastocyst.

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    Embryonic Development

    The process by which a single-celled zygote develops into a multicellular embryo.

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    Amnion

    The outer layer of the embryo that protects and nourishes the developing embryo.

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    Gastrulation

    The process that transforms the bilaminar embryonic disc into a trilaminar disc, marking the transition from a single layer to three distinct germ layers.

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    Primitive Streak

    A thickened linear band of epiblast cells on the dorsal surface of the embryonic disc, crucial for establishing the embryo's body plan.

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    Cell Migration

    The process of epiblast cells moving towards the primitive streak, initiating the formation of the three germ layers: ectoderm, mesoderm, and endoderm.

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    Definitive Endoderm

    The innermost germ layer formed during gastrulation, giving rise to the lining of the digestive tract and respiratory system.

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    Intraembryonic Mesoderm

    The middle germ layer formed during gastrulation, responsible for creating diverse structures like muscles, bones, and blood vessels.

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    Ectoderm

    The outermost germ layer formed during gastrulation, giving rise to the skin, nervous system, and sense organs.

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    Primitive Line

    The early phase of the primitive streak.

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    Syngamy

    The merging of the male and female pronuclei during fertilization, restoring the diploid state after haploid gametes unite.

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    Zona Pellucida

    The glycoprotein layer surrounding the zygote, preventing premature implantation and protecting the developing embryo.

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    Zygote

    The single diploid cell formed after fertilization, containing 46 chromosomes.

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    Neural Plate

    The thickened region of ectoderm on the dorsal surface of the embryo, which later gives rise to the central nervous system.

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    Neural Groove

    The inward folding of the neural plate, forming a groove that eventually closes to form the neural tube.

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    Definitive Endoderm Formation

    The process of epiblast cells migrating through the primitive line and replacing the original hypoblast to form the innermost germ layer, the definitive endoderm.

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    Syncytiotrophoblast Formation

    The process where the trophoblast cells differentiate and fuse to form a multinucleated structure that secretes hCG.

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    Human Chorionic Gonadotropin (hCG)

    The hormone secreted by the syncytiotrophoblast that maintains the corpus luteum and prevents menstruation.

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    Trophoblast Invasion

    The process where the trophoblast cells penetrate the uterine lining and connect to the maternal blood supply.

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    Neural Tube Formation

    The process where the neural plate folds inward to form the neural tube, which eventually becomes the brain and spinal cord.

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    Amniotic Cavity Formation

    The process where the ectoderm cells invaginate to form a cavity that becomes the amniotic sac.

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    Lacunar Spaces

    The spaces that precede the development of the uteroplacental circulation, which is responsible for nutrient and waste exchange between mother and fetus.

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    Mesoderm

    The cellular layer between the ectoderm and endoderm that gives rise to muscles, bones, blood, and many other internal structures.

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    Hypoblast

    The cell layer lining the blastocoel in early development. It forms the extraembryonic membrane.

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    Blastocoel

    A cavity filled with fluid in the blastocyst. It eventually becomes the yolk sac.

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    Nidation

    A process during which the blastocyst implants into the uterine wall.

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    Primary Yolk Sac

    A structure derived from the hypoblast that provides early nutrient exchange for the developing embryo.

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    Neural Crest Cells

    Specialized cells that migrate and contribute to the formation of various tissues, including nerves, pigment cells, and parts of the face.

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    Para-Axial Mesoderm

    A component of the mesoderm that gives rise to the vertebrae, skeletal muscles, and skin.

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    Intermediate Mesoderm

    A component of the mesoderm that forms the kidneys and gonads.

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    Lateral Mesoderm

    A component of the mesoderm that forms the heart, blood vessels, and lining of the body cavity.

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    Somatic Mesoderm

    The mesodermal layer that lines the cytotrophoblast and amnion (outermost embryonic membranes).

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    Splanchnic Mesoderm

    The mesodermal layer that surrounds the yolk sac.

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    Chorionic Cavity

    A cavity that forms within the extraembryonic mesoderm, separating the developing embryo from the trophoblast.

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    Secondary Yolk Sac

    A new yolk sac structure that replaces the primary yolk sac, providing nutrition and supporting blood cell formation.

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    Lacunae

    These are spaces filled with maternal blood within the syncytiotrophoblast, enabling nutrient exchange between mother and embryo.

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    Study Notes

    Third Week of Development

    • Gastrulation converts the bilaminar embryonic disc into a trilaminar disc.
    • The primitive streak appears, establishing the embryo's axis and symmetry.
    • Epiblast cells migrate, forming definitive endoderm (gastrointestinal and respiratory lining) and intraembryonic mesoderm (muscles, bones, blood).
    • Ectoderm thickens into the neural plate, precursor to the central nervous system.
    • The neural plate folds to form the neural groove.

    Primitive Streak

    • The primitive line is the initial phase of the primitive streak.
    • Migratory epiblast cells through the primitive line form the definitive endoderm.
    • Cells migrating between ectoderm and endoderm create the mesoblast for connective tissues, cardiovascular structures.
    • The cloacal membrane, without mesoderm, will form the future anal membrane.
    • The primitive node (Hensen's node) is at the cranial end, organizing notochord and axial formation.
    • The oropharyngeal membrane, without mesoderm, will develop into the mouth opening.

    Primitive Node and Oropharyngeal Membrane

    • Mesodermal cells from the primitive streak form the cardiogenic zone.
    • The heart primordium develops in the cardiogenic zone.
    • The primitive node extends the chordal process cranially.
    • The chordal process develops into the notochord, vital for neural tube and surrounding tissue differentiation.
    • The chordal canal forms within the chordal process and facilitates amniotic/yolk sac communication.
    • The neurenteric duct is a temporary connection between these cavities.

    Dorsal Chord and Trilaminar Disc Formation

    • The dorsal chord is a rod-like structure along the midline.
    • This structure acts as a signaling center to guide neural tube and somite development.
    • The embryo transforms into a trilaminar disc with ectoderm, mesoderm, and endoderm.

    Neural Plate and Neuroectoderm

    • The neural plate originates from thickened ectoderm cranial to the primitive node.
    • Neural plate cells become neuroectoderm, forming the brain, spinal cord, and peripheral nervous system.
    • The neural groove forms as the neural plate invaginates.

    Neural Groove and Neural Crests

    • Neural crest cells, at the neural plate edges, migrate to form peripheral nerves, melanocytes, and craniofacial structures.

    Neural Tube Formation

    • Neural plate edges elevate and fuse, forming the neural tube.
    • Closure starts mid-embryo and progresses cranially and caudally.

    Para-Axial Mesoderm

    • Forms somites, which develop into vertebrae, skeletal muscles, and dermis.

    First Week of Development

    • Zygote formation from fertilization (single diploid cell).
    • Cleavage begins with mitotic divisions.
    • Blastomeres are totipotent (potential for complete embryo development).
    • Morula forms at day 3 (16-cell stage).
    • Blastocyst formation (day 4-5) occurs with a central blastocoel and inner/outer cell masses (embryoblast/trophoblast).

    Second Week of Development

    • Implantation begins during days 6-7 and completes by day 12.
    • Trophoblast differentiates into cytotrophoblast (cellular layer) and syncytiotrophoblast (multinucleate layer invading the uterine wall).
    • Syncytiotrophoblast secretes hCG and establishes maternal blood supply.
    • Lacunae (spaces filled with maternal blood) form in the syncytiotrophoblast, preluding the uteroplacental circulation.
    • Amniotic cavity appears within the epiblast.
    • Amnion forms around the embryo.
    • Hypoblast forms the exocoelomic membrane, lining the blastocoel.
    • The blastocoel transforms into the primary yolk sac.
    • Extraembryonic mesoderm forms, splitting into somatic and splanchnic layers.
    • Chorionic cavity (extraembryonic coelom) separates the embryo from the trophoblast.
    • Primary yolk sac transforms into the secondary yolk sac.
    • A bilaminar embryonic disc, comprised of epiblast and hypoblast, forms.

    Mesoderm Differentiation

    • Differentiates into intermediate, lateral, and para-axial mesoderm.
    • Intermediate mesoderm forms the urogenital system (kidneys, gonads).
    • Lateral mesoderm forms heart, blood vessels, and body cavities.
    • Para-axial mesoderm forms somites, crucial for skeletal muscle and vertebrae.
    • Nephrogenic cord forms part of the intermediate mesoderm, leading to early kidney development.
    • Intraembryonic coelom develops into pericardial, pleural, and peritoneal cavities.

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    Description

    This quiz focuses on the third week of embryonic development, covering key processes such as gastrulation, the formation of germ layers, and the development of the neural plate. Test your knowledge on important structures like the primitive streak and Hensen's node, as well as their roles in embryonic axis and symmetry formation.

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