Embryology 3rd Week Development Processes
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Questions and Answers

What is the role of the notochord in the development process?

  • Stimulates the development of the epithelial lining of the digestive canal
  • Forms the neural tube cells
  • Forms the skeletal muscles of the trunk and limbs
  • Induces certain mesodermal cells to develop into vertebral bodies (correct)

    • What is the function of the cloacal membrane in the embryo's development?

  • Becomes the epithelial lining of internal organs
  • Develops into muscles, bones, and connective tissues
  • Forms the openings of the anus and urinary and reproductive tracts (correct)
  • Induces the formation of the neural tube

    • Which structure breaks down to connect the mouth cavity to the pharynx?

  • Cloacal membrane
  • Notochordal process
  • Neural fold
  • Oropharyngeal membrane (correct)

    • What is formed when the neural plate develops neural folds that approach and fuse together?

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

    Where do neural crest cells migrate from to give rise to various tissues and structures?

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

    What plays a role in inducing certain ectodermal cells to form the neural plate?

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

    Which part of the embryo forms a hollow tube of cells called the notochordal process?

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

    What is the first major event that occurs in the third week of development?

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

    What is the structure that establishes the head and tail ends of the embryo during gastrulation?

    <p>Primitive streak</p> Signup and view all the answers

    Which cells form a rounded structure called the primitive node at the head end of the primitive streak?

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

    How many primary germ layers are formed during early embryonic development?

    <p>Three: Ectoderm, Mesoderm, and Endoderm</p> Signup and view all the answers

    What does the primitive streak transform into during gastrulation?

    <p>Trilaminar embryonic disc</p> Signup and view all the answers

    Which event marks the beginning of gastrulation?

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

    What is the structure that elongates from the posterior to the anterior part of the embryo during gastrulation?

    <p>Primitive streak</p> Signup and view all the answers

    Which layer of the trilaminar embryonic disc gives rise to tissues and organs like skin, nervous system, and eyes?

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

    What does the trilaminar embryonic disc consist of?

    <p>Ectoderm, mesoderm, endoderm</p> Signup and view all the answers

    Which event establishes the right and left sides of the embryo?

    <p>Primitive streak formation</p> Signup and view all the answers

    The mesoderm gives rise to muscles, bones, and other connective tissues, and the peritoneum.

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

    The notochord induces certain ectodermal cells to develop into the vertebral bodies.

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

    The oropharyngeal membrane degenerates in the fourth week to form the openings of the anus and urinary and reproductive tracts.

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

    The lateral edges of the neural plate form the neural groove.

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

    The neural crest cells give rise to muscles and bones of the head.

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

    The paraxial mesoderm segments into paired cylindrical masses called lateral plate mesoderm.

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

    Each somite differentiates into three distinct regions: a dermomytome, a sclerotome, and a myotome.

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

    The sclerotomes give rise to the muscles of the trunk and limbs.

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

    The spaces that appear in the lateral plate mesoderm during the third week of development are large in size.

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

    The notochord plays a minor role in inducing the development of adjacent tissues.

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

    During the 3rd week of development, the embryonic disc changes from bilaminar to trilaminar, consisting of ectoderm, mesoderm, and endoderm.

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

    The primitive streak is a raised structure on the dorsal surface of the epiblast during gastrulation.

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

    Gastrulation is the process where cells migrate from the hypoblast to form the primitive streak.

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

    Somite formation occurs before notochord formation in the 3rd week of development.

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

    The primitive node forms at the tail end of the primitive streak during gastrulation.

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

    The intraembryonic coelom develops before neural tube formation in the 3rd week of development.

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

    The primitive streak establishes the right and left sides of the embryo but not its head and tail ends.

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

    Blood and blood vessel formation are not part of the processes that occur in the 3rd week of development.

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

    The trilaminar embryonic disc consists of epiblast, hypoblast, and mesoderm.

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

    Neural tube development is one of the last events to occur in the 3rd week of development.

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

    Match the following events with their occurrence in the 3rd week of development:

    <p>Notochord formation = Occurs before somite formation Primitive cardiovascular system development = Not part of the processes in the 3rd week Somite formation = Occurs before notochord formation Intraembryonic coelom development = Develops before neural tube formation</p> Signup and view all the answers

    Match the following structures with their role in embryonic development:

    <p>Primitive node = Forms at the head end of the primitive streak Notochord = Induces certain ectodermal cells to form the vertebral bodies Neural crest cells = Migrate from the neural folds to give rise to various tissues Paraxial mesoderm = Segments into lateral plate mesoderm</p> Signup and view all the answers

    Match the following statements with the correct process in embryonic development:

    <p>Gastrulation = Establishes right and left sides of the embryo Neural tube development = Occurs before somite formation Blood and blood vessel formation = Part of processes in the 3rd week Primitive streak elongation = Establishes head and tail ends of the embryo</p> Signup and view all the answers

    Match the following structures with their contribution to tissue differentiation:

    <p>Ectoderm = Gives rise to skin, nervous system, and eyes Mesoderm = Forms muscles, bones, and connective tissues Endoderm = Develops into peritoneum Sclerotome = Differentiates into dermomytome, sclerotome, and myotome</p> Signup and view all the answers

    Match the following structures with their part in cell migration during gastrulation:

    <p>Epiblast cells = Rearrange and migrate to form primitive streak Hypoblast cells = Migrate from epiblast to form primitive groove Lateral plate mesoderm = Segments into paired masses called sclerotomes Neural plate cells = Form neural folds that approach and fuse together</p> Signup and view all the answers

    Match the following structures with their respective embryonic germ layer origin:

    <p>Endoderm = Epithelial lining of digestive canal Mesoderm = Muscles and bones Ectoderm = Epidermis of the skin Neural crest cells = Sensory neurons and connective tissues</p> Signup and view all the answers

    Match the following developmental structures with their functions:

    <p>Notochord = Induces mesodermal cells to form vertebral bodies Oropharyngeal membrane = Connects mouth cavity to pharynx Cloacal membrane = Forms openings of anus and urinary tracts Neural crest cells = Give rise to melanocytes and peripheral nerves</p> Signup and view all the answers

    Match the following somite differentiation regions with their respective contributions:

    <p>Dermomytome = Subcutaneous tissue and dermis Myotome = Skeletal muscles of trunk and limbs Sclerotome = Vertebrae and ribs Intermediate mesenchyme = Unknown</p> Signup and view all the answers

    Match the following structures involved in neurulation with their functions:

    <p>Neural plate = Develops into brain and spinal cord Neural fold = Forms neural tube by fusion Neural tube = Converted from neural plate through fusion Neurulation = Process of neural tube formation</p> Signup and view all the answers

    Match the following mesoderm derivatives with their descriptions:

    <p>Paraxial mesoderm = Segments into somites Lateral plate mesoderm = Forms paired cylindrical masses Intermediate mesenchyme = Unknown Notochordal process = Forms solid cylinder of cells</p> Signup and view all the answers

    Match the following events during development with their descriptions:

    <p>Gastrulation = Formation of primitive streak and germ layers Neurulation = Formation of neural tube from neural plate Notochord induction = Stimulates mesodermal cells to form vertebral bodies Somite formation = Differentiation into dermomytome, sclerotome, and myotome</p> Signup and view all the answers

    Match the following structures with their respective roles in embryonic development:

    <p>Primitive node = Formation of notochordal process Notochordal process = Induces adjacent ectodermal cells to form neural plate Neural plate = Converted into neural tube during neurulation Lateral plate mesoderm spaces = Appear during third week of development</p> Signup and view all the answers

    Match the following membranes with their outcomes during development:

    <p>Oropharyngeal membrane degeneration = Connects mouth cavity to pharynx Cloacal membrane degeneration = Forms openings of anus, urinary, and reproductive tracts Primitive streak transformation = Establishes right and left sides of embryo Notochord induction process = Stimulates unspecialized tissue to become specialized</p> Signup and view all the answers

    Match the following weeks of development with significant events:

    <p>16 days after fertilization = Notochordal process forms hollow tube called notochordal process 22-24 days after fertilization = Notochord becomes solid cylinder of cells called notochord 17th day after fertilization = Mesoderm forms paraxial mesoderm columns adjacent to notochord and neural tube Third week of development = Neural crest cells migrate from neural tube to give rise to various tissues</p> Signup and view all the answers

    Match the following structures with their respective developmental timings:

    <p>Neural tube development = One of the last events in third week of development Spaces in lateral plate mesoderm appearance = Occurs during third week of development but small in size Somite formation timing relative to notochord formation = Before notochord formation in third week of development timeline Intraembryonic coelom development timing relative to neural tube formation = Before neural tube formation in third week of development timeline</p> Signup and view all the answers

    What is the first major event that occurs in the third week of development?

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

    What structure establishes the head and tail ends of the embryo during gastrulation?

    <p>Primitive streak</p> Signup and view all the answers

    Which cells form a rounded structure called the primitive node at the head end of the primitive streak?

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

    What is formed when the neural plate develops neural folds that approach and fuse together?

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

    What is the role of the notochord in the development process?

    <p>Inducing adjacent tissues to develop</p> Signup and view all the answers

    What is the structure that elongates from the posterior to the anterior part of the embryo during gastrulation?

    <p>Primitive streak</p> Signup and view all the answers

    Which layer of the trilaminar embryonic disc gives rise to tissues and organs like skin, nervous system, and eyes?

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

    What is the function of the cloacal membrane in the embryo's development?

    <p>Forms openings of the anus and urinary/reproductive tracts</p> Signup and view all the answers

    Where do neural crest cells migrate from to give rise to various tissues and structures?

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

    How many primary germ layers are formed during early embryonic development?

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

    What structure induces certain mesodermal cells to develop into the vertebral bodies?

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

    What structure breaks down to connect the mouth cavity to the pharynx?

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

    What is the function of the cloacal membrane in the embryo's development?

    <p>Forms openings of the anus and urinary/reproductive tracts</p> Signup and view all the answers

    Which structure induces certain ectodermal cells to form the neural plate?

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

    What structure establishes the head and tail ends of the embryo during gastrulation?

    <p>Primitive streak</p> Signup and view all the answers

    What is formed when the neural plate develops neural folds that approach and fuse together?

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

    Where do neural crest cells migrate from to give rise to various tissues and structures?

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

    What does the trilaminar embryonic disc consist of?

    <p>Ectoderm, mesoderm, and endoderm</p> Signup and view all the answers

    What is the first major event that occurs in the third week of development?

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

    Which event marks the beginning of gastrulation?

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

    Study Notes

    Gastrulation and Embryonic Development

    • The bilaminar embryonic disc, consisting of epiblast and hypoblast, transforms into a trilaminar embryonic disc consisting of three layers: Ectoderm, Mesoderm, and Endoderm.
    • These primary germ layers are the major embryonic tissues from which the various tissues and organs of the body develop.
    • Gastrulation involves the rearrangement and migration of cells from the epiblast.
    • The first evidence of gastrulation is the formation of the primitive streak, a faint groove on the dorsal surface of the epiblast that elongates from the posterior to the anterior part of the embryo.
    • The primitive streak clearly establishes the head and tail ends of the embryo, as well as its right and left sides.

    Formation of Germ Layers

    • Cells of the epiblast move inward below the primitive streak and detach from the epiblast in a process called invagination.
    • Some of the invaginated cells displace the hypoblast, forming the endoderm.
    • Other cells remain between the epiblast and newly formed endoderm to form the mesoderm.
    • Cells remaining in the epiblast then form the ectoderm.
    • The endoderm ultimately becomes the epithelial lining of the digestive canal, respiratory tract, and several other organs.
    • The mesoderm gives rise to muscles, bones, and other connective tissues, and the peritoneum.
    • The ectoderm develops into the epidermis of the skin and the nervous system.

    Notochord Formation

    • About 16 days after fertilization, mesodermal cells from the primitive node migrate toward the head end of the embryo and form a hollow tube of cells in the midline called the notochordal process.
    • By days 22-24, the notochordal process becomes a solid cylinder of cells called the notochord.
    • The notochord plays an extremely important role in induction, the process by which one tissue stimulates the development of an adjacent unspecialized tissue into a specialized one.

    Neural Tube Development

    • The notochord induces ectodermal cells over it to form the neural plate.
    • By the end of the third week, the lateral edges of the neural plate become more elevated and form the neural fold.
    • The depressed midregion is called the neural groove.
    • Generally, the neural folds approach each other and fuse, thus converting the neural plate into a neural tube.
    • This occurs first near the middle of the embryo and then progresses toward the head and tail ends.
    • The process by which the neural plate, neural folds, and neural tube form is called neurulation.
    • The neural tube cells develop into the brain and spinal cord.

    Somite Formation

    • By about the 17th day after fertilization, the mesoderm adjacent to the notochord and neural tube forms paired longitudinal columns of paraxial mesoderm.
    • The mesoderm lateral to the paraxial mesoderm forms paired cylindrical masses called intermediate mesenchyme.
    • The mesoderm lateral to the intermediate mesenchyme consists of a pair of flattened sheets called lateral plate mesoderm.
    • The paraxial mesoderm soon segments into a series of paired, cube-shaped structures called somites.
    • The number of somites that develop over a given period can be correlated to the approximate age of the embryo.
    • Each somite differentiates into two distinct regions: a dermomytome and a sclerotome.
    • The dermomytome further differentiates into a dermatome that will contribute to the formation of the subcutaneous tissue and dermis, a myotome, which will give rise to all the skeletal muscles of the trunk and limbs.
    • The sclerotomes give rise to the vertebrae and ribs.

    Other Processes

    • In the third week of development, small spaces appear in the lateral plate mesoderm.
    • Processes that occur in the 3rd week of development include:
      • Gastrulation
      • Notochord formation
      • Neural tube development
      • Somite formation
      • Intraembryonic coelom
      • Primitive cardiovascular system
      • Blood and blood vessel formation### Formation of Germ Layers
    • After the formation of the primitive streak, cells of the epiblast move inward and detach from the epiblast through a process called invagination.
    • Invaginated cells displace the hypoblast to form the endoderm, while others remain between the epiblast and endoderm to form the mesoderm.
    • Cells remaining in the epiblast form the ectoderm.

    Fate of Germ Layers

    • The endoderm develops into the epithelial lining of the digestive canal, respiratory tract, and other organs.
    • The mesoderm gives rise to muscles, bones, and other connective tissues, as well as the peritoneum.
    • The ectoderm develops into the epidermis of the skin and the nervous system.

    Formation of the Notochord

    • Around 16 days after fertilization, mesodermal cells from the primitive node migrate towards the head end of the embryo and form the notochordal process.
    • By days 22-24, the notochordal process becomes a solid cylinder of cells called the notochord.
    • The notochord plays a crucial role in induction, stimulating the development of adjacent tissues.

    Neural Development

    • The notochord induces ectodermal cells to form the neural plate.
    • The lateral edges of the neural plate become elevated to form the neural fold, and the depressed midregion forms the neural groove.
    • The neural folds approach and fuse, converting the neural plate into a neural tube.
    • The process of neural plate, neural fold, and neural tube formation is called neurulation.
    • Neural tube cells develop into the brain and spinal cord.

    Formation of the Neural Crest

    • As the neural tube forms, some ectodermal cells migrate to form the neural crest.
    • Neural crest cells give rise to sensory neurons, postganglionic neurons, suprarenal medullae, melanocytes, arachnoid mater, and pia mater.

    Mesoderm Development

    • By around the 17th day after fertilization, the mesoderm adjacent to the notochord and neural tube forms paired longitudinal columns of paraxial mesoderm.
    • The mesoderm lateral to the paraxial mesoderm forms paired cylindrical masses called intermediate mesenchyme.
    • The mesoderm lateral to the intermediate mesenchyme consists of a pair of flattened sheets called lateral plate mesoderm.
    • The paraxial mesoderm soon segments into a series of paired, cube-shaped structures called somites.

    Somite Development

    • Each somite differentiates into a dermomytome and a sclerotome.
    • The dermomytome further differentiates into a dermatome and a myotome.
    • The sclerotome gives rise to the vertebrae and ribs.

    Lateral Plate Mesoderm

    • Small spaces appear in the lateral plate mesoderm in the third week of development.

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    Description

    Explore the key processes that take place in the third week of embryonic development, such as Gastrulation, Notochord formation, Neural tube development, and more. Understand the transformation from a bilaminar embryonic disc to a trilaminar embryonic disc and the significance of each stage.

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