Embryology Chapter Cell Layers
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Questions and Answers

Which embryonic layer is responsible for forming the epithelial lining of the digestive tract?

  • Endoderm (correct)
  • Hypoblast
  • Mesoderm
  • Ectoderm

    • What structure is formed from the mesoderm layer?

  • Epidermis of skin
  • Nervous system
  • Circulatory system (correct)
  • Lining of the bladder

    • What occurs first during the process of gastrulation?

  • Ingression of epiblast cells
  • Formation of the primitive streak
  • Mesoderm formation
  • Asymmetric development of the embryo (correct)

    • Which layer forms the epidermis of the skin?

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

    What is the source of all germ layers in the embryo?

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

    What is formed by the cells that migrate through the primitive pit and lie between the epiblast and endoderm?

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

    At what stage do epiblast cells begin migrating medially toward the streak?

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

    What type of transition do epiblast cells undergo at the primitive streak during gastrulation?

    <p>Epithelial to mesenchymal</p> Signup and view all the answers

    What structure forms the outer cell mass of the blastocyst?

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

    Which layer is formed from the inner cell mass within the blastocyst?

    <p>Bilaminar disc</p> Signup and view all the answers

    During implantation, what do trophoblast cells do in relation to the uterine wall?

    <p>They invade the uterine wall.</p> Signup and view all the answers

    What is the main function of the zona pellucida during early development?

    <p>Protect the embryo from implantation in the fallopian tubes</p> Signup and view all the answers

    Which two layers make up the bilaminar disc?

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

    What role do hydrolytic enzymes play during implantation?

    <p>They break down uterine tissue.</p> Signup and view all the answers

    What is the significance of gastrulation and neurulation during embryonic development?

    <p>They establish the three germ layers and the nervous system.</p> Signup and view all the answers

    What is NOT a characteristic of the morula stage?

    <p>It is a hollow structure.</p> Signup and view all the answers

    What is the primary outcome of gastrulation in embryonic development?

    <p>Differentiation into the trilaminar disc</p> Signup and view all the answers

    Which structure is critical for inducing neurulation?

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

    What drives the cellular rearrangement during gastrulation?

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

    What is the role of the primitive streak in embryonic development?

    <p>To identify embryonic axes</p> Signup and view all the answers

    During which week does the primitive streak appear in the embryonic disk?

    <p>Third week</p> Signup and view all the answers

    What is formed from the epiblast layer during gastrulation?

    <p>Three germ cell layers</p> Signup and view all the answers

    Which germ layer is formed last during gastrulation?

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

    What cellular process is NOT involved during gastrulation?

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

    At which site does the intraembryonic mesoderm not separate the ectoderm and endoderm?

    <p>Cloacal membrane caudally</p> Signup and view all the answers

    What causes the growth and elongation of the embryonic disc?

    <p>Continuous migration of cells from the primitive streak region</p> Signup and view all the answers

    During which week does the primitive streak begin to regress and shrink?

    <p>Week 4</p> Signup and view all the answers

    Which process refers to the folding of vertebrate embryos to form the neural tube?

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

    Which area is specified as the location where the heart will form during embryonic development?

    <p>Cardiogenic area</p> Signup and view all the answers

    What is the term for the process that describes the formation of germ layers?

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

    In which direction does the continuous migration of cells occur from the primitive streak?

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

    What anatomical structure is formed by the invagination of surface cells in the primitive streak?

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

    What is the term given to the embryo during the neurulation process?

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

    Which structure is formed from the mesoderm in the development of the embryo?

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

    What induces the ectoderm to become neuroectoderm during development?

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

    What do the elevated lateral edges of the neural plate form?

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

    At what point does the closure of the cranial neuropore typically occur?

    <p>Day 25</p> Signup and view all the answers

    What structure represents the central nervous system after neurulation is complete?

    <p>Closed tubular structure</p> Signup and view all the answers

    What are the inexperienced ends of the neural tube called before fusion is complete?

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

    What is the broader portion of the central nervous system referred to after neurulation?

    <p>Cranial portion</p> Signup and view all the answers

    Study Notes

    Germ Layers Formation

    • Three primary germ layers form during embryonic development: endoderm, mesoderm, and ectoderm.
    • Endoderm produces the epithelial lining of the digestive and respiratory tracts, urethra, bladder, reproductive system, liver, and pancreas.
    • Mesoderm gives rise to the notochord, musculoskeletal system, muscular layers of the stomach and intestines, and the circulatory system.
    • Ectoderm develops into the epidermis of the skin, cornea and lens of the eye, and the nervous system.

    Gastrulation Process

    • Gastrulation involves cell migration and differentiation, resulting in a trilaminar disc.
    • Begins with asymmetric embryo development, formation of the primitive streak, and epithelial to mesenchymal transition of epiblast cells.
    • By day 16, epiblast cells migrate medially towards the primitive streak and laterally to form intraembryonic mesoderm.
    • Extra-embryonic mesoderm exists outside the embryo.

    Early Development Stages

    • Zygote: A diploid cell from the fusion of two haploid gametes.
    • Blastomeres: Individual cells formed during early cleavage stages.
    • Morula: A solid ball of cells from the 16-cell stage.
    • Blastocyst: Composed of the outer cell mass (trophoblast) and inner cell mass (embryoblast) that forms the bilaminar disc.

    Key Structure Formation

    • Amniotic sac: Develops above the epiblast, providing cushioning.
    • Primary yolk sac: Forms below the hypoblast, providing nutrition.

    Implantation

    • Occurs around days 7–9 post-fertilization as trophoblast cells lose outer membranes and release hydrolytic enzymes to penetrate the uterine wall.
    • The process of implantation results in a layer of endometrium covering the blastocyst.

    Importance of Neurulation

    • Neurulation follows gastrulation and involves the forming of the neural tube from ectoderm.
    • Begins with the appearance of the notochord, which signals nearby ectoderm to form the neural plate.
    • Neural plate undergoes folding and fusion to create a tube that will differentiate into the central nervous system.

    Embryonic Growth and Structure

    • The embryonic disc elongates as cells migrate from the primitive streak.
    • The primitive streak identifies cranial and caudal ends, and facilitates cellular rearrangement.
    • Growth continues through the 4th week as differentiation takes place in cranial structures while gastrulation proceeds in caudal segments.

    Closure of Neural Tube

    • Neural tube closure occurs around days 25 (cranial neuropore) and 28 (caudal neuropore).
    • By the end of the 4th week, the central nervous system is established as a closed tubular structure.

    Key Definitions

    • Primitive streak: A midline groove in the epiblast crucial for establishing embryonic axes and facilitating germ layer formation.
    • Notochord: A rod-like structure from mesoderm essential for inducing neurulation, placed along the dorsal side of the embryo.

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    Description

    Explore the three primary cell layers in embryology: endoderm, mesoderm, and ectoderm. This quiz delves into how these layers are formed from epiblast cells and their roles in developing fetus tissues. Perfect for students studying embryological development.

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