Embryology 5: 4th Week & Establishing Body Plan MCQ
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Questions and Answers

What structure develops at the caudal position relative to the heart during embryonic folding?

  • Septum transversum (correct)
  • Foregut
  • Ventricular wall
  • Primordial heart

    • Which of the following structures is formed from the oropharyngeal membrane breaking?

  • Umbilical cord
  • Cloacal membrane
  • Stomodeum
  • Esophagus (correct)

    • What is the relationship between the foregut and the heart during embryonic development?

  • The heart develops anterior to the foregut (correct)
  • The foregut develops into the heart
  • They develop next to each other
  • They are formed from the same embryonic layer

    • During which embryonic folding does the body stalk become ventral?

    <p>Median plane fold (tail region)</p> Signup and view all the answers

    How does the midgut interact with the vitelline sac during development?

    <p>It communicates with the vitelline sac through the vitelline duct</p> Signup and view all the answers

    What is a significant evolutionary benefit of bilateral symmetry?

    <p>Improved mobility and food seeking</p> Signup and view all the answers

    During which weeks does the organogenetic period occur?

    <p>4 to 8 weeks</p> Signup and view all the answers

    At what stage can the heartbeat of an embryo typically be detected by Doppler ultrasonography?

    <p>5th week</p> Signup and view all the answers

    What was a major consequence of thalidomide when taken by pregnant women?

    <p>Resulted in limb deformities</p> Signup and view all the answers

    What is the phylotypic stage of the embryo characterized by?

    <p>Similarity to vertebrates' embryos</p> Signup and view all the answers

    Which process occurs in the paraxial mesoderm during development?

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

    What two major events occur during the 4th week of development?

    <p>Folding and segmentation</p> Signup and view all the answers

    What is the primary function of the cardiovascular system during the organogenetic period?

    <p>Transporting nutrients</p> Signup and view all the answers

    What occurs when the concentrations of retinoic acid and FGF8 reach a reciprocal level?

    <p>The paraxial mesoderm gets segmented.</p> Signup and view all the answers

    Which genes oscillate between permissive and non-permissive states during somitogenesis?

    <p>Notch family genes</p> Signup and view all the answers

    What is the primary outcome of mesenchymal-to-epithelial transition during somitogenesis?

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

    Which structure will differentiate into the dermatome?

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

    Which part of the sclerotome forms the intervertebral disks?

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

    What does the medial sclerotome primarily differentiate into?

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

    What are the three main territories that each somite differentiates into?

    <p>Sclerotome, dermatome, myotome</p> Signup and view all the answers

    What role does the central sclerotome play in development?

    <p>Formation of proximal ribs and certain processes of vertebrae</p> Signup and view all the answers

    What is the primary function of the serosa in coelomic cavities?

    <p>To allow organs to move and grow independently</p> Signup and view all the answers

    What layers constitute the serous membrane?

    <p>Mesothelium and connective tissue</p> Signup and view all the answers

    What evolutionary advantage does the intraembryonic coelom provide to tripoblastic animals?

    <p>Fluid-filled space for organ protection and movement</p> Signup and view all the answers

    What role does the serous space play in organ function?

    <p>Cushions organs against shocks and allows free movement</p> Signup and view all the answers

    How does the presence of a true coelom benefit the circulatory system?

    <p>It enables the formation of a more complex circulatory system</p> Signup and view all the answers

    What happens during the splitting of the lateral plate mesoderm?

    <p>A true coelom is formed</p> Signup and view all the answers

    What is the relationship between the visceral layer and the organs?

    <p>It covers the organs directly</p> Signup and view all the answers

    Which of the following is NOT an advantage of having a coelomic cavity?

    <p>Enables direct attachment of organs to the body wall</p> Signup and view all the answers

    What type of bones do the somites primarily give rise to?

    <p>Axial bones</p> Signup and view all the answers

    Which structure is responsible for guiding the cells of the ventral sclerotome to form vertebrae?

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

    What do epaxial muscles primarily develop from?

    <p>Dorsal myotome</p> Signup and view all the answers

    The ventral muscle mass formed from myogenic cells gives rise to which types of muscles?

    <p>Flexors and pronators</p> Signup and view all the answers

    How many vertebrae does one sclerotome form?

    <p>Two vertebrae</p> Signup and view all the answers

    What is the primary origin of craniofacial bones?

    <p>Mesoderm of the head and neural crest cells</p> Signup and view all the answers

    Which part of the myotome divides into epimere and hypomere?

    <p>Ventral myotome</p> Signup and view all the answers

    The nucleus pulposus of intervertebral disks is primarily derived from which structure?

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

    What is the fate of the yolk sac during embryonic development?

    <p>It degenerates and is no longer needed.</p> Signup and view all the answers

    What is formed from the cranial, caudal, and lateral margins of the disc during embryonic development?

    <p>The ventral surface of the body.</p> Signup and view all the answers

    What roles do the splanchnic and somatic mesoderm play in embryonic development?

    <p>The splanchnic mesoderm surrounds the gut tube, while somatic mesoderm forms the body wall.</p> Signup and view all the answers

    What distinguishes lateral folding from other forms of folding in embryonic development?

    <p>It is driven by the folding of the amniotic sac.</p> Signup and view all the answers

    What happens to the vitelline sack during embryonic folding?

    <p>It elongates and becomes part of the primitive intestinal tube.</p> Signup and view all the answers

    What structural formation occurs due to the folding concentrated in the outer rim of the embryonic disc?

    <p>The transition from a trilaminar disc to a cylindrical embryo.</p> Signup and view all the answers

    What is necessary for the organs to be suspended in the coelomatic cavity during development?

    <p>Both dorsal and ventral mesentery are essential.</p> Signup and view all the answers

    During the development process, what structure completely envelops the embryo in the rostral and caudal regions?

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

    Study Notes

    Embryonic Development

    • Early Development (Weeks 1-3):
      • The anterior-posterior and dorsoventral axes form.
      • Three tissue layers develop.
      • Bilateral symmetry emerges, enabling movement and survival.
    • Organogenesis (Weeks 4-8):
      • All major internal and external structures are created.
      • Organ functions are minimal, except the cardiovascular system.
      • Heart starts beating around days 21-22.
      • Doppler ultrasonography can detect heartbeats in week 5.
      • Teratogens can cause major abnormalities during this period.
    • Thalidomide:
      • A drug previously used to alleviate pregnancy-related nausea and depression.
      • Was not tested on pregnant animals.
      • Administered to pregnant women, leading to limb defects (upper limbs with 4th week exposure, lower limbs with 5th week exposure).

    Embryo Body Plan Development

    • Phylotypic Stage (4th Week):
      • The embryo resembles all other vertebrate embryos.
    • Evolution of Animal Body Plan:
      • Tissue formation
      • Bilateral symmetry
      • Development of body cavities (lined by serosa)
      • Segmentation (paraxial mesoderm, only in the trunk, not the head)

    Segmentation

    • Occurs in the paraxial mesoderm of the trunk region (around embryonic day 20).
    • Proceeds from rostral to caudal.
    • Determined by gene expression and gradients.
    • Results in the formation of somitomers (35-37 somites).
    • Somites lead to the development of vertebrae.

    Segmentation of the Neural Tube

    • The neural tube, adjacent to the somites, develops into functional segments.
    • Each segment innervates associated dermatomes, myotomes, and sclerotomes
    • Develop from adjacent somites

    Folding and Development of Body Cavities

    • The embryonic disk folds laterally and rostrocaudally.
    • A tube develops within a tube
    • Development of the primitive intestine
    • Development of coelomic cavities, lined by serosa (membranes).
    • The coelomic cavities evolve in the embryo.

    Formation of Somite Derivatives

    • Sclerotome—forms vertebrae, ribs, and parts of the skull
    • Myotome—forms skeletal muscles
    • Dermatome—forms the dermis
    • Syndetome—forms some tendons

    Heart Development

    • Formation of the heart starts around day 22 (of gestation).
    • Endocardial heart tubes form in the primary heart field of the embryo.
    • Tubes merge, forming a single heart tube.

    Primitive Circulation

    • Blood vessels form from the extraembryonic mesoderm.
    • Networks of vessels develop in the yolk sac, body stalk, chorion, and embryo.
    • Heart tube connects to vessels (vitelline, umbilical, and cardinal).
    • Vitelline veins carry poorly oxygenated blood from the yolk sac.
    • Umbilical veins carry oxygenated blood from placenta.

    Additional Notes

    • Thalidomide use in pregnant women led to severe limb birth defects.
    • Congenital diaphragmatic hernia (CDH) is a condition.

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    Embryology 5 - 4th Week Body Plan PDF

    Description

    Explore the stages of embryonic development from early formation to organogenesis. This quiz covers critical periods such as the phylotypic stage and the impact of teratogens like thalidomide on embryonic health. Test your knowledge on how these processes are crucial for the formation of a healthy organism.

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