Embryology Limb Development

  1. What are the embryonic tissues and structures that give rise to the limbs?
  2. When does gastrulation occur?
    Week 3
  3. When do limb buds start to appear?
    Week 4
  4. When do limbs start to rotate and have positional changes?
    Week 7
  5. What are the three parts of mesoderm?
    • Paraxial mesoderm
    • Intermediate mesoderm
    • Lateral mesoderm
  6. What forms the motor axon and which embryonic layer is it from?
    Neural tube, from ectoderm
  7. What forms sensory nerves and which embryonic layer is it from?
    Neural crest, from ectoderm
  8. Which part of embryonic tissue is most important for limb development?
    Paraxial mesoderm
  9. When does major change in morphology occur?
    Week 4 body folding
  10. What happens during embryo folding?
    Lateral folding and craniocaudal folding
  11. Describe lateral folding:
    • Lateral aspects fold ventrally toward the midline
    • Split mesoderm
  12. What becomes the space between the layers of mesoderm?
    Future body cavities
  13. Which embryonic layer forms the inner gut tube?
  14. Describe cranial caudal folding:
    Head and tail region of embryo bend towards each other
  15. Where did somitomeres come from?
    Organized segments of paraxial mesoderm
  16. When do somites appear?
    Between the third and fifth week of development
  17. What are somitomeres?
    Loose condensations or “swirls” of mesoderm
  18. How do somitomeres proceed?
    Cephalo-caudal development (head first) and turn into somites
  19. What are somites
    Formed from somitomeres
  20. What do somites eventually become?
    Tissues and structures like dermis and skeletal muscle and vertebrae
  21. When do the first pair of somites appear?
    Around day 20 post-fertilization
  22. What are the breakdowns of somite pairs in each region?
    • 4 pairs in occipital region
    • 12 in thoracic
    • 5 lumbar
    • 5 sacral
    • 8-10 coccygeal paired somites
  23. Whath are sclertome?
    Sub-division of somite which contribute to future vertebral segments
  24. Which appears first, forelimbs or hindlimbs?
  25. Where do limbs differentiate from/ which germ layer?
  26. What is the most distal aspect of the limb bud called?
    Apical ectodermal ridge
  27. Where can you find the progress zone of undifferentiated rapidly dividing cells?
    Adjacent to the apical ectodermal ridge
  28. When do cell death occurs after the initial appearance of future digits?
    Around 54 days
  29. What happens to the embryo at about six weeks?
    Terminal portion of limb buds becomes flattened into hand/ footplate.
  30. When does limb rotation occur?
    Week 7
  31. How do limbs rotate, which way do upper and lower extremities rotate?
    • Opposite directions
    • Upper- laterally
    • Lower- medially
  32. Where are extensor musculatures located in upper and lower extremities?
    • Upper- posterior laterally
    • Lower- anteriorly
  33. When do we start to see cartilage models/ bone formation?’
    Around week 6
  34. What is it called when the process of bone formation involves putting down a precursor template made of cartilage?
    Endochondral ossification
  35. When do ossification begin?
    By the end of embryonic period
  36. True/False: By birth, the diaphysis of long bones is completely ossified
  37. When do epiphyses (ends of long bone) start ossification?
    At time of birth
  38. True/False: it is possible to over-stimulate bone growth in a child as a result of growth plate fracture
  39. What is amelia?
    Complete absence of one or more limbs
  40. What is tetra-amelia?
    Absence of all four limbs
  41. What is phocomelia?
    • Upper portion of a limb is absent or poor developed
    • What is micromelia?
    • Segments of the extremities are present but are abnormally short
  42. What is macrodactyly?
    There is enlargement of one or more digits likely due to abnormal nerve or blood supply
  43. What is ectrodactyly?
    Fewer than normal digits
  44. What is another name of ectrodactyly?
    Lobster claw deformity
  45. What is clubfoot?
    Excessively plantar felxed with the forefoot swung medially and sole facing inward
  46. What is the likely cause of clubfoot?
    Oligohydramnios; restrictive uterine environment
Card Set
Embryology Limb Development
NMSK Exam 2 limb development embryology