Mod 3 Embryology

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Mod 3 Embryology
2012-12-04 17:35:36
Muscle Bone

Muscle (and bone) Embryology
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  1. What are the embryological origins of bone?
    • Mesoderm
    •    -paraxial - parts of skull, axial skeleton (from sclerotomes)
    •    -lateral plate (somatic layer) - appendicular skeleton
    • Ectoderm
    •    -Neural crest cells (parts of skull)
  2. How does intramembranous ossification work?
    • -Occurs in some bones of the skull
    • -Cells from paraxial and neural crest cells differentiate directly into osteoblasts
    • -These osteoblasts secrete the bony matrix
  3. Describe endochondral ossification
    • -Occurs in all other bones
    • -Cells form cartilage models of bone, which later ossify into bones
    • 1) cells differentiate into chondrocytes
    • 2) secrete cartilage matrix model of bone
    • 3) Vascularization and invasion by osteoblasts and osteoclasts
    • 4) Calcification of cartilage
    • 5) resorption of cartilage
  4. Which are the bones of the axial skeleton?
    Skull, vertebral column, ribs, sternum
  5. Describe the purpose of the Apical Ectodermal Ridge
    • -promotes limb outgrowth and differentiation.
    • -lays down cartilage model from proximal to distal
    • -causes proximal cells to differentiate appropriately
    • -AER undergoes apoptosis to separate digits
  6. Describe the development of the skull
    • Top of skull (intramembranous ossification)
    •   -posterior (paraxial mesoderm)
    •   -anterior (neural crest)

    • Bottom of skull (endochondral ossification)
    •   -posterior (paraxial mesoderm)
    •   -anterior (neural crest)

    • Face (both)
    •   -neural crest
  7. Describe the development of the vertebral column.
    • 1) sclerotome cells migrate around neural tube and notochord
    • 2) caudal half of upper sclerotome fuses with the cranial half of the lower sclerotome to form the future vertebral body
    •    -imagine that the spinal nerves are bisecting these sclerotomes
    • 3) endochondral ossification

    • Discs:
    • -midpoint of original sclerotome becomes annulur fibrosis
    • -the notocord becomes the nucleus pulposis
  8. Describe the develoment of the appendicular skeleton
    • 1) AER moved from proximal to distal, inducing differentiation of cells just proximal and leaving behind a cartilage model of the skeleton
    • 2) Ossification begins in the diaphysis, completed by birth
    • 3) Epiphysis ossifies after birth
    • 4) Epiphysial plate continues to be important in long bone development.
  9. Embryological origins of achondroplasia, congenital scoliosis, congenital kyphosis
    • -achondroplasia: mutation of FGR gene, chondrocyte proliferation disrupted in growth plates, stops long bone growth.
    • -congenital scoliosis: failure of either left or right scelerotome to ossify, causes a kink from side to side
    • -congenital kyphosis: failure of both ossification sites to form, causes an excessive front to back curve (hunchback)
  10. Define the following: amelia, meromelia, phocomelia
    • amelia: absence of 1 or more limb
    • meromelia: absence of part of limb
    • phocomelia: absence of proximal part of limb
    • (all caused by thalidomide)
  11. What are the two types of craniosynostosis?
    • Scaphocephaly: premature fusion of saggital suture (long alien head)
    • Brachycephaly: premature coronal suture fusion  (tall head)
  12. What are the embryological origins of the three muscle types?
    • skeletal: paraxial mesoderm
    • Cardiac: lateral plate mesoderm (splanchnic layer)
    • Smooth:
    •    -viscera and blood vessels: LPM (splanchnic layer)
    •    -blood vessels of body wall: LPM (somatic layer)
  13. Define epimere and hypomere.
    • Mytome is in two parts:
    • epimere: adjacent to neural tube, forms the intrinsic extensor muscles of the back, innervated by dorsal rami
    • hypomere: lateral part, all muscles of body walls and limbs (not head and neck), innervated by ventral rami