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75 Cards in this Set
- Front
- Back
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What sort of ossification forms the clavicle?
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Intramembranous.
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What does the paraxial mesoderm form?
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Future somites.
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What are the two layers of lateral plate mesoderm?
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Parietal and visceral layers.
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When does skeletal development begin in the embryonic period?
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Week 4.
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What are cartilage and bone of the body derived from?
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Mesoderm
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What does the sclerotome form?
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Axial skeleton in body and some in head.
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What does lateral plate mesoderm form?
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Appendicular skeleton and body wall (soma)
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What forms the vertebral column?
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Sclerotome (mesenchyme)
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What induces sclerotome formation? What secretes these proteins?
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Noggin and Sonic hedgehog induce sclerotome formation and are secreted by the notochord and neural tube floor plate.
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What does PAX 1 do? What expresses it?
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PAX1 initiates a cascatde of cartilage and bone forming genes for vertebral column development. It is expressed by Scleretome cells.
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How are the vertebrae formed?
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Endochondral ossification of sclerotome regions.
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How do the ribs develop?
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As outgrowths of lateral processes of thoracic vertebrae.
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How is the sternum formed?
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First seven ribs unite ventrally to form sternum.
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How many somite pairs are there? Occipital, Cervical, Thoracic, Lumbar, Sacral, coccygeal?
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42-44
Occipital 4 Cervical 8 Thoracic 12 Lumbar 5 Sacral 5 Coccygeal 8-10 |
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What forms the base of the skull?
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The first cervical and occiptal somites.
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How are vertebrae formed?
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By fusion of sclerotome cells from two somite levels.
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When do sclerotome cells surround the developing neural tube and notochord?
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During week 4.
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What part of each vertebrae forms a centrum (future body) around the notochord?
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The ventral part.
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What does the dorsal part of each vertebrae form?
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Costal prcesses (transverse), vertebral arch.
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WHat forms the nucleus pulposis?
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Notochord.
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What do spinal nerves pass through?
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Intervertebral foramen.
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What do cells from the proatlas contribute to?
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Formation of basiocciptal bone and dens.
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What does the normal atlas form?
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The anterior arch instead of body.
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What stimulates cells to express PAX1?
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SHH (sonic hedgehog)
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What guides ventromedial sclerotome cells to form centrum?
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PAX1
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What does induction of the roof plate of neural tube result in?
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PAX9, MSX1, and MSX2 expression.
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What do PAX9, MSX1, and MSX2 do?
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Guide lateral sclerotome to form dorsal vertebral arch.
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How are individual vertebrae specified?
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Specific combinations of Hox genes.
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What is Klippel Feil syndrome?
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Short neck/decreased cerical motion, multiple fused cervical somites.
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What causes Hox gene misexpression?
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Retinoic acid.
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What activates cranial caudal gradient of hox genes?
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Retinoic acid.
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What causes spinal bifida (2)?
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1) Failure of normal vertebral induction.
2) Failure of the neural tube to close dorsally. |
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What do ribs develop from? How?
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Costal processes of thoracic vertebrae. Sclerotome cells migrate within somatic lateral plate mesoderm around the body curvature toward the ventral surface.
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Which ribs form the sterum?
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First 7
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What does the sternum arise from?
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A pair of cartilagenous bands around the ventral midline.
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What is cleidocranial dysplasia?
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Abnormal development of head. Flat wide nose, no bridge, supernumerary and unerupted teeth, aplasia of clavicles.
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What is included in the appendicular skeleton?
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Appendicular girdles, intrinsic limbbones.
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What type of ossification forms the appendicular skeleton?
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Endochondral ossification.
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What does somatic lateral plate mesoderm form?
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All cartilages and bones of appendicular skeleton, and the body wall.
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What does the somitic sclerotome form?
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All cartilages and bones of axial skeleton in the body (some in head).
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When are limb buds visible?
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End of week 4.
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What is the mesenchyme core of limbs formed by?
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Derivied from somatic layer of lateral plate mesoderm.
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What surrounds the mesenchyme core of the limbs?
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Ectoderm.
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What are the 3 things found initially in the limb bud? What do each of them form?
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Mesenchyme from lateral plate mesoderm (forms skeleton, CT, and some blood vessels)
Mesenchymal from somites (forms muscle) Neural crest cells (forms schwann cells and melanocytes) |
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What is the apical ectodermal ridge? What does it do?
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A thickend distal border of the limb bud that exerts an inductive influence on the underlying mesenchyme. IT prevents its differnetiation and causes it to proliferate rapidly.
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What does the dorsal ectoderm of the limb bud do?
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Expreses radical fringe (signalling molecule)
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What does the ventral ectoderm do?
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Expresse engrailed (transcription factor)
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WHat is limb outgrowth initiated by?
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Factors secreted by lateral plate mesoderm.
Upper limb FGF10 +TBX5 Lower limb FGF10 +TBX4 |
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WHat induces apical ectodermal ridge formation?
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Bone modeling proteins (homeobox gene MSX2)
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What restricts the apical ectodermal ridge to the distal tip of thel imb?
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The radical fringe (dorsal ectoderm)
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What does the radical fringe induce?
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SER2
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What produces engrailed? What does it do?
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Ventral ectoderm represses expression of the radical fringe to maintain the border.
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What do FGF4 and FGF8 do?
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Maintain a progress zone in the developming limp of rapidly proliferating mesenchymal cells adjacent to apical ectodermal ridge.
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What happens to proximal mesenchymal cells as they move further from the AER?
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Decrease rate of division and begin differentiation.
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What is the zone of polarizing activity?
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A cluster of cells at the posterior border of the limb (near flank)
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What determines the location of the zone of polarizing activity?
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Transcription factors.
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What do zone of polarizing cells produce?
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Retinoic acid which initiates expression of sonic hedgehog.
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What happens in the absence of sonic hedgehog?
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Regression of Apical ectodermal ridge.
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What determines proper location of the digits?
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Zone of polarizing activity.
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What is the patterning along the dorsoventral axis regulated by?
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Bone modeling proteins in ventral ectoderm.
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What does EN1 do?
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represses WNT7a expression and restricting it to dorsal ectoderm.
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What does WNT7a do?
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it induces LMX1 in dorsal mesenchyme and maintains sonic hedgehog expression in the zone of polarizing activity (indirectly affects anterior/posterior patterning)
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What does LMX1 do?
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Specifies cells to be dorsal.
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What patterns limbs along the proximodistal limb?
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Hoxd genes.
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What do mutations in Hoxd-13 cause?
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Reduction defects of digits.
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What does apoptosis play a role in?
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Formation of axillary region, radius/ulna, tibia/fibula.
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What do specific HOX expression results from?
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Combinatorial expression of SHH, FGFs and WNT7a.
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What determines digit identity?
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BMP concentration.
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What digit has the highest/lowest BMP concentration?
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Thumb = lowest
Pinky = highest |
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Which direction do the legs rotate? The arms?
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Upper limbs rotate laterally. Lower limb rotates medially.
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What arrests limb divelopment?
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Removal of apical ectodermal ridge.
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What is amelia?
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Complete absence of limbs.
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What is phocomelia?
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Proximal structures absent, hands or feet attached to trunk by irregularly shaped bones.
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WHen does endochondral ossifaction begin?
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End of embryonic period (week 12)
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What forms the joint cavity?
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Surrounding cells, cartilagenous condensations, and cell death. (WNT14 appears to be the inductive signal)
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