Bone Objectives Flashcards
Ectoderm
On the external surface of the embryo
- skin, adnexa, neural tissue
Mesoderm
Middle layer
- bone, muscle, and all connective tissues
Endoderm
Inner layer, is an outpocket of the pharynx
- epithelial lining of GIT, associated ducts/glands, viscera
- also lines pharynx, respiratory tract, urethra, bladder
Mesenchyme originates from which tissue layer?
Mesoderm
How does undifferentiated mesenchyme become organized and develop into a limb?
Mesoderm of left and right lateral body wall forms Wolff’s crest (cylindrical thickening) –> focal ectodermal thickenings occur over Wolff’s crest at sites of future limb placements = apical ectodermal ridge
- AER initiates and organizes limb bud formation and remains throughout limb development
_______ induces mesenchymal cells to condense to form a cartilage model for each bone of the developing limb
Apical ectodermal ridge
What is the difference in how bone and cartilage grow?
Bones only undergo appositional growth (new chondrocytes applied to existing structure), cartilage tissue grows by appositional growth and by interstitial growth (cartilage tissue expands within)
Long bone development
Condensation of mesenchyme to form cartilage model –> formation of perichondrium and invasion of nutrient artery –> degeneration of chondrocytes to form medullary cavity –> perichondrium becomes periosteum –> periosteum forms concentric layers of cortical bone in diaphysis –> vessels at joint capsule insertion invade epiphyseal area –> epiphyseal and metaphyseal physes form
Epiphyseal physis
3D growth of epiphysis by proliferation of chondrocytes followed by enchondral ossification to form epiphyseal cancellous and subchondral bone
Epiphyses
Ends of long bone
Diaphysis
Long compact shaft of the bone
Epiphyseal plate
Separates the epiphysis and diaphysis
- growth plate
Metaphysis
Transitional spongy bone that joins the diaphysis to the epiphyseal plate
Medullary space
Area of spongy bone in the middle of the diaphysis
- is not hollow, consists of bony spicules to provide space for bone marrow (cancellous bone)
Periosteum
Outside of bone covered by cells
Endosteum
Internal surfaces of bone trabeculae within the marrow cavity
- also lined with osteoprogenitor cells
Osteoblasts
- line periosteal and endosteal surface
- produce collagen-rich osteoid matrix that later mineralizes
- main cells involved in ossification process
Osteoclasts
- derived from mononuclear phagocyte cell line
- fusion of cells to form multinucleated cell, responsible for dissolving bone matrix and collagen to allow reshaping of bone to accommodate stress
How does growth in length occur?
Osteoblasts differentiate –> layer of loosely organized collagen matrix is deposited –> new bone matrix calcifies –> osteoclasts move into the metaphysis to resorb the woven bone and calcified cartilage –> new osteoblasts form organized sheets of type 1 collagen
*cells of the zone of proliferation are advancing the growth plate away from the diaphysis, while the ostoblasts/clasts are converting primary woven bone to lamellar bone at the diaphyseal side of the growth plate
How does growth in diameter occur?
Deposition of new bone on the outside by cells within the periosteum
- bone resorption is key
- deposition of new bone is accompanied by resorption of older bone at the interior edge of the shaft of the diaphysis
- allows marrow cavity within the bone to expand
Anatomy of a growth plate
- zone of proliferation: chondrocytes furthest from the diaphysis
- zone of maturation: chondrocytes are not dividing and are enlarged
- zone of hypertrophy: hypertrophy and vacuolation of the chondrocytes
- zone of calcified cartilage: cartilaginous matrix surrounding cells begins to calcify
Process of endochondral ossification
Proliferating chondrocytes from inner mitotic layer mature to produce collagen and proteoglycan matrix –> mature chondrocytes hypertrophy –> hypertrophic chondrocytes form matrix vessicles and die –> hydroxyappetite crystals form at matrix vesicle sites calcifying the cartilage –> capillary loops with osteogenic mesenchyme invade tunnels formed by dying hypertrophic chondrocytes after cartilage calcifies –> osteoblasts layer woven bone on spicules of calcified cartilage = bony trabeculae –> osteoclasts remodel calcified cartilage spicules and bone trabeculae to produce cancellous bone
What allows bone to bend and absorb concussion?
Trabecular plates (cancellous bone)
What portion of bone is dense and strong?
Cortical bone of the diaphysis
- compact bone
