Bone architecture
The roles of cartilage in bone formation
Hyaline cartilage acts as a scaffold, providing a structural support system
Identify specific cells in:
- red marrow
- yellow marrow
Identify the stem cells
- red marrow: myeloid cells
- yellow marrow: adipocytes
- stem cells: hematopoietic stem cells, mesenchymal stem cells, and endothelial stem cells
What bone shapes use endochondral ossification?
long, short, and irregular bones
What bone shape occurs in intramembranous ossification?
flat bones (with the exception to the costal bones (ribs) and sternum)
List bone pathologies
- dwarfism
- gigantism
- rickets
- osteomalacia
- metabolic bone disease
Direction of stable bone growth formation
Occurs from the ossification zone toward the epiphysis
Identify the cells found in the stroma (supportive framework) in yellow bone marrow
- fibroblasts
- macrophages
- adipocytes
- osteoblasts
- osteoclasts
- endothelial cells
What do bones that go through endochondral ossification use as a scaffold?
hyaline cartilage
What does the center of bone undergoing intramembranous ossification form through?
condensation of mesenchyme on fibrous connective tissue membrane
Describe dwarfism
- pituitary dwarfism: no growth hormone production by the pituitary gland
List zones of bone growth
- Epiphysis
- Resting zone
- Proliferating zone
- Degenerating zone
- Ossification zone
What do osteogenic cells in the endosteum, periosteum, or central canals give rise to?
new osteoblasts
What models do bones undergoing endochondral ossification develop from?
- perichondrium
- hyaline cartilage
How do osteoblasts form spongy bone and periosteum?
Osteoid is laid down between embryonic vessels forming osteoblasts in spongy bone which condenses on the external bone face, becoming periosteum
Define gigantism
excessive bone growth
- Resorption: osteoclasts resorb calcified matrix
- Reversal: osteoclasts prepare surface
- Formation: osteoblasts replace bone
- Resting: osteoblasts cover with lining cells
What do the new osteoblasts do in the endosteum, periosteum, or central canals arise from?
embryonic fibroblasts
Why do the costal bones (ribs) and sternum undergo endochondral ossification instead of intramembranous ossification (process for flat bones)?
- Requires a cartilage model for flexibility and longitudinal growth.
Briefly describe the process of intramembranous ossification
Growth of osseous tissue within mesenchymal tissue without prior cartilage formation
Compare and contrast rickets from osteomalacia
- rickets: lack of calcium in children
- osteomalacia: lack of calcium in adults
- Both result in warping bones
Describe the zones of bone growth
- epiphysis: end of the bone mostly composed of spongy bone with an outer layer of compact bone
- resting zone: made of cartilage
- proliferating zone: chondrocytes proliferate
- degenerating zone: older chondrocytes add more hydroxyapatite (hypertrophy & calcification)
- ossification zone: fully mineralized
Identify and describe bone cell types.
- osteogenic cells: in endosteum, periosteum, central canals in new osteoblasts
- osteoblasts: mineralize matrix using osteonectin, Ca2+, and PO42- from plasma
- osteocytes: mature bone cells trapped in matrix, in lacunae, and connected by gap junctions in projects called canaliculi
- osteoclasts: 3-50 fused stem cells, lie under periosteum, H+ pumped into the space between ruffled border and bone, Cl- follows with a pH of 4 to dissolve minerals, needs acid phosphatase to break down collagen in bone
Describe the process of endochondral ossification.
1. Early cartilage model involving periosteum and hyaline cartilage
2. Primary ossification center with osteoblasts and cavities -where chondrocytes swell and die
3. Vascularization, secondary ossification center, primary marrow cavity
4. Birth, enlarged marrow cavity, one epiphysis
5. Bone of child with epiphyseal plate distal
6. Adult bone with osteocytes (mature bone cells) and a sealed epiphyseal plate
Describe the process of intramembranous ossification
1. From scratch, mesenchyme condenses into trabeculae
2. Osteoblasts lay down matrix
3. Hydroxyapatite is deposited
4. Osteoclasts carve out marrow cavities and blood vessels grow into holes/cavities
5. Osteoblasts form compact bones at surfaces
6. Periosteum forms
Describe metabolic bone disease