03 - Bone Flashcards
(38 cards)
Primary/Immature/Woven bone
Formed during fetal development & healing
- contains abundant osteocytes & collagen 1
Secondary/Mature/Lamellar bone
- concentric lamella
- highly organized
- contains osteons, osteocytes, Haversian canals, and Volksman canals
Compact/Cortical bone
- external hard layer of all bones
- contains osteons
Compact bone development
OPCs form new osteoblasts that secrete osteoid which calcifies at the matrix and remodels with osteocytes to form compact bone
Spongy/Trabecular/Cancellous bone
- network of trabeculae with red bone marrow in between
- inner layer of all bones
- NO osteons
Osteons
Contribute to bone resilience
- aligned in parallel with long axis of bone
- has lamellae (layers of matrix) cocentrically around Haversian canal
Haversian canals
surrounded by lamella of an osteon and contain blood vessels and nerves
Canaliculi
Thin branch like structures extending from osteocytes in lacunae within lamellae
- contain cellular extensions (formed by matrix) to transport nutrients and blood vessels to osteocytes
Ossification (Osteogenesis)
New bone formation
Template –> new bone forms (woven) –> remodeling into lamellar bone (for strength)
2 Types = intramembranous & endochondral
Lamella
Contain mineralized collagen fibrils aligned at angels that vary from layer to layer.
Intramembranous Ossification
- Begins at 8 weeks in utero
- Bone forms on embryonic mesenchyme in sheets of condensed mesenchyme
- Skull, mandible, clavicles
- Some mesenchymal cells –> osteoblasts –> secrete osteoid –> osteoid calcifies –> traps osteoblasts –> osteocytes
- Spongy bone on outer edges remodels into compact bone
- Condensed mesenchyme that doesn’t ossify gives rise to endosteum & periosteum
What type of template does endochondral ossification form on?
hyaline cartilage template
How long does endochondral ossification take?
many weeks
Endochondral ossification (EO)
bone collar forms around middle underlying cartilage degenerates
- forms ossification center
- blood vessels and OPC cells invade
- long bones
Where and when do the primary and secondary ossification centers develop? When and how do they separate?
primary = diaphysis; fetal life
secondary = epiphysis; birth
During childhood, they get separated by the epiphyseal (growth) plate
5 Zones of growth plate; EO
- Reserve Zone
- Zone of Proliferation
- Zone of Maturation & Hypertrophy
- Calcified Cartilage Zone
- Ossification Zone
Reserve Zone
small, flat quiescent chondrocytes (stratified squamous)
Zone of Proliferation
- mitotically active chondrocytes
- produce daughter cells in stacks or columns
Calcified Cartilage Zone
- hypertrophic/dying chondrocytes compress matrix and trigger CaPO4 deposits (calcification = basophilic)
- dead chondrocytes reabsorbed and lacunae eroded leaving spaces –> invaded by thin walled blood vessels to form bone marrow
Zone of Maturation & Hypertrophy
- chondrocytes and lacunae enlarge and accumulate glycogen and lipids
- as they regenerate, they release alkaline phosphatase
Ossification Zone
osteoblasts line up on calcified cartilage and secrete osteoid which becomes mineralized to form bone (woven)
6 Components of bone
ECM (hydroxypatite)
Osteoid
Matrix
Cells
Hormones
Signaling mediators
components of osteoid
Collagen 1, GAGs, osteopointin or osteocalcin (marker of osteroblast activity)
Matrix of bone
Woven & lamellar bone
Organic
- PGs, collagen 1, ground substance (GAGs), osteopontin, osteocalcin
Inorganic
- hydroxyapatite (Ca10, [PO4]6 [OH]2) - main component, citrate, carbonate, hydration shell
