1.7 Bone Flashcards
Primary osteons
- Formed on the outer surface of the cortical bone
- increase the outer diameter of the diaphysis
Secondary osteons
- Formed by osteoclasts tunneling through the bone
- Followed by osteoblasts which create new bone to fill in the tunnel
- Produces a new Haversian system that contains a blood vessel
what are the components that make
up bone?
Organic: structural proteins provide
strength & flexibility
Mineral: provides rigidity & resistance to
compression
Bone matrix composition:
- Type I Collagen
- Other non-collagenous proteins
- Hydroxyapatite mineral —> Ca10(PO4)6(OH)2 Water
- Proteoglycans
Woven bone
collagen fibers randomly orientated
- first bone formed in fetal development & repair
Lamellar bone
mature bone in sheets called lamellae (organized)
- collagen fibers orientated in 1 direction in each layer but in different directions in different layers for strength
What is the function of bone?
-Formation of blood cells
-Protection
-articulation (joints/muscles)
-tendon, muscle, joint capsule attachment
-resistance to forces
-vibration transmission
-stores minerals
Reabsorb bone, multinucleate cells, least abundent
Osteoclasts
Form bone
Osteoblasts
Within the bone / master cell
Osteocyte
Osteoblasts characteristics
- The “bone-forming” cell
- Extensive ER & Golgi apparatus —> synthesize, modify & export proteins needed for bone formation
- Express high levels of alkaline phosphatase
- Secrete / respond to many growth factors & cytokines
- Active or inactive (flattened) osteoblasts cover most bone surfaces
Bone formation by mature osteoblasts
Synthesis & deposition of the organic matrix of bone (osteoid)
- type 1 collagen (90%)
- non-collagenous proteins (NCPs)
Mineralisation
calcium + Phosphate = hydroxypatite
Tissue non-specific alkaline phosphatase TNAP -drives mineralization
NPP1 Ecto-nucleotide pyrophosphatase/phosphodiesterase 1 - inhibits
Osteoblasts can become incorporated into bone matrix & differentiate into
Osteocytes
Which collagen type is most important in bone?
Type 1
What is the most abundant cell type in bone?
osteocyte
Where is the osteocytes cell body located?
in lacunae
Functions of the osteocyte?
- sense load imposed on bone
- trigger remodeling process/apoptosis
- release proteins/cytokines to modulate osteoblast and osteoclast functions
Osteoclast
- “bone resorbing “ cell
- formed by fusion of monocyte, macrophage precursors present in marrow/circulation
- large, multinucleate cell
- bind to mineralized matrix –> specialized organ of reabsorption = “ruffled border”
bone MODELING definition & characteristics:
-bone formation or resorption with a net change in bone shape
-Evens out stresses, strains
-Occurs at different sites
bone REMODELING definition & characteristics:
-bone resorption followed by formation filling in the resorption pit
-Repairs damage
-Occurs at the same location
Cell signaling in bone is done by
Osteoclastogenesis which is synthesized by osteoblasts/osteocytes
endocrine signaling in bone includes:
-Sex hormones
(estrogen& androgens)
-PTH/ calcitonin: maintain blood Ca2+ homeostasis
-Vitamin D: needed for mineralization
-Thyroid hormone: promotes proliferation/ differentiation
-insulin
-leptin
-growth hormone
which ways can bones form
-endochondral ossification
-intramembranous ossification
endochondral ossification
-forms most of the skeleton during embryonic development
-Involves a cartilage template which is replaced by bone
-is essential for bone growth & healing
intramembranous ossification characteristics
-no cartilage template
-(MSCs) differentiate directly into osteoblasts
(example: in the flat bones of the skull)
Fracture healing process:
1) inflammatory
2) reparative
3) remodeling
Fracture healing process: inflammatory phase
-hours to days after fracture
-blood from broken vessels forms hematoma around break
Fracture healing process: reparative phase
-days to weeks after fracture
-soft cartilage callus forms which is replaced by a boney callus of woven bone
Fracture healing process: remodeling phase
-months to years after fracture
-compact bone replaces hard callus through bone remodeling
Endochondral ossification process:
1) MSCs differentiate into chondrocytes and secrete ECM rich in collagen II
2) Chondrocytes undergo proliferation, maturation, hypertrophy & cell death which defines bone shape
3) Primary ossification center forms in the diaphysis of the developing bone
4) Invasion of blood vessels allows infiltration of osteoblasts & osteoclasts
5) Calcified cartilage surrounding hypertrophic chondrocytes is worn away by osteoclasts
6) Bone starts replacing calcified cartilage & spreads longitudinally away from the primary ossification center
7) Secondary ossification centers start forming at the epiphyses
8) Bone replaces cartilage & epiphyseal plate is retained to allow further growth
9) When skeletally mature epiphyseal plates ossify
A) Articular Cartilage
B) Trabecular Bone
C) Epiphyseal Plate
D) Marrow Cavity
E) Periosteum
D) Cortical Bone
A) Proximal Epiphysis
B) Metaphysis
C) Diaphysis
D) Distal Epiphysis
