Bone as a tissue Flashcards
Structure of bone
Compact cortical bone
cancellous trabecular bone
Lamellar bone=mature bone that replaces woven bone
Woven bone=immature/unorganized
Diaphysis
shaft of bone
epiphysis
Ends of the long bones, separated from metaphysis by a physis
Metaphysis
region between epiphysis and diaphysis
rich in trabecular bone
Cortical Bone porosity
Very dense compact bone
5-30% porosity
diaphysis of long bones and thin shell of bone ends
Trabecular bone porosity
cancellous bone
30-90% porosity
axial skelton and ends of long bones
Osteons/Haversian System
make up majority of cortical bone in diaphysis
where artery, vein and nerve pass through the bone
osteocytes live within lacunae
trabecullar bone
Fine interlacing network surrounded by fat and hematopoietic marrow
Compared to cortical bone:
greater SA and more metabolically active
Woven bone
greater cellularity
variable direction of collagen fibrils
immature, randomly and rapidly produced osteoid
predominates in the fetus and pathology (fracture)
Lamellar bone
parallel collagen fibrils
mature bone progressively replaces woven bone
1) Cortical: circumferential, concentric, interstitial
2) Trabecullar: trabecular lamellae, parallel to long axis
Inorganic component
60-65%
total body mineral stores–Ca, P, Na and Mg
Calcium hydroxypatite (HA) has close aposition with collagen for bone strength and hardness
matrix formation to mineralization takes 12-15days
Organic component
35-40%
bone cells and extracellular matrix proteins
predominant cells are osteoblasts,osteocytes, and osteoclasts
ECM proteins=collagen(95%) and ground substance(5%)
Factors for generation stimulation of bone formation
insulin-like growth factors
bone morphogenetic proteins
Osteoblasts
found on bone surface; derived from mesenchymal cells
Inadequate Ca/P, mineralization lag–>osteoid accumulates
morphology depends on activity: Cuboidal (active) flattened(resting)
Osteoblast function
deposit osteoid-type I collagen and ground substance
Initiate mineralization
non-invasive assessment of osteoblast activity
measured in the serum:
1-bone specific alkaline phosphatase
2-type I procollagens
2-osteocalcin
Osteocytes
Inactive osteoblasts (10%) trapped in formed bone mechanosensors cytoplasmic processes and cannaliculi: 1-transportation and communication 2-continuous mineral regulation
osteoclast
multinucleate phagocytic cells responsible for resorption
derived from hematopoetic heirarchy-tissue macrophages and circulating monocytes
can be reconstituted quickly
Noninvasive monitor of osteoclast activity
1-tartrate-resistant acid phosphatase (TRAP)=osteoclast specific
2-Type I collagen degradation products (cross-linking telopeptides)
Howship’s lacunae
Formed by osteoclasts
Ruffled border of Osteoclast composed of microvilli that appose bone increasing the SA
Self-containing extracellular space of Osteoclast
Howship’s lacunae confines destruction to one area:
1-microvilli attach
2-create an isolated enviroment
3-pour hydrogen ions to destroy bone matrix
Lysosomal function of osteoclast
1-H+ pumps acidify, solubilizing mineral
2-acid phosphatase and collagenase, cathepsins proteases degrade matrix
Collagen
major fibrous component synthesized by connective tissue cells (in bone, osteoblasts)
- -19 types with triple helix hallmark
- -aggregates with ECM proteins for tensile strength and integrity
- -vary in amino acid composition, moleculat size, structure, and ability to form fibrillar to hexagonal aggregates
Ground substance
Proteoglycans: flexibility and resilience
Glycosaminoglycans: bound to proteoglycans; cementing substance in lamellar bone between mineralized collagen fibril layer
