Cartilage and Bone Flashcards
3 types of cartilage
hyaline
elastic
fibrocartilage
Why doesnt cartilage heal well?
Bc it is avascular and have immoble chondrocytes with limited proliferation
Components of the Hyaline cartilage matrix
Homogenous amorphous matrix of:
- type II collagen
- GAGs
- proteoglycans
- glycoproteins
Characteristics of Hyaline Cartilage
Chondrocytes located in lacunae
Hyaline cartilage has perichondrium except at articular surfaces
Low friction
Highly hydrated
calcifies with aging
Componets of elastic cartilage matrix
Hyaline Matrix:
- proteoglycan
- glycoproteins
- type II collagen
- GAGs
PLUS elastic fibers and materials
Charcteristics of elastic cartilage
elastic properties
doesnt calcify with aging
Components of fibrocartilage
Hyaline cartilage PLUS dense regular connective tissue
Chondrocytes, some fibroblasts
Collagen fibers (type I and type II)
No perichondrium
Characteristics of fibrocartilage
Resistance to compression and shearing (‘shock absorber’)
Intervertebral discs, symphysis pubis, menisci of knee joint
Calcification of fibrocartilaginous callus during bone repair)
Steps of chondrogenesis
mesenchyme generates chondroblasts
chondroblasts secrete matrix, become isolated chondrocytes
chondroblasts replicate creating isogenous groups of chondrocytes
interstitial growth
new cartilage formed within existing cartilage
appositional growth
new cartilage formed at the surface of existing cartilage
Extracellular matrix of Bone
Mineralized with calcium phosphate (hydroxyapatitecrystals)
type I collagen (primarily)
proteoglycans
glycoproteins (osteonectin, osteopontin)
bone-specific Vitamin K-dependent (osteocalcin, protein S)
growth factors & cytokines
functions of bone
Structural support
Protection
Calcium regulation
Hemopoiesis
Osteons (Haversian)
Cylindrical structural units of bone
5 cell types in bone
Osteoprogenitor cells
Osteoblasts
Osteocytes
Bone-lining cells
Osteoclasts
collagen fiber organization within bone
Collagen fibers are parallel within a lamella, but run different direction than adjacent lamella
( right → left, then, left → right)
The canal in bone contains
blood supply
Osteoprogenitor cell
Funtion, location
Function
Resting’ mesenchymal stem cell
- CBFA1 (core binding factor alpha-1) triggers differentiation into osteoblast
Location
Localized to external and internal surfaces of bone (periosteal and endosteal cells)
Osteoblast
Funtion and location
Function
- bone forming cell
- secretes matrix = type I collagen (90% protein in bone)
- secretes vesicles that initiate matrix calcification
Location
- Single layer of cells opposed to forming bone
- gap junctions between osteoblasts
Steps of bone matrix calcification
vesicles exocytosed from the osteoblast - contain alkaline phosphatase and pyrophosphatase → the initial site of mineralization
*elevated local extracellular Ca2+ and PO4 required (osteocalcin)
*crystallization of CaPO4 = hydroxyapatite crystals [Ca10(PO4)6(OH)2]
osteocyte
Function and location
Maintians bone matrix
Mechanotransduction: sensing physical forces and translating them into biochemical responses
Found completely enclosed by bone matrix
processes extend thtough cannaliculi to connect w/ other osteocytes
Bone lining cells
function and location
Function
provide nutritional support to help maintain osteoblasts
regulate Ca2+ and PO4 movement
Location
develop from osteoblasts and line external (periosteal cells) and internal (endosteal cells) bone surfaces
gap junctions are found in between
Osteoclast
Function and location
Function
Bone reabsorption
stimulated by parathyroid hormone and reduced by calcitonin
Location
Arise from fusion of mononuclear hematopoetic cells
Steps of Osteoclast resorption
- A clear (sealing) zone adjacent to ruffled border is formed (integrins–actin)
- Free H+ from Carbonic acid (H2CO3) actively pumped out of cell.
- Acid environment causes breakdown of Ca10(PO4)6(OH)2 to
Ca2+, PO4, H2O
* Release of lysosomal enzymes (cathepsin K, matrix metalloproteinases) into extracellular space degrade protein component of bone matrix
- Osteoclasts ‘tunnel’ into existing bone, osteoblasts follow and rebuild
