Histology of Cartilage and Bone Flashcards
Types of fibres in ECM
- Collagen
- Reticular fibres
- Elastic fibres
What are the main types of fibril in bone and cartilage?
- B = type I collagen
- C = type II collagen
Which glycosaminoglycans are present in bone and cartilage?
- Hyaluronan (hyaluronic acid)
- Chondroitin 4-sulfate
- Keratan sulfate
What is hyaluronic acid synthesised?
Enzymes on the cell surface
How much water can hyaluronan bind?
1000x its weight
How are proteoglycans made?
GAGs covalently bonding to proteins
How are proteoglycan aggregates made?
Proteoglycans bind to hyaluronan
Where are proteoglycan aggregates abundant?
Cartilage
What property does cartilage get from proteoglycan aggregates?
Resisting compression without inhibiting flexibility (so good shock absorber)
What are proteoglycan monomers?
Different numbers of glycosaminoglycans bound to a core protein
How does the structure of the proteoglycan monomer aggrecan give cartilage some of its properties?
- Has chondroitin sulfate and keratan sulfate attached to the core protein
- Is able to bind a lot of water
- Allows cartilage to be flexible and take lots of pressure without change in shape
Types of fixed connective tissue cells
- Fibroblast
- Adipose/fat cell
- Pericyte
- Mast cell
- Histiocyte
- Osteoblast
- Chondrocyte
- Osteoclast
- Osteocyte
Types of transient connective tissue cells
- Plasma cell
- Lymphocyte
- Neutrophil
- Eosinophil
- Basophil
- Monocyte
- Macrophage
Composition of hyaline cartilage
- Cells = 3-5%
- Multiadhesive glycoproteins = 5%
- Proteoglycans (aggrecan) = 9%
- Collagens = 15%
- Intercellular water = 60-80%
Features of hyaline cartilage
- Avascular
- Surrounded by perichondrium (except articular cartilage)
- Consists of chondrocytes surrounded by matrices containing type II collagen interacting with proteoglycans
Features of elastic cartilage
- Avascular
- Surrounded by perichondrium
- Consists of chondrocytes surrounded by matrices containing type II collagen interacting with proteoglycans and elastic fibres
What can elastic fibres be stained with for light microscopy?
Orcein
Features of fibrocartilage
- Generally avascular
- Lacks perichondrium
- Consists of chondrocytes and fibroblasts surrounded by type I collagen and a less rigid ECM
Composition of bone
- Inorganic = 67%
> Predominantly calcium phosphate (present in hydroxyapatite) - Organic = 33%
> Collagen = 28%
> Non-collagenous proteins = 5%
What do osteogenic cells do?
Form and maintain bone
Different morphologies of osteogenic cells (and their specific functions)
- Osteoprogenitors (develop into osteoblasts)
- Osteoblasts (make bone)
- Osteocytes (maintain bone)
- Bone lining cells
What do bone remodelling cells do?
Resorb bone
Morphology of remodelling cells
Osteoclasts
What is bone surrounded by and what is inside the bone?
- S = Periosteum
- I = Endosteum
Process of formation of bone
- Secretion by osteoblasts
> Forms osteoid (soft, “bendy” layer)
> Type I collagen, glycoproteins and proteoglycans
> Membrane-enclosed matrix vesicles containing alkaline phosphatase and other enzymes to increase local phosphate ion concentrations
> Protein called osteocalcin binding Ca2+ and local concentration increases - Calcified nanocrystals form
- Eventual formation of calcium hydroxyapatite
- Calcium hydroxyapatite surrounds collagen and merges into a confluent solid mass (mineralised bone)
2 processes of osteogenesis
- Intramembranous ossification
- Endochondral ossification
How does intramembranous ossification work?
- Pre-existing medium of mesenchyme
- Osteoblasts differentiate directly from mesenchymal cells + begin to secrete osteoid
- No hyaline cartilage predecessor
How does endochondral ossification work?
- Pre-existing medium of hyaline cartilage
- Populated by osteoblasts that begin to secrete osteoid
What are resorption/Howship lacunae?
U-shaped dips formed when osteoclasts resorb bone
Structure of mature bone
- Multiple osteons side by side with concentric lamellae
- Interstitial lamellae fill in the gaps between osteons
- Osteonal arteries run in Haversian canals in the centre of each osteon
- Osteonal arteries are connected through horizontal Volkmann canals
