Session 9 - Cartilage and Bone Flashcards
What are the 3 main types of cartilage?
Hyaline - Collagen 2 - tough dense tissue often containing fluid (around 70%)
Elastic - Elastic fibres and Collagen 2 - tough but flexible tissue
Fibrocartilage - Collagen 1 mainly, small amounts of collagen 2 - such as in intervertebral discs
Describe the main features of hyaline cartilage
- Chondrocytes are the only cell present. They can be present as single cells or, if recently divided, in small clusters called isogenous groups
- Chondrocytes lay down extracellular matrix containing collagen 2, Hyaluronic acid and Proteoglycans.
- Avascular
- High water content increases resilience to pressure
Describe the ground substance and extracellular matrix in cartilage
- About 100 hyaluronate proteoglycan aggregates per collagen fibre
- Makes a very “stiff” gel-like substance
- Attracts a lot of water-preventing compression
- Hyaluronic acid together with its attached proteoglycan monomers, forms hyaluronate proteoglycan aggregate
Describe chondrocytes and how they lay down the extracellular matrix
- Each chondrocyte lies within a lacuna
- When placed under pressure, mechanical signals increase synthetic activity to lay down more extracellular matrix
What is the difference between appositional and interstitial growth?
- Appositional growth - growth from the periphery
- Interstitial growth - growth from the centre
Describe the growth of hyaline cartilage
It shows appositional growth. The perichondrium covers the top and bottom of the cartilage which is where fibroblast like cells develop into chondroblasts and progress inwards to the maturing chondral region to become chondrocytes. Which lay down and maintain the extra cellular matrix.
Describe the structure of the hyaline cartilage found in the trachea and on articular surfaces
Trachea/tracheal wall - The lumen of the trachea is maintained by C shaped tracheal cartilages. It prevents collapse. It is lined with pseudostratified ciliated epithelium
Articular Surfaces - Provides smooth surface for movement. In the adult cells don’t proliferate enough to repair damage. Fibroblasts lay down scar tissue instead. Calcifies with age. Also only in articular hyaline cartilage there is no perichondrium on the articular surface. This surface has more type 3 collagen than normal as it provides for an even smoother surface
Outline the structure and distribution of elastic cartilage
- Only chondrocytes present
- contain elastic fibres as well as collagen 2 conferring elasticity
- It is found in 3 places:
- The pinna of the ear
- Eustachian tube
- Epiglottis
Outline the structure and distribution of fibrocartilage
- Contains chondrocytes and fibroblasts
- It’s a combination of dense regular connective tissue and hyaline cartilage
- cells distributed in rows, no surrounding perichondrium
It can be found in:- Intervertebral discs
- Articular discs of sternoclavicular and temporomandibular joints
- Menisci of knee joint
- Pubic symphysis
- They act as a shock absorber and to resist shearing forces
Explain what is involved in bone development and growth and what is this process called?
1) Initial hyaline model (embryo 5-6 weeks)
2) collar of the periosteal bone appears in the shaft (embryo 6-8 weeks)
3) Central cartilage calcifies. Nutrient artery penetrates. supplying bone - depositing osteogenic cells. Primary ossification center formed (8-12 weeks)
4) Medulla becomes cancellous bone. Cartilage form epiphyseal growth plates. Epiphyses develop secondary centers of ossification (post natal)
5) Epiphyses ossify and growth plate continues t0 move apart, lengthening bone (prepubertal)
6) Epiphyseal growth plates replaces by bone. Hyaline articular cartilage persists.
What is the composition of bone (matrix and cells)?
Matrix:
- 65% inorganic:
- Calcium hydroxyapatite and magnesium/aluminium salts
- resists bending and compression
- 35% organic:
- 1) Collagen 1
- 2) GAGs and proteoglycans
- 3) Non-collagenous proteins
- resists pulling and tension forces
Cells:
- Osteoprogenitor cells:
- undifferentiated- stem cell
- Inner later of endosteum and periosteum
- Osteoblast:
- Intermediate cells that can’t divide
- Inner layer of endosteum and spicules
- lay down new bone
- Osteocyte:
- Terminally differentiated bone cell
- Trapped within osteon
- No longer lay down matrix - tissue maintenance (stress and strain sensed)
- Osteoclast:
- Huge cell (up to 50 nuclei)
- Fused monocytes (WBCs)
- Surface of cortical bone (endosteum)
- Resorption of existing bone
Describe the structure of compact bone
The functional unit (the osteon):
- Made from layers (lamellae) of compact mineralised collagen
- Trap osteoblasts that produce the bone, osteocytes are terminally differentiated
- They sit in small depressions called lacunae
- send out long filipodia to “communicate” with other osteocytes
What is the difference between osteoarthritis and rheumatoid arthritis?
Osteoarthritis - is a degenerative disease as a result of over use. It is the mechanical failure of the articular cartilage narrowing the joint space.
Rheumatoid Arthritis - is an autoimmune disease which results in the inflammation of the synovial membrane and thickening of the joint capsule
Name 3 different functions of bone
Mechanical - protect delicate organs, framework for shape of body, leaver for movement
Synthetic - Heamopoeisis
Metabolic - Mineral storage (calcium and phosphorus), fat storage (yellow bone marrow), acid base regulation (absorbs/releases alkaline salts for pH regulation)
What are the 2 ossification types?
Endochondral Ossification:
- formation of long bones from a cartilage template
- continued lengthening by ossification at epiphyseal plate
- appositional growth (growth at edges; grows in one direction, Which pushes out in the opposite)
Intramembranous ossification:
- formation of bone from clusters of MSC (mesenchymal stem cell) in the center of bone - trabecular bone
- interstitial growth (growth in the middle pushing out)
