Cartilage and Bone Flashcards
Functions of cartilage
- Support soft tissue
- Shock absorber
- Low friction surface
- Model of skeleton
Three types of cartilage
- Hyaline cartilage
- Elastic cartilage
- Fibrocartilage
How is cartilage different from CT proper?
Avascular One cell type present - chondrocyte Type II cartilage present Aggrican found in hyaline ECM Chondronectin found in ECM
From what cells are cartilage cells derived?
Mesenchymal stem cells
What is a Type I collagen molecule made of?
Helix of 3 alpha chains
Hydroxyproline and Hydroxylysine - Made by prolyl hydroxylases and lysyl hydroxylases
Why is vitamin C important?
Essential for proline hyhdroxylation
Why are hydroxyproline and hydroxylysine important?
Required for assembly of collagen fibrils and fibers
What does the ground substance do?
Contains proteoglycan aggregates, water and ions, giving matrix high tensile strength and resiliency
Where is hyaline cartilage located?
Permanent: - Walls of respiratory passages - Larynx, nose - Articular surfaces of bones (movable joints) - Ventral ends of ribs Transient: - Model of skeleton - Epiphyseal growth plate Most widely distributed of types of cartilage
How is hyaline cartilage composed?
Type II collagen doesn’t form large fibers
Matrix is hydrated
Glassy look
Smooth strong surface
What is hyaline cartilage made of?
Proteoglycan aggregates - including aggrecan Bound water Type II collagen fibrils Chondronectin - attaches cells to ECM Chondrocytes
Perichondrium
Sheath of dense connective tissue Type I collagen fibers that surrounds permanent hyaline cartilage, except articular cartilage
Source of chondrogenic cells and chondroblasts
Supplies nutrients, removes wastes
Lacunae
Cavities that surround chondrocytes
Territorial matrix
Matrix rich in GAGs that surrounds chondrocytes
Stains darker
Interterritorial matrix
Lighter staining matrix that is between lacuna and chondrocytes
Isogenous groups/aggregates/nests
Groups of 4-8 chondrocytes that originate from divisions of a single chondrocytes
Reside in a single lacuna
How does cartilage grow?
Appositional growth - division of chondrocytes in the perichondrium
Interstitial growth - division of chondrocytes existing in the cartilage
Articular cartilage
No perichondrium
Does not repair quickly
Nutrients gained from synovial fluid in joint capsule
Where is elastic cartilage found?
Auricle of ear, Eustachian tubes, epiglottis, larnx
How is elastic cartilage different?
More cells and matrix than hyaline cartilage
Large aggregates of elastic fibers
Fewer isogenous groups than hyaline cartilage
Where is fibrocartilage found?
Pubic symphysis, intervertebral disks
How is fibrocartilage different?
Very little ground substance, mostly fibers
Lots of Type I and Type II cartilage
No Perichondrium
Merges with adjacent tissues
What’s different about intervertebral disks?
Nucleosis pulposis is liquid form of fibrocartilage, more proteoglycans and water than annulus fibrosis
Functions of bone
- Levers for movement
- Support and protection
- Hematopoiesis in marrow
- Store and regulate serum levels of Ca and P
Organization of adult bone
Outer walls: compact (cortical) bone
Interior: Trabecular (spongy, cancellous) bone and merrow
Periosteum
Dense connective tissue that covers outer surfaces of bone
Attached to bone via Sharpey’s fibers (type I collagen)
Endosteum
Covers interior surfaces
Osteoprogenitor cells
Stem cells found in periosteum and endosteum
Proliferate and produce osteoblasts
Osteoblasts
Bone-forming cells
Secrete osteoid (ECM)
Mineralize the matrix
Non-mitotic
Osteocytes
Derived from osteoblasts
Principal cell in adult bone (95% of cells in bone)
Reside in lacunae between layers (lamellae) of adult bone
Caniculi
Canals formed around osteocyte processes that allow communication and nutrients to pass from cell to cell
Osteoclast
Multinucleated cells derived from Macrophages from bone marrow
Resorb bone
Form a space called Howship’s lacunae
Activity regulated by PTH and calcitonin
What is bone made of?
Organic components - type I collagen, GAGs and proteoglycans
Inorganic components - hydroxyapatite (Ca and P) and trace minerals
Intramembranous Bone Formation
Osteoblasts begin to make bone within loose connective tissue
Forms flat bones of skull and mandible
Also responsible for initiate of bone formation in diaphysis and growth in diameter of long bones
Endochondral Bone Formation
Osteoblasts begin to make bone within cartilage matrix
Forms growth in length of long bones
Secondary center of ossification develops in epiphysis
In what order is bone made?
- Primary/Woven Bone - temporary random collagen fiber orientation
- Secondary/Lamellar Bone - parallel layered collagen fibers, continuously remodeled
- — Compact/Cortical bone
- — Spongy/Cancellous/Trabecular Bone
Osteons/Haversian systems
Compact bone
Lamellae of bone surrounding Haversian canals which contain nerves, blood vessels lymphatics
Haversian canals joined by Volkmann’s canals
Osteons joined together by cement lines
Zones of epiphyseal growth plate
Resting cartilage Proliferation Maturation/Hypertrophy Calcification Ossification
Which hormone triggers bone growth?
Growth hormone
Bone remodeling
Constant process
Osteoclasts degrade old osteons
Osteoblasts generate new osteons
About 10% of total bone is replaced yearly
Fracture repair process
- Blood clot
- Soft callus - loose CT and hyaline cartilage, intramembranous and endochondral bone formation
- Hard callus - primary woven bone
- Repaired, remodeled bone - secondary, lamellar bone
What is the overriding factor of bone mass regulation?
Calcium mobilization
Osteoporosis
Osteoclast activity outpaces Osteoblast activity
Osteopetrosis
Decreased bone resorption due to defective osteoclasts
Reduced marrow cavity and blood formation
Osteoarthritis
Joint disease with loss of articular cartilage
Hypertrophic chondrocytes secrete proteases and destroy matrix
