Lecture 17: Cartilage And Bone Flashcards
What is the composition of cartilage in terms of its cells and extracellular components?
Chondrocytes surrounded by a dense network of collagen and elastic fibres embedded in a gel-like matrix that also contains water and ground substance
What are the 3 components of the cartilage matrix?
Fibres, water and ground substance
What are the 3 types of cartilage?
Hyaline
Elastic
Fibrocartilage
What are the 3 components present in hyaline cartilage matrix?
- Type II collagen
- Hyaluronate proteoglycans aggregates bound to collagen matrix
- Tough dense tissue often containing fluid
How do chondrocytes present in hyaline cartilage?
Present as single cells or if recently divided in small clusters, isogenous groups but separate as they lay down extracellular matrix
What are the 2 components of ground substance?
Hyaluronic acid and proteoglycans
What is the function of chondrocytes?
Produce and maintain the extracellular matrix
Lies in a lacuna
What are the 2 main layers in hyaline cartilage?
Perichondrium and cartilage extracellular matrix with chondrocytes
What is perichondrium?
Dense connective tissue that covers the margin of hyaline cartilage
What does perichondrium contain?
Elongated, fibroblast-like cells that become chondroblasts and then chondrocytes
Why is the cartilage extracellular matrix highly hydrated?
Water is non compressible and so permits resilience to increased pressure
What are 2 examples of hyaline cartilage?
C-shaped tracheal cartilage in tracheal wall Articular surfaces (joints)
What is the function of cartilage in the tracheal wall?
Reinforces trachea and helps to protect and maintain airway
What are the 3 components of the elastic cartilage matrix?
- Elastic Fibres
- Type II collagen
- Hyaluronate proteoglycans aggregates
What are the 3 locations where elastic cartilage can be found?
Pinna of the ear
Eustachian tube (connects ear to mouth)
Epiglottis (flap that ensures food goes to the right tube)
What are the 2 layers in elastic cartilage?
Perichondrium and cartilage itself
What are the 3 main components of fibrocartilage matrix?
A lot of type I collagen
Small amount of type II
Hyaluronate proteoglycan aggregates
How are the cells distributed in fibrocartilage?
Rows
Do fibrocartilage have perichondrium?
No they only have fibroblasts
What are 2 examples of places where fibrocartilage can be found?
Intervertebral discs
Menisci of the knee joint
What is the function of fibrocartilage?
Shock absorber and to resist shearing forces - that’s why it’s quite messy inside - have to resist forces from diff directions
How does cartilage grow?
Appositional growth - growing from the periphery
Can cartilage be repaired?
No chondrocytes cannot undergo mitosis, fibroblasts lay down scar tissue instead
What are the 2 main components of bone?
Matrix and cells
What are the 2 inorganic components of the bone matrix?
Calcium hydroxyapatite
What is the function of the inorganic components of bone matrix?
Resists bending and compression forces
What proportion of the matrix is inorganic?
65%
What proportion of the matrix is organic?
35%
What are the 3 organic components of bone matrix?
Collagen 1
GAGs and proteoglycans
Non-collagen out proteins
What is the function of organic component of bones?
Resist pulling and tension forces
What are the 4 types of cells present in bones?
Osteoprogenitor
Osteoblasts
Osteocytes
Osteoclasts
What is a osteoprogenitor?
Undifferentiated stem cell that eventually develops into an osteoblast
What is a osteoblast?
Intermediate cells that can’t divide
Lays down new bone
What are osteocytes?
terminally differentiated bone cell trapped within osteon, maintains bone and resists stress and force
What are osteoclasts?
Multinucleated cell that secretes acids and enzymes to dissolve bone matrix
What is the general structure of compact/cortical bone?
Functional unit is osteon, which is made up of layers of compact mineralized collagen which traps osteoblasts that produce bone,
How do bones form from cartilage?
Endochondral ossification
What are the 6 stages of emdochondral ossification?
- Bone collar forms around the diaphysis of the hyaline cartilage model
- Central cartilage calcifies and nutrient artery penetrates the centre of the bone to supply osteoblasts (primary ossification centre formed)
- Medulla becomes cancellous bone, cartilage forms epiphyseal growth plates and epiphyses develop secondary centers of ossification
- After birth: Epiphyses ossify and growth plates moves apart to lengthen bone
- Adult: Epiphyseal growth plates replaced by bone but hyaline articular cartilage remains
How does bone increase in length?
Endochondral ossification
How does bone increase its girth?
Periosteal ossification
What are the 5 zones of epiphyseal growth plate?
- Zone of reserve cartilage
- Zone of proliferation
- Zone of hypertrophy
- Zone of calcified cartilage
- Zone of resorption
What happens at the zone of reserve cartilage?
No cellular proliferation of active matrix production
What happens at the zone of proliferation
Cellls actively dividing to form columns, cells enlarge and secrete matrix
What happens at the zone of hypertrophy?
Cells enlarge greatly, matrix compressed into linear bands between cell columns
What happens at the zone of calcified cartilage?
Enlarged cells begin to degenerate and matrix calcifies
What happens at zone of resorption?
Small blood vessels and connective tissue invade the region occupied by dying chondrocytes, leaving the calcified cartilage as spicules between them
What are osteons?
Cylindrical structures that contain a mineral matrix and living osteocytes connected by canaliculi
What is a canaliculi?
Tiny canals that transport stuff
What is lamellar?
Layers of compact matrix that surround a central canal called the Haversian canal
What is Haversian canal?
Contains the bone’s blood vessels and nerve fibers
What are Volkmann canals?
Transverse vessels that connect adjacent osteons connect blood vessels of the Haversian canals
What is the periosteum?
Tissue covering bone’s outer surface
What is osteoarthritis?
Age-related degeneration leading to mechanical failure of the articular cartilage as joint space narrows due to bone rubbing against bone
What is rheumatoid arthritis?
Autoimmune disease where the synovial membrane is inflamed, leads to damage of underlying bone and articular cartilage and they disintegrate
What are osteophytes?
Growth of bony spurs
