In general, what two components make up cartilage?
- Chondrocytes
- Extensive ECM
Is cartilage vascular or avascular
-Avascular
What is the function of the chondrocytes within cartilage?
-To produce and maintain ECM
What is the ECM of cartilage made up of?
- Hyaluronic acid and proteoglycan aggregates
- Proteoglycan monomers have a core protein with gags attached
- Collagen fibres
What are the characteristic features of cartilage?
- Resilience to repeated applied pressure
- Non-compressibility
- Solid but pliable
- Elasticity
What does the gag:collagen ratio of the ECM ensure?
-The ratio permits diffusion of nutrients to the chondrocytes from the surrounding blood vessels
Which type of collagen is predominantly found in cartilage?
-Type 2
What type of tissue is cartilage?
-Connective tissue
Name the three type os cartilage
- Hyaline
- Elastic
- Fibrocartilage
What is the ECM of hyaline cartilage made of?
- Hyaluronic acid and proteoglycan aggregates bound to type II collagen
- Proteoglycan monomers have a core protein with gags attached
What is the main characteristic feature of hyaline cartilage?
-Resilience to repeated pressure loads
What occurs when pressure loads are applied to hyaline cartilage?
-Creates mechanical, electrical and chemical signals which direct the synthetic activity of the chondrocytes
What cell type is found in hyaline cartilage?
-Chondrocytes
Where in the body is hyaline cartilage found?
- larynx, trachea, bronchus
- ear and nose
- ribs
- articulating surfaces of joints
- At the epiphyseal growth plate
What surrounds cartilage?
-Perichondrium
What is particular about the hyaline cartilage at articulating surfaces of joints?
- No perichondrium as would be damaged, needs to be smooth and thus cannot repair itself, gets nutrients from surrounding fluid
- Also contains type III collagen
Why does hyaline cartilage at articulating surfaces have irregular boundaries?
-To prevent shearing off
Describe how chondrocytes are distributed in hyaline cartilage
-Lie in lacunae, separated by ECM that they secrete or in isogenous groups if just recently divided, which eventually become to lie separately
Why does hyaline cartilage remain at the epiphyseal growth plates?
-To allow elongation of long bones
What is interstitial growth in cartilage?
-Growth which occurs as a result of isogenous groups secreting matrix and becoming single cells laying in separate lacuna
What is appositional growth?
- Growth from the periphery
- The perichondrium contains elongate fibroblast-like cells which develop into chondroblasts and then into chondrocytes, laying down ground substance as they develop
What is the territorial matrix?
-The highly sulphated deeply staining matrix immediately surrounding chondrocytes
What is the interterritorial matrix?
-The matrix which lies in between chondrocytes and their lacunas
How is the ECM of elastic cartilage similar/different from that of hyaline cartilage, and what extra feature does this add?
- ECM made of hyaluronic acid and protein aggregates providing resilience
- Contains many elastic fibres conferring elasticity upon the cartilage
What colour is elastic cartilage in FRESH tissue?
-Yellowish
Where is elastic cartilage found in the body?
- Pinna of the ear
- Eustachian tube
- Epiglottis
- Auditory meatus
Does hyaline cartilage or elastic cartilage have more abundant chondrocytes?
-Elastic
What cell type(s) does fibrocartilage contain?
-Chondrocytes and fibroblasts (in relatively low numbers)
Why is fibrocartilage different from hyaline and elastic cartilage?
-It is a mixture of dense irregular connective tissue and hyaline cartilage
Does fibrocartilage have a surrounding perichondrium?
-No
Describe the distribution of cells within fibrocartilge
- Often found in rows or isogenous groups
- Few
What fibres does fibrocartilage contain?
-TI and TII collagen
How are the fibres arranged in fibrocartilage? Relate the structure to its function
- Fibres run in parallel with direction of force exerted upon it
- Provides high tensile strength and non-compressibility
What is the main function of fibrocartilage?
-Shock absorber and resistance of shearing force
Where is fibrocartilage located in the body?
- Intervertebral discs
- Sternoclavicular and temperomandibular joints
- Menisci of the knee joing
- Pubic Synthesis
- Ethesis
What is ethesis?
-Point of attachment of tendon to bone
Which type of cartilage calcifies with age?
-Hyaline
Which cartilage is the most common?
-Hyaline
In general, what are the three constituents of bone?
- Cells
- ECM
- Fibres
What is specific about the ECM of bone?
-Integrated with mineral salts, particularly calcium phosphate for rigidity and hardness
How is bone specialised for its function?
-High mechanical strength with minimal weight
Name the different groups of bones
- Long bones
- Short bones
- Flat bones
- Sesamoid bones
What are the two types of bone?
- Compact
- Spongy (Cancellous/trabecular)
What is the macroscopic histiological appearance of compact bone?
-Dense bone with no cavities
Where is compact bone found?
-External surfaces of bones
Microscopically, into what is compact bone arranged?
-Into osteons
What are osteons?
-Concentric lamellae of bone arranged around a central haversian canal, joined to other osteons, periosteum and bone marrow by volkmann canals
What do haversian canals carry?
-Blood vessels, lymphatics and nerves
What is cementing substance?
-A thin homogenous layer of amorphous material between osteons
Are volkmann canals surrounded by concentric lamellae?
-No
What are interstitial lamellae?
-Remnants of lamellae which used to be concentrically arranged around an osteon have been remodelled
What is the macroscopic structure of cancellous bone?
-Interconnecting network of cavities, filled with bone marrow separated by numerous irregular trabeculae
What is the microscopic structure of trabeculae?
- No haversian systems
- Lamellae not arranged in concentric circles but irregularly
How does trabecular bone receive nutrients?
-By diffusion from the marrow
What is periosteum?
-Vascular connective tissue which surrounds bone
What cell types are found in bone?
- Osteoblasts (which develop into osteocytes)
- Osteoclasts
What is the function of osteoblasts?
-Lay down new osteiod in bone remodelling
What is the function of osteoclasts?
-To resorb bone during bone remodelling
How do osteoclasts exert their action?
-Through H+ and lysosomal enzymes
In what do osteocytes lie?
-Lacunae
How are osteocytes arranged in immature and mature bone?
- Immature-> fairly randomly arranged
- Mature-> in the concentric lamellae
What is different about the lacunae of bone to lacunae of cartilage?
-Radiate canaliculi which anastomose with canaliculi of other lacunae
What is the function of canaliculi?
-Permit osteocyte cytoplasmic processes and passage of ions and nutrients to those osteocytes which lay far away from the artery
What is the sheath of neumann?
-fine fibrous tissue which lines lacunae and canaliculi
What must happen to bone in order for it to be histologically viewed?
-Decalcified which kills organic material
or
-Ground
Describe the action of bone remodelling
- Osteoclasts resorb bone through H+ and lysosomal enzymes which forms a cutting cone which runs parallel to the direction of the haversian canal creating a resorption cavity, osteoclasts lie in the resulting depression
- Osteoblasts deposit osteoid in sucessive lamellae creating a closing cone, filling the resorption cavity with new bone
Why can the bone resist fracture until a certain point?
- High tensile strength
- Degree of flexibility- lamellae can slip relative to one another before excessive force causes fracture
What are the four stages of bone repair following a fracture?
- Haematoma formation
- Fracture repair
- Bony callus formation
- Bone remodelling
Describe haematoma formation following a fracture
- Blood vessels in bone and periosteum break
- Haematoma (mass of clotted blood) forms
- Cells at periphery of fracture die due to lack of blood supply
- Removed by macrophages
Describe fracture repair following haematoma in a bone fracture
- New blood vessels infiltrate haematoma
- Procallus of granulation tissue (tissue rich in fibroblasts and capillaries) forms
- Fibroblasts produce collagen fibres which span the break, others differentiate into chrondrocytes and form a sleeve of hyaline cartilage across the break
- An externally buldging fibrocartilagineous matrix splints the bone
Describe bony callus formation after procallus formation following a fracture
- Trabeculae develop and a spongy callus is formed
- Edochondral ossification replaces cartilage with bone
- Fibrocartilagineous callus is know a hard bony callus of cancellous bone
- Continues for 2 months until hard union is formed
Describe bone remodelling following a fracture
- Spongy bone remodelled to compact bone at cortical regions
- Osteoclasts remove externall budlging bone and bone protruding into medullary cavity
- Final shape will be the same as the original bone as remodelling will be in response to the same mechanical stressors
