Cartilage and Bone Flashcards
Is cartilage a vascular or avascular tissue?
Vascular
What does cartilage consist of?
An extensive cellular matrix in which lies chondrocytes
What is the space for each chondrocyte called?
Lacuna
What is the role of chondrocytes?
Produce and maintain the extracellular matrix
What does the large ratio of GAGs to type II collagen in the cartilage matrix permit?
Ready diffusion of substances between chondrocytes and the blood vessels surrounding the cartilage
How could the extracellular matrix of cartilage be described?
Solid and firm, but also rather pliable
What is the advantage of the cartilage matrix being pliable?
It makes it resilient to repeated application of pressure, and so allows cartilage to act as shock absorbance
What is there a large amount of in the extracellular matrix?
Hyalyronic acid
What is the purpose of the hyaluronic acid in the extracellular matrix?
It assists the resilience to repeated application of pressure
What are the 3 types of cartilage?
NAME?
What does hyaline cartilage matrix contain?
Proteoglycans, hyaluronic acid and type II collagen
What are the hyaluronic proteoglycan aggregates bound to in hyaline cartilage?
Fine collagen matrix fibres
What is the matrix of elastic cartilage like?
Like that of hyaline cartilage, but with addition of many elastic fibres and elastic lamellae
What does fibrocartilage have it its matrix?
Abundant type I collagen fibres, in addition to matrix material of hyaline cartilage
What is the cell type in hyaline cartilage?
Chondrocytes
No other cell type present
How are chondrocytes present in hyaline cartilage?
Singly, or, if recently divided, in small clusters called isogenous groups
What happens to chondrocytes within the isogenous groups?
They separate as they elaborate extracellular matrix
Why is hyaline cartilage important in early fetal development?
It is the precursor model of those bones which develop by endochondral ossification
What happens as long bones develop?
Some hyaline cartilage remains at the articulating surface, and at epiphyseal growth plate until growth ceases
Where is hyaline cartilage seated?
NAME?
What covers the margin of hyaline cartilage?
Perichondrium
What does perichondrium contain?
Many elongated, fibroblast-like cells
What can happen to the fibroblast like cells in perichondrium?
They can develop into chondroblasts, and thereafter chrondrocytes
Where do chrondrocytes lie?
In cartilage extracellular matrix
What is the function of chondrocytes in the extracellular matrix?
They produce and maintain the matrix
What type of tissue is perichondrium?
A dense connective tissue
What do the fibroblast-like cells of the perichondrium give rise to?
Flat, newly formed chondroblasts
What do chondroblasts secrete?
Matrix components
What eventually happens to chondroblasts?
They round up to develop chondrocytes
What is the result of the formation of chondrocytes from chondroblasts?
The formation of cartilage
What is the cartilaginous growth from the periphery known as?
Appositional growth
What may happen to chondrocytes deeper in the cartilage?
They may divide and give rise to isogenous groups by mitosis
What is the result of deposition of further matrix by the isogenous groups formed deeper in the matrix?
Interstital growth
What happens to the cells of isogenous groups as they lay down further matrix?
They separate
How can you tell when chondrocytes have recently divided?
They are close together
What features of cartilage permit resilience to varying pressure levels?
NAME?
Why does territoral matrix tend to stain darker with H&E stain than interterritoral matrix?
It is more highly sulphated
What directs the synthetic activity of chondrocytes?
Pressure loads applied lead to the cartilage creating mechanical, electrical and chemical signals
What is the precursor of most bones?
A hyaline cartilage model or template
What happens to the hyaline cartilage model for bones?
It’s mineralised to form bone
What happens to the hyaline cartilage of developing tarsal bones?
It will ossify
What is not present at articulating surfaces?
Perichondrium
Where is perichondrium found?
At non-articulating surfaces and contributing to developing joint capsule
How is hyaline cartilage positioned at the end of a long bone that hasn’t finished developing?
It lines the articulating surface of the bone, and forms the epiphyseal growth plates
What is the epiphysis?
The head of bone
What is found at the epiphysis?
Spongy/cancellous bone, with compact bone at sides
What does the growth plate separate?
The epiphysis and metaphysis
What is the metaphysis?
The wide region between the epiphysis and diaphysis
What is the diaphysis?
The shaft of the bone
Where do the chondrocytes of the cartilage at the epiphyseal edge of long bones lie?
In lacuna
Is the articular surface of bone smooth or rough?
Smooth
What is the advantage of the articular surface of bone being very smooth?
Provides relatively friction free articulation
What is the articular surface of long bone composed of?
Hyaline cartilage without perichondrium
What is the advantage of the irregular boundary between articular cartilage and underlying bone?
There’s less likelihood of one sliding of the other
Do elastic fibres calcify with ageing?
No, unlike hyaline
Where is elastic cartilage found?
- Pinna of ear
- External acoustic meatus
- Epiglottis
- Eustachian tube
What are the layers of the pinna of the ear?
- Muscle
- Adipose tissue
- Fibrocollagenous tissue
- Elastic cartilage
- More fibrocollagenous tissue
- Dermis
- Epidermis
How do elastic fibres lying in the extracellular matrix stain?
Darkly
What are the cell types in fibrocartilage?
Chondrocytes and fibroblasts
What is fibrocartilage a combination of?
Dense regular connective tissue and hyaline cartilage
How are cells often seen to be distributed in fibrocartilage?
In rows
Does fibrocartilage have surrounding perichondrium?
No
What kind of locations does fibrocartilage tend to be present?
Places where huge amounts of pressure can be applied
Give 4 locations fibrocartilage is found
- Sternoclavicular joint
- Temperomandibular joint
- Menisci of knee
- Pubic symphysis
What is the advantage of the resilience of fibrocartilage?
It can act as a shock absorber and resist shearing forces
How are chondrocytes arranged in fibrocartilage?
In rows or as isogenous groups
How many elongated fibroblast nuclei are evident?
Relatively few
What are entheses?
Points of attachment between tendons and bones
What is present at some entheses?
Fibrocartilage
What happens at the head of some bones?
Cancellous bone forms a network of fine body columns or plates
What is the advantage of the cancellous bone at the head?
Combines strength with lightness
What fills the spaces in cancellous bone?
Bone marrow
What does compact bone form?
The external surfaces of bones
How much of the bodies skeletal mass is compact bone?
~80%
What is the shaft of a long bone made up of?
- Endosteum
- Periosteum
What is endosteum?
Inner surface
What is periosteum?
The outer surface
What is next to the endosteum in the shaft of bones?
Inner circumferential lamellae
What are inner circumferential lamellae?
Layers of bone that run right round the shaft of the bone
What runs in parallel with the direction of the bone?
The lamellae of the bone
What forms osteons?
Different layers of lamellae forming concentric circles around the osteonal artery
What canals does a bone section have?
- Haversian canals
- Volksmann’s canals
How does the arrangement of osteocytes differ between mature and immature bone?
NAME?
What type of bone has reabsorption canals?
Mature
In what direction do reabsorption canals run?
Parallel with the osteons long axes
How is bone remodelled using resorption canals?
By boring a hole then laying down new osteon
What is found when bone has been remodelled?
Interstital lamallae
What are interstitial lamallae?
Bits of lamallae that seem to have belonged to complete circular system, but superseded by new osteon
What are the spaces where osteocyte lies in bone called?
The osteocyte lacunae
What is at the centre of each osteon?
A Haversian canal
In what direction do Haversian canals run?
Longitudinally along the bone
What cross connects between Haversian canals?
Volkmanns canal
What does each Haversian canal have around?
A system of lamallae around it
What does the Volksmann canals go through?
Lamallae belonging to adjacent osteons
What do Haversian and Volkmann canals carry?
Blood and lymph vessels, and nerves
What does an osteon consist of?
A Haversian canal and it’s concentric lamallae
What can happen when attempting to section bone?
Damage to microtone blades
What is normally done to make bone easier to section?
Decalcified
What is the problem with decalcifying bone to section?
The agents that do it damage the Haversian canal
How can the problem of the Haversian canals being damaged by decalcification agents be overcome?
By grinding the bone down to a very thin layer to look at
What happens to osteons as bone develops?
Resorption canals are bored down by osteoclasts, and then new lamallae are laid down by osteocytes, but bone remodelling doesn’t always follow exact course of preceding osteoclasts
Are osteons longitudinal or latitudinal?
Roughly longitudinal
What do osteons have the ability to as they go down bone?
Branch and terminate
What do osteocytes posses?
Canaliculi
What are canaliculi?
Tiny interconnecting tunnels
Where are tiny protoplasmic threads found in bone?
In the osteocytes entombed in lacunae between bony lamallae
What are protoplasmic threads?
Tiny cytoplasmic process
What do the osteocytes protoplasmic threads do?
Reach out to adjacent osteocytes via canaliculi
How to protoplasmic threads connect?
Via gap junctions
What is the purpose of the connections of protoplasmic threads?
Allow nutrients to be passed between osteocytes
What are canaliculi believed to connect with?
The central Haversian canal
What is the internal histological structure of trabeculae similar to?
That of compact bone
What is the difference between spongy bone and compact bone?
Spongy bone doesn’t have Haversian or Volksmann canals
Why doesn’t spongy bone have canals?
It seems it can get its nutrient form bone arrow, so doesn’t need blood vessels
What does each trabeculum consist of?
Numerous osteocytes embedded within irregular lamallae of bone
What is on the surfaces of trabeculae?
Osteoblasts and osteoclasts
What do osteoblasts do?
Build up bone
What do osteoclasts do?
Eat away
What do the cavities of trabeculae have around them?
Central lamallae
What are in the trabeculae cavities?
Adipose and haemopoietic cells
In do you have in growing bone spicles?
Osteoblasts depositing new osteon
What happens to the osteoblasts once they have deposited new bone?
They are now surrounded by new osteoid, and so are now osteocytes
What results from osteoclasts reabsorbing bone in spicules?
A depression in bone where they have eaten away
What is boring the tunnel through bone in remodelling?
A cutting cone
How to osteoclasts remove bone?
By releasing H + and lysosomal enzymes
Where do osteoblasts lay down new concentric lamallae?
On sides of boring tunnel
What is the composition of bone?
- 65% mineral (calcium hydroxyapatite crystals)
- 23% type I collagen
- 10% water
- 2% non-collagen proteins
Why does bone resist fracture?
Because it has great tensile and compressive strength, and also a degree of flexibility
What is thought to be able to happen before excessive load causes fracture?
The lamallae can slip relative to one another
What results between broken bone ends when it breaks?
Haemotoma
What results in the haemotoma when bone breaks?
Bleeding from multiple blood vessels
What are the 4 stages in fracture repair?
- Haemotoma formation
- Fibrocartilaginous callous formation
- Bony callus formation
- Bone remodelling
What leads to haemotoma formation in broken bone?
Blood vessels in bone and periosteum break
What is a haemotoma?
A mass of clotted blood
What happens to the bone cells at the fracture edge?
They die
Why do bone cells at the fracture edge die?
Because they have no blood supply
What happens as a result of the haemotoma?
Swelling and inflammation
What tissue needs to be removed when the bone breaks?
Dead/damaged tissue
What removes the dead/damaged tissue when the bone breaks?
Phagocytic cells and osteoclasts
What eventually happens to the haemotoma formed when bone breaks?
It’s removed by macrophages
How is a fibrocartilaginous callus formed?
- New blood vessels infiltrate the fracture haemotoma
- A procallus (soft callus) of granulation tissue develops
- Fibroblasts produce collagen fibres that span the break. Others differentiate into chrondroblasts, which give rise to a sleeve of hyaline cartilage
- An externally bulging, fibrocartilaginous matrix therefore splints the bone
What is granulation tissue rich in?
Capillaries and fibroblasts
What is happening concurrently to the formation of a fibrocartilaginous callus?
Osteoblasts of nearby periosteum and endosteum, and multipotent cells from the bone marrow invade the fracture site, and being bone formation by forming spongy bone
What begins to appear within a week of the formation of the fibrocartilaginous callus?
New trabecular within the callus
How to the trabeculae in the callus develop?
As former fibrocartilaginous callus is converted to hard callus of cancellous bone
What ultimately happens to the fibrocartilaginous callus?
Endochondrial ossification replaces it all with cancellous bone
What is the role of intramembranous ossification in bone healing?
It produces new cancellous bone in the area
How soon do the processes that form a bony callus occur in a young person?
2 days after fracture
How long does bony callus formation continue for?
~2 months
What needs to happen as soon as the callus of spongy, cancellous bone is formed?
It needs to be remodelled into compact bone
Where is the remodelling into compact bone especially important?
In the cortical region
What is the cortical region?
The region of the former bone shaft
How long does the bone remodelling process happen for after a bone fracture?
Several months
What material is removed in bone remodelling?
The material bulging from the outside of the bone, and inwards into the medullary cavity
How is the bone for remodelling removed?
Osteoclasts
What is the final shape of the remodelled area of bone?
Same as that of original unbroken bone
Why is the final shape of remodelled bone the same as that of the original bone?
It responds to the same set of mechanical stressors
What can sometimes happen to fragments of bone in fractures?
It can be pulled away from the fracture sit by periosteum
What happens to fragments of bone pulled away from the fracture site?
It is removed by osteoclasts
When is a bony union and callus formation not possible?
If a fracture involves loss of bone fragments
What is the purpose of bone banks?
They are available to supply viable bone for grafting purposes
What happens to bone in bone banks?
It’s frozen then used by orthopaedic surgeons
What are the types of bone graft?
- Autograft
- Homograft
- Heterograft
Where does the bone graft in an autograft come from?
The person themselves
Where does the bone graft come from in a homograft?
A different human
Where does the bone graft come from in a heterograft?
A different species
What is the advantage of using calf bone in heterograft?
It loses antigenicity with refrigeration
