Bone and Cartilage Flashcards
What are they two types of bone (macroscopic)
Cortical, compact bone
Canellous, spongy bone
What is cortical, compact bone like
dense outer plate
80-85% of skeleton
what is cancellous, spongy bone like
internal trabecular scaffolding
15-20% of skeleton
what is alveolar bone like
- cortical bone has nutrient canals, containing blood vessels
- cortical bone lining tooth sockets is penetrated by buncles of collagen fibres of PDL (sharpey’s fibres)
- this bone is also called ‘bundle’ bone
what is the composition of bone
60% inorganic
- hydorxyapatite
25% organic
- collagen (90%)
- glycoproteins
- Proteoglycan’s (GAGs)
15% water
how does the composition of bone compare to the composition of dentine
lower inorganic, greater water and organic compared to dentine
what is ECM made up of
“ground substance”
- semi-fluid gel
- long polysaccharide molecules
- glycos-amino-glycans (GAGs) (hyaluronic acid, proteoglucans)
Fibres (reinforce ground substance)
- collagen
- elastin
- other non-collagenous proteins
what are the two different types of bone (microscopic)
Woven bone
Lamellar bone
Features of woven bone?
- rapidly laid down
- irregular deposition of collagen
- present in fetus
- fracture repair (callus)
- contains many osteocytes
Features of lamellar bone?
- laid down more slowly
- collagen fibres laid down in parallel
- normal form in adult
What is the structure of compact bone like
- laid down in concentric lamellae
- form longitudinal columns
- organised in Haversian systems around central (Haversian) canal
- lateral (Volkman’s) canals
- canals contain blood vessels
what do volkman’s canals link
two haversian canals
what is another name for a haversian system
osteon
Features of cancellous bone?
- network of thin trabeculae
- trabeculae consist of lamellae
- osteocytes present
- no obvious Haversian systems
- the bone is thin, and nutrients can diffuse in
- bone marrow present in the spaces between trabeculae
Characteristics of osteoblasts
- lie on surface of bone
- derived from mesenchymal stem cells
- synthesise and secrete collagen fibres forming a matrix
- the matrix is mineralised by calcium salts
(same group as osteocytes)
Characteristics of osteocytes
- osteoblasts that become trapped in mineralised bone
- lie within spaces - lacunae
- contact other osteocytes via cytoplasmic processes that run in canaliculi
- osteocytes also appear to communicate with osteoblasts
(same group as osteoblasts)
Characteristics of osteoclasts
- large, mulinucleate cells, derived from haemopoietic stem cells
- related to macrophages
- they resorb bone (acid phosphatases)
- lie in concavities in bone: Howship’s lacunae
Describe bone remodelling
- removal and replacement of bone tissue without change in overall shape
- resorption balanced by deposition (apposition)
- each year ~2% of cortical bone and ~25% of cancellous bone is replaced
- controlled by osteoblasts
- regulated by hormones (parathyroid and calcitonin), and paracrines
What is a reversal line
scalloped edge shows where bone resorption changes to bone deposition
How can tooth movement occur
during eruption
post-eruptive (e.g. mesial drift)
orthodontic forces
What is cartilage
semi-rigid, unmineralised connective tissue
what are the different types of cartilage
- hyaline cartilage
- fibrocartilage
- elastic cartilage
where would you find hyaline cartilage
widespread e.g. nasal septum
where would you find fibrocartilage
intervertebral discs, pubic symphysis
where would you find elastic cartilage
external ear, epiglottis, eustacian tube
Characteristics of cartilage cells
- formed by chondroblasts
- these get trapped the matrix and become chondrocytes
- avascular
- nutrient diffuses in
- some channels are present in thick areas of cartilage
- chondrocytes contain stores of lipid, glycogen
what bones undergo endochondral ossification
‘long’ bones
what bones undergo intramembranous ossification
‘flat’ bones
how is bone tissue created
endochondral and intramembranous ossification
in which type of ossification is cartilage present
endochondral ossification
Process of intramembranous ossification
Formation of bone spicules
Formation of woven bone
Primary centre of ossification
Formation of osteon
Process of endochondral ossification
Initially, a cartilage skeleton is laid down. The cartilage is replaced with bone. There are several centres of ossification. Ossification is going outwards
Cartilage proliferation and growth occurs at the epiphyses
what type of ossification happens in the skull
endochondral and intramembranous ossification (need horizontal and vertical growth)
In achondroplasia, what type of growth is impaired
endochondral bone growth as a defect in cartilage growth
What is an anatomical characteristic of achondroplasia
base of skull is minimised –> small maxilla
What gets resorbed after tooth loss
alveolar process
During formation of a flat bone, much of it will become ossified by spread of bone from the centre of ossification, what will the remainder become?
the periosteum surrounding the bone
what are the cells on the surface of bone spicules during flat bone formation
osteoblasts
what is the narrow ‘pink’ zone between the bone surface and osteoblasts during flat bone formation
osteoid - the unmineralised organic matrix of bone
what is the name of the prominent cartilage which is in the lower jaw
meckel’s cartilage
by what mechanism does the bone of the mandible form
the mandible forms by intramembranous ossification. Meckel’s cartilage forms the cartilaginous ‘skeleton’ of the developing jaw. But the bone of the mandible forms lateral to Meckel’s cartilage. As the mandible grows, Meckel’s cartilage regresses, and disappears. It has a few remnants, such as the malleus and incus of the middle ear, and the spenomandibular ligament
what important structures are between the developing mandible and Meckel’s cartilage
inferior alveolar nerve and artery
What happens to the bone lining the ‘socket’ as the tooth roots grow
the bone will resorb to accomodate them
If you are looking at the inner wall of the tooth socket, what are the large multinucleated cells called? what do they do?
osteoclasts, they resorb bone
where would you find howship’s lacunae
inner wall of tooth socket, saucer-shaped depressions in bone
What feature is present in bone but is absent from cartilage
cartilage is avascular. blood vessels migrate into the region, bringing osteoprogenitoor cells which differentiate into osteoblasts. These cells then lay down osteoid on the mineralised cartilage spicules
