Bone and Cartilage Flashcards
What are the 2 types of bone
cortical/compact
cancellous/spongy
describe cortical bone
Cortical bone is the dense outer layer of bone
It is compromised of structural units called osteon
Each osteon is composed of layers called lamellae
The central canal of each osteon contains nerves, capillaries and lymphatics
Forms 80-85% of the skeleton
describe cancellous bone
Contains lamellar bone – the osteocytes are housed in lacunae
Lattice like network of rods called trabeculae
Orientated to provide maximum strength for minimum mass
Spaces between trabeculae occupied by red and yellow marrow
Externally lined by endosteum
Makes up 15-20% of the skeleton
what are the 3 components to alveolar bone
An external plate of cortical bone
The inner socket wall of thin cortical bone called the alveolar bone proper
Cancellous bone (between these two compact layers)
what does the cancellous bone contain
blood vessels, nerves and lymphatics that send their branches through the cortical bone through small openings called Volkman’s canals to supply the periodontal ligament
what does the cortical bone lining tooth sockets penetrated by
bundles of collagen fibres of PDL (Sharpey’s fibres)
what is the composition of bone
60% inorganic
15% water
25% organic
what makes up the organic component
collagen (90%)
glycoprotiens
proteoglycans
what is the function of the proteoglycans
responsible for jelly structure of the matrix
what are the two different ways bone can be resorbed
horizontal
vertical
what is horizontal resorption
generalized bone loss occurs most frequently as horizontal bone loss. Horizontal bone loss manifests as a somewhat even degree of bone resorption so that the height of the bone in relation to the teeth has been uniformly decreased. It occurs in a plane parallel to the CEJs of the adjacent teeth
what is vertical resorption
occurs adjacent to the tooth and usually in the form of a triangular area of missing bone known as triangulation.
what is the ECM made up of
ground substance and fibres
what is ground substance
semi fluid gel
what does ground substance contain
long polysaccharide molecules
glycosaminoglycans
what are the fibres found in the ECM
Collagen
Elastin
Other non-collagenous proteins
what are the two types of microscopic bone
woven
lamellar
describe woven bone
rapidly laid down
irregular deposition of collagen
contains many osteocytes
where is woven bone found
fetus
fracture repair
describe lamellar bone
Laid down more slowly so well organised
Collagen fibres laid down in parallel
Normal form in adult
contains fewer osteocytes
what is the structure of compact bone
Compact bone is laid down in concentric lamellae (lamellar bone)
it forms longitudinal columns
It is organized in haversian systems around the central (Haversian canal)
There is also lateral (volkman’s) canals – these link haversian canals
The canals contain blood vessels
There are small ‘lacunae’ with radiating canaliculi
what is the function of the interconnecting projections of the osteocytes
their function is nutrition but also communication
describe cancellous bone
Cancellous bone is made up of a network of thin trabeculae
The trabeculae consist of lamellae
There are osteocytes present
There is no obvious haversian systems
The bone is thin and nutrients can diffuse in
Bone marrow is present in the spaces between the trabeculae
describe osteoblasts
Lie on the surface of the bone
Derived from mesenchymal stem cells
Synthesize and secrete collagen fibres forming a matrix - matrix that is not yet mineralized is called osteoid
The matrix is then mineralized by calcium salts
describe osteocytes
Osteocytes are osteoblasts that become trapped in mineralized bone
They lie within spaces called lacunae
They contact other osteocytes via cytoplasmic processes that run in canaliculi
Osteocytes also appear to communicate with osteoblasts
how can we tell the difference between bone and cementum from osteocytes
We can tell the difference between cementum and bone through the osteo/cementocytes as in cementum we cannot usually see the canaliculi and if we can see them then the canaliculi are only on one side, facing the PDL as this is where the cementum’s nutrients comes from
describe osteoclasts
Large, multinucleate cells derived from haemopoietic stem cells
They are related to macrophages
They resorb bone (acid phosphatases)
They lie in concavities in bone called howship’s lacunae
what is bone remodelling controlled by
osteoblasts
what i the process of bone turnover regulate dby
hormones - PTH, calcitonin
paracrine - various cytokines
what happens in bone turnover
PTH and signaling molecules increase the number and activity of the osteoclasts – osteoclasts which will resorb bone on one side
On the other side the osteoblasts work to secrete osteoid (matrix)
what is the reversal line
There is a scalloped edge which shows where the bone resorption changes to bone deposition
what does tooth movement require
remodeling of adjacent soft and hard tissues
when do tooth movements occur
During eruption – tooth eruption requires the resorption of the crypt where the tooth is actually present and resorption of where the root will form so that the root can take this place
Post-eruptive (e.g mesial drift)
Orthodontic forces
what is cartilage
semirigid, unmineralized connective tissue
how is cartilage similar to bone
Its matrix is similar to bone, made up of:
Ground substance
Fibres
what are the 3 types of cartilage
hyaline
fibrocartilage
elastic
where is hyaline cartilage found
Widespread (present almost everywhere)
Larynx, nasal septum, trachea, ends of ribs (costal cartilages), articular surfaces, embryonic skeleton (precursor to bone)
where is fibrocartilage found
Found in intervertebral discs, pubic symphysis
where is elastic cartilage found
External ear
Epiglottis
Eustacian tube
what is cartilage formed by
chondroblasts
how is cartilage different to bone
avascular
what are the two ways bone can grow
endochondral ossification
intramembranous ossification
what bones are formed via endochondral classification
long bones
base of the skull
what does endochondral ossification consist of
cartilage being replaced by bone - the cartilage serves as a template to be completely replaced by new bone
what bones are formed via intramembranous ossification
flat bones
describe intramembranous ossification
o Bone is formed de novo in C.T
o There is no cartilage precursor
what are the bones of the skull formed by
intramembranous ossification – it forms the vault of the skull
calcification occurs between membranes
describe endochondral ossification
Initially a cartilage skeleton is laid down
The cartilage is replaced with bone
There are several centres of ossification
Cartilage proliferation (and growth) occurs at the epiphyses
What is the process of endochondral ossification
Mesenchymal cells differentiate into chondrocytes that produce a cartilage model of the future bony skeleton
Blood vessels on the edge of the cartilage model bring osteoblasts that deposit a bony collar
Capillaries penetrate cartilage and deposit bone inside the cartilage model forming the primary ossification centre
Cartilage and chondrocytes continue to grow at the ends of bone while medullary cavity expands and remodels
Secondary ossification centres develop after birth
Hyaline cartilage remains at growth plate and at joint surface as articular cartilage
what is synchondrosis
is an almost immovable joint between bones bound by a layer of cartilage
what is the sphenooccipital synchondrosis a major contributor to
post natal growth – growth at the synchondrosis lengthens this area of the cranial base and bone remodelling on surfaces is also important
what is achondroplasia
It is a defect in cartilage growth
Endochondral bone growth is impaired while intramembranous bone growth is unaffected
what does the condylar cartilage form by
forms by endochondral calcification
what dissapears when teeth are extracted
alveolar process
What are the steps to intramembranous ossification
Mesenchymal cells group into clusters, differentiate into osteoblasts and ossification centres form
Secreted osteoid traps osteoblasts which then become osteocytes
Trabecular matrix and periosteum form
Compact bone develops superficial to the trabecular bone, and crowded blood vessels condense into red bone marrow
How does the mandible grow
through both endochondral and intramembranous ossification
What is the sphene-occipital synchondrosis
This is the joint between the sphenoid and occipital bone
There is endochondral ossification here because we require the base of the skull to elongate
