Bone, Cartilage & Joints 2 Flashcards
what are osteoprogenitor cells
become osteoblasts and produce osteoid
gives rise to outer/inner circumferential lamellae of bone (bony layers)
what are volkmann’s canals and haversian (central) canals
BVs and osteoprogenitor cells continuous with the periostem and endostem penetrate inwards to give rise to volkmann and haversian (central canals)
carrying blood vessels that nourish cells –> giving rise to circular structure
where do haversian systems develop
around the central canals which run parallel to the long axis of the bone
central canal
osteo-progenitor cells
osteoblasts form concentric lamellae depending on stage of growth –> specific orientation of collagen fibres in each lamaellae gives strength
constantly being remodelled
how does the haversian system form
during appositional growth the bone will grow around some of the blood vessels
blood vessels are arranged parallel to the long axis of the bone and occupy shallow groove on its surface
what structures can be seen
haversian system (osteones) in compact bone
CL- central line
L- lacuna
Osteocyte
osteoprogenitor cell (OP)
osteoblast (OS)
what is another type of lamellar bone
spongy, trabecular, cancellous bone
no haversian systems
consists of bony spicules/trabeculae covered with endosteum –> within will be osteoprogenitor cells
what type of bone is this
spongy, trabecular, cancellous bone
what are the two major methods of osteogenesis
- intramembranous
- endochondral
what is intramembranous ossification
no cartilagenous stage –> mesenchymal (neural crest) condense to form osteoblast –> form osteoid matrix –> calcified/osteocytes (flat bone of the skull)
what is endochondral ossification
mesenchymal cells –> cartilage –> ossification into bone (long bones)
where does intramembranous ossification occur
in few localized sites in embryo
does not involve a cartilaginous model
how does endochondral ossification occur
begins with cartilage model –> subsequently replaced by bone
what are stages 1-3 in formation and growth of long bones
- hyaline cartilage is the template of a long bone
2a. proliferation of chondrocytes followed by their hypertrophy at the midpoint of the shaft initiates the formation of the primary ossification centre –> hypertrophic chondrocytes secrete vascular endothelial cell growth factor to induce sprouting of blood vessels from the perichondrium –> calcification of the matrix and apoptosis of hypertrophic chondrocyte occur
2b. osteoprogenitor cells of the perichondrium form the periosteal collar - blood vessels, forming the periosteal bud in opposite directions
what is primary centre of ossification
- the calcified cartilage matrix is replaced by bone
- osteoprogenitor cells associated with periosteum produce bony collar around diaphysis, some of these cells accompany blood vessels that penetrate calcified cartilage matrix
- calcified cartilage matrix is replaced by osteoid produced by osteoblasts
what are stage 3-6 as formation and growth of long bones
- blood vessels and mesenchyme infiltrate the epiphysis and a secondary centre is established
- a similar secondary ossification centre appears in the opposite epiphyses
growth of long bones continues by endochondral ossification at the epiphyseal growth plates –> keeps metaophysis and epipythesis apart
what is the cellular processes in the growth of long bones
-
vascular invasion zone: osteoprogenitor cells, derived from the perivascular mesenchyme, reach the primary ossification centre and generate osteoblasts
- osteoblasts begin to deposit osteoid along the calcified cartilage –> the osteoid calcifies - hypertrophic zone: chondrocytes become hypertrophic as the ossification front approaches
3. proliferative zone: proliferative chondrocytes start expressing transcription factor
4. reserve zone: reserve chondrocytes
5. epiphyseal cartilage: cartilage grows up
- reserve chondrocyte
what is the osteoclastic chase and chondrocytic run
differentiate the types of bone
what type of osteogenesis is being shown here
intramembranous ossification
doesn’t involve a cartilagenous model
osteoblasts line the bony spicule where they are secreting osteoid onto the bone
osteoclasts may be observed housed in Howship’s lacunae
how does activation occur in compact bone remodelling
osteoclast precursors are recruited to the haversian canal and differentiate into osteoclasts
- line the bone lamella facing the canal and start the bone resorption process of the inner lamella and consecutive lamellae towards the outer lamella
- interstitial lamellae are residulas of the remodelling osteon
how does resorption occur in compact bone remodelling
additional osteoclast precursors are recruited as lamellar bone resorption progesses slightly beyond the boundary of the origional osteon
when osteoclasts stop removing bone osteoblasts appear (osteoclast to osteoblast reversal)
how does reversal occur in compact bone remodelling
osteoblasts reverse the resorption process by organizing a layer inside the reabsorption cavity and starting to secrete osteoid
the cement line indicates the boundary of the newly organized lamella
new bone lamella continue to be deposited toward the centre of osteon
how does formation occur in compact bone remodelling
osteoblasts continue laying dow bone and eventually become trapped within the mineralized bone matrix and become osteocytes
a new osteon or haversian system is formed
how does remodelling of bone on the surface occur
in trabecular bone
osteoclasts create resorption space limited by a cement line
then osteoblast line the cement line surface and start to deposit osteoid until new bone closes the resorption space
