Cartilage, Bone and Ossification Flashcards Preview

MJM anatomy > Cartilage, Bone and Ossification > Flashcards

Flashcards in Cartilage, Bone and Ossification Deck (40):

What are the main functions of bone?

1) support for the body and protection for vital organs
2) bone marrow for blood cell production
3) calcium and phosphate resevour


What is connective tissue made of?

calcium, ECM and 3 major cells; osteocytes, osteoblasts and osteoclasts


What does endosteum and periosteum do?

endosteum lines the marrow cavity internally
periosteum externally surrounds


What are the layers of periosteum?

There is the fibrous layer and the cellular layer, the fibrous layer is on the outside


What are osteoblasts?

mesenchymal origin
produce organic component of bone matrix, type 1 collagen, proteoglycan and osteonectin
mainly found on surface on bone matrix and bound via integrins
single layer of cuboidal cells
single nucleated


What do the osteoblasts do?

produce organic component of bone matrix, type 1 collagen, proteoglycan and osteonectin


What is an osteoid?

newly formed matrix
which needs to be mineralised


What happens after matrix synthesis?

- the majority undergoes apoptosis
- others flatten and line bone
- differentiate into osteocytes entrapped within lacunae surrounded by matrix


What happens in Mineralization?

- one of the organic products produced, osteocalcin, binds calcium and raises local concentration
- osteoblasts secrete vesicles enclosed by membranes, ALP
- hydrolyse phosphate from macromolecules to increase phosphate concentration
- both ion concentrations become high and the calcified crystals form around matrix vessicles
- crystal size increases with formation of calcium hydroxyapatite which is solidified mineralised bone matrix
- osteocalcin raises calcium, osteoblasts secrete ALP, calcium and phosphate levels rise, mineralise the crystals, hydroxyapatite makes crystals bigger


What happens from osteoblasts, osteoid layer to mineralised bone ?

1) osteoblasts release matrix vesicles
2) in the osteoid matrix layer, released matrix vesicles and collagen fibres and early mineralisation around the vesicles
3) mineralised, matrix becoming confluent between vesicles


What are osteocytes?

these form when osteoblasts become stuck in the matrix and differentiate
sit within lacunae of matrix
they have cytoplasmic processes that sit in the lacunae
importance of lacunae and canaliculi for diffusion of nutrients


Histologically, what do osteocytes look like?

Less RER
smaller Golgi
more condensed chromatin


What is the function of an osteocyte?

maintain calcified matrix and regulate bone remodelling


What are Osteoclasts?

large, multinucleated
resorb calcified matrix via sealing zone where integrin tightly binds bone matrix
low pH- dissolution of calcium hydroxyapatite
hydrolase activation- matrix resoroption
calcium is released into blood


What causes Osteoperosis?

osteoperosis secondary to inefficient sealing zone so there is overgrow and thickening of bone, bone resoprion is greater than formation so calcium is lost


What is contained within the matrix?

50% inorganic, calcium hydroxyapatite
type 1 collagen and multiadhesive osteonectin
high collagen content makes it acidophilic


What is in the Periosteum?

outer layer dense
type 1 collagen
blood vessels
Perforating (sharpeys fibres) bind periosteium to bone
inner layer is cellular containing fibroblasts


What is Lamellar bone?

multiple layers of calcified matrix
aligned type 1 collagen
concentric and parallel arrangement
osteon/haversian canal, make up most of it
between each lamellae is the lacunae where osteocytes sit
blood vessels from central canal


How do the canals from the Lamellar bone communicate?

VOlkmanns canal, between intact osteons are intersititial lamellae which are remains of previous osteon which have been destroyed for remodelling
- Haversians canal (central canal) will communicate via Volkmanns canal


What is Woven bone?

random orientation of type 1 collagen
appear in embryonic development and fracture repair
temporary and is replaced by lamellar bone
less calcium, more osteocytes


What is Osteogenesis ?

Intramembranous and Endochondral Ossification


What is intramembranous ossification?

formation of skull, jaw, scaupla and clavicle
- mesenchymal stem cells come together and replicate
- mesenchymal stem cells become osteoblasts
- osteoblasts release osteoid which becomes calcified
- osteocytes embedded in lacunae surrounded by matrix in ossification
- as IM continues, spicules form


What is Endochondral Ossification?

1) fetal hyaline cartilage develops
2) cartilage calcifies and a periosteal bone collar forms around diaphysis
3) primary ossification center forms in diaphysis
4) secondary ossification center forms in epiphysis
5) bone replaces cartilage , but not articular and epiphysial plates
6) epiphyseal plates ossify and form epiphyseal lines


What are the two types of cartilage that remain from endochondrial ossification?

1) articular, such as hyaline, found on the end of long bones
2) epiphyseal plate, epiphysis to diaphysis to enable longitudinal growth


What are the different zones of the epiphyseal plate ?

ZONE 1 - zone of resting cartilage (hyaline cartilage)
ZONE 2 - zone of proliferating cartilage (cartilage cells divide rapidly)
ZONE 3 - zone of hypertrophic cartilage
ZONE 4 - zone of calcified cartilage(death of chondrocytes but prior to this release osteocalcin for matrix ossification)
ZONE 5- zone of ossification, osteoblasts invade cartilage to form osteoid


What is Rickets?

deformity in bone shape
compression of epiphyseal plate
lack of Vit D or calcium
osteomalacia is the adult form of rickets


Why do we need calcium?

cell adhesion
cytoskeletal movements
membrane permeability


How is calcium increased?

acts on OB receptors
they secrete RANKL
stimulate osteoclasts


What are the different types of joint?

synarthorsis, limited or no movement
synostoses, no movement
syndesmoses, dense Connective tissu ebetween bones
symphysis, thick pad of cartilage


What is the Annulus Fibrosis

collagen bundles arranged at right angle layers
toughness and withstand pressure


What is the Nucleous Pulposus

type 2 collagen
viscous rich fluid


What are the cell types of Synovial membrane?

type A cells, remove wear and tear debris, resemble epithelium but have no basal lamina or cell junctions
Type B cells, form synovial fluid to lubricate the joint


What is Hyaline Articular Cartilage?

type 2 collagen fibres parallel near surface but perpendicular as you move deep
between collagen fibres have proteoglycan aggregates which hudrates the cartilage


What is Cartilage?

an avascular connective tissue which is on the articular surfaces of joints
highly hydrated so can withdtand compressive forces


What is Hyaline Cartilage?

has a white glassy appearance in living tissue with highly hydrated ground substance


What are the three glycosaminoglycans of Hyaline cartilage?

Hyalouronic acid
chondroitin sulphate
keratin sulphate


What do GLycosaminoglycans do?

they trap water


What are the different layers of Hyaline Cartilage?

tangenital layer
intermediate layer
radial layer
calcified layer


Where are chondrocytes large and the collagen fibres obliquely orientated?

in the tangenital layer collagen fibres are parallel, they are parallel in the radial layer also, in the transitional layer however they are oblique and there are lots of chrondrocytes


What are Chondrocytes?

They secrete cartilage