2 Flashcards
whats epiphyseal growth plate
cartilage plate
when do epiphyseal growth plate close
16 17
clavicle up to 23 yo
how do bones develop
intramembranous and endochondral ossification but end product is the same
how do bones grow in width
apposition
what is the major type of bone in mature skeleton
lamellar bone.
made of two layers
cortical bone: outer part of bone gives structure. dense. 80% of adult skeleton in mass
cancellous/trabeular bone is the layer inside that’s made of a mesh gives bone bendability. 20% of adult skeleton mass
woven bone
its in diff directions. a lot in children skeleton. makes bone softer. can be remodelled.
its immature healing and pathological
does collagen run in same direction
yes per layer.
diff layers diff directions.
what are osteons
cylinders that make up cortical bone
what type of collagen is found in bones
type 1
whats matrix made up of
40% organic (mostly collagen but also proteogluycans)
60% inorganic (calcium hydroxiapetite)
a bit of water
how does hydroxyapatite allow for some movement
form blocks around collagen fibre
whats the cycle of development of bone cell
from osteoprogenitor cell to osteoblast and Ince that forms matrix it becomes osteocyte and then that becomes osteoclast
osteoblast found where
line bone trabedculae
whats makes new bone matrix organic component
osteoblast
what sense how well bone is doing (bone maintainer)
osteocyt
where do osteoprogenitor cells found
perioctyoum or endostium
where do osteoclast come from
cousin of macrophage. it destroys bone.
remove woven bone so osteoblast can remodel it so you have cortical and spongy bone.
osteoclast remove bone from medullary cavity and fills with red bone marrow
special feature of osteoclast
multi nucleated
when does ossification happens
week 6 7 of intrauterine life
how does ossification happens
2 mechanisms:
- intramembranous for skull where bone forms directly
- endochondral: from cartilage precursor to endpoint.
explain the process of intramembranous ossification
you start w mesenchymal cells in skull which become osteoblasts directement.
so mesenchymal cells are quite multipotent. osteoblasts becomes osteocytes. and so that becomes bone when calcified with caliusm hydropaetite.
whats the periocytium
its mesenchymal cells that’s on outside and condenses to host all osteoprogenitor cells your gonna need and remodel bone from woven bone to lamellar bone
why do you need blood supply
mesenchymal stem cells make osteoblasts and osteocytes. but osteoclasts come from hematopoeitic stem cells so the only way it can get in is if it comes via blood.
explain the process of endochondra ossification
mesenchymal cells get signals that make them differentiate as chondroblast (cartilage cell lineage) forming hyaline cartilage.
then perichondrium forms around cartilage.
perichondrium holds stem cell mesenchymal cells. and can change ECM so that they can become chondroctyes. then chondrocyte divide to form isogenic groups. each chondrocyte lays down matrix and forms its own lacunae and spread apart.
increase in matrix means appositional growth and interstitial growth.
what happens to chondrocytes in centre of cartilage model
hypertrophy so release alkali which triggers calcification
condroctye death within calcifying matrix forms small cavities for new osteoblasts to move into the bone collar from the periochrondrium (so becomes periosteum)
nutrient artery penetrates periochondreium via nutrient foramen. on outside periochndrium changes to periosteum
