Lecture 2 - Bone development and growth Flashcards
what is an osteoprogenitor cell?
a mesenchymal stem cell derivative that differentiates into osteoblasts
how does the ECM become calcified?
by the precipitation of calcium salts such as calcium hydroxyapatite
ossification = ?
deposition of collagen + calcification
true or false -> calcification can occur independently of ossification
true
where can calcification occur that isnt bone as an example?
aging blood vessels
what are the two types of ossification?
intramembranous and endochondrial
briefly describe intramembranous ossification
bone forms directly within mesenchymal connective tissue or ‘fibrous membrane’
mesenchyme stem cells —> osteoblasts
which types of bones form via intramembranous ossification
flat bones of the skull, lower mandible and most facial bones
describe step 1 of intramembranous ossification
mesenchyme cells will move into the ossification centre and differentiate into osteoblasts
describe step 2 of intramembranous ossification
osteoblasts deposit osteoid and become trapped. from here the bone increases in diameter and grows outwards.
describe step 3 of intramembranous ossification
ECM develops into trabeculae that fuse to form spongy bone, trapping blood vessels in the process.
describe step 4 of intramembranous ossification
the mesenchyme at the periphery of the growing bone develops into the periosteum. bone remodelling occurs.
briefly describe endochondrial ossification
cartilage is used as an intermediate model, which is eventually replaced by bone. again, bone grows from the inside out.
mesenchymal stem cells -> condroblasts -> osteoblasts
what is the most common type of ossification in our bodies?
endochondrial
describe step 1 of endochondrial ossification
mesenchymal cells develop into chondroblasts which form the cartilage model
how does the perichondrium change to the periosteum?
after chondrocytes undergo hypertrophy, they encourage vascularisation, which causes blood vessels to invade the perichondrium and bring osteoprogenitor cells. stem cells begin to favour osteoblast formation, which causes the periosteum.
where is the first change of perichondrium -> periosteum?
at the bone collar, where osteoblasts have just begun depositing osteoid.
describe step 2 of endochondrial ossification
growth of the cartilage model by cell division of chondrocytes causes the innermost ECM to calcify due to lack of O2 and nutrients, and the innermost chondrocytes die.
describe step 3 of endochondrial ossification
a nutrient artery enters the cartilage model in a small hole in the calcified ECM, which provides O2 and nutrients, which stimulates the formation of the primary ossification centre.
the nutrient artery brings osteoprogenitor cells in which eventually change into osteoblasts to begin bone formation.
describe step 4 of endochondrial ossification
osteoclasts (also delivered indirectly by the nutrient artery) begin to create the medullary cavity in the diaphysis
describe step 5 of endochondrial ossification
another blood vessel stimulates the formation of the secondary ossification centre in the epiphyses of the bone, which also brings in osteoprogenitor cells which will then differentiate into osteoblasts for bone formation
describe step 6 of endochondrial ossification
as the secondary ossification centre grows in diameter, there is formation of the epiphyseal line and articular cartilage at the epiphysis.
what are the articular cartilage and epiphyseal line made of?
hyaline cartilage
if we can’t see an epiphyseal line, what does that tell us?
the patient is a full grown adult.
what are the similarities between the two types of ossification?
- both occur from mesenchymal cells
- both begin in utero
- involve formation of osteoblasts that secrete osteoid
- involve blood vessel invasion
- they are both forms of interstitial growth
during adolescence, our bones grow in length via?
the epiphyseal growth plate
how many growth plates do normal long bones have?
2, but the hip has three growth plates.
what is the least stable area of the epiphysis?
the epiphyseal growth plate
from epiphysis to diaphysis, name the regions of the epiphyseal growth plate
- resting zone
- proliferative zone (cells divide up and down and provide length to bone)
- hypertrophic zone (chondrocytes secrete matrix and type X collagen which promotes calcification)
- calcified zone
- early bone formation (osteoblasts and osteoclasts come in)
which direction does bone grow in length?
towards the epiphysis
what is the epiphyseal growth plate aka?
the physis
