Ossification (Bone growth) Flashcards
What (4) principal situations does ossification occur?
- Initial formation of bones in an embryo and foetus (b/w 6th and 7th week of embryonic life)
- Bone growth during infancy, childhood and adolescence until their adult size
- Bone remodelling
- Fracture repairs
When does intramembranous ossification begin?
When mesenchymal cells differentiate into osteoblasts, which secrete an extracellular matrix that hardens into bone
Where does endochondral ossification mainly occur?
- Physis
- Epiphysis
- Cuboidal bones of the carpus and tarsus
What is endochondral ossification?
Where bones form in hyaline cartilage which has been produced by chondroblasts
What is intramembranous ossification?
Where bone forms on or within loose, fibrous connective tissue membranes without first going through a cartilage stage
What is bone growth in length called?
Interstitial growth
What is bone growth in diameter called?
Appositional growth
What is bone growth primarily controlled by?
Hormones
Describe the steps involved in intramembranous ossification
- Clusters of osteoblasts form a centre of ossification that secretes the organic extracellular matrix.
- The extracellular matrix hardens by deposition of the calcium and mineral salts.
- Bony matrices fuse to form trabeculae.
- Periosteum develops on the bone’s periphery.
- Spongy bone is replaced with compact bone on the bone’s surface.
What (during childhood) promotes growth at epiphyseal plate, and has production stimulated by human growth hormone?
Insulin like growth factors
What is involved in bone growth by increasing osteoblast activity, and also causes long bones to stop growing in length?
Sex hormones
What decreases blood calcium levels by accelerating calcium depositions in bones and inhibiting osteoclasts?
CT (Calcitonin)
