long bone growth (diaphysis)

What happens in POC

arrival of bone forming precursor cells via blood vessels

1. osteoclast mature and resorb cartilage ECM - make room for osteoblasts

2. osteoblasts produce osteoid

3. osteoid surrounds osteoblasts

• trapped osteoblasts → osteocytes

in POC what is the first type of bone laid down

trabecular (spongy) bone matrix of osteoid forms

• woven spongy bone

• fill entire diaphysis

in POC after bone is laid down…

• blood vessels invade - condense into red marrow

• osteoblasts from periosteum begin to produce compact bone

where does the medullary cavity form

in POC

• osteoclasts in POC activated

how does medullary cavity form

osteocalsts in POC are activated

• resorb woven spongy bond from center-outwards → medullary cavity

during medullary cavity formation bone is added where?

to outside of diaphysis walls

• appositional growth via intramembranous ossification

what is appositional growth

growth the is ‘next to’ or ‘side by side’

• creates lamellar, compact bone

modeling occurs via

appositional growth

modeling step 1

osteoblasts from periosteum produce osteoid

modeling step 2

osteoid ‘seeps’ under periosteum and forms bone

modeling step 3

osteoid calcifies

modeling step 4

calcified osteoid traps osteoblasts → osteocytes

modeling step 5

bone lining cells proliferate

• some go on to next round of osteobalsts

modeling step 6

osteoclasts in medullary cavity resorb bone

• without this bones would become too thick and heavy

modeling creates what type of bone

lamellar, compact bone

what is an osteon

column of compact bone that runs the length of the diaphysis

• formed from concentric lamellae and compact bone ECM

what about other bones?

some form via intramembranous ossificaion

• ex. flat bones of skull and mandible

others form via endochondral ossification

• ex. vertebrae

timing of growth termination depends on …

• genetics

• nutrition

• metabolic changes (often associated with sexual maturity)

• mechanical factors - compressional force inhibits growth