bone development Flashcards
intramembranous ossification (general)
direct mineralization of matrix secreted by osteoblast
endochondral ossification (general)
-formation of bone matrix on a pre-existing cartilage model
what forms by intramebranous ossification
majority of the bones of the face, and flat bones of the skull, clavicle
requirements for intramembranous ossification
- enough tissue mass to produce appropriate amount of bone producing cells
- well vascularized tissue
- adequate maternal nutrition
developmental time frame of intramembranous ossification
end of the 7th week of development
intramembranous bone formation
- mesenchymal migrate and aggregate in areas where bone will form
- cells trapped din the calcifying matrix differentiate into osteocytes
- woven bone is formed
- remodeling of the initial bone forms compact bone with a lamellar arrangement surrounding the cancellous/ spongy bone
intramembranous ossification summary
- mesenchumal models of bone form during the embryonic period
- msenchyme that contributes to the formation of most of the skull and all of the facial skeleton is derived from cephalic neural crest cells
endochondral ossification
- takes place in a hyaline cartilage model
- responsible for the formation for the bones that participate in weight-bearing
1. long bones of extremities
2. pelvic and shoulder girdle
3. vertebral column
step 1 in endochondral ossification
-begins with formation of hyalin cartilage in the shape of the future bone
step 2 in endochondral ossification
- appearance of bone collar around the cartilage model
- stem cells in the perichondrium give rise to bone forming osteoblast
- the perichondrium is transformed to a periosteum
- blood vessels invading the future bone
step 3 in endochondral ossification
- bone collar prevents diffusion of oxygen’s- results in degenerative changes in the underlying cartilage
- chondrocytes hypertrophy
- surrounding matrix undergoes calcification
- death of the chondrocytes results in a calcified cartilage matrix that will break down giving rise to a large cavity
step 4 and 5 in endochondral ossification
- stem cells from the periosteum follow the blood vessels and organize on the calcified cartilage
- stem cells differentiate not osteoblasts and form the bone matrix
- calcified cartilage is broken and removed by osteoclasts that reach the area through blood vessels that penetrate the bone collar
- there is a mix of calcified cartilage and primary bone
secondary ossification in endochondral ossification
- appear later usually post natal
- cartilage remains in 2 regions
1. articular cartilage
2. epiphyseal cartilage
time frame for endochondral bone formation
-6 weeks post fertilization
-hyaline cartilage bone model forms
time frame for endochondral bone formation
-8-12 weeks post fertilization
-primary centers of ossification are formed
