6.7 Bone development, growth, and remodeling

What can be transformed into bone?

Cartilage and fibrous CT

What is ossification?

osteogenesis-bone tissue formation

What are the 2 types of ossification?

endochondral and intramembranous

What is endochondral?

bone replaces hyaline cartilage; ex: all bones below base of skull except clavicles

What is intramembranous?

bone replaces fibrous CT; mostly flat bones; ex: bones of skull and clavicles

What are the steps of Endochondral ossification?

1. Bone collar forms around the diaphysis; ossification from outside

2. Cartilage around primary ossification center calcifies

3. periosteal bud (contains veins, nerves, osteoprogenior cells and clasts) invades new cavities, form spongy bone

4. secondary ossification centers form in epiphyses

5. Epiphyses ossify

What are the steps of Intramembranous ossification?

1. Embryonic cells differentiate into osteoblasts, forming ossification center in fibrous CT

2. Osteoblasts secrete osteoid, which calcifies in a few days to become spongy bone and periosteum

3. Osteoblasts mature to osteocytes

4. Some spongy bone remodeled to become compact bone; remaining spongy matures and red marrow developes in spaces

Longitudinal (responsible for bone growth) mimics what?

endochondral ossification

What is bone resorption?

to break down; osteoclast

What is bone formation?

Osteoblasts

What occurs around age 18 in females and age 21 in males?

Epiphyseal plate closure; permanent ossification of plate

What happens every year and every ten years?

one year- 5-10% of our skeleton is remodeled

10 years- our entire skeleton is replaced

Remodeling is controlled by what?

hormones and osteocytes

Osteoclasts resorb bone by secreting what?

acid to break down the inorganic portion and lysosomal enzymes to break down the organic portion

When resorption is complete in an area what happens?

osteoclasts undergo apoptosis (programmed cell death)

What are the stages of bone repair?

1.Blood vessels broken and bleeding, hematoma (blood clot) forms

2. New blood vessels form, fibrocartilage form soft callus (acts as splint)

3. fibrocartilage > spongy bone by osteoblasts; about 2 months

4. spongy bone > compact bone; several months