Bone Growth and Formation

Question 1

What is ossification?

Answer 1

formation of bones that begins in early embryonic life

Question 2

What are the 2 methods of ossification?

Answer 2

Intramembranous and Endochondral

Question 3

Intramembranous ossification: bone forms from ________, and what types of bones are formed?

Answer 3

Connective tissue

flat and irregular bones

Question 4

Endochondral ossification: bone forms from ________, and what type of bone is formed?

Answer 4

hyaline cartilage

long bones formed

Question 5

4 steps of intramembranous ossification:

Answer 5

1. mesenchymal cells (like embryonic fibroblasts) to osteogenic cells to osteoblast
2. osteoblasts to osteocytes to calcification
3. formation of bone trabeculae, blood vessels penetrate bringing in osteoclasts to form medulla spaces
4. at periphery, mesenchymal cells to fibroblasts to periosteum

Question 6

6 steps of endochondral ossification:

Answer 6

1. development of a hyaline cartilage model by mesenchymal cells
2. growth of cartilage model, length: chondrocyte division within matrix, width: formation of new cartilage at edge by chondroblasts
3. cells in mid-region burst, changing pH of matrix and causing calcification and chondrocyte death
4. development of primary ossification centre (artery penetrates into centre and brings in osteoblasts and osteoclasts, osteoblasts form new bone, osteoclasts form medullary cavity)
5. development of secondary ossification centre (blood vessels enter epiphyses at birth and spongey bone is formed)
6. hyaline cartilage remains (over epiphyses (articular cartilage), at epiphyseal plate for bone growth)

Question 7

What are the 2 types of bone growth?

Answer 7

interstitial and appositional

Question 8

Where does interstitial bone growth occur and what happens? What happens once this growth is finished?

Answer 8

within bone at epiphyseal plate

hyaline cartilage gradually becomes bone (similar to endochondral ossification)

cartilage cells stop dividing, replaced by bone, stops growing in length

Question 9

Where does appositional growth occur? What happens?

Answer 9

edge of bone

osteogenic cells to osteoblasts to bone laid down around blood vessels, concentric lamellae formed to osteons

Question 10

During remodeling, bone is laid down along line of _____

Answer 10

stress

Question 11

What is a stress fracture?

Answer 11

break in bone caused by physical trauma

Question 12

What is a pathological fracture?

Answer 12

break in bone caused by weakening by disease

Question 13

What are the four stages of healing after a fracture and how long does it usually take to complete?

Answer 13

8-12 weeks

1. formation of blood supply (clot, bone cells die, macrophages)
2. formation of fibrocartilaginous callus (fibroblasts enter and lay down collagen)
3. formation of bony callus (osteoblasts create spongey bone)
4. bone remodeling (compact replaces spongey)

Question 14

What happens when bone ages? (3)

Answer 14

demineralization, decrease in protein synthesis, osteoporosis