Bone Development

Question 1

name the two methods for bone formation

Answer 1

intracellular ossification and endochondrial ossification

Question 2

describe intracellular ossification

Answer 2

mesenchymal cells differentiate into osteoblasts, which create immature/woven bone. these initial osteoblasts become nidus for additional osteoblasts, which continue to grow and add layers. these layers will form trabeculae. the spaces in between these trabeculae will be filled with hematapoetic tissues in spongy bone, or compacted in compact bones

Question 3

compaction

Answer 3

in intracellular ossification, after trabeculae have formed, compaction is the process of getting rid of the spaces between trabeculae in future compact bone

Question 4

intracellular ossification forms what types of bones?

Answer 4

many flat and irregular shaped bones (skull bones). it also remains as a mechanism for perosteum and endosteum division

Question 5

fontanelles-

Answer 5

the spaces between skull bones

Question 6

describe the 9 step process of endochondrial ossification

Answer 6

1. formation of chondroblasts from mesenchyme
2. interstitial and appositional growth of cartilage model
3. perichondrium differentiates into osteoblasts- forms bone collar on diaphysis underneath periosteum
4. lack of nutrient diffusion to middle of cartilage causes hypertrophy
5. hypertrophic chondrocytes release a variety of growth factors etc.
6. chondrocytes die and the matrix disintegrates
7. blood vessels and osteoblasts invade the diaphysis
8. osteoblasts secrete osteoid
9. formation of secondary ossification centers on epiphysis

Question 7

what are the relevant chemicals released during the hypertrophic chondrocyte stage of endochondrial ossification

Answer 7

VGEF- promotes vascularization
Collagen X
alkaline phosphate- promotes calcification

Question 8

what carries out matrix disintegration

Answer 8

matrix metalloproteases

Question 9

in the epiphyseal growth plate, describe 5 stages

Answer 9

1. resting zone- hyaline cartilage
2. zone of proliferation- mitosing chondrocytes
3. zone of hypertrophy- secretion of VGEF, collagen x, alkaline phosphate
4. zone of calcification- cell death
5. zone of ossification- osteoblasts and blood vessels invade

Question 10

how is calcium regulated

Answer 10

calcitonin- secreted by thyroid d/t high levels of serum calcium
parathyroid hormone- secreted by parathyroid d/t low levels of serum calcium

Question 11

what is the primary purpose of osteogenesis at various stages of life? (embryo, adolescence, adult)

Answer 11

embryo- formation, adolescence- growth, adult- maintenance and repair