bone

4 stages of intramembranous ossification

mesenchymal cell condensation, osteoblast differentiation, matrix deposition, remodeling

mesenchymal cell condensation

mesenchymal cells form a dense group of cells

osteoblast differentiation

mesenchymal cells turn into osteoblasts

matrix deposition

osteoblasts secrete osteoid, which becomes mineralized into woven bone, osteblasts become trapped in lacunae are now osteocytes

remodeling

osteoclasts form/dissolve the bone, forming 2 outer layers of cortical bone w/a thin layer of spongy bone

steps of an endochondral ossification

formation of cartilage model, formation of a bone collar, formation of a primary ossification center, formation of secondary ossification centers, epiphyseal plate formation

formation of a cartilage model

mesenchymal cells differentiate into chondrocytes, forming a hyaline cartilage model surrounded by perichondrium

formation of a bone collar

central chondrocytes hypertrophy & secrete factors that trigger calcification of the surrounding cartilage

calcified cartilage cells promote

perichondrial osteogenesis

VEGF

vascular growth factor

formation of a primary ossification center

VEGF promotes a nutrient artery to pass thru the bone collar & invade the calcified cartilage, bringing in osteoprogenitor cells

osteoblasts digest the calcified cartilage forming

the marrow cavity (hollow center)

osteoblasts form osteoid onto the calcified cartilage which is

the future diaphysis of the long bone

formation of the secondary ossification

can occur at both ends, hyaline cartilage remains on their surface as future articular cartilage

epiphyseal plate formation

specialized band of hyaline cartilage is maintained btwn the primary/secondary ossification centers

The primary ossification center forms which future portion of a long bone?

future diaphysis of the long bone

The secondary ossification centers form which future portions of a long bone?

future epiphyses of the long bone

epiphyses, diaphyses

ends, shafts

What type of cartilage remains at the epiphyseal (growth) plate?

hyaline cartilage

What basic structure is required for a long bone to increase (grow) in length?

Epiphyseal plate (physis)

4 zones of physis

zone of reserve cartilage, zone of proliferation, zone of hypertrophy, zone of calcification

zone of reserve cartilage

resting cartilage, inactive hyaline cartilage cells, anchors growth plate to the epiphysis

zone of proliferation

actively dividing cells, tightly packed flattened cells arranged in vertically stacked columns

zone of hypertrophy

maturation, chondrocytes are increasing in size via hypertrophy and secrete factors like VEGF, promoting capillary invasion

zone of calcification

ossification, cartilage mineralizes & is invaded by capillaries from the metaphysis, osteoclasts free the chondrocytes from their lacunae, chondrocytes differentiate into adipocytes, osteoblasts secrete osteoid onto the calcified cartilage

funnel-shaped region btwn the physis and diaphysis

metaphysis

simplistic bone growth

growth occurs via appositional growth on the outer periosteal surface

bone resorption occurs

on the inner endosteal surface, enlarging the marrow cavity as the diaphysis widens

What type of cartilage remains on the articular surfaces of the future long bone?

Hyaline cartilage (specifically articular cartilage)

Will hyaline cartilage become covered in perichondrium? Why or why not?

no, b/c it allows diffusion of nutrients/gas exchange directly w/synovial fluid since articular cartilage has no blood supply of its own