Exam #2: Bone Histogenesis Flashcards
Intramembranous Ossification
Bone forms directly within a membrane of highly vascular mesenchyme
Which bones form via intramembranous ossification?
Flat bones of the skull, face, mandible, & clavicle
Steps of intramembranous ossification
1) Mesenchymal cell–>osteoprogenitor–>osteoblast
2) Osteoblast synthesize osteoid (organic matrix of bone)
3) Primary bone is deposited, which takes the form of spicules & trabeculae
4) Mineralization
5) Resportion by osteoclasts
6) Deposition of secondary bone by osteoblasts
7) Spongy bone
8) Compact bone
Endochonrial Ossification
A cartilage model of bone is formed first, then it becomes calcified, eroded, & is replaced by bone
Where is the primary ossification center?
Diaphysis
Where is the secondary ossification center?
Epiphysis
Outline the steps of endochondrial ossification in the primary ossification center
1) Form hyaline cartilage model of bone-to-be
2) Grow hyaline cartilage interstitially (length) & appositionally (width)
3) Perichondrium–>Periosteum
4) Bony collar forms
5) Cartilage cells hypertrophy (accumulating glycogen & vacuoles)
6) Hypertrophied cartilage cells produce alkaline phosphatase
7) Calcification of cartilage
8) Chondrocytes die & Osteoclasts make holes for periosteal buds
9) Bone forms
What is the major difference between bone formation at the primary & secondary ossification centers?
Secondary Center of Ossification= NO bone collar
Where is cartilage being replaced in a growth plate?
Epiphyseal side
Where is ossification occurring in a growth plate?
Diaphyseal side
Zone of Reserve Cartilage
Typical hyaline cartilage that is mitotically active
Zone of Proliferation
- Intense mitosis
- Cells multiply & increase in number
- Chondrocytes appear as stacks of pennies
- Cartilage growth here is INTERSTITIAL
Zone of Hypertrophy
- Chondrocytes accumulate glycogen & become vacuolated
- Chondrocytes swell
- No addition of new cells
Zone of Calcified Cartilage
- Lacunae coalesce
- Calcification of cartilage matrix
- Chondrocytes die
Zone of Ossification
- Toward diaphysis
- Osteoprogenitor cells emigrate to the calcified cartilage matrix area & become osteoblasts
