Ossification and Development of Bone - Endochondral ossification Flashcards
Where does endochondral ossification occur?
Occurs in the majority of bones n the body, except those formed by intramembranous ossification
(Skull vault, maxilla, mandible)
What does endochondral ossification allow?
Stresses to be sustained during growth e.g. especially in the limbs
What is endochondral ossification?
Endochondral ossification involves the replacement of hyaline cartilage with bony tissue.
What is the difference between endochondral and intramembranous ossification?
In intramembranous ossification, bone develops directly from sheets of mesenchymal connective tissue. In endochondral ossification, bone develops by replacing hyaline cartilage
What are the first 2 stages of endochondral ossification?
- First formed by Chondrocytes, small solid hyaline cartilage model of the future bone is first created by chondrocytes
- Interstitial growth creates an elongated shape to form epiphyses, diaphysis and an outer layer called the perichondrium (still cartilage cells at this stage)
What does interstitial growth form?
Created an elongated shape to form epiphyses, diaphysis and an outer layer called the perichondrium
What are stages 3 and 4 of endochondral ossification?
- Inside the shaft of the diaphysis some of the chondrocytes cells enlarge and begin to resorb, cartilage leaving a trabecular cartilaginous matrix
- Trabecular matrix ossifies (becomes calcified/mineralised) and chondrocyte cells degenerate leaving spaces
What are stages 5-7 of endochondral ossification?
- Blood vessels and mesenchymal cells invade these spaces (degenerated chondrocytes) in the diaphysis
- Perichondrium cells become periosteum cells
- Osteoblasts in the periosteum begin to create woven bone (osteoid) on surface of the diaphysis and on cartilaginous matrix
What do periochondrium cells become?
Periosteum cells
What is a primary and secondary centre for ossification?
Primary ossification center forms in the diaphyseal region of the periosteum called the periosteal collar.
Secondary ossification centers develop in the epiphyseal region after birth.
What is present between the cartilaginous epiphysis and diaphysis?
Epiphyses growth plate
(Will form)
What is the structure of ‘intermediate’ one ossification?
The ‘bone’ still has cartilaginous epiphyses with a bony centre in the middle of the diaphysis
What lays down more cartilage on the epiphseal side?
Chondrocytes
What replaces chondrocytes and what do they do? (Diaphyses side)
Chondrocytes are replaced by osteoblasts which create bone
With more cartilage being layed down on the epiphyseal side and osteoblasts making bone on the diaphyseal side, what is the result?
There is continual lengthening of the diaphysis
Where does the ossification of the epiphyses occur/begin?
In the centre of each epiphysis, a secondary centre of ossification forms and ossification of the epiphysis begins
Where is the secondary centre located?
The centre of the epiphyses
What are the white arrows pointing to?
Epiphyseal growth plate
What are the first 4 zones of the epiphyseal growth plate?
What is in the reserve cartilage zone of the epiphyseal growth plate?
Chondrocytes
Where does cartilage start to proliferate?
Zone of proliferation
Mitosis, columns of cells
Dividing chondroblasts
What occurs in the zone of maturation?
No division
cell size increases
What occurs in the zone of hypertrophy?
Chondrocytes large and vacuolatedge
Matrix calcifies
What are the last 2 zones of the epiphyseal growth plate?
Degeneration
Osteogenic zone
What occurs in the degeneration zone?
Chondrocytes degeneration/ resorb
Osteogenic cells invade lacunae left by dying chondrocytes
What occurs in the osteogenic zone?
Osteogenic cells become osteoblasts and converge on trabecular remnants of cartilage matrix
Osteoblasts create bone
