5.1 Flashcards
(26 cards)
What is ossification?
The formation and remodelling of bone tissue
When does ossification begin and end?
Begins during early embryonic development
Finishes at end of life
What are the two methods of bone formation?
Intramembranous ossification (in embryonic tissues membrane)
Endochondral ossification (in embryonic hyaline cartilage)
What is step one of intramembranous ossification?
- stem cells cluster at ossification center in embryonic connective tissue
- differentiation into the bone environment is initiated
- mature osteoblasts begin to produce bone at the ossification centre.
What is step 2 in intramembranous ossification?
- bone deposits grow outwards from ossification centre
- trapped osteoblast —> osteocytes
- osteoblasts on the surface begin to promote calcification (hardening the bone with inorganic materials)
What is step 3 of intramembranous ossification?
- blood vessels grow to provide nutrients
- with new blood vessels comes the delivery of osteoclasts
- osteoclasts resorption begins from internal trabecular structure.
What is step 4 of intramembranous ossification?
- continued bone remodelling forms typical bony product
(Flat bones of the skull, mandible and clavicle)
What is stop 1a of endochondral ossification
- chondroblasts secrete cartilage matrix.
- Trapped chondroblasts become chondrocyte in lacunae
- chondrocytes divide (mitosis) inside lacunae.
- new daughter cell secretes cartilage matrix from within lacunae enlarging cartilage model
Cartilage also deposited on external surface by chondroblasts.
What is stop 1b of endochondral ossification?
- hyaline model continues to grow
Chondrocytes at center absorb fluid, swell and burst
Dead chondrocytes disintegrate leaving cavities in centre of hyaline model.
What is step 2 in endochondral ossification
- blood vessels grow around d edge of cartilage model
- osteogenic cells within perichondrium differentiate
- osteoblasts lay down superficial bone to form edges of diaphysis
What is step 3 in endochondral ossification?
- blood vessel penetrates cartilage at diaphysis
- osteoblasts enter alongside blood vessels to produce spongy bone template within cartilage model diaphysis
- bone growth increases and spreads towards both ends of cartilage model
What is step 4 in endochondral ossification?
- osteoclasts enter from blood vessel and remove spongy bone template
- osteoblasts lay down new bone to form cortical bone at diaphysis
- cartilage and bone continues to grow increasing size of model.
What is step 5 in endochondral ossification?
- Blood vessels penetrates cartilage at heads
- osteoblasts follow and lay down spongy bone template within
What is step 6 in endochondral ossification?
- epiphysis remodelled to from trabecular (spongy) bone
- line between epiphysis and metaphysis remains cartilage
Cartilage plate grows to lengthen the long bone.
What is interstitial growth of bone?
Growth in length
What is appositional growth in bones?
Growth in the width
Where does interstitial growth occur?
- Within the bone
- occurs at epiphyseal plate
Where does appositional growth occur?
Occurs on the edge of the bone
What is bone remodeling?
- Process of bone cells removing old bone and replacing with new bone
Osteoclats removing bone at equal rates of osteoblast forming new bone
What is the role of osteoblasts/clast in bone growth?
If osteoblasts are more active = more bone formation
If osteoclasts are not active = less bone resorption
What is the role of osteoblasts/clast in bone loss?
If osteoclasts are more active = more bone loss
If osteoblasts are not active = less bone formation
What factors affect bone remodeling?
Nutrition, hormones, disease, age/mortality
What is step 1 in fracture repair?
- formation of blood clot (hematoma)
- ruptured blood vessels due to fracture
- local cells die from industry
- macrophages transported in blood arrive and cleanse area
What is step 2 in bone fracture repair?
Formation of fibrocarilaginous callus
- once area clear of debris and hematoma cleared
- fibroblasts and chondroblasts deposit collagen fibres to form a fibro cartilage mould around fracture sight
- known as the soft callus
