WEEK 6: 6.7 Bone Growth and Repair Flashcards
What is ossification?
the process of bone formation, or the formation/remodelling of bone tissue
What are the two main types of ossification?
Intramembranous and endochondral ossification
Define intramembranous ossification
Bone formation within the embryonic tissue membrane
What is step 1 to IM ossification?
Mesenchymal stem cells differentiate into osteoprogenitor cells and then osteoblasts, which then produce bone at the ossification centre
What is step 2 of IM ossification?
Bone deposits grow outwards from ossification centre as trapped osteoblasts become osteocytes. Osteoblasts on surface and osteocytes in lacunae begin to promote calcification, which causes hardening of the bone
What is step 3 of IM ossification?
Blood vessels grow in ossification area to provide nutrients, which causes the delivery of osteoclasts, and osteoclastic resorption begins to form internal trabecular structure
What is the final step of IM ossification?
continued bone remodelling forms typical bony product
provide eg. of IM ossification products?
flat bones of the skull, mandible, clavicle
What is the difference between interstitial and appositional growth
Interstitial- bone growth in length- new cell growth from within tissue (chondorcytes dividing and secrete matrix from within cartilage)
Appositional growth- bone growth in width- growth on the surface of tissue (cartilage deposited on external surface by chondroblasts)
Define endochondral ossification
Bone formation within the cartilage model
Describe step 1a of EC ossification
-Forming hyaline cartilage model
- Interstitial and appositional growth
- chondroblasts secrete cartilage matrix -> trapped within matrix -> chondrocytes in lacunae -> divide inside lacunae (mitosis)
Describe step 1b of EC ossification
enlarging hyaline cartilage model
- chondrocytes at centre absorb fluid, swell and burst which changes pH of environment and calcifies cartilage and also triggers step 2
Describe step 2 of EC ossification
- ossification at edges of bone (formation of diaphysis)
- blood vessels grow around edge of cartilage model
-osteoblasts lay down superficial bone and form edges of diaphysis
Describe step 3 of EC ossification
- primary ossification centre formation
- blood vessel penetrates cartilage at diaphysis
- osteoblasts enter alongside blood vessel to create spongy bone template within cartilage model
-bone growth increases and spreads towards both ends of cartilage model
Describe step 4 of EC ossification
remodelling of primary oss centre
osteoclasts enter from blood vessel and remove spongy bone
- form medullary cavity
- osteoblast lay down bone to form cortical bone
- osteon formation and remodelling
- cartilage and bone continues to grow increasing size of model
Describe step 5 of EC ossification
Formation of secondary ossification centres
Blood vessels penetrate cartilage at heads (epiphyses)
Osteoblast follow and lay down spongy bone
Secondary ossification centres
Describe step 6 of EC ossification
Epiphyseal line formation and interstitial growth
- epiphysis remodelled to form trabecular bone
- line between epiphysis and metaphysis remains as cartilage until puberty
Where exactly does interstitial growth occur?
‘within bone’ at the epiphyseal plate
How does this interstitial growth increase the length of a bone?
- chondrocytes dividing increase hyaline cartilage
- growth of cartilage pushes epiphysis further from metaphysis
- hyaline cartilage gradually ossifies and forms the epiphysial line
Where does appositional growth occur?
on the edges of bones, where bony structure is formed
What is the process of appositional growth?
osteogenic cells differentiate to from osteoblasts
Osteoblasts lay down new layers of bone (lamellae) on edges of bone
Osteoblasts trap themselves and become osteocytes
what factors can affect bone remodelling?
Nutrition- adequate minerals like calcium and phosphate & vitamin D and C
Hormones- human growth hormone, sex hormones at puberty stimulate bone & cartilage cells
Loss of oestrogen in menopause
Disease: cancer & inflammation
Age & Motility: cells become less active as they age and
Describe the first step involved in bone fracture repair
step 1: formation of a blood clot, as ruptured blood vessels due to fracture, macrophages transported in blood arrive to clean said area, which can take hours to days
Describe the second step involved in bone fracture repair
formation of fibrocartilaginous callus
- once area is clear of debris, fibroblasts and chondroblasts deposit collagen fibres to form fibro-cartilage mold around fracture - soft callus
