S8 Bone Formation And Repair Flashcards
What are the two types of bone?
Cortical and cancellous
What is the structure of cancellous bone?
Avascular
Made up of trabeculae with bone marrow in the spaces
What is the structure of cortical bone?
Vascular (Haversian and Vaulkmann’s canals)
Made up of osteons which are made up of lamallae, caniculi and lacuna (containing osteocytes) surrounded by periosteum
What are the cell types in bone?
- Osteoprogenitor cells - produce osteoblasts
- Osteocytes - mature osteoblasts (embedded in bone matrix)
- Osteoblasts - make bone (lay down osteoid)
- Osteoclasts - break down bone
What are the 3 sections of bone called?
Epiphysis, metaphysis, diaphysis
What is the precursor model for bones growing by endochondral ossification?
Hyaline cartilage
Where does hyaline cartilage grow from and by what sort of growth?
Grows from pericondrium but appositional growth
What are the organic and inorganic compositions of bone?
- Inorganic (65%) - Ca2+, Mg2+ and Al3- (helps to resist bending and compression)
- Organic (35%) - collagen 1, GAGs (help to resist pulling and tension)
Describe the process of endochondral ossification (5 steps)
- Hyaline cartilage model and collar of periosteal bone
- The central cartilage calcifies, a nutrient artery penetrates (providing osteogenic cells and forming the primary ossification centre)
- The medulla becomes cancellous bone, the cartilage forms epiphyseal growth plates. Secondary ossification centres develop in epiphyses
- Epiphyses ossify and the growth plates move apart (lengthening the bone)
- Epiphyseal growth plates are replaced by bone and hyaline articular cartilage (at ends of bone) remains
What is the importance of vitamin D in bones?
Vitamin D provides bone stability, it produces calcitriol which is used for Ca2+ absorption.
A deficiency in vitamin D leads to rickets/osteomalacia.
Describe the process of bone repair after a fracture (6 steps)
- Haematoma formation
- Inflammation (e.g. macrophages, neutrophils, etc.) to remove dead tissue
- Granulation, fibroblasts lay down collagen,
- Chondroblasts lay down hyaline cartilage forming soft callus
- Ossification occurs (hard callus formation)
- Bone remodelling
What are the two steps in bone remodelling?
- Osteoclasts make a wide tunnel in the bone (cutting cone)
2. Osteoblasts make a smaller tunnel of cortical bone (closing cone)
What is osteomalacia?
Adult version of rickets.
Vitamin D deficiency - there’s less Ca2+ resorption so less mineralisation/osteoid.
Soft bones, easy fracturing, muscle weakness.
What is rickets?
Vitamin D deficiency - poor calcium mobilisation so ineffective mineralisation.
Short stature, weakened bones, soft bones, painful to walk, bowed legs
What is primary osteoporosis?
Type 1 and type 2
- Post-menopausal women, increased osteoclast number due to loss of oestrogen
- Older men and women, decreased osteoblast number due to loss of both oestrogen and androgen
What is secondary osteoporosis?
- A result of drug therapy
2. Processes affecting bone remodelling 3. Metabolic bone diseases - metastatic cancer, hyperparathyroidism
What does osteoporosis result in?
Gaps in cancellous bone
Incomplete filling of osteoclast resorption bays
What are modifiable risk factors for osteoporosis?
- Increase calcium intake
- Exercise
- Don’t smoke cigarettes
What is osteogenesis imperfecta?
Brittle bone disease.
A mutation of the COL1A gene results in incorrect collagen 1 production.
Blue sclera, short stature, weakened bones.
What is achondroplasia?
Mutation in FGF3 receptor gene.
Endochondral ossification occurs from cartilage, however this mutation prevents cartilage forming bone. But intramembranous ossification occurs as normal.
Short stature, normal sized head and torso.
