What are the functions of bone?
1. Support: Provides framework supporting organs
2. Protection: Skull (brain), rib cage (thoracic organs)
3. Movement: Skeletal muscles use bone as leverage
4. Mineral storage: Bones store calcium, phosphorus and fat
5. Haematopoiesis: Bone marrow produce red blood cells
What are the different types of bone?
1. Trabecular bone: Spongy and delicate
2. Compact bone: Regular and dense
What is the periosteum?
Thin layer of richly innervated and vascularised connective tissue lining the outside of bones.
What is the endosteum?
Layer of connective tissue lining the bone marrow cavity.
What are the different types of cells in bones?
- Osteoprogenitor cells: Bone stem cells (located in periosteum and endosteum
- Osteoblasts: Bone-producing cells
- Osteocytes: Quinescent osteoblasts
- Osteoclasts: Bone-resorbing cells
What is the structure of a bone?
- Diaphysis (ends)
- Epiphysis (shaft)
What are the components of the bone matrix?
- Amorphos material (e.g. glycosaminoglycans)
- Both in hydroxyapatite
What is the microstructure of compact bone?
- Basic unit of compact bone called osteon
- Consists of concentric circles of osteocytes around central Haversian canal
What is the cause of osteogenesis imperfecta?
Mutations in COL1A1 and COL1A2
What are the symptoms of OI?
- Grwith retardation
- Hearing loss
- Joint laxitu
What are the causes of osteomalacia (rickets)?
Vitamin D deficiency
What is the sequence of events in endochondrial ossification?
1. Cartilage model of bone is laid down.
2. Hypertrophy and death of chondrocytes in centre of cartilage model.
3. Invasion of bone by blood vessels allow osteoprogenitor cells to enter catilage.
4. These differentiate into osteoblasts that begin secreting bone ECM and causing ossification at primary ossification centre (forms diaphysis).
5. Secondary centres form epiphysis.
What factors are responsible for differentiation of osteoblasts?
What is the location of the epiphyseal plate?
At the junction between diaphysis (primary ossification centre) and epiphysis (secondary ossification centre)
What is the structure of the epiphyseal plate?
1. Zone of quinescence
2. Zone of proliferation (cells divide)
3. Zone of hypertrophy (cells swell)
4. Zone of calcification (chondrocytes die and osteoblasts ossify bone, which is added to diaphysis
What is the importance of bone remodelling?
- Making compact bone
- Calcium homeostasis
- Response to mechanical stress
- Removal/replacement of ageing bone
- Repair of fractures
What is the role of IHH?
Stimulates cell division in growth plates
What is the role of FGF?
Stops growth in growth plate
How is compact bone created?
1. Osteoclasts dig into bone to form cutting cone
2. Cutting cone lined by osteoblasts lay down matrix and then become quinescent
3. Blood vessel grows into the growth cones
How is a fracture repaired?
1. Haematoma forms in fracture
2. Fibrocartilage forms in fracture
3. Fibrocartilage is ossified
4. Ossified bone is remodelled