Bone Flashcards
What is the composition of bone?
Calcium hydroxyapatite crystals
Type 1 collagen
Water
Non-collagen proteins
What do Haversian and Volksmann canals do?
Carry blood vessels, lymph vessels and nerves
Give the four main stages of fracture repair
- Haematoma formation
- Fibrocartilaginous callus forms
- Bony callus formation
- Bone remodelling
What are the functions of bone?
Support
Protection
Mineral storage
Haemopoiesis
What is the marrow cavity lined with?
Endosteum
How is calcium concentration in the blood maintained?
When low: parathyroid hormone stimulates osteoclasts to reabsorbed bone matrix -> higher calcium in the blood
When high: calcitonin inhibits osteoclast activity and decreases bone reabsorption
Describe what happens in the first stage of fracture repair
Haematoma forms in which granulation tissue arises.
Describe what happens in the second stage (fibrocartilaginous callus formation)
The procallus of granulation tissue is replaced by a fibrocartilaginous callus in which bony trabeculae develop.
Describe what happens in the third stage of fracture repair,
Endochondral and intramembranous ossification give rise to a bony callus of spongy/cancellous bone
Describe what happens in the fourth stage of fracture repair
Cancellous bone is replaced by compact cortical bone until remodelling is complete
Describe the process of endochondral ossification.
Cartilage is reabsorbed and replaced with bone.
This begins at the primary centre of the shaft - diaphysis - and continues at the epiphysis.
Growth in length is at the epiphyseal growth plates.
Describe the process of intramembranous ossification.
Bone begins as highly vascularised connective tissue.
Mesenchymal cells differentiate into osteoblasts surrounded by collagen fibres and ground substance
They secrete uncalcified matrix (osteoid) and become osteocytes.
Describe growth of long bone by endochondral ossification.
Begins as hyaline cartilage
Collar of periosteal bone appears in the shaft
Central cartilage calcifies
Nutrient artery penetrates - supplying osteogenic cells
Primary ossification centre is formed
Medulla becomes cancellous bone
Cartilage forms epiphyseal growth plates
Epiphyses develop secondary ossification centre
Epiphyses ossify and growth plates continue to move apart, lengthening bone
Epiphyseal growth plates are replaced by bone.
Which type of bones develop by intramembranous ossification?
Flat bones
How is osteogenesis imperfecta inherited?
Autosomal dominant
What is osteogenesis imperfecta caused by?
A mutation in the gene for type I collagen so abnormal collagen synthesis by osteoblasts and fibroblasts
What can osteogenesis imperfecta lead to?
Where it is not fatal before birth (Type II), bones are thin, delicate and abnormally curved.
Multiple fractures of long bone which leads to deformities because they don’t heal correctly.
Also affects ears, teeth, sclerae, ligaments, skin and joints.
What effects can growth hormone have on bones before puberty?
Excessive - promotion of epiphyseal growth plate activity leads to gigantism
Insufficient - effect epiphyseal cartilage and cause pituitary dwarfism
What does excessive growth hormone cause in adults and how?
Acromegaly
Increase in bone width by promoting periosteal growth
What effect can a deficiency in thyroid hormone have on newborns?
Cretinism - neurological and intellectual damage, and short stature
List some risk factors for osteoporosis
Genetics Gender Age Insufficient calcium intake Insufficient calcium absorption and vitamin D Lack of exercise Smoking
What happens in osteoporosis?
Bone density reduced to a point where there is a risk of fractures
Collagen framework and deposited minerals are broken down faster than they are being replaced
Medullary canals become enlarged, gaps develop in lamellae, bones become more fragile
How is achondroplasia inherited?
Autosomal dominant
What does achondroplasia result in?
Decreased endochondral ossification
Inhibited proliferation of chondrocytes in growth plate cartilage
Decreased cellular hyper trophy
Decreased cartilage matrix production
Describe the features of bones affected by rickets
Bone matrix fails to calcify properly - osteoid
Epiphyseal plate becomes distorted by body weight
Bones grow slowly and deformed
Bones are prone to fractures
Describe what happens to a bone affected by osteomalacia
Deficient calcification of recently formed bone results in bone softening
What is osteomalacia caused by?
A calcium deficiency
Which bone disease has medicolegal significance?
Osteogenesis imperfecta
What does a deficiency in vitamin d cause and why?
Rickets and osteomalacia
It is involved in absorption of calcium from the small intestine. Without calcium, the bone matrix cannot mineralise.
