13 - Bone Formation, Fracture And Repair Flashcards
What is the function of bone?
- Mechanical: Protection of organs, Maintain shape, Levers for movement
- Synthetic: Haemopoiesis
- Metabolic: Mineral and fat storage (Ca/P/yellow bone marrow), Acid-base homeostasis (absorb or release alkaline salts)
Describe endochondral ossification.
- Bony collar formation
- Cavitation
- Periosteal Bud Invasion
- Diaphysis elongation
- Epiphysis elongation
What are the zones at the epiphyseal growth plates?
EXPLAIN ALL STEPS - CHECK GOOGLE
What is interstitial growth?
Growth from the middle, increases length, can only occur when growth plates are there, not like appositional which can occur throughout life
How is bone remodelled?
- Remodels down stress lines by osteoclasts and blasts
- Osteocytes arrange in concentric lamellae
Explain the process of intramembranous ossification.
What is osteoid?
Osteoblasts secreting extracellular matrix containing type I collagen
Unmineralised organic content of bone
What is a resorption canal?
Tube running parallel to osteons containing osteoclasts
What does immature bone look like?
Osteocytes randomly arranged rather that in concentric circles
What is the difference between appositional and interstitial growth?
Appositional = remodelling
Interstitial = elongating
Label the following diagram.
What is the structure of mature cancellous and cortical bone?
What are the different forces that can act on bone and what fractures can they cause?
Why does bone resist fracture?
- Great tensile and compressive strength, good flexibilty
- Force lines through cortical bone
- Lamellae are thought to be able to slip relative to one another until excessive force applied
What happens to bones when you are immobile?
Osteoblasts rely on the stress of mobility and weight bearing to perform their function. During immobility and bedrest, the process of building new bone stops, but the osteoclasts still break down bone, resulting in a loss of bone density, leaving the bone structure soft and weak.
What factors affect bone stability?
What does parathyroid hormone do?
What does calcitonin do?
Prevent bone resorption, binds to parathyroid receptors and prevents parathyroid being released
Describe calcium homeostasis with hormones
Low calcium:
- Kidneys release calcitriol (activated Vitamin D3)
- This increases absorption from SI and kidney tubules
- Increases bone resorption by osteoclasts
- Inhibits calcitonin production
How does a bone fracture repair itself?
1. Haemotoma = granulation tissue
2. Fibrocartilaginous Tissue = granulation tissue forms
3. Bony Callus = endochondral ossification forms spongy bone
4. Bone remodelling = spongy converted to cortical bone. Bone only remodels with stressors so important not to immobilise
What is the mechanism of bone disease of osteogenesis imperfecta?
What is rickets?
- Vitamin D deficiency (lack of sunlight or diet)
- Ineffective mineralisation =
- Weakened soft bones prone to fracture
- Bowed legs as bones can’t suppport weight
- Short and painful
What is osteomalacia?
- Adult rickets, increase in bone resorption due to lack of vitamin D
Causes:
- Protection from sunlight (muslim ladies)
- Kidney Disease (activates vit d)
- Surgery on stomach or intestine
- Drugs like phenytoin preventing vit d absorption
- Common in pregnant women
What does Vitamin D do?
What is osteoporosis and what are the different types?
- Loss of bone matrix, loss of structural density and bone demineralisation
- Increased bone resorption but lowered osteoblast numbers so HOLES IN TRABECULAE
- Over age 50, mainly women
How do you diagnose osteoporosis?
DEXA scan
Dual energy x-ray absorption to measure bone density
Where do fractures most likely occur in osteoporosis?
Spine, Hip, Wrist
Osteoporosis, osteomalacia, osteogenesis imperfecta and rickets all susceptible to bone fractures
What are risk factors for osteoporosis?
- Insufficient calcium intake (700mg for pm women)
- Age
- Lack of exercise
- Genetics
- Smoking (women not men)
What is achondroplasia?
- Autosomal dominant dwarfism
- Mutation in FGFR3 gene which normally stimulates collagen formation from cartilage
- Endochondral ossification poor so long bones don’t grow
- Intramembranous ossification not affected so short bones occur
- Normall have flattened nose, enlarged skull and normal trunk
Why are some babies born with achondroplasia and their parents dont have it?
- Even though autosomal dominant, mutation may have occurred during meiosis of the gametes
- Homozygous is fatal
What is pituitary dwarfism?
- Lack of growth hormone from pituitary gland during years individual normal grows
What is gigantism?
- Increase growth hormone from pituitary gland during growth years so very tall individual
What happens if you have elevated growth hormones in adult?
Bone length will not increase as no epiphyseal growth plates,but bone width will
Acromegaly
What is the issue with neonatal hypothyroidism and how can it be treated?
- Lead to infant with permanent neurological and intellectual damage and short stature. (cretinism)
- Administer levothyroxine (T4)
