Bone, bone disorders and arthritis Flashcards
What is bone formed of?
Organic 1/3 - type 1 collagen + other proteins
Inorganic 2/3 - hydroxyapatite
Cellular structure of bone?
Osteoblasts
Osteocytes
Osteoclasts
Osteoprogentior cells
What do osteoblasts do?
- Produce bone by secreting collagen matrix + calcium salts
Where do osteocytes come from?
- Once osteoblasts lay down lamellar bone then get trapped in their lacunae and become osteocytes
What do osteocytes do?
Maintain bone production and secrete enzymes into matrix to maintain mature bone
What are osteoprogenitor cells? Where found?
- In bone marrow
- Responsible for producing new osteoblasts and osteocytes
- Osteoblasts and osteocytes unable to undergo mitosis
What do osteoclasts do?
- Resorb bone
How do osteoclasts resorb bone?
Release proteolytic enzymes and hydrochloric acid which breakdown the bone
List some chemical messengers associated with bone resorption
Vit D
Para + thyroid hormones
Growth hormones
Ca 2+
List some chemical messengers associated with bone formation
Oestrogen
Calcitonin
Androgens
What happens when metabolic homeostasis not maintained?
Bone formation > bone resorption
OR
Bone resorption > bone formation
What is 1st type of bone laid down?
Woven bone / immature bone
What is immature / woven bone remodelled into?
Secondary bone
What 2 types of bone is secondary bone divided into?
Cortical / lamellar bone - 80%
Cancellous / trabecular / spongy bone - 20%
Describe structure of cancellous bone
- Low density
- Spongy appearance
Describe structure of cortical bone
- Dense
- Compact
- Contains bone marrow
What is role of vit D in bone metabolism?
Increases calcium and phosphate circulating in body
How is vit D obtained?
Sun exposure
Diet - oily fish, red meat, egg yolks
What does a deficiency in vit D lead to in adults / children?
Children - rickets = bowing of long bones
Adults - osteomalacia = softening of bones, bone aches / pains / fractures
Where does parathyroid hormone come from?
Thyroid, bow tie shape gland, 4 parathyroid glands which secrete PTH
What is the role of PTH in bone resorption?
- Promotes kidneys to make vit D
What 2 types of disease are due to malfunctioning PTH gland?
- Primary hyperparathyroidism
- Secondary hyperparathyroidism
What causes primary hyperparathyroidism, what are the effects?
- Due to adenoma (benign glandular tumour) of a PTH gland
- Increases PTH level
- Increases Ca2+ (hypercalcaemia)
- Promotes bone resorption
What causes secondary hyperparathyroidism, what does it lead to?
- Chronic renal disease gives urinary calcium
- To compensate PTH gland secretes more PTH
- Promotes bone resorption
- Leads to kidney failure - renal osteodystrophy
How might hyperparathyroidism present facially?
- In jaws
- Central giant cell granuloma
How might hyperparathyroidism present facially?
- In jaws
- Central giant cell granuloma
How does calcium homeostasis occur? (Briefly)
- PTH secreted
- Ca 2+ and PO4 3- resorbed and Ca2+ reabsorbed from kidneys
- Ca 2+ rises
- Calcitonin secreted
- Ca2+ excreted in urine and deposited in skeleton
- Ca 2+ falls
- Causing PTH to be secreted
What are the 3 stages of healing bone fractures?
- Early inflammatory
- Repair
- Remodelling
What happens during early inflammatory stage?
- 1st 2 weeks
- Bleeding at fracture = form haematoma
- Inflammatory cells and fibroblasts at clot
- BVs enter haematoma forming granulation tissue
What happens during repair stage?
- Takes 4-5 weeks
- Granulation tissue become callus
- Primary callus becomes secondary callus
- Osteoid secreted into area forming new bone
- Proteases degrade ECM
- Collagen fibres enter area
- New woven bone created at fracture