CMS - bone & joints 1&2 Flashcards
How does bone growth change with age?
Different at stages of aging:
rapid in infants and slows as we age into childhood.
There is a growth spurt during adolescence.
By age 18, adult bone levels have been achieved.
What are the types of bone?
Cortical / compact / lamellar bone - outer layer
Cancellous / trabecular bone - inner layer. Contains bone marrow.
Woven bone - immature / pathologic bone. Higher vol of osteocytes.
What is Cortical / compact / lamellar bone ?
Bone that forms the shaft of long bones and outer layer of flat bones.
Highly organised.
Arranged in concentric rings of bones, adapted to withstand strain of pressure.
What is cancellous / trabecular bone ?
Found in flat bones and end of long bones.
Interconnected network of rods and plates of bones.
Allows for resistance of compression of loads.
Main site of turnover where mineral turnover occurs.
What is woven bone ?
A more disorganised type of bone.
Appears in early years or fracture sites. E.g. when sustaining an injury.
Also present in diseases with high bone turnover e.g. Paget’s disease.
What makes bone mineralisation important?
If the osteoid (collagen) is not mineralised, it would be soft and “bendy”, leading to bone disorders
What is hydroxyapatite?
Bone mineral
What are bones made of?
Calcified connective tissue
Matrix of collagen fibres containing osteocytes.
Type 1 collage (osteoid)- main protein forming parallel lamallae - offers different densities.
Non-collagen proteins e.g. osteopontin (bone remodelling) and osteocalcin, fibronectin (tissue repair)
Within the bone matrix, Ca and phosphate minerals are found abundantly - adds strength and density to the structure.
What are the receptors found on osteoblasts?
Express receptors for (Parathyroid hormone “PTH”, oestrogen, glucocorticoids, vitamin D, inflammatory cytokines and TGF beta) which influence bone modelling
An _______ is derived form local mesenchymal stem cells and synthesises bone. What happens during apoptosis?
Osteoblast
After they die, osteocytes will line the bone in its’ place.
What is an osteocyte?
cells derived from osteoblasts.
Activate bone formation by responding to mechanical strain. Key roles within bone resorption.
What is the bone cell involved in bone resorption?
Osteoclast
What are the functions of osteoclasts?
Rich in Alkaline phosphatase - regulates bone mineralisation.
Also express receptors for hormones etc that influence bone remodelling for instance - oestrogen, PTH, glucocorticoids, vit D, inflammatory cytokines and TGF-B (transforming growth factor beta – tumour suppressor).
Bone formation, metabolism and blood Ca levels are affected by _______________, ________________ and ___________.
parathyroid hormone, Vit D and calcitonin.
What are the effects of bone morphogenic proteins?
These proteins affect bone formation - available as recombinant proteins, they are sometimes used in grafting procedures or regeneration procedures in oral surgery.
The parathyroid hormone is regulated by blood ________, ____________, and ____________ levels.
blood calcium, vit D levels and phosphate levels.
When PTH is secreted, intestinal transport of calcium & phosphate are _________, and removal of Ca from bones is ____________.
Ca & phosphate promoted
Removal of CA from bone is accelerated
Dietary Vit D is fat soluble, and absorbed from the upper small intestine – which promotes _____________________________________________________________.
intestinal absorption of Ca and phosphate.
Vit D is also synthesised in the skin from UV sunlight. How is it converted from the skin?
Vit D in the skin is converted by the liver and then kidney into the most active metabolite.
Skin: 7-dehydrocholesterol
-> Cholecalciferol (Vit D3)
-> Liver: 25- hydroxycholecalciferol
-> Kidney: 1,25 - dihydroxycholecalciferol
How is Vit D from food converted in the body?
Ergosterol (Vit D2) is converted in the Liver to 25- hydroxycholecalciferol
-> then Kidney: 1,25 - dihydroxycholecalciferol
What is the active metabolite of Vit D, and its role in bone?
1,25 - dihydroxycholecalciferol
- controls bone metabolism & enhances Ca absorption.
The process is enhanced by the parathyroid hormone and low phosphate levels.
What is the role of calcitonin in bone?
apposes the action of PTH & lowers blood Ca levels mainly by promoting the deposition of Ca in the bones.
Which other hormones may affect bone formation & metabolism?
Growth hormone and oestrogen hormones
How does blood Ca level affect on the activity of Parathyroid hormone?
Decreased Ca in blood will stimulate parathyroid gland to secrete PTH (increased), leading to:
1) ↑ Osteoclast bone resorption (taking Ca from bone)
2) ↑ Synthesis of 1,25- dihydroxyvitamin D3 (active D3 to absorb Ca and PO4 from intestines)
3) ↑ Intestinal Ca absorption (taking Ca from intestines)
4) ↑ Renal tubular resorption Ca (taking Ca from kidneys)
So increasing Ca in the blood