Metabolic bone diseases Flashcards
List the four stages of new bone formation over the old bone.
- Activation
- Resorption
- Reversal phase
- Formation
What does activation phase do?
Osteoclasts are recruited to the surface of the bone.
What does resorption phase do?
Osteoclasts generate acidic microenvironment between cell and surface of the bone by dissolving mineral content of bone.
What does reversal phase do?
Osteoclasts undergo apoptosis and osteoblasts are recruited to the surface of the bone.
What does formation phase do?
Osteoblasts deposit collagen and mineralised bone to form new bone.
What is osteoporosis?
Active remodelling of bone in response to mechanical stresses and hormonal changes. Bone remodelling begins with bone resorption.
Osteoclasts resorb bone matrix and initiate apoptosis followed by coupling signals sent to osteoblasts. Osteoblasts synthesise bone matrix causing mineralisation. It is initiated by cytokines IL-1, 6, 11 and calcitrophic hormones such as PTH, 1,25-dihydroxy vitamin D, calcitonin and oestrogen.
How does post-menopausal bone resorption occur?
Oestrogen deficiency impairs the normal cycle by increasing osteoclastic activity (bone resorption).
Age-related decrease in calcium starts after 60s, associated with malabsorption.
What is the criteria for osteoporosis on the BMD scan? (using T score)
T score:
-1.0 to +2.5 is normal
-2.5 to -1.0 is osteopenia
≤-2.5 is osteoporosis
What is osteomalacia?
Osteomalacia occurs when there is a defect in bone mineralisation process. It results from absence of one or more factors needed in osteogenesis: calcium, phosphate, vitamin D.
what is function of vitamin D in osteogenesis?
It maintains calcium and phosphate homeostasis due to actions on the GI tract, kidneys, bones and parathyroid glands. Low activated vitamin D levels may contribute to secondary hyperparathyroidism.
What is the function of hyperparathyroidism?
Low calcium stimulates parathyroid hormone (PTH) secretion, whereas high calcium levels suppress PTH secretion.
Excessive PTH leads to bone resorption with cortical bone affected more than cancellous bone.
PTH causes kidneys to reabsorb calcium and convert vitamin to more active form of vitamin D, increasing GI uptake of calcium.
What is Paget’s disease of bone?
Localised areas of metabolic hyperactivity of bone. Osteoclasts cause large resorption in pits and cavities, and osteoblastic activity is dramatically increased in pagetic lesions. Osteoblastic activity is so rapid that newly-formed bone is not organised and remains irregular.
Bone is weaker because the Haversian systems are not organised parallel to the lines of disease.
What changes on X-Ray can you see with Paget’s disease?
Lytic lesions (commonly skull), occasional fractures, areas of dense uptake.
Serum: normal calcium, P1NP elevated CTX initially elevated.
What is renal osteodystrophy?
It occurs when kidney fails calcium and phosphate homeostasis in the blood. There is high levels of phosphate and low calcium with low activated levels of vitamin D. It is common in people with kidney disease and affects dialysis patients.
It may be asymptomatic, but it can also present as: bone pain, joint pain, bone deformation, bony fractures.
