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Osteoporosis
- Brittle bone
- Imbalance between resorption and bone building processes
- Bone matrix is appropriately mineralized
- Normal bone, just less of it
- Because the balance is tipped more towards resorption (which affects both the mineral and organic components of bone equally) so amount of bone matrix relative to bone mineral is normal
- Lab results
- Low bone mineral density
- Normal Ca
- Normal PO4
- 4 high yield example causes for osteoporosis where there is an imbalance between resorption and building
- Woman undergoes menopause, estrogen (which causes osteoclast apoptosis, increases OPG and decreases RANKL) decreases, results in increase in bone resorption
- Glucocorticoids inhibit OPG production and also stimulate RANKL production, results in increase in bone resorption
- Thin individuals or small frame increase risk for osteoporosis possibly due to a lower peak bone mineral density or sub-optimal mechanical weight load on bones (weight on bones is needed for bone remodeling), balance is therefore tipped towards osteoclastic activity
- Immobile individuals are not placing any mechanical load on their bones which is needed for healthy bone remodelling, balance is tipped towards osteoclastic activity
Osteomalacia
- Soft bone
- Insufficient Ca and phosphate to mineralize newly formed osteoid (typically from vitamin D deficiency)
- Bone matrix is inappropriately mineralized
- Abnormal bone, normal amount of bone
- More bone matrix (i.e. osteoid), less bone mineral (i.e. Ca, PO4)
- Lab results
- Low bone mineral density
- Low Ca (consequently high PTH)
- Low PO4
- Why is bone soft in osteomalacia?
- Well to understand this, let’s understand what is bone
- Bone is made up of an organic and inorganic component
- Organic: osteoid also known as bone matrix (primarily made of type I collagen) – gives bone resistance to stretching
- Inorganic: hydroxyapatite crystals (primarily Ca and PO4) – gives bone resistance to compression
- In osteomalacia, we have bone that is deficient in the inorganic component which we say gives the bone its hardness and resistance to compression, therefore the bone becomes soft!