Endo: Metabolic Bone Dz Flashcards
What is the function of osteoclasts?
What is the function of osteoblasts?
- Osteoclasts degrade bone using acid and collegenases
- Obsteoblasts lay down osteoid (unmineralized bone)
- Catalyze calcification if there is sufficient calcium and phosphorus
What are osteocytes?
Name 3 functions
- Terminally differentiated osteoblasts embedded in bone matrix
- Have mechanoreceptors that sense stress on bones
- Secrete sclerostin and FGF-23
- Orchestrate bone remodeling process
Describe the role of RANK (3)
- Osteocytes secrete RANK-Ligand
- RANK-L bind to RANK on osteoclasts to activate them
- Osteoprotegrin binds and sequesters RANK-Ligand (preventing activation of osteoclasts)
- RANK-L stimulates osteoclasts
- Wnt/B-catenin stimulate osteoblasts
- Sclerostin inhibits WNT/B-catenin pathway
Describe 2 ways of measuring the result of a bone density (DXA) scan.
- T-Score: Bone Mineral Density compared to young, healthy Caucasian woman at their peak BMD
-
Z-score: BMD compared to age & gender matched controls
- Useful in younger men and pre-menopausal women
Define osteoporosis
Impaired bone strength that predisposes it to fractures
Name 3 ways to diagnose Osteoporosis
- DEXA T-score of -2.5 or lower
- Fragility fracture
- Greater than 20% Major Osteopathic Fracture risk or greater than 3% hip fracture risk
What demogrpahic is at highest risk for osteoporosis?
Why does low BMI increase osteoporosis risk?
- Highest risk: Caucasian women with positive family history and early menopause
- Low BMI (less than 20) increases risk b/c there is less weight-dependence during every day activities
What are the 2 components of bone strength?
- Bone density (assessed with DEXA)
- Bone quality
Name one drug that causes significant bone resportion
Glucocorticoids
What is the effect of estrogen on bones?
What effect does menopause have?
- Estrogen promotes osteoblast survival and apoptosis of osteoclasts (promotes overall bone strength)
- Menopause = estrogen deficiency, increases osteoporosis risk
What are two common Ca supplements?
Which is preferable?
- Calcium carbonate
- Highest calcium, so generally preferred
- Calcium citrate
- Used if low gastric acid production (using PPI, H2 blocker)
Define Osteomalacia and Rickets
- Impaired mineralization of osteoid (due to inadequate calcium or phosphate)
- Osteomalacia = adult version
- Rickets = kids version
What is the most common cause of osteomalacia/rickets?
Mechanism?
Vitamin D disorders
Low Vitamin D -> low serum Ca -> increased PTH -> decreased phosphate
What would be the values of Ca, Phos, PTH, and ALP in osteomalacia and rickets?
- Low Ca, low Phosphate
- Elevated PTH
- Elevated ALP
What cells release FGF-23?
What is the function of FGF-23?
- FGF-23 released by osteocytes
- It increases phosphate excretion in urine and decreases phosphate absorption in gut (overall decreases serum phosphate)
Is osteomalacia/rickets painful?
Is osteoporosis?
- Osteomalacia/rickets often is painful
- Osteoporosis is not painful
Deformities of rickets? (3)
- Bowing of legs
- Widened wrists
- Rachitic rosary
Define Paget’s disease of bone.
Where does it occur?
- Idiopathic condition of excessive and unregulated bone remodeling
- Disease process is localized to one or a few sites
Characteristics of the bone in Paget’s disease (3)
- Increased osteoclast number and activity
- Disorganized woven and lamellar bone
- Hypervascular
Paget’s symptoms (4)
- Pain
- Deformity
- Fractures
- Osteoarthritis (secondary to altered gait)
3 potential complications of Paget’s disease of bone
- CN compression (especially CN 8, causing deafness) or spinal cord compression
- High output HF due to atriovenous shunts
- Increased risk of osteogenic sarcoma
Describe the clinical course of Paget’s disease
- Only osteoclast activity
- both osteoclast and osteoblast activity
- ONLY osteoblast activity (sclerosis)
X-Rays in Paget’s disease? (3)
Bone scan in Paget’s? (1)
- X Ray
- Osteolytic lesion
- Osteosclerotic lesions nearby
- Thickened cortex and trabecula
- Bone scan
- Focal area of intense uptake
