calcium and phosphate metabolism Flashcards
what is osteoporosis and what are the 6 causes
is loss of bone mass( mineral and organic matrix) causes are: endocrine malignancy drug-induced real disease nutritional age
how is diagnosis of osteoporosis done
measurement of bone mineral density( BMD) using dual-energy X-ray absorptiometry( DEXA OR DXA scan)
T score= number of SDs below average for young adult at peak bone density
Z score=matched to age and/or group
what are the t-score of normal, osteoporosis and severe osteoporosis
normal- -1 or above
osteoporosis- -2.5 or lower
severe osteoporosis - -2.5 or lower and presence of at least one fragility fracture
endocrine causes of osteoporosis
Hypogonadism — notably any cause of oestrogen deficiency Excess glucocorticoids — endogenous or exogenous Hyperparathyroidism Hyperthyroidism
Treatments for osteoporosis
• Ensure adequate calcium and vit D intake, appropriate
exercise
• Postmenopausal: HRT— effects well established but safety
of long term treatment was questioned in early 2000s
Bisphosphonates — inhibit function of osteoclasts:
risedronate, alendronate
• PTH analogues
• Denosumab — human monoclonal antibody against RANK ligand
• Romosozumab— human monoclonal antibody against
sclerostin (very recent)
what is osteomalacia
loss of bone mineralization (termed rickets in children
signs and symptoms of osteomalacia
permanent deformations in bone growth (rickets) diffuse aches and pains chronic fatigue weak bones low Ca, Pi Elevated alkaline phosphate PTH may be elevated
causes of osteomalacia
Vit D deficiency (most common)
mutation leading to error in vit d metabolism (rare)
hypophosphatemia
what 3 things increase calcitriol synthesis
PTH
Low Ca
Low Pi
what 3 things decrease calcitriol synthesise
FGF-23
High Ca
High Pi
what is the principle effect of FGF-23
increase phosphate excretion
it is secreted when there is high level of phosphate
What is FGF-23
a hormone secreted by osteocytes
Disorders to do with osteomalacia and hypophosphatemia
oncogenic (tumour secreting FGF-23)
X-linked hypophosphatemia rickets
autosomal dominant hypophosphatemia rickets (gain of function mutation)
what does decrease renal function cause in reference to phosphate
decreased renal function means increase phosphate concentration. this leads to inhibition calcitriol production. Which leads to reduced calcium level and increased PTH levels which can cause bone erosion
what is renal osteodystrophy
its a blanket term used to cover spectrum of conditions associated with bone lesions in renal failure and these include:
- impaired Pi excretion
- high plasma Pi
- Impaired Vit D activation
- Low plasma Ca
- PTH rises
- Excess bone reabsorption
- May be augmented by acidosis (impaired renal H+ excretion)