calcium and phosphate metabolism Flashcards

1
Q

what is osteoporosis and what are the 6 causes

A
is loss of bone mass( mineral and organic matrix)
causes are:
endocrine
malignancy
drug-induced
real disease
nutritional 
age
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2
Q

how is diagnosis of osteoporosis done

A

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

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3
Q

what are the t-score of normal, osteoporosis and severe osteoporosis

A

normal- -1 or above
osteoporosis- -2.5 or lower
severe osteoporosis - -2.5 or lower and presence of at least one fragility fracture

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4
Q

endocrine causes of osteoporosis

A
Hypogonadism — notably any cause of oestrogen 
deficiency 
Excess glucocorticoids — endogenous or 
exogenous 
Hyperparathyroidism 
Hyperthyroidism
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5
Q

Treatments for osteoporosis

A

• 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)

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6
Q

what is osteomalacia

A

loss of bone mineralization (termed rickets in children

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7
Q

signs and symptoms of osteomalacia

A
permanent deformations in bone growth (rickets)
diffuse aches and pains 
chronic fatigue
weak bones 
low Ca, Pi
Elevated alkaline phosphate 
PTH may be elevated
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8
Q

causes of osteomalacia

A

Vit D deficiency (most common)
mutation leading to error in vit d metabolism (rare)
hypophosphatemia

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9
Q

what 3 things increase calcitriol synthesis

A

PTH
Low Ca
Low Pi

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10
Q

what 3 things decrease calcitriol synthesise

A

FGF-23
High Ca
High Pi

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11
Q

what is the principle effect of FGF-23

A

increase phosphate excretion

it is secreted when there is high level of phosphate

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12
Q

What is FGF-23

A

a hormone secreted by osteocytes

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13
Q

Disorders to do with osteomalacia and hypophosphatemia

A

oncogenic (tumour secreting FGF-23)
X-linked hypophosphatemia rickets
autosomal dominant hypophosphatemia rickets (gain of function mutation)

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14
Q

what does decrease renal function cause in reference to phosphate

A

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

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15
Q

what is renal osteodystrophy

A

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)
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