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MBD > Calcium And Phosphate Metabolisms > Flashcards

Calcium And Phosphate Metabolisms Flashcards

1
Q

Describe the function of PTH

A

Prolonged, high levels will promote bone remodelling

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2
Q

Describe the function of FGF23

A

Decreases phosphate and vitamin D (so Calcium)

  • inhibits the formation of active vitamin D3
  • will increase phosphate excretion
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3
Q

In response to what is FGF23 secreted?

A
  • High phosphate levels
  • Will cause the excretion and so the decrease in phosphate
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4
Q

Describe the function of Vitamin D

A
  • Promotes calcium absorption in the gut
  • So deficiency in Vitamin D may cause osteomalacia
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5
Q

Describe what osteoporosis is

A

Loss of both the cortical and trabecular bone mass - loss of the mineralisation of bone AND loss of the organic bone matrix (collagen)

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6
Q

Name some causes of osteoporosis?

A
  • age (endocrine)
  • malignancy
  • drug induced
  • renal disease
  • nutritional
  • age
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7
Q

How do we diagnose osteoporosis?

A

Measure bone mineral density and compare it to cut-off points

  • Is done with dual-energy X-ray absorptiometry (DEXA or DXA scan)
    • gives a T score and a Z score which are part of a statistical test where if the T score is lower than -2.5 then = diagnosed osteoporosis
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8
Q

What is the T score?

A

Number of standard deviations below average for young adult at peak bone density

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9
Q

What is osteopenia?

A

When the T score is between -1 and -2.5 so it is not enough for osteoporosis diagnosis (less than -2.5)

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10
Q

What is the Z score?

A

Matched to age and/or group

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11
Q

Name some endocrine causes of osteoporosis

A
  • Hypogonadism (especially any cause of oestrogen deficiency but also seen in men due to no conversion of androgen → oestrogen peripherally)
  • Exogenous glucocorticoids or also endogenous (think, Cushing’s)
  • Hyperparathyroidism (excess resorption)
  • Hyperthyroidism
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12
Q

How can we treat osteoporosis?

A
  • Ensure adequate calcium and vitamin D intake, appropriate exercise
  • HRT for Postmenopausal women
  • Biphosphonates
  • PTH analogues
  • Denosumab
  • Romosozumab
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13
Q

What is romosozumab?

A

Human monoclonal antibody against sclerostin

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14
Q

What is denosumab?

A

Human monoclonal antibody against RANK ligand

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15
Q

What do bisphosphonates do?

A

Inhibits function of osteoclasts

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16
Q

What is osteomalacia?

A

Loss of bone mineralisation (this is different to osteoporosis as osteoporosis is a loss of bone mineralisation AND the loss of the organic bone matrix)

  • so makes bone soft and malleable - known as rickets in children
17
Q

What is loss of bone mineralisation called in children?

A

Rickets

18
Q

What are the symptoms of osteomalacia?

A
  • Diffuse aches
  • Chronic fatigue
  • Weak bones
19
Q

What deficiencies cause osteomalacia?

A
  • Deficiency in Ca or Phosphate (or PTH nmy be elevated as well as in osteoporosis)
20
Q

What is a marker for osteomalacia?

A

Alkaline phosphatase

21
Q

What are the causes of osteomalacia?

A
  • Vitamin D deficiency (most common)
  • Mutations leading to errors in vitamin D metabolism
  • Hypophosphataemia
22
Q

Name the immediate precursor to active Vitamin D

A

25 Hydroxy Vitamin D3

23
Q

What is vitamin D increased by?

A
  • PTH
  • Low calcium
  • Low phosphate
24
Q

What is vitamin D decreased by?

A
  • FGF-23
  • High calcium
  • High phosphate
25
Q

Name 2 rare mutations that can cause osteomalacia

A
  • 1-alpha hydroxylase mutation
  • Vitamin D receptor mutation
26
Q

How does the alpha hydroxylase mutation work?

A

no/low conversion of immediate precursor to active vitamin D3 (calcitriol)

27
Q

How does the Vitamin D receptor mutation work?

A

No binding of vitamin D3 to its receptor so increased production of vitamin D3

28
Q

What is type 1 vitamin D dependant rickets caused by?

A

An alpha hydroxylase mutation

29
Q

What is type 2 vitamin D dependant rickets caused by?

A

Vitamin D receptor mutation

30
Q

What does type 1 vitamin D dependant rickets cause?

A

Low calcium and phosphate

31
Q

What does type 2 vitamin D dependant rickets cause?

A

High calcitrol (vit D) production

32
Q

What is renal osteodystrophy?

A

Spectrum of conditions associated with bone lesions in renal failure

33
Q

What are the lab signs of renal osteodystrophy?

A
  • Low plasma calcium
  • PTH rises
  • Excess bone resorption
34
Q

What causes renal osteodystrophy?

A
  • Impaired phosphate excretion
  • Impaired vitamin D activation
35
Q

In renal disease (CKD) describe the levels of Ca, P, Vit D precursor, Vit D and PTH

A
  • low Ca
  • high P
  • normal 25 OH D3
  • low active D3
  • very high PTH
35
Q

What is the most common cause of hypercalcaemia in non-hospitalised patients?

A

Hyperparathyroidism

MBD (23 decks)

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