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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?

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
Name 2 rare mutations that can cause osteomalacia
* 1-alpha hydroxylase mutation * Vitamin D receptor mutation
26
How does the alpha hydroxylase mutation work?
no/low conversion of immediate precursor to active vitamin D3 (calcitriol)
27
How does the Vitamin D receptor mutation work?
No binding of vitamin D3 to its receptor so increased production of vitamin D3
28
What is type 1 vitamin D dependant rickets caused by?
An alpha hydroxylase mutation
29
What is type 2 vitamin D dependant rickets caused by?
Vitamin D receptor mutation
30
What does type 1 vitamin D dependant rickets cause?
Low calcium and phosphate
31
What does type 2 vitamin D dependant rickets cause?
High calcitrol (vit D) production
32
What is renal osteodystrophy?
Spectrum of conditions associated with bone lesions in renal failure
33
What are the lab signs of renal osteodystrophy?
* Low plasma calcium * PTH rises * Excess bone resorption
34
What causes renal osteodystrophy?
* Impaired phosphate excretion * Impaired vitamin D activation
35
In renal disease (CKD) describe the levels of Ca, P, Vit D precursor, Vit D and PTH
* low Ca * high P * normal 25 OH D3 * low active D3 * very high PTH
35
What is the most common cause of hypercalcaemia in non-hospitalised patients?
Hyperparathyroidism

MBD (23 decks)

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