Calcium and Phosphate Metabolism Flashcards

1
Q

What is osteoporosis

A

Loss of bone mass (mineral and organic matrix)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the causes of osteoporosis

A
  • Endocrine
  • Malignancy
  • Drug-induced
  • Renal disease
  • Nutritional
  • Age
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How is osteoporosis diagnosed

A

Measurement of bone mineral density (BMD)

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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What T-values are classified as normal and osteoporosis

A

Normal: -1 or above
Osteopenia: Lowe than -1 and greater than -2.5
Osteoporosis: -2.5 or lower
Severe osteoporosis: -2.5 or lower and presence of at least one fragility fracture

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the endocrine causes of osteoporosis

A
  • Hypogonadism – notably any cause of oestrogen
    deficiency
  • Excess glucocorticoids - endogenous or exogenous
  • Hyperparathyroidism
  • Hyperthyroidism
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the risk factors for osteoporosis

A
  • Low peak bone mass
  • Early menopause
  • Faster post-menopausal decline
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the 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)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is osteomalacia

A

Loss of bone mineralisation (termed rickets in children)

Soft and pliable like cartilage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the signs and symptoms of osteomalacia?

A
  • Permanent deformities in bone growth (rickets)
  • Diffuse aches and pains
  • Chronic fatigue
  • Weak bones
  • Low Ca, Pi
  • Elevated alkaline phosphatase
  • PTH may be elevated
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the causes of osteomalacia

A
  • Vitamin D deficiency (most common) - Lack of sunlight, lack of Vitamin D supplementation
  • Mutations leading to errors in vitamin D metabolism (rare)
  • Hypophosphataemia

Treatment most commonly involves ensuring adequate Vit D and Ca

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Describe 1a hydroxyls mutation

A
  • The enzyme converts Vit D into calcitriol, here that doesn’t occur due to enzyme mutation
  • Cause of Vit D dependant rickets type 1
  • Excess Vit D but low calcitriol concentration
  • High PTH
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Describe Vit D receptor mutation

A
  • Low Ca and Pi stimulate calcitriol production but the excess calcitriol has no effect as its receptor doesn’t work
  • Cause of Vit D dependant rickets type 2
  • High PTH
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Describe how vitamin D is regulated

A

Increased by:
- PTH
- Low Ca
- Low Pi

Decreased:

  • FGF-23 - Osteocytes secrete in response to rise in PO3
  • High Ca
  • High Pi
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is Autosomal dominant hypopho-phataemic rickets

A

Mutation leading to excess FGF-23 activity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is Oncogenic osteomalacia

A

Ectopic FGF secretion (benign tumour)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is FGF-23

A
  • A hormone secreted by osteocytes
  • Increases renal excretion
17
Q

what are the disorders involved with FGF-23

A
  • Oncogenic osteomalacia (tumour
    secreting FGF-23)
  • X-linked hypophophataemic rickets
  • Autosomal dominant hypopho- phataemic rickets (gain of function mutation)
18
Q

What is renal osteodystrophy

A

Spectrum of conditions associated with bone lesions in renal failure

19
Q

What are the characteristics of renal osteodystrophy

A
  • Impaired Pi excretion
  • High plasma Pi
  • Impaired Vit D activation
  • Low plasma Ca
  • PTH rises
  • Excess bone resorption
  • May be augmented by acidosis (impaired renal H+ excretion)