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Path - chempath > Calcium metabolism > Flashcards

Calcium metabolism Flashcards

1
Q

Name 3 Common metabolic bone disorders

A

○ Osteoporosis
○ Osteomalacia/Rickets
○ Paget’s disease

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2
Q

An ___ in calcium will cause a failure of depolarisation

A

increase

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3
Q

A ___ in calcium will cause a very trigger happy neurological system leading to epilepsy and fits

A

decrease

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4
Q

99% of calcium stored in?

A

bone

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5
Q

In what forms is calcium found most abundantly?

A

Free (ionised) - 50% - BIOLOGICALLY ACTIVE

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6
Q

In what forms is calcium found?

A
  1. Free (ionised) - 50%
  2. Protein-bound - 40% - bound to albumin
  3. Complexed - 10% - citrate/phosphate
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7
Q

A patient has liver disease which calcium reading is most representative of their true calcium? why?

A

corrected calcium

low albumin can cause low total calcium reading

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8
Q

free calcium is what % of total serum calcium?

A

50%

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9
Q

how to calculate corrected calcium?

A

Total serum calcium + 0.02

x (40 - albumin)

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10
Q

PTH obtains calcium from which THREE sources?

A

○ Bone (osteoclast activation)
○ Gut (absorption)
○ Kidneys (calcium reABsorption and renal 1a-hydroxylase activation)

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11
Q

what is the role of 1a-hydroxylase in increasing calcium ?

A

it results in the production of calcitriol (1,25-dihydroxycholecalciferol) - from kidney

which helps absorb calcium from gut

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12
Q

2 hormones involved in calcium homeostasis?

A

PTH

Vitamin D3 (steroid hormone) (1,25)

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13
Q

25-OH vit d3 is made where?

A

liver

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14
Q

calcitriol 1,25-dihydroxycholecalciferol D3 is made where?

what’s the trigger?

A

kidney

trigger - PTH

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15
Q

which vitamin d3 is the only active form?

A

calcitriol 1,25-dihydroxycholecalciferol

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16
Q

when you measure blood vitamin d which form is it usually?

A

25-OH D3

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17
Q

which is the vitamin d from plants?

A

D2 is from plants – ergocalciferol.

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18
Q

when UV hits the skin how is vitamin d made?

A

converts 7-dehydrocholesterol to

cholecalciferol (D3)

19
Q

which enzyme catalyses the conversion of cholecalciferol to 25-hydroxycholecalciferol

and where?

A

25-hydroxylase in the liver

20
Q

why can sarcoid cause high calcium?

A

1a hydroxylase expression in lung

21
Q

what do PTH and vit d do to Phosphate?

A

vit d - Increased PO4 absorbed from gut

PTH - PO4 loss in urine

22
Q

differnence between osteoporosis and osteomalacia?

A

osteoporosis - normal structure but less bone

osteomalacia - abnormal structure as low calcium due to vitamin d deficiency

23
Q

2 types vit d deficiency?

A

Childhood - Rickets

Adults - Osteomalacia

24
Q

Biochemical picture in osteomalacia?

A

□ Low Calcium
□ Low Phosphate
□ High ALP - increased resorption

§ Looser’s zones - pseudofractures

25
Q

symptoms in rickets vs osteomalacia?

A 
Rickets
       § Bowed legs 
	§ Costochondral swelling 
	§ Widened epiphyses at wrists 
	§ Myopathy 
- no fracture risk

osteomalacia
bone and muscle pain, fracture risk

26
Q

what is secondary hyperparathyroidism ?

A

Vitamin D deficiency which leads to osteoclasts eating up the bone to liberate calcium and normalise the plasma calcium levels

27
Q

why can kidney failure lead to osteomalacia?

A

insufficient 1a hydroxylase = vit d deficiency

28
Q

biochemical picture in osteoporosis?

A

□ Normal Calcium

□ Normal Phosphate

29
Q

where do fractures occur in osteoporosis?

A

wrist (Colle’s), hip and spine

30
Q

Hyperthyroidism and Cushing’s syndrome can cause osteoporosis because?

A

increased catabolism

31
Q

major cause of osteoporosis in women?

A

oestrogen loss in menopause

32
Q

treatment for osteoporosis?

A

○ Drugs:
§ Vitamin D
§ Bisphosphonates - reduce breakdown
§ Teriparatide (PTH derivative) - build bone

		§ Strontium (anabolic and anti-resorptive)
		§ HRT (oestrogens) 
		§ SERMs (e.g. raloxifene) - agonist at bone
33
Q

Mmemonic for hyperPTH hypercalcaemia?

A

BONES: path bone disease
STONES
MOANS: constipation, pancreatitis
GROANS - psych; confusion

34
Q

patients presents with Polyuria / polydipsia
Constipation
Neuro – confusion / seizures / coma

what do they have?

A

hypercalcaemia

symptoms not unless calcium is at least 3

35
Q

patient with symptoms of hypercalcaemia what is first thing to do?

A

Is it a genuine result (repeat)

total vs adjusted

then measure PTH levels

36
Q

High Calcium High PTH is ?

A

primary HyperPTH

37
Q

High Calcium Normal PTH is ?

A

Cancer
sarcoid
Vit d overdose
thyrotoxicosis

38
Q

what is PO4 in primary HyperPTH?

A

LOW

39
Q

what condition is there hypercalceamia with no symptoms?

what is the aetiology?

A

familial benign hypercalcaemia,

mutation in the CaSR

40
Q

most common cause of hypercalceamia?

A

primary HyperPTH

41
Q

NON PTH related hypercalcaemia.

Which cancers can cause hypercalcaemia?

A

Bone metastases (eg breast Ca)

small cell lung Ca - PTHrP release

Haematological malignancy (eg myeloma)
cytokines
42
Q

patient taking Chlorothiazide is brought in with constipation and flank pain radiating from loin to groin.

on examination he does not know the day or year.

what could be the problem?

how to manage?

A

He is taking Thiazide diuretics which is causing symptoms of hypercalcaemia through renal Ca2+ transport.

Management;

  1. Fluids+++
  2. Bisphosphonates eg zolendronic acid (if cause known to be cancer) otherwise avoid
43
Q

mechanism of hypercalcaemia of malignancy?

A

the tumours:

80% - production of PTHrp
20% - osteolytic bone mets
1% - pth producing tumours, vit d producing tumours and others

44
Q

side effects of bisphosphonates?

A

osteonecrosis of jaw and teeth

acute renal failure

Path - chempath (25 decks)

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