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regub > 10. Calcium Metabolism and Disorders of Calcium Balance > Flashcards

10. Calcium Metabolism and Disorders of Calcium Balance Flashcards

1
Q

Why is calcium absorption in the GIT considered incomplete?

A

Requires activated vitamin D

Calcium containing salts aren’t absorbed

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2
Q

What happens to the calcium that is ingested?

A

1/2 is absorbed
Some lost in stool
In a steady state, remaining calcium is excreted in urine

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3
Q

What form is calcium stored as in bone?

A

Hydroxyapatite

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4
Q

How is calcium reabsorbed in the kidneys?

A

Only ionised calcium is filtered
Some reabsorbed passively
Active under endocrine control

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5
Q

What are the forms of calcium in circulation?

A

40% bound to albumin
15% bound to citrate, nitrate and phosphate
45% ionised/free

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6
Q

How does hypoalbuminaemia affect calcium balance?

A

Less bound to albumin

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7
Q

How does alkalosis affect calcium balance?

A

More bound calcium

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8
Q

Which hormone reacts first to a dip in calcium?

A

PTH: peptide

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9
Q

What effect does PTH have on the GIT?

A

Increases absorption of calcium and phosphate

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10
Q

What is the overall effect of PTH?

A

Increase calcium but reduce phosphate

‘Phosphate Trashing Hormone’

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11
Q

What effect does PTH have on bone?

A

Increases number and activity of osteoclasts

Increased bone resorption

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12
Q

What effect does PTH have on the kidneys?

A

Increase calcium absorption in the distal nephron
Increase 1a hydroxylase enzyme activity > increased calcitriol
Increased excretion of phosphate into urine

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13
Q

What effect does calcitriol have on the GIT?

A

Increased TRPV6 channels to increase calcium absorption

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14
Q

What effect does calcitriol have on the bone?

A

Bind to osteoblasts and osteocytes

Increase pyrophosphate levels which inhibits calcium uptake into bone

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15
Q

What effect does calcitriol have on the kidneys?

A

Increase TRPV5 channels and calbindin D28K
-increases resorption in distal tubule
No loss of phosphate

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16
Q

What are the clinical effects of hypercalcaemia?

A 
Stones
Bones
Groans
Psychiatric overtones
Short QT interval
Dehydration (diuretic effects)
Chronic kidney disease due to deposition
Nephrogenic diabetes insipidus (reduced response to ADH)
Type 1 renal tubular acidosis
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17
Q

What are the causes of hypercalcaemia?

A

PTH excess
Vitamin D excess
Bone turnover
Thiazide diuretics

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18
Q

What is the most common cause of hypercalcaemia in asymptomatic outpatients?

A

Hyperparathyroidism

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19
Q

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

A

Malignancy

Immobility

20
Q

Give causes of PTH excess

A

Hyperparathyroidism
Familial hypocalciuric hypercalcaemia
PTHrP secreting cancer
Lithium

21
Q

What diseases can cause vitamin D excess?

A

Granulomatous disorders can secrete ectopic calcitriol

eg. sarcoid, TB

22
Q

What are the reasons for hormone independent bone turnover?

A

Bone mets
Paget’s disease
Hyperthyroidism
Immobilisation

23
Q

How is a diagnosis of hypercalcaemia made?

A

Correct for hypoalbuminaemia
Physical exam and CXR
PTH level
-if suppressed check PTHrP, calcidiol, calcitriol

24
Q

How is serum calcium corrected for hypoalbuminaemia?

A

(0.02 x (40-albumin)) + serum calcium

25
Q

How does a physical exam and chest x ray help in the diagnosis of hypercalcaemia?

A

Cancer should be obvious at this stage

Granulomatous disease on CXR

26
Q

What does high PTH suggest?

A

Primary hyperparathyroidism

27
Q

What does high PTHrP suggest?

A

Malignancy

28
Q

What does high calcidiol suggest?

A

Vitamin D excess

29
Q

What does high calcitriol but not calcidiol suggest?

A

Ectopic calcitriol production

30
Q

What is the treatment for hypercalcaemia?

A 
0.9% saline
Furosemide
Bisphosphonates
Calcitonin
Steroids
Parathyroidectomy
31
Q

Why is furosemide given?

A

Prevents resorption of calcium

32
Q

What bisphosphonate is given and why?

A

Pamidronate IV

Reduces bone resorption

33
Q

What side effect is associated with bisphosphonates?

A

Osteonecrosis of the jaw

34
Q

Why is calcitonin given?

A

Lowers osteoclast activity, but weak action

35
Q

Why are steroids given?

A

In granulomatous disease

36
Q

What are the symptoms of hypocalcaemia?

A 
Tetany, spasms, cramps
Perioral parasthesia
Chvostek's sign (facial nerve)
Hyperreflexia
Trousseau's sign (pinching hand)
37
Q

What are the causes of hypocalcaemia?

A 
Hypoparathyroidism
Vitamin D deficiency
Increased bone uptake
Pancreatitis (saponification)
Transfusions
Alkalosis
Chronic kidney disease
38
Q

What are the causes of hypoparathyroidism?

A

Autoimmune
Surgery
Low Mg

39
Q

What are the causes of vitamin D deficiency?

A

Lack of sunlight

Low CYP450

40
Q

How does chronic kidney disease cause tertiary hyperparathyroidism?

A

Low calcitriol due to reduced 1a hydroxy enzyme and increased phosphate as GFR too low to excrete
Reduced GIT, renal and bone resorption of calcium
Results in low ionised calcium and high phosphate
-increased PTH > Increases calcium
Causes chronic kidney disease mineral bone disorder
Results in vascular calcifications and adenoma in parathyroid

41
Q

What else should be measured in hypocalcaemia?

A 
PTH
Creatinine
Phosphate
Magnesium
Calcidiol and calcitriol
42
Q

What are the test results for primary hypoparathyroidism?

A

Low PTH

high phosphate

43
Q

What are the test results in chronic kidney disease?

A

High creatinine

Low calcitriol

44
Q

What is the treatment for hypocalcaemia?

A

Oral calcium
Vitamin D
Magnesium IV slow infusion

45
Q

What is the treatment for severe hypocalcaemia symptoms?

A

10ml of 10% calcium gluconate over 10 mins

46
Q

What is the preferred form of vitamin D to give in hypocalcaemia?

A

Calcidiol in general

In chronic kidney disease and hypoparathyroidism calcitriol preferred as they can’t convert to calcidiol

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