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7. Endocrinology (Medical Knowledge)a > Clinical Calcium Homeostasis > Flashcards

Clinical Calcium Homeostasis Flashcards

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USMLE® Step 1 flashcards
1
Q

What are some dietary sources of calcium?

A
  • Milk, cheese and other dairy foods
  • Green leafy vegetables such as broccoli
  • Soya beans
  • Tofu
  • Nuts
  • Bread and anything made from fortified flour
  • Fish where you eat the bones
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2
Q

What are some functions of calcium?

A
  • Bone formation
  • Cell division and growth
  • Muscle contraction
  • Neurotransmitter release
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3
Q

What percentage of calcium is found where?

A

98.9% in bones

1% in cells

0.1% in ECF

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4
Q

What are the proportions of plasma calcium concentrations?

A
  • 40% bound (mainly to albumin)
  • 10% non-ionised (or complexed to citrate)
  • 50% ionised (or free)
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5
Q

What is the normal range of calcium?

A

2.2 - 2.6mmol/L

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6
Q

How is free calcium calculated?

A
  • Increased albumin decreases free calcium
  • Decreased albumin increases free calcium
  • Adjust calcium by 0.1mmol/L for each 5g/L reduction in albumin from 40g/L
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7
Q

How does increased albumin impact free calcium levels?

A

Decreases free calcium

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8
Q

How does decreased albumin impact free calcium levels?

A

Increases free calcium

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9
Q

When working out free calcium, how is calcium adjusted for reduction in albumin?

A

Adjust calcium by 0.01mmol/L for each 5g/L reduction in albuymin from 40g/L

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10
Q

Does acidosis increase or decrease ionised calcium?

A

Increases

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11
Q

Since acidosis increases ionised calcium, what does it predispose?

A

Hypercalcaemia

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12
Q

If Mr Bloggs has calcium of 2.55mmol/L and his albumin is 30g/L, what is his corrected calcium?

A
  • his albumin is low and so the free proportion of calcium will be higher
  • increase his calcium by 0.2mmol/L giving his corrected calcium as 2.75mmol/L
  • which would put it above the reference range
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13
Q

What foods is vitamin D found in?

A
  • Oily fish such as salmon
  • Eggs
  • Fortified fat spreads
  • Fortified breakfast cereals
  • Some powdered milks
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14
Q

What are some groups at risk of vitamin D deficiency?

A
  • Pregnancy
  • Children
  • Elderly
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15
Q

What part of parathyroid glands respond directly to changes in calcium concentrations and secrete parathyroid hormone?

A

Chief cells

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16
Q

How are alterations in ECF calcium levels transmitted into parathyroid cells?

A

Via calcium-sensing receptor (CaSR)

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17
Q

How does increases serum calcium impact secretion of parathyroid hormone?

A
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18
Q

How does decreased serum calcium impact secretion of parathyroid hormone?

A
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19
Q

What are the effects of parathyroid hormone (PTH)?

A

encourages increase in serum calcium

  • promote reabsorption of calcium from renal tubules and bones
  • mediates conversion of vitamin D from its inactive to active form
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20
Q

What does PTH stand for?

A

Parathyroid hormone

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21
Q

What can lengthy exposure to inappropriate levels of PTH lead to?

A
  • osteoporosis
  • PTH promotes bone reabsorption of calcium from renal tubules and bones
22
Q

Where does the conversion of vitamin D to its active form take place?

A

Kidneys

23
Q

What enzyme is responsible for the conversion of vitamin D to its active form?

A

25(OH) vitamin D 1α- hydroxylase

24
Q

When does acute hypocalcaemia occur?

A

Serum calcium < 2.2mmol/L

25
Q

What is the clinical presentation of acute hypocalcaemia?

A
26
Q

What is the clinical presentation of chronic hypocalcaemia?

A
27
Q

What are clinical signs of acute hypocalcaemia?

A

Trosseau’s sign and Chovstek’s sign

28
Q

What is the aetiology of hypocalcaemia?

A
  • Disruption of parathyroid gland due to total thyroidectomy
  • Following selective parathyroidectomy
  • Severe vitamin D deficiency
  • Magnesium deficiency
  • Cytotoxic drug induced hypocalcaemia
  • Pancreatitis
29
Q

What are the different classifications of hypocalcaemia cause?

A
  • hypoparathyroidism (low PTH)
  • secondary hyperparathyroidism in response to hypocalcaemia (high PTH)
  • drugs
30
Q

What aspects of the history are particularly important for diagnosing hypocalcaemia?

A
  • Symptoms
  • Calcium and vitamin D intake
  • Neck surgery
  • Autoimmune disorders
  • Medications
  • Family history
31
Q

What part of the examination is particularly important for diagnosing hypocalcaemia?

A

Neck scars

32
Q

What investigations should be done for hypocalcaemia?

A
  • ECG
  • Serum calcium
  • Albumin
  • Phosphate
  • PTH
  • U and Es
  • Vitamin D
  • Magnesium
33
Q

Explain the process of investigations for hypocalcaemia?

A
  1. confirm hypocalcaemia (adjusted for albumin)
  2. check PTH
  • if PTH low or normal, check magnesium
  • if PTH high check urea and creatinines
  1. if magnesium is low it is magnesium deficiency, if its normal its hypoparathyroidism or calcium-sensing receptor defect
  2. if urea and creatine is high it is renal failure, if its low check vitamin D
  3. if vitamin D is low its vitamin D deficiency, if its normal its pseudohypoparathyroidism or calcium deficiency
34
Q

What are the most common causes of hypocalcaemia?

A

Vitamin D deficiency

Hypoparathyroidism

35
Q

What can cause hypoparathyroidism?

A
  • agenesis: DiGeorge syndrome
  • destruction: neck surgery, autoimmune disease
  • infiltration (haemochromotosis or wilson’s disease)
  • reduced secretion of PTH (neonatal hypocalcaemia, hypomagnesaemia)
  • resistance to PTH (pseudohypoparathyroidism)
36
Q

What is agenesis?

A

Failure of an organ to develop during embryonic growth

37
Q

What is haemochromotosis?

A

Condition where iron levels slowly build up in the body, which can damage many organs

38
Q

What is pseudohypoparathyroidism?

A

group of disorders defined by target organ (kidney and bone) unresponsiveness to PTH

39
Q

What is pseudoparathyroidism characterised by?

A

Hypocalcaemia

Hyperphosphatemia

Elevated rather than reduced PTH concentrations

40
Q

What is a syndrome that that allows agenesis hypoparathyroidism?

A

DiGeorge syndrome

41
Q

What can cause hypoparathyroidism due to destruction?

A

Neck surgery

Autoimmune disease

42
Q

What can cause hypoparathyroidism due to infiltration?

A

Haemochromotosis

Wilson’s disease

43
Q

What can cause hypoparathyroidism due to reduced secretion of PTH?

A

Neonatal hypocalcaemia

Hypomagnesaemia

44
Q

What does treatment of hypocalcaemia depend on?

A

How severe the hypocalcaemia is

45
Q

When is hypocalcaemia considered to be mild?

A

Asymptomatic, >1.9mmol/L

46
Q

When is hypocalcaemia considered to be severe?

A

Symptomatic, <1.9mmol/L

47
Q

What is the treatment for mild hypocalcaemia?

A
  • commence oral calcium tablets
  • if post thyroidectomy repeat calcium 24 hours later
  • if vitamin D deficient, start vitamin D
  • if magnesium low, stop any precipitating drug and replace magnesium
48
Q

What is the treatment for severe hypocalcaemia?

A
  • most tablets contain a combination of vitamin D and calcium (dose is about 400-1000 international units)
  • higher loading dose required, such as 3200 units daily for 12 weeks
  • vitamin D requires hydroxylation by the kidney to its active form, therefore the hydroxylated derivatives alfacalcidol or calcitriol should be prescribed if patients with severe renal impairment require vitamin D therapy
49
Q

What is severe hypocalcaemia considered to be?

A

A medical emergency

50
Q

What does the Scottish government recommend in relation to vitamin D?

A

Everyone above the age of 5 should be taking a daily supplement of 10mg vitamin D, particularly during winter months of october to march

7. Endocrinology (Medical Knowledge)a (28 decks)

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