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2A - Endocrine System > Clinical Calcium Homeostasis > Flashcards

Clinical Calcium Homeostasis 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
  • 45% bound (mainly to albumin)
  • 10% non-ionised or complexed to citrate
  • 45% ionised (biologically important)
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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 0.01mmol/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 albumin 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
  1. 27mmol/L
    - remember the albumin reduction means more calcium is free
    - Adjust calcium by 0.01mmol/L for each 5g/L reduction in albuymin from 40g/L
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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
  • Direct effects that promotes reabsorption of calcium from renal tubules and bones
    • Lengthy exposure to inappropriate levels of PTH can lead to osteoporosis
  • Mediates the conversion of vitamin D from its inactive to active form
    • This conversion takes place in the liver
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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 due to the direct effects of PTH that 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
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 hyperthyroidism in reponse 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

3) If magnesium is low it is magnesium deficiency, if its normal its hypoparathyroidism or calcium sensing receptor defect
4) If urea and creatine is high its renal failure, its its low check vitamin D
5) 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
    • Such as DiGeorge syndrome
  • Destruction
    • Neck surgery, autoimmune disease
  • Infiltration
    • Such as haemochromotosis or Wilson’s disease
  • Reduced secretion of PTH (neonatal hypocalcaemia, hypomagnesaemia)
  • Resistance to PTH (known as pseudohypoparathyroidism)
    • Presents in childhood
    • Refers to group of disorders defined by target organ (kidney and bone) unresponsiveness to PTH
    • Characterised by hypocalcaemia, hyperphosphatemia and elevated rather than reduced PTH concentrations
    • Albright’s hereditary osteodystrophy (AHO): short stature, obesity, shortening of metacarpal bones can occur in these patients
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

Resistance 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
  • Maintenance 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

2A - Endocrine System (26 decks)

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