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Clinical Pathology > Calcium/Phosphate/Magnesium Metabolism And Disorders > Flashcards

Calcium/Phosphate/Magnesium Metabolism And Disorders Flashcards

1
Q

Describe the distribution of body calcium

A

99% is part of bone

1% is in the blood and ECF
•45% as free Ca2 ions
•40% bound to proteins like albumin
•15% to anions like HCO3, citrate, PO4 and lactate

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2
Q

What is the reference interval for total plasma calcium❓

A

2.15-2.55mmol/L

  • Ca> 3.5mmol/L can lead to cardiac arrest/arrhythmias
  • Medical emergency
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3
Q

What is the reference interval for free ionized calcium in plasma❓

A

1.1-1.4mmol/L

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4
Q

Free ionized calcium is physiologically ________ and the calcium bound to albumin is physiologically ________

A

Active

Inactive

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5
Q

What are the factors involved in the control of calcium❓

A
  • Diet
  • Vitamin D
  • Parathyroid glands
  • Thyroid glands
  • Normal functioning intestines
  • Normal functioning kidneys
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6
Q

The parathyroid hormone is a single chain polypeptide containing ____ amino acids

The amino acid on the ____ terminal mediates it’s biological activity

A

84

34N

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7
Q

What are the actions of parathyroid hormone❓

A

On bones:
⬆️plasma concentration of Ca and Ph
⬆️osteoclastic bone activity

On the kidneys:
⬆️plasma concentration of Ca by increasing reabsorption
⬇️plasma concentration of Ph by ⬇️Ph reabsorption and causing phosphaturia

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8
Q

The control of PTH depends on:

A
  1. Free ionized calcium conc in plasma

2. Extracellar magnesium conc

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9
Q

How is PTH affected in severe chronic hypomagnesaemia❓

A

PTH conc. is reduced

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10
Q

The parathyroid hormone related protein is seen in what disease state❓

A

⬆️in certain tumors

Causes humoral hypercalcaemia of malignancy

b/c it has a similar amino acid sequence with PTH at the biologically active end

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11
Q

What is calcitonin❓

What is it’s role in calcium metabolism❓

A

A hormone secreted by the medullary cells of the thyroid gland

Secreted in ⬆️blood calcium

🚫PTH
🚫Vit D

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12
Q

What are the two forms of vitamin D❓

Where are obtained❓

A

VitD2 Ergocalciferol
From plants in diet

Vit D3 Cholecalciferol
Formed on skin by the action of UV light on 7-dehydrocholestrol

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13
Q

Speak briefly on the metabolism of Vitamin D

A

•Transported bound to vitamin D binding protein

•7-dehydrocholesterol
  ⬇️UV
 Cholecalciferol (Liver)
  ⬇️25-hydroxylase 
 25-hydroxycholecalciferol* (Kidney)
  ⬇️1-alpha-hydroxylase
 1,25-dihydroxycholecalciferol
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14
Q

What can stimulate the action of 1-alpha-hydroxylase❓

A

⬇️plasma phosphate

⬆️PTH

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15
Q

What can inhibit the action of 1-alpha-hydroxylase❓

A

Hyperphosphataemia

⬆️free ionized calcium

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16
Q

What can inhibit the synthesis of 1,25-dehydroxycholecalciferol❓

What can it lead to❓

A

Renal disease

Hypocalcaemia

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17
Q

What the functions of 1,25-dehydroxycholecalciferol❓

A

On intestinal mucosal cells:
⬆️Ca and Ph reabsorption

On bones:
⬆️Ca by stimulating osteoclastic activity with PTH

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18
Q

Describe the synergistic effect of PTH and VitD

A
  • The action of PTH on bone is impaired in the absence of 1,25-(OH)Vit D
  • PTH enhances 1-hydroxylase activity and therefore promotes 1,25-(OH)Vit D synthesis
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19
Q

What are the effects of hypercalcaemia❓

A

Renal:
Renal calculi (ppt of Ca Ph stones)
Polyuria
Renal damage

Hypokalemia:
⬆️Ca 🚫K reabsorption

Neuromuscular effects:
Hypotonia

CNS:
Nausea
Vomiting 
Anorexia 
Depression

GIT:
Constipation
Peptic ulceration
Abdominal pain

Cardiac:
Shortened Q-T interval
Broadened T waves

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20
Q

What are the causes of hypercalcaemia?

A

Thiazide diuretics

Bony metastasis

Hyperthyroidism

High bone turnover in thyrotoxicosis and immobilization

⬆️Vit D

21
Q

Primary hyperparathyroidism is caused by an ⬆️PTH due to an adenoma/hyperplasia/carcinoma of the PTH gland

True or false

A

True

22
Q

What happens in tertiary hyperparathyroidism❓

A
  • PTH gland have been subjected to chronic +ve feedback by hypocalcaemia of secondary parahyperthyroidism which has been corrected
  • Hypertrophy of PTH gland
  • PTH secretion is partly autonomous and isn’t suppressed by -ve feedback of hypercalcaemia
23
Q

In malignant disease of the bone…

A
  • bony metastasis from tumors of breast, lungs etc
  • malignant deposits stimulate local osteoblastic reaction
  • plasma alkaline phosphatase activity is raised
  • ⬆️plasma phosphate
24
Q

What protein is involved in humoral hypercalcaemia of malignancy❓

A

Parathyroid Hormone related protein is involved in humoral hypercalcaemia of malignancy

It is not subject to normal feedback control

Results in hypercalcaemia

25
Q

Hypercalcaemia can be drug-induced.

What drugs do you know that could cause ⬆️Ca❓

A

Thiazides (⬇️Renal Ca excretion)

Lithium

Vitamin A

26
Q

How is Ca metabolism affected in sarcoidosis❓

What other conditions can produce the same effect❓

A
  1. Granulomatous tissue synthesize 1,25(OH)2 Vit D

⬆️Ca reabsorption from GIT

  1. Histoplasmosis and leprosy
27
Q

How would you treat hypercalcaemia❓

A
  • Rehydration
  • Bisphosphonates (bind calcium) eg pamidronate
  • Steriods esp. in Vit D intoxication and sarcoidosis
  • Calcitonin
28
Q

What are the clinical effects of hypocalcaemia❓

A 
Tetany
Carpo-pedal spasm 
Generalized seizure
Laryngospasm
Hyperreflexia 
Cataract 
Cardiac arrhythmias 
Paraesthesiae hypotension 
Prolonged Q-T interval on ECG
29
Q

What are the clinical signs of hypocalcaemia❓

A

Trousseau’s Sign

Chvosteks’s Sign

30
Q

Describe the Trousseau’s Sign

When is it observed❓

A

Carpopedal spasm and tetany by inflating a BP cuff to 10-20mmHg above systolic BP for 3-5minutes

It is observed in hypocalcaemia

31
Q

Chvosteks’s Sign is seen in hypocalcaemia. Give a brief description

A

It is elicited by tapping the facial nerve anterior to the ear, ipsilateral facial muscle contraction may occur

32
Q

Classify hypocalcaemia

A

Hypocalcaemia with hypophosphataemia

Hypocalcaemia with hyperphosphataemia

33
Q

What are the causes of hypocalcaemia with hypophosphataemia❓

A

Inadequate intake of Ca, Vit D and phosphate

Secondary parahypothyroidism

Steathorhoea (impaired absorption of Vit D)

Renal disease (impaired metabolism of 1,25-(OH) Vit D)

Anticonvulsant therapy (increased inactivation of Vit D)

Renal tubular disorders of phosphate disorders

34
Q

What are the causes of hypocalcaemia with hyperphosphataemia❓

A

Renal dysfunction (acute and chronic renal failure- 1-alpha-hydroxylase is affected)

Primary hypoparathyroidism causes by surgical damage to parathyroids

Pseudohypoparathyroidism (in-born error, end organ resistance)

35
Q

How would you treat hypocalcaemia❓

A

Mild hypocalcaemia:
Oral calcium
Vit D supplements

OR

IV calcium- 10mls of 10% calcium gluconate over 5 minutes
Continue with oral supplement

36
Q

Describe the distribution of body phosphate

A

Major intracellular divalent anion

80% in skeleton
20% in soft tissues and muscle

90% excreted via renal route

37
Q

Causes of hyperphosphataemia❓

A

⬆️phosphate intake, esp. IV

⬆️tissue breakdown

Tumor lysis syndrome

Malignant hyperpyrexia

Crush injuries

ARF or CRF

Acidaemia

DKA

Acromegaly

⬆️Vit D intake

38
Q

How would you treat hyperphosphataemia❓

A

Use of oral phosphate binding agents eg magnesium hydroxide or calcium carbonate

Hemodialysis or peritoneal dialysis

39
Q

Causes of hypophosphataemia❓

A

Poor intake

Malabsorption states

Chronic alcoholism

Renal tubular acidosis

Hyperparathyroidism

Cellular redistribution

  • IV glucose
  • Alkalemia
  • Insulin administration
40
Q

Describe the distribution of body magnesium

A

Major intracellular divalent cation

Cereals, nuts and vegetables are dietary sources

Absorbed in upper small intestine w/o Vit D

Eliminated in faeces and via the kidney

41
Q

Magnesium acts as an antagonist to calcium in cellular responses

True or false❓

A

True

42
Q

Causes of hypermagnesaemia❓

A

Increased intake of:
Antacids
Purgatives
Parenteral nutrition

Renal failure (Impaired renal excretion)

Hypothyroidism
Adrenal insufficiency

43
Q

What the clinical consequences of hypermagnesaemia❓

A

Mg>2mmoles/L

Cardiac arrhythmias
Cardiac arrest 
Seizures 
Hyporeflexia 
Paralytic ileus 
Nausea 
Respiratory depression 
Hypotension
44
Q

How would you manage severe hypermagnesaemia❓

A

10ml of 10% calcium gluconate given slowly

Insulin/ glucose infusion

Dialysis

45
Q

The symptoms of hypomagnesaemia are not similar to those of hypocalcaemia

True or false

List them

A

False

Tetany
Carpo-pedal spasm 
Generalized seizure
Laryngospasm
Hyperreflexia 
Cataract 
Cardiac arrhythmias 
Paraesthesiae hypotension 
Prolonged Q-T interval on ECG
46
Q

Hypomagnesaemia can result in…

A

Cardiac arrhythmias
Digoxin sensitivity
Abdominal discomfort
Anorexia

Neuromuscular sequelae:
Parasthesia 
Vertigo 
Tetany
Seizures 
Irritability
47
Q

Will severe hypomagnesaemia lead to hypercalcaemia or hypocalcaemia❓

Why❓

A

Hypocalcaemia

⬇️PTH release and activity

48
Q

Long term magnesium deficiency may be a risk factor for coronary artery disease

True or false

A

True

49
Q

⬆️Mg intake is associated with hypertension and insulin resistance

True or false

A

False

⬇️Mg intake is associated with hypertension and insulin resistance

Clinical Pathology (6 decks)

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