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

Calcium/Phosphate/Magnesium Metabolism And Disorders Flashcards

(49 cards)

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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?

Study These Flashcards
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

22
Q

What happens in tertiary hyperparathyroidism❓

Study These Flashcards
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…

Study These Flashcards
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❓

Study These Flashcards
A

Parathyroid Hormone related protein is involved in humoral hypercalcaemia of malignancy

It is not subject to normal feedback control

Results in hypercalcaemia

25
Hypercalcaemia can be drug-induced. What drugs do you know that could cause ⬆️Ca❓
Thiazides (⬇️Renal Ca excretion) Lithium Vitamin A
26
How is Ca metabolism affected in sarcoidosis❓ What other conditions can produce the same effect❓
1. Granulomatous tissue synthesize 1,25(OH)2 Vit D ⬆️Ca reabsorption from GIT 2. Histoplasmosis and leprosy
27
How would you treat hypercalcaemia❓
* Rehydration * Bisphosphonates (bind calcium) eg pamidronate * Steriods esp. in Vit D intoxication and sarcoidosis * Calcitonin
28
What are the clinical effects of hypocalcaemia❓
``` Tetany Carpo-pedal spasm Generalized seizure Laryngospasm Hyperreflexia Cataract Cardiac arrhythmias Paraesthesiae hypotension Prolonged Q-T interval on ECG ```
29
What are the clinical signs of hypocalcaemia❓
Trousseau’s Sign Chvosteks’s Sign
30
Describe the Trousseau’s Sign When is it observed❓
Carpopedal spasm and tetany by inflating a BP cuff to 10-20mmHg above systolic BP for 3-5minutes It is observed in hypocalcaemia
31
Chvosteks’s Sign is seen in hypocalcaemia. Give a brief description
It is elicited by tapping the facial nerve anterior to the ear, ipsilateral facial muscle contraction may occur
32
Classify hypocalcaemia
Hypocalcaemia with hypophosphataemia Hypocalcaemia with hyperphosphataemia
33
What are the causes of hypocalcaemia with hypophosphataemia❓
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
What are the causes of hypocalcaemia with hyperphosphataemia❓
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
How would you treat hypocalcaemia❓
Mild hypocalcaemia: Oral calcium Vit D supplements OR IV calcium- 10mls of 10% calcium gluconate over 5 minutes Continue with oral supplement
36
Describe the distribution of body phosphate
Major intracellular divalent anion 80% in skeleton 20% in soft tissues and muscle 90% excreted via renal route
37
Causes of hyperphosphataemia❓
⬆️phosphate intake, esp. IV ⬆️tissue breakdown Tumor lysis syndrome Malignant hyperpyrexia Crush injuries ARF or CRF Acidaemia DKA Acromegaly ⬆️Vit D intake
38
How would you treat hyperphosphataemia❓
Use of oral phosphate binding agents eg magnesium hydroxide or calcium carbonate Hemodialysis or peritoneal dialysis
39
Causes of hypophosphataemia❓
Poor intake Malabsorption states Chronic alcoholism Renal tubular acidosis Hyperparathyroidism Cellular redistribution - IV glucose - Alkalemia - Insulin administration
40
Describe the distribution of body magnesium
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
Magnesium acts as an antagonist to calcium in cellular responses True or false❓
True
42
Causes of hypermagnesaemia❓
Increased intake of: Antacids Purgatives Parenteral nutrition Renal failure (Impaired renal excretion) Hypothyroidism Adrenal insufficiency
43
What the clinical consequences of hypermagnesaemia❓
Mg>2mmoles/L ``` Cardiac arrhythmias Cardiac arrest Seizures Hyporeflexia Paralytic ileus Nausea Respiratory depression Hypotension ```
44
How would you manage severe hypermagnesaemia❓
10ml of 10% calcium gluconate given slowly Insulin/ glucose infusion Dialysis
45
The symptoms of hypomagnesaemia are not similar to those of hypocalcaemia True or false List them
False ``` Tetany Carpo-pedal spasm Generalized seizure Laryngospasm Hyperreflexia Cataract Cardiac arrhythmias Paraesthesiae hypotension Prolonged Q-T interval on ECG ```
46
Hypomagnesaemia can result in...
Cardiac arrhythmias Digoxin sensitivity Abdominal discomfort Anorexia ``` Neuromuscular sequelae: Parasthesia Vertigo Tetany Seizures Irritability ```
47
Will severe hypomagnesaemia lead to hypercalcaemia or hypocalcaemia❓ Why❓
Hypocalcaemia ⬇️PTH release and activity
48
Long term magnesium deficiency may be a risk factor for coronary artery disease True or false
True
49
⬆️Mg intake is associated with hypertension and insulin resistance True or false
False ⬇️Mg intake is associated with hypertension and insulin resistance

Clinical Pathology (6 decks)

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