Disorders of Calcium, phosphate and magnesium

Question 1

Why is calcium physiologically important?

Answer 1

Muscle contraction
Neuronal signalling
Coagulation
Enzyme activity

Key mineral component of bone (hydroxyapatite)

Question 2

What is the importance of phosphate?

Answer 2

ATP
Intracellular signalling
Cellular metabolic process
Backbone of DNA

INTRACELLULAR

Question 3

What is the importance of magnesium?

Answer 3

Cofactor for ATP
Neuromuscular excitability
Enzyme fucntion
Ion channel regulation

INTRACELLULAR

Question 4

What mechanisms are involved in homeostasis of ions?

Answer 4

• Storage
• Tissue redistribution
• Intake (dietary)
• Excretion

Question 5

What are the key factors that control calcium levels?

Answer 5

PTH

Vit D

Question 6

What is the only fraction of calcium that is physiologically active?

Answer 6

Ionised calcium

Question 7

What other forms of calcium are there?

Answer 7

Bound calcium e.g. to albumin

Complexed - salts e.g. calcium phosphate, calcium citrate

Question 8

What is the normal range for total calcium>

Answer 8

2.2-2.6 mol/L

Question 9

What is the distribution for physiologically active Ca and inactive (i.e.bound/complexed)

Answer 9

50:50

Question 10

How does alkalosis and acidosis change proportion of bound calcium?

Answer 10

Alkalosis - increased calcium-albumin, reduced ionised calcium

Acidosis - reduced calcium-albumin, increases ionised calcium

Because H+ ions compete with Ca++ for albumin binding sites

Question 11

What can alkalosis cause?

Answer 11

Tetany - increased ionised calcium

Question 12

What are the endogenous factors for vit D

Answer 12

Endogenous - skin colour, ageing

Question 13

What are the exogenous factors for vit D

Answer 13

Ozone, sunscreen and clothing (cultural), season, time of day, supplements

Question 14

What else does fit D fall with?

Answer 14

Age
BMI
body fat

Question 15

Whats effect does PTH have on the gut?

Answer 15

Increased vit D release from kidney

Increased bit D increases calcium absorption from gut

Question 16

What effect does PTH have on the kidney?

Answer 16

Reduced calcium clearance but increase phosphate excretion

Question 17

What effect does PTH have on bones?

Answer 17

Increased bone turnover with net reabsorption

Question 18

What its the plasma Ca?

Answer 18

Total Ca = ionised calcium + bound calcium + complexed calcium

Question 19

What is magnesium required for?

Answer 19

Release of PTH from zymogens

Question 20

What are the causes for hypocalcaemia?

Answer 20

Hypoproteinaemia - reduced album

Reduced vit D - dietry/malabsorption, hepatic/renal disease, end organ bit D resistance

Hypoparathyroidism - primary, secondary - Mg deficiency

Inadequate intake of calcium

Question 21

What does a low Ca but high PTH indicate?

Answer 21

Vit D deficiency

Question 22

What does a low Cal, high phosphate and low PTH indicate?

Answer 22

Hypothyroidism (primary or secondary to magnesium def)

Question 23

What are the simple clinical features of hypercalcaemia?

Answer 23

Stones bones (pain) moans (ab pain) and groans (load mood/depression)

Question 24

What are the causes of hypercalcaemia?

Answer 24

Hyperparathyroidism
Malignancy e.g. primary tumour of PT
Bone disease and immobilisation
Excessive vit D 
Drugs e.g. lithium

Question 25

If you have high Ca, high PTH and low phosphate, whats the cause?

Answer 25

Hyperparathyroidism

Question 26

If you have high calcium and low PTH, whats the cause?

Answer 26

Bone malignancy

Question 27

What are the main causes of phosphate deficiency?

Answer 27

-Hyperparathyroidism -Excess losses - renal tubule damage, GI, diabetes (diuresis) - Insufficient intake - malnutrition ECF/ICF redistribution e.g. refeeding

Question 28

What are the symptoms of phosphate deficiency?

Answer 28

- Haemolysis, thrombocytopenia, poor granulocyte function - Muscle weakness, resp muscle failure, rhabdomyolysis - confusion/irritability

Question 29

What is hypomagnesaemia associated with?

Answer 29

Hypokalaemia Hyponatraemia Hypophosataemia Hypocalcaemia LOOK AT THESE!!!

Question 30

What is the major causes of hypomagnesaemia?

Answer 30

Renal - acute tubular necrosis Hypercalaemic states Drugs e.g. antibiotics, diuretics GI - malnutrition, diarrhoea, malabsorption

Question 31

What are the effects of magnesium depletion?

Answer 31

Cofactor of ATP - so anything requiring ATP in effected! Impaired PTH release - required for PTH release from zymogens