Disorders of Calcium, phosphate and magnesium Flashcards
Why is calcium physiologically important?
Muscle contraction
Neuronal signalling
Coagulation
Enzyme activity
Key mineral component of bone (hydroxyapatite)
What is the importance of phosphate?
ATP
Intracellular signalling
Cellular metabolic process
Backbone of DNA
INTRACELLULAR
What is the importance of magnesium?
Cofactor for ATP
Neuromuscular excitability
Enzyme fucntion
Ion channel regulation
INTRACELLULAR
What mechanisms are involved in homeostasis of ions?
- Storage
- Tissue redistribution
- Intake (dietary)
- Excretion
What are the key factors that control calcium levels?
PTH
Vit D
What is the only fraction of calcium that is physiologically active?
Ionised calcium
What other forms of calcium are there?
Bound calcium e.g. to albumin
Complexed - salts e.g. calcium phosphate, calcium citrate
What is the normal range for total calcium>
2.2-2.6 mol/L
What is the distribution for physiologically active Ca and inactive (i.e.bound/complexed)
50:50
How does alkalosis and acidosis change proportion of bound calcium?
Alkalosis - increased calcium-albumin, reduced ionised calcium
Acidosis - reduced calcium-albumin, increases ionised calcium
Because H+ ions compete with Ca++ for albumin binding sites
What can alkalosis cause?
Tetany - increased ionised calcium
What are the endogenous factors for vit D
Endogenous - skin colour, ageing
What are the exogenous factors for vit D
Ozone, sunscreen and clothing (cultural), season, time of day, supplements
What else does fit D fall with?
Age
BMI
body fat
Whats effect does PTH have on the gut?
Increased vit D release from kidney
Increased bit D increases calcium absorption from gut
What effect does PTH have on the kidney?
Reduced calcium clearance but increase phosphate excretion
What effect does PTH have on bones?
Increased bone turnover with net reabsorption
What its the plasma Ca?
Total Ca = ionised calcium + bound calcium + complexed calcium
What is magnesium required for?
Release of PTH from zymogens
What are the causes for hypocalcaemia?
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
What does a low Ca but high PTH indicate?
Vit D deficiency
What does a low Cal, high phosphate and low PTH indicate?
Hypothyroidism (primary or secondary to magnesium def)
What are the simple clinical features of hypercalcaemia?
Stones bones (pain) moans (ab pain) and groans (load mood/depression)
What are the causes of hypercalcaemia?
Hyperparathyroidism Malignancy e.g. primary tumour of PT Bone disease and immobilisation Excessive vit D Drugs e.g. lithium
If you have high Ca, high PTH and low phosphate, whats the cause?
Hyperparathyroidism
If you have high calcium and low PTH, whats the cause?
Bone malignancy
What are the main causes of phosphate deficiency?
-Hyperparathyroidism
-Excess losses - renal tubule damage, GI, diabetes (diuresis)
- Insufficient intake - malnutrition
ECF/ICF redistribution e.g. refeeding
What are the symptoms of phosphate deficiency?
- Haemolysis, thrombocytopenia, poor granulocyte function
- Muscle weakness, resp muscle failure, rhabdomyolysis
- confusion/irritability
What is hypomagnesaemia associated with?
Hypokalaemia
Hyponatraemia
Hypophosataemia
Hypocalcaemia
LOOK AT THESE!!!
What is the major causes of hypomagnesaemia?
Renal - acute tubular necrosis
Hypercalaemic states
Drugs e.g. antibiotics, diuretics
GI - malnutrition, diarrhoea, malabsorption
What are the effects of magnesium depletion?
Cofactor of ATP - so anything requiring ATP in effected!
Impaired PTH release - required for PTH release from zymogens
