Disorders of calcium, phosphate & magnesium Flashcards
What is the physiological importance of calcium?
- Muscle contraction
- Neuronal excitation
- Blood clotting
- Enzyme activity (Na/K ATPase)
What is the physiological importance of phosphates?
- Intracellular signalling
- ATP
- Cellular metabolic processes (glycolysis)
- Predominantly intracellular
What is the physiological importance of magnesium?
- Enzymatic function
- Regulates ion channels
- Cofactor for ATP
- Neuromuscular excitability
What 2 factors control calcium?
- PTH
- Vit D & metabolites
What is the normal range of calcium?
2.20-2.60
What is total calcium made up of? Describe each component
Total= Ionised + bound + complexed I= active, Ca sensing receptor, cellular effects, regulation of PTH B= inactive, albumin main binding protein C= salts- Ca phosphate & Ca citrate
What is adjusted calcium?
Calcium values corrected for changes in albumin (range stays the same)
What are problems with lab measurements for calcium?
- Doesn’t reflect ionised Ca
- pH influences ionised Ca
- Total Ca affected by albumin
What clinical conditions can cause altered binding of Ca to albumin?
-Acidosis= reduces Ca-albumin
-Alkalosis= increases Ca-albumin
Ca & H+ ions compete for albumin binding sites
What are the effects of pH change/acidosis on Ca levels?
- Inc ionised Ca
- Dec bound Ca
What are the effects of pH change/alkalosis on Ca levels?
- Dec ionised Ca
- Inc bound Ca
What are the clinical implications of pH change on Ca?
- Alkalosis, hyperventilation can precipitate tetany
- Hypocalcaemic patients with acidosis- asymptomatic
What are effects of changes in binding proteins on Ca?
- Total Ca reduced
- reduced bound calcium
Describe the pathophysiology of calcium
- Disorders of homeostatic regulators (PTH, Vit D)
- Disorders of skeleton (bone mets)
- Disorders of effector organ (GI-malabsorption)
- Diet
What are the endogenous & exogenous factors affecting vitamin D?
- Endo= aging, skin colour
- Exo= ozone, sunscreen & clothing, time of day, diet & supplements, latitude & season
What factors cause vitamin D levels to fall?
- Age
- BMI
- Body fat
Describe the mechanism of the parathyroid hormone loop
- Parathyroid hormone produce PTH
- Acts on bones, kidneys, GI
- Positive feedback
- Calcium produced
- As plasma levels inc acts as negative feedback on parathyroid glands
How does PTH act on bones, GI and kidneys?
- Bones= Inc Ca turnover with net resorption
- GI= Vit D inc, Ca absorption
- Kidneys= Dec Ca clearance & inc phosphate excretion
What are causes of hypocalcaemia?
- Hypoproteinaemia
- Inadequate intake of Ca
- Vit D deficiency (renal/hepatic disease, dietary, end organ it D resistance)
- Hypoparathyroidism (1° or 2° to Mg depletion)
- Pseudohypoparathyroidism (end organ PTH resistance)
What are causes of hypercalcaemia?
- Hyperparathyroidism
- Malignancy (lytic lesions)
- Drugs
- Vit D excess (sarcoidosis, cholecalciferol)
- Bone disease & immobilisation
What are causes of phosphate deficiency?
- Hyperparathyroidism
- Excess losses (GI, diabetes, renal tubular damages)
- Poor intake (malnutrition)
- ECF/ICF redistribution
What are symptoms of phosphate deficiency?
- Haemolysis
- Thrombocytopenia
- Poor granulation function
- Severe muscle weakness
- Respiratory muscle failure
- Rhabdomyolysis
- Renal dysfunction
- Confusion
- Irritability
- Coma= metabolic encephalopathy
What are 40% of hypomagnesaemia cases associated with?
Hypokalaemia
What are causes of magnesium depletion?
- Renal: Drugs (antibiotics, chemo, diuretics), hypercalcaemic states, diuretic phase of acute tubular necrosis
- GI: malnutrition, diarrhoea, malabsorption, IV nutrition
What are the effects of magnesium depletion? (Cells, bio and endocrine)
- Cellular: reduced mitochondrial respiration, imparied phosphorylation, defective Na/K ATPase activity, impaired DNA synthesis
- Bio: hypokalaemia/calcaemia/phosphataemia
- Endocrine: impaired PTH release, PTH resistance in bone
What are the clinical features of magnesium depletion?
- Cardiac irritability
- Reduced contractility
- Tetany
- Hyper-reflexia
- Ataxia/vertigo
- Psychosis/depression
- Muscle weakness/fibrillation
- Myopathic EMG
