52 Calcium metabolism disorders Flashcards
Where are phosphate and magnesium predominantly found?
Intracellularly.
What are the three key controlling factors of calcium?
PTH.
Vitamin D.
Klotho.
Which form of calcium is physiologically active?
Ionised calcium.
Which protein is used to bound Ca?
Albumin.
How is calcium complexed? (2)
Calcium phosphate.
Calcium citrate.
What is ‘adjusted calcium’?
Calcium values that have been adjusted for changes in albumin levels.
What is the distribution of calcium in the plasma?
Ca: 2.3mmol/L.
Ionised: 1.3mmol/L.
Bound: 0.95mmol/L.
Complexed: 0.05mmol/L.
How is calcium measured?
What are the drawbacks of this?
Total calcium.
Affected by albumin concentration.
pH influences ionised calcium.
How and why does Ca distribution change with pH?
Ca and H+ compete for Albumin binding sites.
Acidosis lowers bound Ca levels, increasing ionised Ca levels.
What is the clinical implication of Ca and H+ competing for albumin?
Alkalosis may stimulate tetany.
How is vitamin D made?
UVB converts pre D2 to D3. Absorbed into blood (or from gut).
Liver concerts it to 25(OH)D.
Kidney converts it to 1α25(OH)D -the active form.
What are the functions of vitamin D? (4)
Increases intestinal Ca and phos absorption.
Increases bone mineralisation.
Induces immune cell differentiation.
Works against tumour microenvironment.
How do vitamin D levels change with age and body fatness?
Decreases.
How does PTH act in homeostasis?
PTH increases bone Ca release and GI absorption. High Ca switches off PTH.
PTH also decreases Ca clearance from kidney and increase PO4- excretion.
What are the causes of hypocalcaemia? (5).
Hypoproteinaemia. Vit D deficiency. Hypoparathyroidism (or Mg deficiency). Inadequate intake. Pseudohypoparathyroidism.
What are the causes of hypercalcaemia? (6).
Hyperparathyroidism. Malignancy. Drugs. Vit D excess - sarcoidosis. Bone disease. Immobilisation.
What are the causes of phosphate deficiency? (3).
Hyperparathyroidism.
Excess losses: renal damage, GI, diabetes.
Poor intake.
What are the symptoms of phosphate deficiency? (8).
Haemoloysis, thrombocytopenia, poor granulocyte function.
Muscle weakness, respiratory failure, rhabdomyolysis.
Metabolic encephalopathy.
Renal dysfunction.
Where is the majority go magnesium reabsorbed in the kidney?
Ascending loop of Henle.
What is hypomagnesaemia associated with?
Low blood levels of calcium, potassium, phosphate and sodium.
How is the bodily distribution of Mg different to calcium and phosphate?
It is found in the intercellular space.
Which drugs can cause magnesium depletion? (4).
Antibiotics - gentamicin / carbenicillin.
Chemotherapy - cisplatin.
Diuretics.
FK506 - tacrolimus.
What are the effects of magnesium depletion? (5).
Low calcium, phosphate and potassium. Impaired PTH release and PTH resistance. Cardiac irritability. Hyperreflexia, tetany, ataxia and psychosis. Muscle fibrillation and weakness.
How can tissue Mg be ascertained? (4).
Value of each measurement?
Serum - poor correlation. Acute value only.
Erythrocyte - poor.
Leucocyte - good.
Muscle - requires biopsy.
