IMED3004 Lecture Notes - Lecture 15: Muscle Weakness, Periosteum, Calcification
1 Nov 2020
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Parathyroid pathology is essentially about calcium, particularly hypercalcaemia: hypercalcaemia may be a cause or effect of parathyroid disease. It is not the only cause of hypercalcaemia. Functionally one cell type (chief) but with variants (oxyphil and water clear) due to accumulation of other material. Admixed with fat (up to 30%) in normal gland. Parathyroid hormone (pth) produced: mainly by chief cells released in response to low serum calcium (free ionised calcium) Increases conversion of vit d to active (hydroxy) form in kidney: with vitamin d, promotes calcium resorption from small intestine. Increases urinary phosphate excretion causing phosphaturia: net effect is to increase serum calcium. Acute: usually due to accidental damage/removal of parathyroids during thyroid surgery. Chronic: usually due to chronic renal failure ( calcitriol/1,25 dihydroxy vit d production and/or hyperphosphataemia, vit d deficiency (diet or sun exposure), drugs or intestinal malabsorption of ca2+ Calcium ca2+ blocks sodium channels (muscle and nerves) ca2+ lowers depolarisation threshold.
