Hypercalcaemia/Parathyroid Disease Flashcards
How much of plasma calcium is bound to albumin?
40% (inactive)
Non-bound is ionized
What effect do acidotic states have on ionized calcium level?
Increase ionized calcium level by decreasing protein binding
What effect do alkalotic states have on ionized calcium level?
Decrease ionized calcium level by increasing protein binding
What are the main factors controlling plasma calcium level?
PT
Vit D
Calcitonin
Where is PTH produced?
Chief cells in parathyroid glands
When is PTH secreted?
Low plasma calcium
Low Vit D
High phosphate
What are the effects of PTH?
Raises plasma calcium
-stimulates cal reabsorption from bone
-increases renal tubular cal reabsorption
-stimulates increased GI cal absorption (indirect)
Increases renal phosphate excretion
Where is Vitamin D produced?
Synthesised in skin (D3 cholecalciferol)
Ingested (D2 ergocalciferol) –> hydroxylated in liver to 25-OH-D2/3 –> hydroxylated in kidney to active Vit D
What are the effects of Vitamin D?
Increases absorption of calcium & phosphate from GI tract
Increases renal re-absorption of Ca
Required for normal bone formation
What are the causes of Vitamin D deficiency?
Inadequate sunlight exposure (rickets)
Malabsorptive condition
Liver/kidney disease
Where is Calcitonin produced?
Parafollicular C cells of thyroid gland
When is Calcitonin secreted?
Increased plasma calcium
What are the effects of Calcitonin?
Decreases plasma calcium by antagonising the effect of PTH on bone
What determines intestinal uptake of calcium?
Ionized calcium levels in lumen
Presence of activated Vit D
What determines renal excretion of calcium?
Na reabsorption in proximal tubule (90%)
PTH regulation in distal tubule (10%)
Vit D in PCT
What is hypercalcaemia?
Plasma calcium
>2.5mmol/L
What is the most common cause of hypercalcaemia?
1o hyperparathyroidism/malignancy (97%)
What are the causes of excessive PTH secretion, leading to hypercalcaemia?
1o hyperparathyroidism
3o hyperparathyroidism
Ectopic PTH secretion (v. rare)
What are the malignant causes of hypercalcaemia?
Myeloma
Metastatic deposits in bone
Paraneoplastic (SCC)
What are the causes of excess Vit D, leading to hypercalcaemia?
Exogenous excess
Granulomatous disease (TB, sarcoid)
Lymphoma