How does the kidney handle calcium?
Approximately 60% of the serum calcium is ionized or complexed and freely filtered by the glomerulus. The kidney reabsorbs 98% of the filtered calcium passively throughout the nephron. Sixty percent of the reabsorption occurs in the proximal convoluted tubule, 30% in Henle’s loop, and 10% in the distal tubule. Furosemide impairs calcium reabsorption in Henle’s loop and increases urinary calcium excretion. Thiazide diuretics impair distal tubule reabsorption of sodium, thereby increasing intracellular negativity and calcium reabsorption. Parathyroid hormone (PTH) increases distal tubular calcium reabsorption by enhancing calcium channel activity.