Calcium homeostasis is largely controlled by the parathyroid glands (tucked away underneath the thyroid). I’ve included a little bit of the vitamin D synthesis pathway as well, though D3 (the form that is absorbed in the intestines) is also synthesized in the skin as long as you’re getting a little bit of sunlight.
Hypercalcemia
- Hyperparathyroidism: usually an adenoma
- Malignancy: PTH-related peptide released by tumor (squamous cell, renal, breast, bladder)
- Vitamin D excess: granulomas (sarcoidosis, TB, Wegener’s)
- Increased bone turnover: hyperthyroidism, Paget’s
- Familial hypocalcuric hypercalcemia: mutation in the calcium-sensing receptor in parathyroid and kidney
Hypocalcemia
- Hypoparathyroidism: sporadic, caused by thyroid surgery, Wilson’s, hypomagnesemia
- Pseudo-Hypoparathyroidism: PTH end-organ resistance
- Vitamin D deficiency: no sunlight, GI disease
- Chronic renal failure: decreased 1,25(OH)D production, increased phosphate
- Calcium sequestration: acute phosphate increase