Calcium homeostasis, parathyroid and vitamin D

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

  1. Hyperparathyroidism: usually an adenoma
  2. Malignancy: PTH-related peptide released by tumor (squamous cell, renal, breast, bladder)
  3. Vitamin D excess: granulomas (sarcoidosis, TB, Wegener’s)
  4. Increased bone turnover: hyperthyroidism, Paget’s
  5. Familial hypocalcuric hypercalcemia: mutation in the calcium-sensing receptor in parathyroid and kidney

Hypocalcemia

  1. Hypoparathyroidism: sporadic, caused by thyroid surgery, Wilson’s, hypomagnesemia
  2. Pseudo-Hypoparathyroidism: PTH end-organ resistance
  3. Vitamin D deficiency: no sunlight, GI disease
  4. Chronic renal failure: decreased 1,25(OH)D production, increased phosphate
  5. Calcium sequestration: acute phosphate increase
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