Hyperparathyroidism Support Group
Hyperparathyroidism is overactivity of the parathyroid glands resulting in excess production of parathyroid hormone (PTH). Increased PTH consequently leads to increased serum calcium (hypercalcemia) due to 1) increased bone resorption, allowing flow of calcium from bone to blood, 2) reduces renal clearance of calcium, and 3) increases intestinal calcium absorption.
Let me link you to this awesome video from Dr Larian who is a specialist. He explained it perfectly. I believe he talks about it at 36 minute mark.
https://www.facebook.com/parathyroideducation/videos/2016757828568178/