Figure 4.

Overall calcium homeostasis in primary hyperparathyroidism. Due to a set-point error in PHPT, circulating PTH levels are inappropriately increased leading to a new steady state with increased PTH and calcium levels. Bone turnover, the renal tubular reabsorption of calcium, the activation of vitamin D followed by calcium absorption from the gut are all increased leading to the new steady state, which in principle is able to be regulated – just at a higher level.