Question

1. Serum calcium and phosphorous levels are under homeostatic control and the body can draw upon bone’s “reservoir” of these minerals if serum levels fall too low. Explain how a drop in serum calcium levels (hypocalcemia) can lead to enhanced bone resorption and a restoration of serum calcium levels without causing hyperphosphatemia.

Answer 1

The use of two hormones is what regulates the levels of these 2 minerals, calcium and phosphorous. The hormones are the PTH (parathyroid hormone) and calcitonin. They have opposit effect, calcitonin lowers calcium in the blood by reducing the activity of osteoblasts and reducing the calcium and phosphorous reabsorption in the kidneys. But the important function here is made by the PTH, this hormone increases the activity of osteoblast, setting free calcium and phosphate, but this hormone also reduces the reabsorption of phosphorous on kidneys, leading to a lowering in phosphorous levels, avoiding hyperphosphatemia.