A patient is on a Low calcium diet for 6 weeks. He is most likely to have:
A. Raised parathyroid hormone levelsB. Raised calcitonin levels
C. Increased phosphate levels
D. None of the above
The
Answer is A. Circulating
ionized calcium acts directly on the parathyroid glands in a negative feedback
fashion to regulate the secretion of PTH. The key to this regulation is a cell
membrane Ca2+ receptor. This serpentine receptor is coupled via a G
protein to phosphoinositide turnover and is found in many tissues. In the
parathyroid its its activation inhibits PTH secretion is habited and the Ca2+ is deposited in the bones. When it is
low, secretion is increased and Ca2+
is mobilized from the bones.
