GLOSSARY

Calcitonin
Calcitonin is secreted by thyroid parafollicular C cells and can inhibit osteoclast-mediated bone resorption. It has a less central role in ordinary adult calcium regulation than PTH and calcitriol.

Three organs in communication

Calcium and phosphate regulation coordinates intestine, kidney and bone through PTH, vitamin D-related signals and FGF23. Ionized calcium, renal function and tissue responsiveness influence the pattern. Serum concentration alone does not measure skeletal mineral stores.

Interpreting the mechanism

Its physiological, pharmacological and tumor-marker uses are different contexts. A calcitonin measurement should not be interpreted as a direct summary of bone strength or calcium intake.

Bone under load

Mechanical loading supplies local signals that interact with endocrine state, adequate energy and nutrient availability. A circulating bone marker can reflect several skeletal sites and does not independently prove stronger bone or predict fracture risk.