Final answer:
Calcitonin is a peptide hormone produced by the thyroid gland that helps lower blood calcium levels by inhibiting osteoclasts, stimulating osteoblasts, and promoting calcium excretion through the kidneys.
Step-by-step explanation:
Calcitonin is a peptide hormone produced by the parafollicular, or C cells, of the thyroid gland. Its main function is to lower blood calcium levels (Ca²+), which it accomplishes by opposing the action of parathyroid hormone (PTH). Calcitonin achieves this by inhibiting osteoclasts, which are responsible for bone resorption and thereby releasing calcium into the bloodstream. It also stimulates osteoblasts to incorporate calcium into bone, promoting bone growth and structural integrity. Additionally, calcitonin enhances calcium excretion by the kidneys, further contributing to a decrease in blood calcium levels.
Calcitonin is particularly significant during periods of physiological stress, such as growth in children, pregnancy, and prolonged starvation. However, in healthy, nonpregnant, unstarved adults, the exact role of calcitonin remains unclear. In some clinical settings, synthetic calcitonin is used as a treatment for conditions like osteoporosis and osteoarthritis, due to its ability to reduce osteoclast activity and cartilage degradation, respectively.