[Physiology of parathyroid hormone and calcitonin]

Parathyroid hormone, 1,25-vitamin D3 and calcitonin are the three major hormones in the control of calcium homeostasis. The physiological function of parathyroid hormone and 1,25-vitamin D3 in the short term regulation of calcium homeostasis by varying intestinal absorption and renal excretion are well established. However, there is still an ongoing debate on the physiological relevance of human calcitonin. Calcitonin seems to play an osteoprotective role over a longer period of time or during times in which the skeleton is under stress because large quantities of calcium are required like during pregnancy, lactation or growth. Some important physiological aspects of the two peptide hormones--parathyroid hormone and calcitonin--should be discussed within this article.