Calcitonin is a
hormone which is released by the
thyroid and parathyroid
glands when the levels of
calcium compounds in the
blood are too high. The
hormone acts to reduce the levels of
calcium and phosphate circulating in the
bloodstream. It is related to (but distinct from) the
hormone thyroxine.
A calcitonin molecule is a small peptide composed of thirty-two amino acids.
Some of the information in this writeup was taken from the science dictionary at http://biotech.icmb.utexas.edu/; I oversaw the development of the dictionary (the website was mothballed in 1998) and believe I wrote the entry this writeup is partly or wholly based upon.