Parathyroid hormone (PTH) is a polypeptide hormone secreted by the parathyroid that enhances bone calcium mobilization, enhances osteoblast activity (anabolic), increases blood calcium levels and calcium:phosphate ratio in the kidney, and promotes absorption of calcium by the intestines. The 1-34 amino acid fragment also induces BMP gene transcription. Agonist of the parathyroid hormone receptors PTH1 and PTH2.