Caption:
A molecular model of parathyroid hormone (PTH), a hormone secreted by chief cells in the parathyroid glands, responsible for increasing calcium concentrations in the blood. An orientation view is located on the right, with the four parathyroid glands situated on the posterior surface of the thyroid. Once activated, PTH regulates osteoclast activity to increase bone resorption of calcium, as well as the reabsorption of calcium from the kidneys and small intestine. The pink helical ribbon model of the protein is surrounded by atoms coloured dark grey (carbon), light grey (hydrogen), blue (nitrogen), red (oxygen) and yellow (sulphur).