Describe how PTH and CT regulate blood calcium levels
What will be an ideal response?
PTH is secreted from the parathyroid glands in response to decreasing blood Ca2+ levels. PTH helps elevate blood Ca2+ levels by stimulating osteoclasts, bone cells that secrete acids that dissolve the bone's matrix, thus releasing Ca2+ into the blood. PTH also causes the kidneys to conserve Ca2+ ions (secrete fewer into the urine), which helps maintain optimum Ca2+ levels in the blood. CT is secreted from the thyroid gland in response to increasing levels of Ca2+ ions in the blood. CT helps lower the blood Ca2+ level in three ways: (1) by stimulating osteoblasts, bone cells that deposit osteoid in which calcium salts precipitate; thus, bones serve as a reservoir or "bank" for Ca2+ ions; (2) CT inhibits osteoclasts thereby inhibiting the process of bone resorption that would raise blood Ca2+ levels; and (3) CT promotes Ca2+ ion excretion by the kidneys.
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