AP BIOLOGY

Detailed explanation-1: -If calcium blood levels are too low, your parathyroid glands will release PTH into the blood. This causes calcium levels to rise. If calcium blood levels are too high, these glands will stop making PTH.

Detailed explanation-2: -Calcitonin, a hormone produced by the thyroid, acts in opposition to PTH by inhibiting osteoclasts, stimulating osteoblasts, and increasing excretion of calcium into the urine by the kidneys.

Detailed explanation-3: -Effects of PTH on the Kidneys Most of the physiologic calcium reabsorption in the nephron takes place in the proximal convoluted tubule and additionally at the ascending loop of Henle. Circulating parathyroid hormone targets the distal convoluted tubule and collecting duct, directly increasing calcium reabsorption.

Detailed explanation-4: -Parathyroid hormone regulates calcium levels in the blood, largely by increasing the levels when they are too low. It does this through its actions on the kidneys, bones and intestine: Bones – parathyroid hormone stimulates the release of calcium from large calcium stores in the bones into the bloodstream.