Which hormone elevates calcium levels in the blood?

The hormone that elevates calcium levels in the blood is Parathyroid Hormone (PTH). PTH is produced by the parathyroid glands and plays a crucial role in regulating calcium homeostasis in the body. When blood calcium levels drop below a certain threshold, PTH is released into the bloodstream.

PTH acts on several target organs to increase calcium levels: it stimulates the release of calcium from bones, enhances the reabsorption of calcium in the kidneys, and promotes the activation of vitamin D, which increases calcium absorption from the intestines. This coordinated approach effectively raises the calcium concentration in the blood, ensuring vital processes such as muscle contraction and nerve signaling are maintained.

Other hormones mentioned in the question do not primarily function to raise blood calcium levels. Insulin is primarily involved in glucose metabolism and regulation. Calcitonin, produced by the thyroid gland, works in opposition to PTH by lowering blood calcium levels when they are elevated. Aldosterone primarily regulates sodium and potassium levels in the blood, influencing fluid balance and blood pressure but not directly affecting calcium homeostasis.