Which hormone promotes calcium reabsorption by the kidneys?

The hormone that promotes calcium reabsorption by the kidneys is parathyroid hormone. This hormone is produced by the parathyroid glands and plays a crucial role in regulating calcium levels in the blood. When blood calcium levels fall, parathyroid hormone is released, stimulating the kidneys to reabsorb more calcium back into the bloodstream rather than excreting it in the urine. This process helps maintain adequate calcium levels, which are essential for various bodily functions, including muscle contraction and nerve transmission.

Calcitonin, produced by the thyroid gland, primarily lowers blood calcium levels by inhibiting bone resorption and promoting calcium excretion in the kidneys, working in opposition to parathyroid hormone. Insulin, while vital for glucose metabolism, does not directly influence calcium reabsorption. Renin is involved in the regulation of blood pressure and fluid balance and does not affect calcium levels. Thus, the role of parathyroid hormone is critical in enhancing renal calcium reabsorption and ensuring calcium homeostasis.