What is the relation of PTH and urinary calcium level?

The relation between parathyroid hormone (PTH) and urinary calcium level is inverse. This means that when PTH levels increase, urinary calcium levels decrease, and conversely, when PTH levels decrease, urinary calcium levels increase.

PTH is a hormone produced by the parathyroid glands, located near the thyroid gland. One of its main functions is to regulate calcium and phosphorus levels in the blood. When PTH levels rise, it acts on the kidneys to increase calcium reabsorption and decrease phosphate reabsorption, leading to higher blood calcium levels and lower blood phosphate levels. Simultaneously, PTH decreases calcium excretion in the urine, resulting in lower urinary calcium levels.

On the other hand, when PTH levels decrease, the opposite effects occur. Calcium reabsorption in the kidneys decreases, phosphate reabsorption increases, and calcium excretion in the urine increases, leading to lower blood calcium levels, higher blood phosphate levels, and higher urinary calcium levels.

The inverse relationship between PTH and urinary calcium helps maintain calcium homeostasis in the body. When blood calcium levels decrease, PTH secretion increases to raise blood calcium levels and vice versa. This regulatory mechanism ensures that the body's calcium levels are within a narrow range necessary for various physiological processes, including muscle contraction, nerve transmission, and bone metabolism.