Hyperparathyroidism is a condition characterized by overactivity of the parathyroid glands, leading to excessive production of parathyroid hormone (PTH). This hormone plays a crucial role in regulating calcium levels in the body. In cases of hyperparathyroidism, there is increased excretion of calcium due to several mechanisms:

  1. Increased Bone Resorption: One of the primary effects of PTH is to stimulate the resorption of calcium from bones. In hyperparathyroidism, where PTH levels are elevated, there is excessive breakdown of bone tissue to release calcium into the bloodstream. This leads to increased levels of calcium in the blood and subsequently increased excretion of calcium by the kidneys.
  2. Enhanced Intestinal Absorption: PTH also acts on the intestines to increase the absorption of dietary calcium. This further contributes to higher levels of calcium in the blood, which ultimately results in increased renal excretion as the kidneys attempt to maintain calcium homeostasis.
  3. Impaired Renal Reabsorption: While PTH promotes calcium reabsorption in the kidneys under normal conditions, prolonged exposure to high levels of PTH can lead to desensitization of renal tubules to its effects. As a result, there may be impaired reabsorption of calcium in the kidneys, leading to increased excretion of calcium in the urine.
  4. Formation of Kidney Stones: The increased excretion of calcium in hyperparathyroidism can also predispose individuals to the formation of kidney stones. High levels of urinary calcium can contribute to the development of calcium-containing stones within the kidneys or urinary tract.
  5. Calcium-Phosphate Imbalance: Hyperparathyroidism can disrupt the balance between calcium and phosphate in the body. Excessive loss of calcium through urine can lead to low levels of serum calcium, triggering compensatory mechanisms that further enhance renal excretion of calcium.

In summary, hyperparathyroidism results in increased excretion of calcium primarily due to enhanced bone resorption, augmented intestinal absorption, impaired renal reabsorption, potential formation of kidney stones, and disruption of calcium-phosphate balance within the body.

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