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💀anatomy and physiology i review

Calcium-Sensing Receptor

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

The calcium-sensing receptor (CaSR) is a G-protein coupled receptor that acts as a molecular sensor, detecting changes in extracellular calcium concentrations and initiating signaling cascades to maintain calcium homeostasis within the body. This receptor plays a crucial role in the regulation of calcium levels, particularly in the interactions between the skeletal system and other organ systems, as well as in the function of the parathyroid glands.

5 Must Know Facts For Your Next Test

  1. The calcium-sensing receptor is primarily expressed in the parathyroid glands, kidneys, and bone, where it plays a crucial role in the regulation of calcium homeostasis.
  2. CaSR activation in the parathyroid glands triggers the release of parathyroid hormone (PTH), which in turn stimulates the mobilization of calcium from bone and the increased absorption of calcium in the intestines.
  3. In the kidneys, CaSR activation regulates the reabsorption of calcium, helping to maintain appropriate calcium levels in the body.
  4. Mutations in the calcium-sensing receptor gene can lead to disorders of calcium homeostasis, such as familial hypocalciuric hypercalcemia and autosomal dominant hypocalcemia.
  5. The calcium-sensing receptor is also expressed in other tissues, such as the thyroid gland, where it plays a role in the secretion of calcitonin, a hormone that helps lower blood calcium levels.

Review Questions

  • Explain the role of the calcium-sensing receptor in the regulation of calcium homeostasis.
    • The calcium-sensing receptor (CaSR) acts as a molecular sensor, detecting changes in extracellular calcium concentrations and initiating signaling cascades to maintain calcium homeostasis. When extracellular calcium levels rise, CaSR activation in the parathyroid glands triggers the release of parathyroid hormone (PTH), which then stimulates the mobilization of calcium from bone and the increased absorption of calcium in the intestines. Conversely, when calcium levels drop, CaSR signaling decreases PTH secretion, helping to restore normal calcium concentrations. The CaSR also regulates calcium reabsorption in the kidneys, further contributing to the body's tight control of calcium levels.
  • Describe the relationship between the calcium-sensing receptor and the parathyroid glands in the context of calcium homeostasis.
    • The calcium-sensing receptor (CaSR) plays a crucial role in the function of the parathyroid glands, which are responsible for the secretion of parathyroid hormone (PTH). When extracellular calcium levels rise, CaSR activation in the parathyroid glands triggers the release of PTH. PTH then acts on various target tissues, such as bone and the kidneys, to increase calcium mobilization and absorption, thereby helping to maintain calcium homeostasis. Conversely, when calcium levels drop, CaSR signaling decreases PTH secretion, allowing calcium levels to return to normal. This tight regulation of PTH release by the CaSR is essential for the body's ability to precisely control calcium concentrations within a narrow physiological range.
  • Analyze the potential clinical implications of mutations in the calcium-sensing receptor gene and how they may affect calcium homeostasis.
    • Mutations in the calcium-sensing receptor (CaSR) gene can lead to disorders of calcium homeostasis, such as familial hypocalciuric hypercalcemia and autosomal dominant hypocalcemia. Familial hypocalciuric hypercalcemia is characterized by a decreased sensitivity of the CaSR to extracellular calcium, resulting in an impaired ability to suppress parathyroid hormone (PTH) secretion, even in the presence of high calcium levels. This leads to persistent hypercalcemia and hypocalciuria (reduced calcium excretion in the urine). Conversely, autosomal dominant hypocalcemia is caused by a gain-of-function mutation in the CaSR, leading to increased sensitivity to calcium and an inappropriate suppression of PTH secretion, even when calcium levels are low. This results in hypocalcemia and hypercalciuria. Understanding the role of the CaSR in calcium homeostasis and the clinical manifestations of its genetic disorders is crucial for the proper diagnosis and management of these conditions.