Calcium-Sensing Receptor

Definition

The calcium-sensing receptor (CaSR) is a G protein-coupled receptor that plays a crucial role in the regulation of calcium homeostasis in the body. It acts as a molecular sensor, detecting changes in extracellular calcium levels and triggering appropriate physiological responses to maintain calcium balance.

5 Must Know Facts For Your Next Test

1. The calcium-sensing receptor is primarily expressed in the parathyroid glands, kidneys, and bones, where it plays a key role in calcium homeostasis.
2. In the parathyroid glands, the CaSR senses changes in extracellular calcium levels and regulates the secretion of parathyroid hormone (PTH) accordingly.
3. Activation of the CaSR in the kidneys promotes the reabsorption of calcium and the excretion of phosphate, helping to maintain serum calcium levels.
4. The CaSR also influences bone metabolism by modulating the activity of osteoblasts and osteoclasts, the cells responsible for bone formation and resorption.
5. Mutations in the CaSR gene can lead to disorders of calcium homeostasis, such as familial hypocalciuric hypercalcemia and autosomal dominant hypocalcemia.

Review Questions

• Explain the role of the calcium-sensing receptor in the regulation of parathyroid hormone (PTH) secretion.
  • The calcium-sensing receptor (CaSR) in the parathyroid glands acts as a molecular sensor, detecting changes in extracellular calcium levels. When extracellular calcium concentrations decrease, the CaSR triggers an increase in the secretion of parathyroid hormone (PTH). PTH then acts on the bones, kidneys, and intestines to increase calcium levels in the blood. Conversely, when extracellular calcium levels rise, the CaSR inhibits PTH secretion, allowing calcium levels to return to the normal range.
• Describe the influence of the calcium-sensing receptor on calcium and phosphate handling in the kidneys.
  • The calcium-sensing receptor (CaSR) expressed in the kidneys plays a crucial role in regulating calcium and phosphate homeostasis. When extracellular calcium levels rise, the activation of the CaSR in the kidneys promotes the reabsorption of calcium and the excretion of phosphate. This helps maintain the appropriate balance between calcium and phosphate in the body. Conversely, when extracellular calcium levels drop, the CaSR inhibits calcium reabsorption and increases phosphate reabsorption, contributing to the restoration of normal calcium and phosphate levels.
• Evaluate the significance of the calcium-sensing receptor in the regulation of bone metabolism and the development of calcium-related disorders.
  • The calcium-sensing receptor (CaSR) is essential for the proper regulation of bone metabolism. By modulating the activity of osteoblasts (bone-forming cells) and osteoclasts (bone-resorbing cells), the CaSR helps maintain the balance between bone formation and resorption. Disruptions in CaSR function, such as genetic mutations, can lead to disorders of calcium homeostasis, including familial hypocalciuric hypercalcemia and autosomal dominant hypocalcemia. These conditions are characterized by abnormal calcium levels and can have significant impacts on bone health and overall physiological function. Understanding the role of the CaSR in calcium regulation is crucial for the diagnosis, management, and potential treatment of these calcium-related disorders.

Related terms

Parathyroid Hormone (PTH): A hormone secreted by the parathyroid glands that helps regulate calcium and phosphate levels in the body by stimulating bone resorption and increasing calcium reabsorption in the kidneys.

Calcitonin: A hormone produced by the thyroid gland that helps lower blood calcium levels by inhibiting bone resorption and increasing calcium excretion in the kidneys.

Extracellular Calcium Concentration: The concentration of calcium ions in the fluid outside of cells, which is tightly regulated by the body to maintain homeostasis.