Calcitonin

Definition

Calcitonin is a hormone produced by the thyroid gland that helps regulate calcium levels in the blood by lowering them when they are too high. This hormone works in conjunction with parathyroid hormone (PTH) to maintain calcium homeostasis, playing a crucial role in bone metabolism and skeletal health.

5 Must Know Facts For Your Next Test

1. Calcitonin primarily lowers blood calcium levels by inhibiting the activity of osteoclasts, reducing bone resorption.
2. The release of calcitonin is stimulated by high levels of calcium in the blood, making it an essential component in calcium homeostasis.
3. Calcitonin can be used therapeutically to treat conditions like osteoporosis and Paget's disease due to its ability to strengthen bones.
4. In humans, calcitonin is produced mainly in the parafollicular cells (C cells) of the thyroid gland.
5. While calcitonin plays a role in calcium regulation, its overall importance in human physiology is less significant compared to parathyroid hormone.

Review Questions

• How does calcitonin function in relation to osteoblasts and osteoclasts in maintaining bone health?
  • Calcitonin plays a key role in maintaining bone health by inhibiting the activity of osteoclasts, which are responsible for breaking down bone tissue. When calcitonin is released due to high blood calcium levels, it slows down osteoclast function, leading to reduced bone resorption. At the same time, osteoblasts, which build new bone, can continue their activity without interference from increased osteoclast activity, promoting a healthier balance in bone metabolism.
• Discuss the physiological response triggered by elevated blood calcium levels and the role of calcitonin in this process.
  • When blood calcium levels rise above normal, it triggers a physiological response involving the secretion of calcitonin from the thyroid gland. This hormone acts to lower blood calcium by inhibiting osteoclast activity and enhancing calcium deposition in bones. As a result, calcitonin helps restore calcium balance in the body, working against parathyroid hormone, which increases calcium levels. This feedback mechanism is essential for maintaining overall skeletal health and preventing hypercalcemia.
• Evaluate the clinical implications of calcitonin therapy for conditions like osteoporosis and how it compares to other treatments.
  • Calcitonin therapy has clinical implications for treating osteoporosis by helping to slow bone loss and reduce fracture risk. Unlike bisphosphonates or estrogen-based therapies that primarily inhibit bone resorption through different mechanisms, calcitonin directly decreases osteoclast activity. While effective for some patients, its use may be limited compared to other treatments due to lower potency and less impact on overall fracture risk. However, its safety profile makes it a viable option for specific populations who may not tolerate other medications.

Related terms

Parathyroid Hormone (PTH): A hormone secreted by the parathyroid glands that increases blood calcium levels by promoting the release of calcium from bones, reabsorption in the kidneys, and absorption from the intestines.

Osteoblasts: Cells responsible for bone formation, which synthesize and secrete the bone matrix and are influenced by hormones like calcitonin to help regulate bone density.

Osteoclasts: Cells that break down bone tissue, releasing calcium into the bloodstream; their activity is inhibited by calcitonin to help lower blood calcium levels.