During bone remodeling, which hormone is primarily responsible for increasing bone resorption when calcium is low?

During bone remodeling, which hormone is primarily responsible for increasing bone resorption when calcium is low?

• A. Parathyroid hormone
• B. Calcitonin
• C. Growth hormone
• D. Estrogen

Answer: (A)

When calcium in the blood is low, the body uses a fast-acting hormonal response to raise it, and the main driver is parathyroid hormone. This hormone signals bone to release calcium by boosting the activity of osteoclasts—the cells that break down bone and release calcium into the bloodstream. It does this in part by stimulating osteoblasts to produce signals like RANKL that promote osteoclast formation and activity. PTH also helps conserve calcium by increasing its reabsorption in the kidneys and by promoting the production of calcitriol, which raises intestinal calcium absorption. Calcitonin would work against this process by inhibiting osteoclasts, growth hormone mainly encourages bone formation rather than rapid resorption, and estrogen reduces bone resorption but isn’t the primary responder to low calcium levels. So, the hormone primarily responsible for increasing bone resorption when calcium is low is parathyroid hormone.

When calcium in the blood is low, the body uses a fast-acting hormonal response to raise it, and the main driver is parathyroid hormone. This hormone signals bone to release calcium by boosting the activity of osteoclasts—the cells that break down bone and release calcium into the bloodstream. It does this in part by stimulating osteoblasts to produce signals like RANKL that promote osteoclast formation and activity. PTH also helps conserve calcium by increasing its reabsorption in the kidneys and by promoting the production of calcitriol, which raises intestinal calcium absorption.

Calcitonin would work against this process by inhibiting osteoclasts, growth hormone mainly encourages bone formation rather than rapid resorption, and estrogen reduces bone resorption but isn’t the primary responder to low calcium levels. So, the hormone primarily responsible for increasing bone resorption when calcium is low is parathyroid hormone.