What is the effect of excessive parathyroid hormone secretion on bones?

• A. Increased bone formation
• B. Inhibition of osteoclasts
• C. Increased bone resorption
• D. Closure of epiphyseal plates

Answer: (C)

Excessive secretion of parathyroid hormone (PTH) has a significant impact on bone metabolism, primarily through its role in regulating calcium levels in the body. When PTH is secreted in excess, it leads to increased bone resorption. This occurs because PTH stimulates the activity of osteoclasts, the cells responsible for breaking down bone tissue. As osteoclast activity is heightened, more minerals, particularly calcium, are released into the bloodstream, contributing to the overall effect of increasing bone resorption.

In this context, the process of bone remodeling is disrupted. Normal bone maintenance involves a balance between bone formation by osteoblasts and bone resorption by osteoclasts. However, excessive PTH skews this balance in favor of resorption, leading to a decrease in bone density and potentially resulting in osteopenia or osteoporosis over time. Understanding this effect is crucial for recognizing the implications of PTH in conditions like hyperparathyroidism, where excessive hormone levels can lead to skeletal complications.