How does Parathyroid Hormone promote bone formation?

• A. By stimulating osteoclast activity
• B. By stimulating osteoblastic formation
• C. By increasing bone resorption
• D. By promoting calcitonin release

Answer: (B)

Parathyroid Hormone (PTH) plays a crucial role in the regulation of calcium levels in the bloodstream and has a significant influence on bone metabolism. When considering how PTH promotes bone formation, it is essential to understand that while PTH is primarily known for its role in increasing calcium levels by stimulating bone resorption through osteoclasts, it also has a direct anabolic effect on bone.

PTH stimulates osteoblast activity, which are the cells responsible for bone formation. It enhances the proliferation of osteoblasts and promotes their differentiation from precursor cells in the bone marrow. This leads to the synthesis of new bone tissue, thus contributing to bone formation. Additionally, PTH initiates a signaling cascade that ultimately leads to increased production of RANKL, a factor that influences the balance between osteoblast and osteoclast activity. However, under certain conditions, such as intermittent exposure, PTH can lead to an increase in bone formation due to enhanced osteoblastic activity.

Understanding PTH's role in bone metabolism illustrates how it not only facilitates the release of calcium from bones but can also promote the growth of new bone tissue through stimulating osteoblasts, which explains why the correct option focuses on this aspect of PTH's function.