American Board of Orthodontics (ABO) Practice Exam 2026 - Free Orthodontics Practice Questions and Study Guide

The primary hormone involved in bone remodeling and calcium homeostasis is parathyroid hormone (PTH). PTH plays a crucial role in regulating calcium levels in the blood by acting on bones, kidneys, and the gastrointestinal tract. When blood calcium levels drop, PTH is released from the parathyroid glands, stimulating the release of calcium from bones into the bloodstream. It enhances reabsorption of calcium in the kidneys and promotes the conversion of vitamin D to its active form, which increases intestinal absorption of calcium.

While calcitonin, vitamin D, and growth hormone also have roles in bone metabolism, they do not primarily drive the same processes as PTH. Calcitonin works to lower blood calcium levels, acting in opposition to PTH. Vitamin D enhances calcium absorption but is more of a co-factor than a primary regulator. Growth hormone influences overall growth and metabolism but is not specifically targeted at bone remodeling and calcium levels. Thus, PTH's decisive role in elevating blood calcium levels and adapting bone structure to maintain calcium homeostasis highlights why it is considered the primary hormone in this context.