Which hormone is primarily responsible for bone maturation and epiphyseal closure?

• A. Growth hormone
• B. Estrogen
• C. Testosterone
• D. Thyroid hormone

Answer: (B)

Estrogen is the primary hormone that drives bone maturation and the closing of the epiphyseal growth plates. It acts on the growth plate to promote chondrocyte maturation and eventually triggers fusion of the epiphysis to the metaphysis, which terminates longitudinal bone growth. Growth hormone fuels overall bone growth by increasing IGF-1, but it doesn’t determine when the growth plates close. Thyroid hormone supports normal growth as well, yet it’s not the main signal responsible for epiphyseal fusion. In males, testosterone contributes to maturation largely by being converted to estrogen, which then promotes plate closure. So the hormone that directly orchestrates both maturation and eventual plate closure is estrogen.