Which hormone increases metabolic rate and supports growth and development?

• A. Insulin
• B. Glucagon
• C. Thyroxine
• D. Calcitonin

Answer: (C)

Thyroid hormones regulate both metabolism and growth. Thyroxine, the main hormone produced by the thyroid, raises the body's basal metabolic rate in nearly all tissues. It does this by increasing transcription of metabolic enzymes, boosting mitochondrial activity, and increasing Na+/K+-ATPase activity, which together raise energy expenditure and heat production. Beyond energy use, thyroxine is essential for normal growth and development—especially of the brain and skeleton—by promoting tissue maturation and enhancing the actions of growth hormone. In children, adequate thyroxine is critical for normal brain development and linear growth. Without enough thyroxine, growth slows and metabolism is dampened. Conversely, too much thyroxine speeds metabolism and can cause weight loss and irritability. Other hormones listed don’t drive overall metabolic rate and maturation in the same way: insulin fosters glucose uptake and anabolic storage; glucagon increases glucose production during fasting; calcitonin mainly modulates calcium and bone turnover.