What is the main action of thyroid hormones (T3 and T4)?

Thyroid hormones, primarily triiodothyronine (T3) and thyroxine (T4), play a crucial role in various physiological processes, with their primary action being the increase of metabolism and the regulation of growth and development.

These hormones influence nearly every cell in the body by enhancing the metabolic activity, which leads to increased oxygen consumption and heat production. This metabolic enhancement stimulates various processes such as protein synthesis, glucose metabolism, and lipid metabolism. Additionally, thyroid hormones are essential for proper growth and development, particularly in the nervous system and skeletal system, influencing brain maturation and overall physical growth.

The role of thyroid hormones extends beyond just metabolism; they are pivotal for maintaining overall homeostasis within the body's systems, allowing for appropriate energy utilization and supporting an individual's growth trajectory. Their influence is critical from early development through adulthood, including supporting cognitive function and influencing reproductive health.

In contrast, the other options do not accurately capture the primary function of T3 and T4. While thyroid hormones do influence metabolic rates, the primary action is not to decrease metabolic rate. Thyroid hormones do not directly stimulate the immune system, nor do they primarily function to regulate calcium levels in the blood, which is more closely associated with parathyroid hormone and