How does thyroid hormone affect metabolism?

Thyroid hormone, particularly thyroxine (T4) and triiodothyronine (T3), plays a crucial role in regulating metabolism within the body. When thyroid hormone levels are adequate, they stimulate various metabolic processes, thereby increasing the metabolic rate. This increase leads to enhancements in both the utilization of carbohydrates and fats for energy, as well as the overall production of heat in the body, a phenomenon known as thermogenesis.

By speeding up metabolic processes, thyroid hormones facilitate the conversion of food into energy and support the growth and differentiation of cells. They influence several physiological functions including cardiac output, respiratory rate, and even the rate of digestion. An increase in metabolic rate helps maintain energy balance and is critical for overall health and homeostasis.

Given that the other choices either suggest that thyroid hormones do not influence metabolism or that they decrease metabolic activities, they do not accurately reflect the established role of thyroid hormones in enhancing metabolic functions. Therefore, the choice indicating that thyroid hormone increases the metabolic rate is the most accurate representation of its physiological effects.