How does thyroid hormone exert its effect on basal metabolic rate?

Thyroid hormone plays a crucial role in regulating the basal metabolic rate (BMR) by increasing the synthesis of Na+/K+ ATPase. This enzyme is essential for maintaining the electrochemical gradient across cell membranes, which is fundamental for various cellular functions, including glucose uptake, muscle contraction, and maintaining resting membrane potential.

When thyroid hormones (primarily thyroxine, T4, and triiodothyronine, T3) are present, they promote increased production of Na+/K+ ATPase. The enhanced activity of this enzyme leads to greater ATP consumption because it actively pumps sodium out of cells and potassium into cells, a process that consumes a significant amount of energy. This increased energy expenditure raises the metabolic rate and promotes the metabolism of carbohydrates and fats, contributing to the overall increase in BMR.

The other options do not accurately describe the direct actions of thyroid hormones in the context of basal metabolic rate. Decreasing muscle metabolism, enhancing fat storage, or inhibiting protein synthesis would not contribute to an increase in BMR, but rather suggest a reduction in metabolic activity or energy expenditure. Therefore, increasing Na+/K+ ATPase synthesis exemplifies how thyroid hormones boost metabolism and regulate energy use in the body.