What is the effect of thyroid hormones on basal metabolic rate and related processes?

• A. Increase basal metabolic rate, heat production, and energy expenditure.
• B. No change in basal metabolic rate, heat production, or energy expenditure.
• C. Decrease basal metabolic rate, heat production, and energy expenditure.
• D. Increase energy expenditure only.

Answer: (A)

Thyroid hormones raise resting energy expenditure by boosting metabolism in nearly all tissues. They increase the basal metabolic rate by upregulating genes for mitochondrial function and oxidation, which makes cells burn more fuel at rest. This includes more mitochondrial biogenesis and greater activity of oxidative enzymes, leading to higher oxygen consumption and more heat produced as a byproduct of increased ATP turnover.

In addition, thyroid hormones stimulate Na+/K+-ATPase activity, which uses energy and adds to overall energy expenditure. They also enhance thermogenesis in brown adipose tissue by increasing UCP1, which uncouples oxidative phosphorylation from ATP production and releases energy as heat.

The combined effect is higher energy expenditure and more heat generation at rest and with activity, explaining why the correct choice notes increases in basal metabolic rate, heat production, and energy expenditure.