Kaplan Nursing Entrance Practice Exam

What do thyroid hormones affect in nearly every cell of the body?

1. Growth of hair

2. Basal metabolic rate

3. Production of bile

4. Red blood cell production

The correct answer is: Basal metabolic rate

Thyroid hormones play a crucial role in regulating the basal metabolic rate (BMR) in nearly every cell of the body. The basal metabolic rate refers to the amount of energy expended while at rest in a neutrally temperate environment, in the post-absorptive state. This means that it reflects the energy required for maintaining essential physiological functions such as breathing, circulation, and cell production when the body is not engaged in physical activity or digesting food. Thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3), influence metabolism by regulating the speed at which cells convert oxygen and calories into energy. An increase in thyroid hormone production generally raises the basal metabolic rate, leading to increased energy expenditure and potentially weight loss. Conversely, low levels of thyroid hormones can lead to a decreased metabolic rate, resulting in weight gain and lethargy. While thyroid hormones do have an indirect effect on various other physiological processes, such as hair growth, bile production, and red blood cell production, their primary and most significant impact is on metabolic rate. This underscores the central role of thyroid hormones in overall metabolic health and energy regulation in the body.