What regulates the Basal Metabolic Rate (BMR) primarily?

The Basal Metabolic Rate (BMR) is primarily regulated by thyroid hormones, particularly thyroxine (T4) and triiodothyronine (T3). These hormones play a crucial role in the body's metabolism, influencing how quickly the body can utilize energy. Thyroid hormones increase the metabolic rate by promoting the oxidation of glucose and fat in cells, thereby enhancing energy production.

When thyroid hormone levels are normal, BMR is maintained at an optimal level, ensuring that the body's energy needs are met even at rest. A deficiency in thyroid hormones can lead to a significant reduction in BMR, resulting in weight gain and reduced energy levels, while an excess can increase BMR, potentially leading to weight loss and hyperactivity.

Insulin, adrenaline, and growth hormones have roles in metabolism and energy regulation but do not directly control BMR to the same extent as thyroid hormones. Insulin is primarily involved in regulating blood glucose levels and facilitating cellular uptake of glucose. Adrenaline, or epinephrine, is more closely associated with the body's fight-or-flight response and can temporarily elevate metabolic activities in response to stress. Growth hormones influence growth and muscle mass but are not the primary regulators of BMR.