Which hormone passes through the cell membrane and mitochondrial membrane to exert some of its influence on metabolism?

The correct choice is thyroid hormone, which is known for its ability to pass through both the cell membrane and the mitochondrial membrane to exert its effects on metabolism. Unlike many other hormones, thyroid hormone is lipophilic, allowing it to easily diffuse through lipid membranes without needing a transport mechanism.

Once inside the cell, thyroid hormone interacts with nuclear receptors to regulate gene expression, ultimately influencing metabolic processes such as glycolysis, gluconeogenesis, and fat oxidation. This direct impact on mitochondrial function also enhances ATP production, thereby increasing overall metabolic activity.

In contrast, hormones like insulin and growth hormone primarily act through membrane-bound receptors, triggering signaling pathways that do not require passage through the membrane. Insulin, for instance, predominantly influences metabolism through its effect on glucose uptake and metabolic pathways via cell surface receptors. Similarly, growth hormone exerts its effects on growth and metabolism through a different signaling mechanism that does not involve crossing into mitochondria.