Which hormone is responsible for stimulating cells to increase in size and divide more frequently?

Growth hormone, also known as somatotropin, plays a crucial role in stimulating growth, cell reproduction, and cell regeneration in humans and other animals. It promotes the increase in size of various body tissues through the stimulation of protein synthesis, encouraging cells to not only grow in size but also to proliferate. This hormone exerts its effects primarily on skeletal muscles and bones, which is essential during growth phases, especially during childhood and adolescence.

Growth hormone exerts its influence by binding to receptors on target cells, which then leads to various metabolic effects, including an increase in the number of cells (hyperplasia) and the size of existing cells (hypertrophy). This dual action significantly contributes to overall growth and development.

Other hormones mentioned, such as insulin, cortisol, and thyroid hormone, have important roles in metabolism and regulation of various bodily functions, but they do not primarily function to stimulate growth in terms of increasing cell size and division in the same manner as growth hormone does. Insulin is involved in glucose metabolism and storage, cortisol plays a key role in stress response and metabolism regulation, and thyroid hormone regulates metabolism but does not directly stimulate cell division and growth like growth hormone does.