The correct answer is option 3, the pituitary gland. The pituitary gland is often referred to as the master gland because it plays a crucial role in regulating the functions of other endocrine glands in the body. It is located at the base of the brain and is responsible for releasing hormones that control various bodily processes such as growth, reproduction, and metabolism. The pituitary gland receives signals from the hypothalamus, another important gland in the brain, which helps to regulate its hormone production. While the other options listed (thyroid, adrenal gland, and pancreas) are also important glands in the body, they do not have the same level of control and regulation over the other glands as the pituitary gland does.