The answer is the "pituitary gland".
Pituitary gland is the gland that regulates all other glands in the endocrine system, it is present at the center of the brain and its size is about a pea. Whenever the size of the pituitary gland increases, it is called pituitary microadenoma that refers to the tumor, but this is a benign tumor. And in this condition, pituitary gland produces more prolactin and disturbs other hormones also.