The major link between the brain and the glandular system is the

The answer is the hypothalamus.

The hypothalamus is a small region of the brain. It's located at the base of the brain, near the pituitary gland.

While it's very small, the hypothalamus plays a crucial role in many important functions, including: releasing hormones, regulating body temperature, maintaining daily physiological cycles, controlling appetite, managing of sexual behavior and regulating emotional responses.