The pituitary gland is often called the master gland because it:

1. The pituitary descends from the hypothalamus at the base of the brain and works in close association with it. 2. It is often referred to as the master gland because its messenger hormones control all the other glands in the endocrine system. 3. The chapter immediately qualifies this: it mostly carries out instructions from the hypothalamus. 4. That qualification rules out option D, since the pituitary is directed by a structure of the nervous system. _Source: OpenStax Psychology (1st ed., CC BY 4.0), Ch 3 "Biopsychology", §3.5 The Endocrine System_