Located in the neck, the thyroid gland releases hormones that regulate growth, metabolism, and appetite. In addition to messenger hormones, the pituitary also secretes growth hormone, endorphins for pain relief, and a number of key hormones that regulate fluid levels in the body.

The pituitary is often referred to as the “master gland” because its messenger hormones control all the other glands in the endocrine system, although it mostly carries out instructions from the hypothalamus. The pituitary gland descends from the hypothalamus at the base of the brain, and acts in close association with it. This section explores some of the major glands that make up the endocrine system and the hormones secreted by these glands ( Table 3.2). Imbalances in hormones are related to a number of disorders. Hormones are involved in regulating all sorts of bodily functions, and they are ultimately controlled through interactions between the hypothalamus (in the central nervous system) and the pituitary gland (in the endocrine system).

Figure 3.30 The major glands of the endocrine system are shown.