The endocrine system is the body’s slower chemical communication network. Glands release hormones into the bloodstream; the hormones travel to target organs and tissues, where they regulate growth, metabolism, reproduction, stress responses, and mood.

Major glands include the pituitary (often called the master gland), thyroid, adrenals, pancreas, and gonads. The hypothalamus sits at the interface of the nervous and endocrine systems, translating neural signals into hormonal commands. Unlike the rapid, targeted messages of the nervous system, hormonal effects can last minutes to hours and influence widespread systems simultaneously.

Feedback loops keep hormone levels within appropriate ranges. Too much or too little of a given hormone produces recognizable syndromes—hypothyroidism, Cushing’s disease, diabetes, and many others. Psychological states influence endocrine activity, and endocrine activity in turn shapes psychological states, creating continuous two-way traffic between mind and body.

When change needs to be sustained rather than momentary, the endocrine system carries the message.