Endocrinology is the branch of medicine dealing with the study of disorders of the endocrine system and its specific secretions called hormones. Hormones are molecules that act as signals from one type of cells to evoke a specific response in other cells. Most hormones reach their targets via the blood. Although every organ system secretes and responds to hormones (including the brain, lungs, heart, intestine, skin, and the kidney), the clinical specialty of endocrinology focuses primarily on the endocrine organs, meaning the organs whose primary function is hormone secretion. These organs include the pituitary, thyroid, adrenals, ovaries and testes, and pancreas.
Endocrinologists are physicians (medical doctors) who specialize in treating disorders of the endocrine system, such as diabetes, hyperthyroidism, and many others. A disease due to a disorder of the endocrine system is often called a "hormone imbalance," but is technically known as an endocrinopathy or endocrinosis.