Endocrinology is the branch of biology that focuses on the endocrine system, its diseases, and the specific chemical messengers known as hormones. This field investigates how glands like the pituitary, thyroid, and adrenals produce and secrete hormones directly into the bloodstream to regulate a multitude of distant physiological processes. These processes are fundamental to life and include growth, development, tissue function, sleep, mood, and, critically, metabolism, which involves the conversion of food into energy and the building blocks for the body. Endocrinologists diagnose and treat hormonal imbalances and the wide range of disorders that result from them, such as diabetes, thyroid disease, and infertility.