Endocrinology is the branch of medicine and biology that deals with the study of the endocrine system, which includes glands and organs that secrete hormones into the bloodstream. These hormones are chemical messengers that help regulate various bodily functions, including metabolism, growth, reproduction, and mood. The endocrine system works in concert with the nervous system to maintain homeostasis, the body's internal balance, and respond to external stimuli.

At the core of the endocrine system are the endocrine glands, which include the hypothalamus, pituitary gland, thyroid gland, adrenal glands, pancreas, ovaries, and testes. Each of these glands produces specific hormones that target various organs and tissues throughout the body. The hypothalamus, located in the brain, acts as the command center for the endocrine system. It sends signals to the pituitary gland, which in turn regulates other glands. The thyroid gland, for example, produces thyroid hormones that control metabolism, while the adrenal glands release corticosteroids and catecholamines in response to stress.

One of the defining characteristics of the endocrine system is its regulation through feedback mechanisms, primarily negative feedback loops. In these loops, the secretion of a hormone is reduced or increased based on the levels of that hormone in the blood. For example, when blood glucose levels rise, the pancreas secretes insulin to lower them. Once glucose levels return to normal, insulin secretion decreases. These feedback systems help the body adapt to changing conditions and maintain a stable internal environment.