Update | August 20, 2026 The endocrine system is composed of several endocrine glands . Some of these are individual organs, while others are specialized parts of larger organs. The function of endocrine glands is to produce hormones and release them into the bloodstream so that they can act on target cells throughout the body . Hormones only act on cells that have receptors capable of recognizing them, thereby triggering a specific response. Hormones help coordinate a wide range of body functions , including growth, sleep, temperature regulation, stress response, reproduction, metabolism, and many others. The endocrine system and the nervous system work in an integrated manner. Together, they are responsible for the functioning of many organs and for maintaining the balance of the internal environment, known as homeostasis. While the nervous system communicates through electrical impulses and neurotransmitters, producing rapid and generally short-lived responses, the endocrine system functions through hormones transported in the bloodstream, producing slower but usually longer-lasting responses. Hormone secretion is mainly controlled by feedback mechanisms. In other words, when there is a sufficient amount of a hormone in the blood, its production decreases; when blood levels fall, production increases. Hormones may act on a single organ or on several tissues simultaneously. Some have very specific effects, while others influence numerous functions throughout the body. Main organs, hormones and actions of the endocrine system The various glands of the endocrine system produce hormones with specific functions in the body. Hypothalamus and pituitary gland The hypothalamus and the pituitary gland form the main control center of the endocrine system and regulate the activity of several other glands through stimulating hormones. Hypothalamus Growth hormone-releasing hormone ( GHRH ): acts on the anterior pituitary gland, stimulating the release of growth hormone. Thyrotropin-releasing hormone ( TRH ): acts on the anterior pituitary gland, stimulating the production of thyroid-stimulating hormone. Gonadotropin-releasing hormone ( GnRH ): acts on the anterior pituitary gland, stimulating the release of luteinizing hormone and follicle-stimulating hormone. Vasopressin or antidiuretic hormone ( ADH ): acts on the kidneys, increasing water reabsorption, and on blood vessels, contributing to the regulation of blood pressure. Oxytocin : acts on the uterus, promoting contractions during childbirth, and on the mammary glands, promoting milk ejection. Pituitary gland The pituitary gland is divided into the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis). The former produces several regulatory hormones, whereas the latter stores and releases oxytocin and vasopressin produced by the hypothalamus. Growth hormone ( GH ): acts on almost all tissues, promoting growth and development. Thyroid-stimulating hormone ( TSH ): acts on the thyroid gland, stimulating the production of T3 and T4. Adrenocorticotropic hormone ( ACTH ): acts on the adrenal glands, stimulating cortisol production. Luteinizing hormone ( LH ): in females, it acts on the ovaries, triggering ovulation and stimulating progesterone production; in males, it acts on the testes, stimulating testosterone production. Follicle-stimulating hormone ( FSH ): in females, it acts on the ovaries, promoting follicle development; in males, it acts on the testes, stimulating sperm production. Prolactin : acts on the mammary glands, stimulating milk production. Pineal gland or epiphysis Melatonin : acts on the brain, particularly on the centers that regulate the sleep–wake cycle. Thyroid gland Thyroxine ( T4 ) and triiodothyronine ( T3 ): act on most cells in the body, influencing growth and development, metabolism and energy production. Calcitonin : acts on bones and kidneys, helping regulate calcium levels. Parathyroid glands Parathyroid hormone ( PTH ): acts mainly on bones and kidneys, regulating calcium and phosphorus levels in the body. Thymus Thymosin : acts on T lymphocytes and other components of the immune system. Pancreas Insulin : acts on the liver, muscles and adipose tissue, facilitating glucose uptake and storage. Glucagon : acts on the liver, promoting the release of glucose into the bloodstream. Somatostatin : acts on the pancreas, digestive tract and pituitary gland, inhibiting the release of various hormones and digestive secretions. Adrenal glands Cortisol : acts on various tissues, including the liver, muscles and adipose tissue, participating in the stress response and the regulation of metabolism. Aldosterone : acts on the kidneys, regulating sodium, potassium and water levels. Adrenal androgen s: act on various organs, influencing the development of certain secondary sexual characteristics, sexual desire, muscle and bone mass, and serving as precursors of testosterone and estrogens. Adrenaline or epinephrine : acts on the heart, blood vessels, lungs, liver and muscles, preparing the body for situations of alertness. Noradrenaline or norepinephrine : acts on blood vessels and the heart and contributes to the maintenance of blood pressure. Ovaries Estrogens : act on the uterus and mammary glands, promoting the development and maintenance of the female reproductive system. Also act on bones, the brain and the cardiovascular system, contributing to the maintenance of bone mass, cognitive function, mood and vascular health. Progesterone : acts mainly on the uterus and mammary glands, preparing and maintaining conditions favorable for pregnancy. Testes Testosterone : acts on the male reproductive organs, muscles, bones, skin, brain and bone marrow. It is essential for the development and maintenance of male sexual characteristics and for sperm production. Other organs and tissues also produce hormones, such as adipose tissue, the kidneys and the placenta during pregnancy, but those described above are the structures that are traditionally considered part of the endocrine system. Sources Kenhub. Sistema endócrino . Manual MSD Versão para a família. Biologia do sistema endócrino . The content published in the Health Guide is intended for the general public and is provided for informational and educational purposes only. It does not replace individual medical assessment, diagnosis, or personalized clinical advice from a qualified healthcare professional. The content is produced or reviewed by physicians and other healthcare professionals at Hospital da Luz and is based on the knowledge available at the time of publication or the most recent update, as indicated at the beginning of each item. English translation generated with AI and reviewed by the editorial team.
