Endocrine Glands and Types of Hormones
Glands are small but powerful organs that are located throughout the body. They control very important body functions by releasing hormones.
The following glands make up the endocrine system:
- Pituitary Gland
- Pineal Gland
- Adrenal Glands
The pituitary gland is sometimes called the "master gland" because of its great influence on the other body organs. Its function is complex and important for overall well-being. It produces hormones that act directly on the body and that stimulate other endocrine glands to produce their own hormones. The anterior pituitary (the front part of the pituitary) produces several types of hormones:
- Prolactin: stimulates milk production from a woman's breasts after childbirth. In pregnant and breastfeeding women, prolactin helps prevent ovulation (the release of eggs from the ovaries).
- Growth hormone (GH): GH stimulates growth in childhood and is important for maintaining a healthy body composition. In adults it is also important for maintaining muscle mass and bone mass. GH also affects fat distribution in the body.
- Adrenocorticotropin (ACTH): ACTH stimulates production of cortisol by the adrenal glands. Cortisol, a so-called "stress hormone," is vital to survival. It helps maintain blood pressure and blood glucose levels, among other effects.
- Thyroid-stimulating hormone (TSH): TSH stimulates the thyroid gland to make thyroid hormones, which, in turn, control (regulate) the body's metabolism, energy, growth and development, and nervous system activity.
- Luteinizing hormone (LH): LH regulates testosterone in men and estrogen in women.
- Follicle-stimulating hormone (FSH): FSH stimulates the ovaries to release eggs (ovulate) in women. LH and FSH work together to allow normal function of the ovaries or testes, including sperm production.
The posterior pituitary (back part of the pituitary) produces two hormones:
- Oxytocin: Oxytocin causes milk to be released in nursing mothers and contractions during childbirth.
- Antidiuretic hormone (ADH): ADH, also called vasopressin, regulates water balance. If ADH is not secreted in the right amount, this can lead to too much or too little sodium (salt) and water in the bloodstream.
The hypothalamus is part of the brain that lies just above the pituitary gland. It releases hormones that start and stop the release of pituitary hormones. The hypothalamus controls hormone production in the pituitary gland through several "releasing" hormones. These include:
- growth hormone-releasing hormone, or GHRH (controls GH release)
- thyrotropin-releasing hormone, or TRH (controls TSH release)
- corticoptropin-releasing hormone, or CRH (controls ACTH release)
Another hormone made by the hypothalamus is gonadotropin-releasing hormone (GnRH). It tells the pituitary gland to make luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which are important for normal puberty and reproduction.
The thymus is a gland needed early in life for normal immune function. It is very large just after a child is born and weighs the most when a child reaches puberty. Then its tissue is replaced by fat. The thymus gland secretes hormones called humoral factors. These hormones help to develop the immune system, which is important in fighting bacteria and viruses.
Scientists are still learning how the pineal gland works. It makes at least one hormone: melatonin.
Melatonin may stop the action of the hormones that produce gonadotropin, which causes the ovaries and testes to develop and function. It also influences when people get sleepy at night.
The testes (testicles) produce the hormone testosterone. During puberty, testosterone helps to bring about the physical changes that turn a boy into an adult male, such as growth of the penis and testes, growth of facial and pubic hair, deepening of the voice, increase in muscle mass and strength, and increase in height. Throughout adult life, testosterone helps maintain sex drive, sperm production, male hair patterns, muscle mass, and bone mass.
The two most important hormones produced by the ovaries are estrogen and progesterone. These hormones are responsible for breast development, ovulation, and menstrual periods, as well as maintaining a pregnancy. The ovaries also produce inhibin, a protein that inhibits the release of FSH from the pituitary and helps control egg development.
The thyroid is a small gland in front of the neck. Thyroid hormones control your metabolism, which is the body's ability to break down food and store it as energy and the ability to break down food and use or store it as energy. The thyroid produces two hormones, T3 (called tri-iodothyronine) and T4 (called thyroxine).
Each adrenal gland is actually two endocrine organs. The outer portion is called the adrenal cortex. The inner portion is called the adrenal medulla.
The adrenal cortex produces glucocorticoids (such as cortisol) that help the body control blood sugar, increase the burning of protein and fat, and respond to stressors like fever, major illness, and injury. It also makes mineralcorticoids (such as aldosterone) which control blood pressure by acting on the kidneys to help them hold onto enough salt and water. The adrenal cortex also produces some androgens (hormones that act like testosterone), and contribute to pubic and underarm hair and adult body odor in both men and women.
The adrenal medulla produces epinephrine (adrenaline), which increases the heart rate, opens airways to improve oxygen intake, and increases blood flow to muscles, usually when a person is scared, excited, or under stress. Norepinephrine also is made by the adrenal medulla, but this hormone is more related to maintaining normal activities as opposed to emergency reactions.
Located behind the thyroid gland are four tiny parathyroid glands. These glands make hormones that help control calcium and phosphorous levels in the body. The parathyroid glands are necessary for proper bone development. They also maintain normal blood calcium levels, which is important for normal heart, muscle, and nerve function. When blood calcium levels are low, the parathyroid glands make parathyroid hormone which takes calcium from bones so that it will be available in the blood for important body functions.
The pancreas is a large gland behind your stomach that helps the body to maintain healthy blood sugar (glucose) levels. The pancreas secretes insulin, a hormone that helps glucose move from the blood into the cells where it is used for energy. The pancreas also secretes glucagon when the blood sugar is low. Glucagon tells the liver to release glucose that is stored in the liver into the bloodstream.
Bradley Anawalt, MD
Susan Kirk, MD
Dorothy Shulman, MD
Illustrator: Molly Feuer, 2013
Last Review: May 2013