What are hormones?

A hormone is a chemical produced in one part of the body and released into the blood to trigger or regulate particular functions of the body. For example, insulin is a hormone made in the pancreas that tells other cells when to use glucose for energy. Synthetic hormones, made for use as medicines, can be the same as or different from those made in the body.

Scientists discovered the existence of hormones in the late 1890s. A hormone, which is an organic product of living cells, regulates specific cellular activities, such as reproduction and growth.

Dr. Jack Merendino, MD

Hormones are chemicals that are made by specific cells, are released into the blood stream and travel through the body to other cells where they have a biological effect. There are many hormones made in the body. Those that are most often associated with health-related issues include thyroid hormones, insulin, parathyroid hormone, prolactin, cortisol, aldosterone, testosterone, estrogen, progesterone, epinephrine and others. Hormone-related problems may result from too much of a given hormone, too little or an abnormal pattern of hormone secretion. In addition, there are many substances that meet the definition outlined above but which are not usually thought of as hormones. For example, mediators of inflammation such as histamine or chemicals broadly labeled “cytokines” that communicate important information between immune cells are made by one cell type, released into the blood and act on other cells at distant locations. These chemicals are not labeled as hormones, but the distinction is a little bit arbitrary. The same is true of neurotransmitters—the chemicals that communicate signals between nerve cells. Epinephrine (also called adrenaline) is an example of a chemical that is sometimes thought of as a hormone—when it is made in the adrenal glands and secreted into the bloodstream–and sometimes thought of a neurotransmitter—when it is released at a nerve cell ending and travels to the adjacent nerve to communicate a signal. Obviously epinephrine is not just a hormone and not just a neurotransmitter, but both. The same is true for a number of other hormones and cytokines.

Hormones are messengers that travel in the blood. They deliver messages that help control lots of things in the human body.

For example, the hormone cortisol controls blood sugar levels and helps the body deal with stresses like injury or  infection. Another hormone, called aldosterone controls blood pressure by telling the body how much salt should be in the blood.

Dr. Dawn Marcus

Hormones are chemical substances that are made by cells in one part of the body, and then released to control and regulate different cells, often in other parts of the body. Hormones can be stored in organs called glands and released later, when needed. Hormones perform a wide range of important functions. They can affect growth, development and reproduction, as well as regulate the body's metabolism, immune system and mood. A wide variety of hormones are produced in many parts of the body.

The Woman's Migraine Toolkit: Managing Your Headaches from Puberty to Menopause (A DiaMedica Guide to Optimum Wellness)

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The Woman's Migraine Toolkit: Managing Your Headaches from Puberty to Menopause (A DiaMedica Guide to Optimum Wellness)

Migraines are a common, controllable type of headache that affects one in every six women, more than 20 million in the United States alone. The Woman’s Migraine Toolkit helps readers take charge of...

Hormones are chemicals that are released by cells that affect other cells in the body. Hormones are transported in the bloodstream and act as chemical messengers.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.