Hormones are substances that are secreted (or released) by cells that act to regulate the activity of other cells in the body. As a result, many activities in the human body are regulated by hormones. For example, reacting to fear, developing male or female characteristics, and growing taller are all regulated by hormones. Hormones are important to keep your body functioning.
There are four major functions identified with hormones. Hormones regulate growth, development, behavior, and reproduction. Hormones coordinate the production, use and storage of energy. Hormones are involved in maintaining nutrition, metabolism, excretion, and water and salt balance. And finally, hormones react to stimuli from outside the body.
Hormones act as chemical messengers that carry instructions to other cells to change their activity. The heart beats faster as hormones carry instructions to the cells of the heart telling it to increase the heartbeat. It was once believed that hormones had to travel through the bloodstream, but scientists know today that that is not true. Some hormones act directly on adjacent cells without traveling through the blood.
The message that a hormone carries is determined by both the hormone itself and the cell it is carrying the message to. A hormone can instruct a cell to produce an enzyme or a specific protein. Simply put, hormones can instruct a muscle cell to relax and a nerve cell to fire.
Each hormone is specific to the cell it is traveling to. Each hormone acts like a key that opens a lock on or inside the cell. A hormone can only act on cells with the right lock.
Endocrine glands are important organs in the human body that hormones are secreted from. All of the endocrine glands together make up the endocrine system. The endocrine system coordinates the body's entire source of hormones.
There are several other organs that contain cells that secrete hormones. These organs include the brain, stomach, small intestine, kidney, liver, and heart.
The endocrine system and the nervous system interact to coordinate the overall activity of the body., and hormones play an important role.
The chemical messengers for the nervous system are known as neurotransmitters while the chemical messengers for the endocrine system are known as hormones. There are some nerve cells that are able to secrete hormones. For example, epinephrine is both a neurotransmitter and a hormone.
Hormones are normally a slower-acting and longer-lived messenger whereas the neurotransmitters are usually fast-acting and short-lived. The effect of a hormone can last for days, weeks, or even years.
After a hormone is released from the cell in which it is made, they bind and act on target cells. A target cell is a specific cell a hormone binds to and carries the message. If the hormone was not specific, all the cells in the body would react to a hormone resulting in uncoordinated activities.
Finally, there are two main hormone classifications. They are either amino-acid-based hormones or they are steroid-based hormones. Amino-acid-based hormones are water soluble and made up of amino acids. Steroid-based hormones are lipid hormones made from cholesterol and are fat soluble.
Since the human body makes more than 40 hormones, it is important that the release of them is regulated regardless of which hormone is being produced.