What Are Hormones?

Growth Hormone

Hormones are proteins that act as chemical messengers, travelling to one or more specific target tissues or organs to fulfill very important regulatory functions in biological processes, enabled by the control of enzyme action. Insulin, for example, plays a very important role in regulating the amount of glucose in the bloodstream; estrogen, which is secreted by the ovaries, is responsible for developing female sexual characteristics and regulating various internal reproductive processes.

Hormones are involved in just about every biological process: immune function, reproduction, growth, mood, even controlling other hormones. They can work at astonishingly small concentrations — in parts per billion or trillion.

Hormones are powerful. It takes only a tiny amount to cause big changes in cells or even your whole body. That is why too much or too little of a certain hormone can be serious. Laboratory tests can measure the hormone levels in your blood, urine or saliva.