How do hormones travel around the body to act on organs?

Endocrine glands such as the pituitary, thyroid, adrenal glands, and pancreas release hormones directly into the blood. These molecules travel throughout the body but only affect cells that have the right receptor proteins. Once a hormone binds, it can switch genes on or off, change metabolism, or trigger growth and reproduction. Because the signals are delivered by blood, hormone responses are often slower than nerve signals but can last much longer. This system helps control everything from stress response to puberty and sleep cycles.