But suppose you want to tell more than just one person. You could call all your friends one at a time, but this would take a very long time. By the time you got the message out, it might be too late.
So how can you get a message to all your friends quickly? Suppose that you drive to your local radio station and broadcast your message. Doing this allows all your friends to hear your message at the same time.
Your endocrine system is similar to a radio broadcast. Instead of using radiowaves to transmit messages, your endocrine system uses chemicals. These chemicals are called hormones. Hormones travel through the blood stream and affect the activities of the various cells within your body.