Importance of Intercellular Communication: an Introduction to Basic Concepts

In the endocrine system, specialized glandular cells secrete hormones, which are carried in the bloodstream to all parts of the body, but only influence the activity of specifically responsive target cells, i.e., those with the appropriate receptor molecules. This is like a TV transmission system, which sends its signal everywhere, but which is only picked up by those receivers tuned to its particular channel. The endocrine system is a diffuse, fairly slow, but long-effect communication system.