Cell-to-cell signaling occurs when a cell directly interacts with its neighboring cell or when signaling molecules are secreted and act as messengers. The different types of signaling through secreted molecules can be categorized into three main groups, depending on the distance over which the signals are transmitted.
Endocrine signaling: Signaling molecules are secreted by specialized cells and carried through the bloodstream to act on distant target cells.
Paracrine signaling: Signaling molecules are released by one cell and affect nearby target cells in the local environment.
Autocrine signaling: Cells respond to signaling molecules that they themselves produce.
