Figure 1
Types of communication between cells. This illustrates the terms used to describe communication between cells (C 1 and C 2 are cells) where a message (M), carried by a molecule (eg. a Ligand) released from one cell into the external environment, is received by a receptor (R) either on another type of cell or on a cell of its own kind. Each term reflects the distance that the message/signal has to travel and is dependent on the separation of the cells involved - between tissues (Circulatory) or within a tissue (Interstitial or Pericellular). The Figure does not illustrate the other possible communication mechanism, Homocrine and Juxtacrine, which are discussed in the main text.