Intercellular interactions as a basis for the expedient behaviour of multicellular systems.

Functional and structural aspects of intercellular interactions are considered. Chemical substances are universal mediators of intercellular interactions. Electrical and mechanical interactions are also involved in cell-cell cooperation. Functional peculiarities of the two principal types of intercellular interactions-ligand-receptor interactions and interactions based on permeable contacts-are compared. Examples of basic tissue processes are given (such as the mechanisms of embryonic induction and differentiation, regulation of cell proliferation, temporal and spatial regulation of the activity of differentiated cells, interactions between excitable cells) to illustrate the notion that the types of intercellular interactions are mutually complementary and fulfill different functions. Ligand-receptor interactions predominantly provide signal functions and ensure intertissue interactions, while the interactions based on permeable contacts mainly fulfill intratissue coordination relying on positional information and the exchange of energy and matter.