In modelling of some physical problems the idealisation concerning in entities (e.g. particles) that are concentrated in a point (mass-points), that leads to local interactions, is usually accepted. Just to give an example, this is the case in kinetic theory and the Boltzmann description of a rarefied gas. However, already in the case of more complicated that a simple rarefied gas systems a non-local type kinetic equations are used (cf. Lachowicz and Szymańska 2015 and references therein). For the biological systems it is obviously more essential to take into account the non-local interactions. 

For instance, in order to describe the phenomena of intercellular communication the nonlocal terms seem to be natural. Examples of such intercellular communication are paracrine signalling, when the cells produce chemical substances – signals – that are secreted to the extracellular space and induce changes in nearby other cells and autocrine signalling when cells produce chemical messengers that bind to the receptors on the same cells. In case of both types of signalling produced chemicals diffuse over some distance. The examples of paracrine signalling agents are various growth factors, whereas examples of autocrine signalling are various cytokines (cf. Lachowicz and Szymańska 2015).

Both types of intercellular signalling seem very important in various biological processes, in both physiological and pathological circumstances. Just mention, the production of growth factors in the healing and regeneration processes and in processes of angiogenesis and tumour growth.

Paracrine signalling.