The expansion by regions in pi K scattering

We discuss a number of two loop (vertex) integrals relevant for pi K scattering at threshold. As such these are functions of two well separated mass scales, M_pi/M_K << 1. The method of regions allows an expansion in this mass ratio prior to the integration. In the cases considered, the coefficients in this expansion can be evaluated with elementary methods. As a first example of an application we present the leading strange quark contributions to the pion mass.