  We study the relation between nuclear massive black holes and their host
spheroid gravitational potential. Using simple models, we analyze how gas is
expected to be transported in the nuclear regions of galaxies. When we couple
it with the expected gas lifetime given by the Kennicutt-Schmidt Law, this
naturally leads to the `M_BH - M_virial' and `M_BH - sigma' relations. We also
numerically test, using AMR simulations, our simple models for the mass
transport with satisfactory results.
