The effects of the finite size of the nucleus in the electromagnetic excitation of the quasi-elastic peak have been studied by comparing the responses calculated for 12C and 40Ca with the Fermi gas and the shell model. The contribution of the Meson Exchange Currents has also been considered. We have investigated the possibility of improving the Fermi gas model with approximate estimations of the finite size effects. We found that the use of an effective Fermi momentum provides a better description of the shell model results than the Local Density Approximation.