Context: In general, studies focused on the Milky Way's structure show a range of values when deriving different Galactic parameters, such as radial scalelengths, vertical scaleheights, or local space densities. Those values are also dependent on the Galactic coordinates under consideration for the corresponding analysis, as a direct consequence of observing a structure (our Galaxy) that is far from being as smooth and well-behaved as models usually treat. Aims: In this paper, we try to find any dependence of the Galactic structural parameters on the Galactic longitude for either the thin disc or the thick disc of the Milky Way that would indicate possible inhomogeneities or asymmetries in those Galactic components. Methods: Galactic model parameters have been estimated for a set of 36 high-latitude fields with Two Micron All Sky Survey (2MASS) photometry. Possible variations with the Galactic longitude in either the scaleheight and the local space density of these components are explored. Results: Galactic model parameters for the different fields show that they are Galactic longitude-dependent. The thick disc scaleheight changes from ~800 pc at 150°