  We present a detailed analysis of the global and fine structure of four
middle-mass disc galaxies obtained from simulations in a $\Lambda$CDM scenario.
These objects have photometric D/T ratios in good agreement with those observed
for late-type spirals, as well as kinematic properties in agreement with the
observational Tully-Fisher relation. We identify the different dynamical
components at z=0 on the basis of both orbital parameters and the binding
energy of stars in the galaxy. In this way, we recognize a slowly rotating
centrally concentrated spheroid, and two disc components supported by rotation:
a thin disc with stars in nearly circular orbits, and a thick disc with orbital
parameters transitional between the thin disc and the spheroid. The spheroidal
component is composed mainly by old, metal-poor and {\alpha}-enhanced stars.
The distribution of metals in this component shows, however, a clear bimodality
with a low-metallicity peak, which could be related to a classical bulge, and a
high-metallicity peak, which could be related to a pseudo-bulge. The thin disc
appears in our simulations as the youngest and most metal-rich component. The
radial distribution of ages and colours in this component are U-shaped: the new
stars are forming in the inner regions, and then migrate through secular
processes. Finally, we also find a thick disc containing about 16% of the total
stellar mass and with properties that are intermediate between those of the
thin disc and the spheroid. Its low-metallicity stars are {\alpha}-enhanced
when compared to thin disc stars of the same metallicity. The structural
parameters (e.g., the scale height) of the simulated thick discs suggest that
such a component could result from the combination of different thickening
mechanisms that include merger-driven processes, but also long-lived internal
perturbations of the thin disc. [Abridged]
