We performed a research of dynamical quark loops as a basis for microscopic modelling of low-energy aspects of Quantum Chromodynamics (QCD). Part of research covers the calculation of the anomalous transition of a virtual photon into three pions, within a constituent quark-meson model. We study the possibility of adding the lowest resonances, e. g. the rho and omega mesons. In the second part mesons are built from quark-antiquark loops (Bethe-Salpeter amplitudes). Quark propagators are generated from the associated Dyson-Schwinger gap equation. Research is first focused on the η−η′ complex, which is in direct relationship with the gluonic sector of the theory. Using the Matsubara formalism, the calculation is generalized to finite temperatures, where it is particularly interesting to observe influence of the medium on restoration of U(1)A. Experimental analysis of data from heavy-ion collisions at RHIC requires that the mass of the η′ particle significantly reduces at finite temperature, consequently leading to partial restoration of U(1)A symmetry. Given result is explained by a modification of the Witten-Veneziano relation at finite temperature. General study of quark models at finite temperature and density is a third subject of this research. By calculating the equation of state it is established that covariant quark models suffer from a thermodynamic instability. Inclusion of the Polyakov loop stabilizes the system. Within the non-local Nambu Jona Lasinio model effect of Lorentz symmetry breaking on the phase diagram is investigated. Under certain approximations the hadron dissociation effect is discussed for the π and the σ particle at finite temperature. We have shown that the meson widths for dissociation into quark-antiquark pairs as functions of temperature are extremely sensitive to the particular way the quark-antiquark interaction is introduced.