\frac{dx_{2}}{dt} = k_{5} \cdot x_{1} + k_{6} \cdot k_{7} \cdot x_{2} \cdot \left(1 - k_{8} \cdot \left(x_{2} + x_{3}\right)\right) - k_{10} \cdot x_{2}\\ \frac{dx_{3}}{dt} = \left(1 - k_{5}\right) \cdot x_{1} + k_{6} \cdot k_{7} \cdot x_{3} \cdot \left(1 - k_{8} \cdot \left(x_{2} + x_{3}\right)\right) - k_{10} \cdot x_{3}\\ \frac{dx_{4}}{dt} = k_{9} \cdot x_{2} - k_{11} \cdot x_{4}