\frac{dx_{1}}{dt} = \left(1 \cdot k_{21} \cdot k_{1} \cdot \operatorname{piecewise}(0, \operatorname{and}\left(t \ge 0, t < 5\right), \operatorname{piecewise}(1, \operatorname{and}\left(t \ge 5, t < 10\right), 0)) / \left(k_{3} + \operatorname{piecewise}(0, \operatorname{and}\left(t \ge 0, t < 5\right), \operatorname{piecewise}(1, \operatorname{and}\left(t \ge 5, t < 10\right), 0))\right) + -1 \cdot k_{21} \cdot k_{4} \cdot x_{1}\right) / k_{21}\\
\frac{dx_{2}}{dt} = \left(1 \cdot k_{21} \cdot k_{5} \cdot \operatorname{piecewise}(1, \operatorname{and}\left(t \ge 0, t < 5\right), 0) / \left(k_{7} + \operatorname{piecewise}(1, \operatorname{and}\left(t \ge 0, t < 5\right), 0)\right) + -1 \cdot k_{21} \cdot k_{8} \cdot x_{2}\right) / k_{21}\\
\frac{dx_{3}}{dt} = \left(1 \cdot k_{21} \cdot k_{14} \cdot x_{1} + 1 \cdot k_{21} \cdot k_{15} \cdot x_{2} + -1 \cdot k_{21} \cdot k_{16} \cdot x_{3}\right) / k_{21}\\
\frac{dx_{4}}{dt} = \left(1 \cdot k_{21} \cdot k_{17} \cdot x_{7} + 1 \cdot k_{21} \cdot k_{18} \cdot x_{3} + -1 \cdot k_{21} \cdot k_{19} \cdot x_{4}\right) / k_{21}\\
\frac{dx_{5}}{dt} = \left(1 \cdot k_{21} \cdot k_{11} \cdot x_{2} \cdot x_{7} + -1 \cdot k_{21} \cdot k_{20} \cdot x_{5}\right) / k_{21}\\
\frac{dx_{7}}{dt} = \left(1 \cdot k_{21} \cdot k_{10} \cdot \left(k_{13} - x_{7} - x_{5}\right) \cdot x_{1} + 1 \cdot k_{21} \cdot k_{9} \cdot \left(k_{13} - x_{7} - x_{5}\right) \cdot x_{4} + -1 \cdot k_{21} \cdot k_{12} \cdot x_{7} + -1 \cdot k_{21} \cdot k_{11} \cdot x_{2} \cdot x_{7}\right) / k_{21}