{ diff(x1, t) = (1*k34*(k1*k2*exp((-k1)*k4*t) + k3*x2)*(k4 + k5*x2) + (-1)*k34*k6*x1)/k34,
  diff(x2, t) = (1*k34*k7 + 1*k34*k8*k9*x1^2/(k10 + x1^4) + 1*k34*k11*k12*x2*(1 - x2/k13) + (-1)*k34*k14*x2 + (-1)*k34*k15*x5*x2)/k34,
  diff(x3, t) = (1*k34*k16 + 1*k34*k17*x2 + (-1)*k34*k18*x3 + (-1)*k34*k19*x3*x4)/k34,
  diff(x4, t) = (1*k34*(k20 + x3/(k21 + k22*x3))*1/(1 + k23*x1)*x4 + 1*k34*(k24 + k25*x3^2/(k26 + x3^4))*piecewise(1 - x5/k27, x5 < k27, 0) + (-1)*k34*(x2 + x4 + x5)/k28*x4 + (-1)*k34*piecewise(0, x4 + x5 < k29, 1)*(k30 + k31*x3)*x4)/k34,
  diff(x5, t) = 1*k34*piecewise(0, x4 + x5 < k29, 1)*(k30 + k31*x3)*x4/k34 }