[ Eq(Derivative(x1, t), (1*k23*k17*k1/(k6 + k1) + (-1)*k23*k13*x1/(k4 + x1))/k23),
  Eq(Derivative(x2, t), (1*k23*k21*(x7 - x2)/(k9 + x7 - x2)*(x1 + x3) + (-1)*k23*k22*x2/(k10 + x2)*x4)/k23),
  Eq(Derivative(x3, t), (1*k23*k18*x2 + (-1)*k23*k14*x4*x3/(k5 + x3))/k23),
  Eq(Derivative(x4, t), (1*k23*k15*x2 + (-1)*k23*k11*x6*x4/(k2 + x4))/k23),
  Eq(Derivative(x5, t), (1*k23*k16*x4 + (-1)*k23*k12*x6*x5/(k3 + x5))/k23),
  Eq(Derivative(x6, t), (1*k23*k19*x5*(x8 - x6)/(k7 + x8 - x6) + (-1)*k23*k20*x6/(k8 + x6))/k23),
  Eq(Derivative(x7, t), 0/k23),
  Eq(Derivative(x8, t), 0/k23) ]