[ Eq(Derivative(x1, t), ((-1)*k13*x1 + 1*k18*x5*k24)/k24),
  Eq(Derivative(x2, t), ((-1)*k13*x2*k24 + 1*k21/k22*x3 + (-1)*k22*k20*x2 + 1*k19*x6*k24)/k24),
  Eq(Derivative(x3, t), ((-2)*k11*x3**2 + 2*k12*x4 + (-1)*k13*x3*k24 + (-1)*k21/k22*x3 + 1*k22*k20*x2)/k24),
  Eq(Derivative(x4, t), (1*k11*x3**2 + (-1)*k12*x4 + (-1)*k13*x4*k24)/k24),
  Eq(Derivative(x5, t), ((-1)*k15*x5 + 1*k8/(k9 + k8)*(k4*(x4*k24/k6 + 1)/(1 + x4*k24/k6 + (x4*k24)**2/k6**2 + k9/k7) + k3*(x4*k24)**2/(k6**2*(1 + x4*k24/k6 + (x4*k24)**2/k6**2 + k9/k7))))/k24),
  Eq(Derivative(x6, t), ((-1)*k15*x6 + 1*(k2*k5/(x4*k24 + k5) + k1*x4*k24/(x4*k24 + k5)))/k24) ]