[ Eq(Derivative(x1, t), (-1)*k11*k2*x1/k11),
  Eq(Derivative(x2, t), (1*k11*k2*x1 + (-1)*k11*k2*x2)/k11),
  Eq(Derivative(x3, t), (1*k11*k2*x2 + (-1)*k11*k10*x3)/k11),
  Eq(Derivative(x4, t), (1*k11*k8 + (-1)*k11*k5*k7**k8/(k7**k8 + x5**k8)*x4*x3)/k11),
  Eq(Derivative(x5, t), (1*k11*k6*x4 + (-1)*k11*k6*x5)/k11) ]