[ Eq(Derivative(x1, t), (1*k13*k8*x1*log(k7/x1) + (-1)*k13*k10*x3*x1 + (-1)*k13*k9*x1)/k13),
  Eq(Derivative(x2, t), (1*k13*k1*k14 + (-1)*k13*k2*x2 + (-1)*k13*k11*x2*x1/(x1 + k12))/k13),
  Eq(Derivative(x3, t), (1*k13*k4*x3*x1/(x1 + k12) + (-1)*k13*k5*x3 + (-1)*k13*k6*x1*x3 + 1*k13*k3*k11*x2*x1/(x1 + k12))/k13),
  Eq(Derivative(x4, t), 0),
  Eq(Derivative(x5, t), 0) ]