[ Eq(Derivative(x1, t), 0),
  Eq(Derivative(x2, t), (1*k3*k4*k14 + (-1)*k3*x4*k6*x2/(k5 + x2) + (-1)*k3*k8*x2 + (-2)*k3*(k9*x2**2 - k10*x5))/k3),
  Eq(Derivative(x3, t), (1*k3*x4*k6*x2/(k5 + x2) + (-1)*k3*k7*x3)/k3),
  Eq(Derivative(x4, t), 0/k3),
  Eq(Derivative(x5, t), (1*k3*(k9*x2**2 - k10*x5) + (-1)*k3*k11*x5 + (-1)*k3*x4*k13*x5/(k12 + x5))/k3) ]