{ diff(x1, t) = ((-1)*k2*x1*x2 + 1*k1*x3 + 1*k10 + (-1)*k3*x1)/k11,
  diff(x2, t) = ((-1)*k2*x1*x2 + 1*k1*x3)/k11,
  diff(x3, t) = (1*k2*x1*x2 + (-1)*k1*x3 + (-1)*k6*x3*x5 + 1*k4*x4 + 1*k5*x4)/k11,
  diff(x4, t) = (1*k6*x3*x5 + (-1)*k4*x4 + (-1)*k5*x4)/k11,
  diff(x5, t) = ((-1)*k6*x3*x5 + 1*k4*x4 + 1*k7 + (-1)*k8*x5)/k11 }