{ diff(x1, t) = (1*k22*k1 + (-1)*k22*k2*x1 + (-1)*k22*k3*x7*x1/(k4 + x1) + 1*k22*k5*x6*x3/(k6 + x3))/k22,
  diff(x2, t) = (1*k22*k3*x7*x1/(k4 + x1) + (-1)*k22*(k7*x2 - k8*x3))/k22,
  diff(x3, t) = (1*k22*(k7*x2 - k8*x3) + (-1)*k22*k5*x6*x3/(k6 + x3) + (-1)*k22*k9*(x3*k10 - k11*x4))/k22,
  diff(x4, t) = ((-1)*k22*k12*(x4 - k23) + 1*k22*k9*(x3*k10 - k11*x4))/k22,
  diff(x5, t) = (1*k22*(k14*(x2/k17)^k20/(1 + (x2/k17)^k20) + k13) + (-1)*k22*k21*x5)/k22,
  diff(x6, t) = (1*k22*(k15*(x2/k18)^k20/(1 + (x2/k18)^k20) + k13) + (-1)*k22*k21*x6)/k22,
  diff(x7, t) = (1*(k16/(1 + (x5/k19)^k20) + k13) + (-1)*k22*k21*x7)/k22,
  diff(x8, t) = 0 }