[ Eq(Derivative(x1, t), ((-1)*k1*k5*x1/k3/(1 + x1/k3)*(1 + k2*x8/k4)/(1 + x8/k4) + 1*k1*k17*x9*x2/k16/(1 + x2/k16))/k1),
  Eq(Derivative(x2, t), (1*k1*k5*x1/k3/(1 + x1/k3)*(1 + k2*x8/k4)/(1 + x8/k4) + (-1)*k1*k17*x9*x2/k16/(1 + x2/k16))/k1),
  Eq(Derivative(x3, t), ((-1)*k1*k8*x2*x3/k6/((1 + x3/k6 + x4/k6)*(1 + x8/k7)) + 1*k1*k21*x10*x4/k20/(1 + x5/k20 + x4/k20))/k1),
  Eq(Derivative(x4, t), (1*k1*k8*x2*x3/k6/((1 + x3/k6 + x4/k6)*(1 + x8/k7)) + (-1)*k1*k11*x2*x4/k9/((1 + x3/k9 + x4/k9)*(1 + x8/k10)) + 1*k1*k19*x10*x5/k18/(1 + x5/k18 + x4/k18) + (-1)*k1*k21*x10*x4/k20/(1 + x5/k20 + x4/k20))/k1),
  Eq(Derivative(x5, t), (1*k1*k11*x2*x4/k9/((1 + x3/k9 + x4/k9)*(1 + x8/k10)) + (-1)*k1*k19*x10*x5/k18/(1 + x5/k18 + x4/k18))/k1),
  Eq(Derivative(x6, t), ((-1)*k1*k13*x5*x6/k12/(1 + x6/k12 + x7/k12) + 1*k1*k25*x11*x7/k24/(1 + x8/k24 + x7/k24))/k1),
  Eq(Derivative(x7, t), (1*k1*k13*x5*x6/k12/(1 + x6/k12 + x7/k12) + (-1)*k1*k15*x5*x7/k14/(1 + x6/k14 + x7/k14) + 1*k1*k23*x11*x8/k22/(1 + x8/k22 + x7/k22) + (-1)*k1*k25*x11*x7/k24/(1 + x8/k24 + x7/k24))/k1),
  Eq(Derivative(x8, t), (1*k1*k15*x5*x7/k14/(1 + x6/k14 + x7/k14) + (-1)*k1*k23*x11*x8/k22/(1 + x8/k22 + x7/k22))/k1),
  Eq(Derivative(x9, t), 0/k1),
  Eq(Derivative(x10, t), 0/k1),
  Eq(Derivative(x11, t), 0/k1),
  Eq(Derivative(x12, t), ((-1)*k1*k26*x12/k27/(1 + x12/k27)*(1 + k28*x8/k29)/(1 + x8/k29) + 1*k1*k30*x13/(k31 + x13))/k1),
  Eq(Derivative(x13, t), (1*k1*k26*x12/k27/(1 + x12/k27)*(1 + k28*x8/k29)/(1 + x8/k29) + (-1)*k1*k30*x13/(k31 + x13))/k1) ]