During haemodialysis, the composition and flow of the dialysis fluid (dialysate) are carefully regulated to mimic the homeostatic functions of a healthy kidney.

Which of the following statements correctly describe how homeostasis of blood solutes is maintained during haemodialysis?

1. The dialysate contains glucose and amino acids at concentrations equal to those of normal blood plasma to prevent their net diffusion out of the patient's blood.
2. The dialysate contains potassium ions ($K^{+}$) at normal physiological plasma concentrations to allow excess potassium to diffuse out of the blood.
3. The dialysate flows in the same direction as the blood (co-current flow) through the dialyser to maintain a constant concentration gradient along the entire length of the membrane.