5. A patient is placed on a kidney dialysis unit three times a week. The dialyzer has a membrane area of 1 m2 and is operated in a countercurrent mode. The blood flow rate is 200 ml/min and the dialysate flow rate is 500 ml/min. Membrane permeability to urea is 10-3 cm/s. Assume that the rate of urea accumulation in the body is the same as that mentioned in the class. Determine blood urea concentration as a function of time.