Kidney Failure

• Importance of kidney

  • kidneys are Excretory organs and play an important part in excreting metabolic waste products such as urea and excess water and mineral salts in the form of urine
  • kidneys are osmoregulators that regulate the water potential in blood thereby maintaining a constant water potential in the blood
• Causes of kidney failure

  • high blood pressure
  • diabetes
  • alcohol abuse
  • severe accidents that physically damage the kidney
  • complications from undergoing major surgery
  • patients with kidney failure may get a kidney transplant, a person only needs one functioning kidney to survive.
  • patients can be treated with dialysis using a dialysis machine. A dialysis machine mimics the functions of a kidney, it cleans the patient's blood from metabolic waste products and toxins. Patients have to undergo dialysis 2-3 times a week, each session lasts about 3-5 hours
• Dialysis Machine

  1. blood is drawn from the vein in the patient's arm and is pumped through the tubing in the dialysis machine
  2. the tubing is bathed in a specially controlled dialysis fluid. the walls of the tubing are partially permeable.
  3. small molecules such as urea and other metabolic waste products diffuse out of the tubing into the dialysis fluid. Blood cells, platelets and large molecules such a as proteins remain in the tubing
  4. the filtered blood returns to a vein in the patients arm
• Feats of a dialysis machine

  • the dialysis fluid contains these same concentration of essentials substances as healthy blood, so that essential substances do not diffuse out of the blood and into the dialysis fluid. If a patient's blood lacks essential substances, these substances will diffuse from the dialysis fluid into the blood
  • the dialysis fluid does not contain metabolic waste products so that there is a concentration gradient to allow waste products to diffuse out of the tubing into the dialysis fluid and be removed from the blood. This maintains the water potential of blood
• Features of a dialysis machine


  • the tubing is also long, narrow and coiled to increase the surface area to increase the rate of exchange of substances between the patient's blood and the dialysis fluid
  • the direction of the blood flow is opposite to the flow of dialysis fluid so that a concentration gradient is maintained for the the removal of water products