excretion — kidney failure and dialysis

• kidney failure

  common causes of kidney failure:

  • high blood pressure
  • diabetes
  • alcohol abuse
  • physical damage to the kidneys

  possible cures to kidney failure are dialysis and kidney transplant
• hemodialysis 

  • short term, repeated treatments are required every 2-3 days
  • inconvenient as treatments are 2-3 times a week and each session lasts a few hours
  • hemodialysis requires patients to constantly maintain a strict diet and limit certain types of activities while treatment is ongoing 
  • risks are lower than kidney transplantation 
  • relatively less complications than kidney transplant 
• access for dialysis is done via grafts or fistula

  • graft: blood is drawn from an artery and returned to a vein
  • fistula: blood is drawn from a vein and returned to the same vein
• structure and function: tubing

  • long, narrow coiled tubing increases SA:V, speeding up rate of diffusion of substances
  • wall of tube is partially permeable, allowing only small substances such as glucose, amino acids, and urea to pass through. large substances such as RBC, platelets, etc. remain in tubing
• structure and function: dialysis fluid

  • consists of sterilised distilled water, salt, bicarbonate, glucose, amino acids
  • same concentration as essential substances in the blood prevents diffusion of essential substances out of the blood and prevents osmotic shock
  • absence of metabolic waste in the fluid allows urea, uric acid, creatinine, excess water, & mineral salts to diffuse into the fluid
• structure and function: dialysis fluid

  • dialysis fluid is changed regularly to remove waste substances in order to maintain the concentration gradient
  • dialysis fluid is maintained at body temperature to ensure that blood re-enters the body at body temperature to prevent hypothermia 
• blood

  • blood flows in the opposite direction of flow of dialysis fluid to maintain the concentration gradient of waste products for maximum removal of waste products from blood into dialysis fluid
  • anti-clotting chemicals are added to blood to prevent it from clotting in the dialysis machine
• what does dialysis fluid consist of?

  sterilised distilled water, salt, bicarbonate, glucose, amino acids
• why is dialysis fluid changed regularly?

  to remove waste substances in order to maintain the concentration gradient