Kidney Failure (Edexcel GCSE Biology)

• The kidneys might not work properly for several reasons, including accidents or disease
• Humans can survive with one functioning kidney, but if both are damaged then there will quickly be a build-up of toxic wastes in the body which will be fatal if not removed
• There are several different treatment options for kidney failure

Treatment options for total kidney failure

Kidney dialysis

• The usual treatment for someone with kidney failure is dialysis
• This is an artificial method of filtering the blood to remove toxins and excess substances
• Patients are connected to a dialysis machine which acts as an artificial kidney to remove most of the urea and optimise the water and salt balance of the blood
  • Unfiltered blood is taken from an artery in the arm, pumped into the dialysis machine and then returned to a vein in the arm
  • Inside the dialysis machine the blood and dialysis fluid are separated by a partially permeable membrane  - the blood flows in the opposite direction to dialysis fluid, allowing the exchange to occur between the two where a concentration gradient exists

• Dialysis fluid contains:
  • A glucose concentration similar to a normal level in blood
  • A concentration of salts similar to a normal level in blood
  • No urea

How dialysis works

• As the dialysis fluid has no urea in it, there is a large concentration gradient - meaning that urea diffuses across the partially permeable membrane, from the blood to the dialysis fluid
• As the dialysis fluid contains a glucose concentration equal to a normal blood sugar level, this prevents the net movement of glucose across the membrane as no concentration gradient exists
• As the dialysis fluid contains a salt concentration similar to the ideal blood concentration, movement of salts across the membrane only occurs where there is an imbalance (if the blood is too low in salts, they will diffuse into the blood; if the blood is too high in salts, they will diffuse out of the blood)
• The fluid in the machine is continually refreshed so that concentration gradients are maintained between the dialysis fluids and the blood
• Dialysis may take 3-4 hours to complete and needs to be done several times a week to prevent damage to the body from the buildup of toxic substances in the blood
• An anticoagulant is added to the blood before it runs through the machine to prevent the blood from clotting and slowing the flow

Kidney transplant

• Kidney transplants are a better long term solution to kidney failure than dialysis; however, there are several disadvantages to kidney transplants, including:
  • Donors won’t have the same antigens on cell surfaces so there will be some immune response to the new kidney (risk of rejection is reduced – but not removed –  by ‘tissue typing’ the donor and the recipient first)
  • This has to be suppressed by taking immunosuppressant drugs for the rest of their lives – these can have long term side effects and leave the patient vulnerable to infections
  • There are not enough donors to cope with the demand

• However, if a healthy, close matched kidney is available, then the benefits of a transplant over dialysis include:
  • The patient has much more freedom as they are not tied to having dialysis several times a week in one place
  • Their diets can be much less restrictive than they are when on dialysis
  • Use of dialysis machines is very expensive and so this cost is removed
  • A kidney transplant is a long-term solution whereas dialysis will only work for a limited time