Kidney failure

• What causes kidney failure?

  • kidney infections- podocytes being damaged
  • raised blood pressure- damages epithelial cells and basement membrane
  • genetic conditions- producing cysts in the kidney
• Explain how renal dialysis works

  • patients blood passed over partially permeable dialysis membrane
  • Dialysis fluid contains the correct concentrations of mineral ions glucose and water as normal blood
  • So any substances in excess in the blood diffuse across the membrane into the dialysis fluid
  • Similarly, substances which are too low in the blood diffuse from dialysis fluid into the blood
• What does the dialysis membrane only allow to diffuse across the membrane?

  • waste
  • excess substances
• What polysaccharide in dialysing fluid can’t pass through the dialysing membrane?

  Dextran
• What does dextran do?

  • Levels ensure the WP of the dialysis fluid is the same as normal plasma
  • If plasma contains excess water, this will move into the dialysing fluid by osmosis
• Why is concurrent flow not used in dialysis?

  • If the blood and dialysing fluid flowed in same direction (concurrent flow)
  • Conc grad between adjacent regions of blood and dialysing fluid will drop as diffusion takes place along length of dialysing membrane
  • Therefore rate of diffusion will slow as you move along length of dialysing membrane
• What process used by a functioning kidney to regulate the composition of body fluids is not possible in renal dialysis?

  Negative feedback
• True or false? Kidney transplant is the best life extending treatment for kidney failure

  True
• How can the body reject a kidney? How can this be prevented?

  • T lymphocytes invade organ and destroy it
  • Rejection can be minimised by tissue matching donor and recipient or using immunosuppressant or anti rejection drugs
  • Unfortunately the immunosuppressant drugs must be taken for life and this increases risk of infection
• What is chronic kidney failure?

  • Progressive, long term kidney failure
  • Takes place over a number of years
• State effects of kidney failure on blood composition

  • Fewer RBCs and plasma proteins
  • Less glucose selectively reabsorbed
  • More urea remains in blood
• What is acute kidney failure?

  • Sudden kidney failure
• state the effects of kidney failure

  • protein in urine- large plasma proteins in urine as basement membrane and podocytes stop working as filters
  • blood in urine
  • loss of electrolyte balance
  • build up of toxic urea which poisons cells
  • high bp because of imbalance of water- causing strokes and heart problems
  • weakened bones as calcium/phosphorus balance is lost
  • pain and stiffness in joints
  • anaemia- blood cells not produced, causes fatigue
• why is a loss of electrolyte balance a bad thing in terms of kidney failure?

  • cannot excrete of excess ions like chloride and sodium ions
  • this causes osmotic imbalances in tissues and eventual death
• how can kidney disease be detected?

  • using GFR, which is a measure of the rate of substances filtered through the kidneys in cm$^3$/min
  • people with kidney disease have a lower GFR
  • measured by a blood test measuring the levels of creatinine in the blood- which is a product of muscle contraction to estimate the measure of GFR, as it cannot be measured directly
• describe the process of haemodialysis

  • Blood from artery passes into a machine and flows between artificial dialysis membranes shaped to mimic the membrane of the Bowman's capsule
  • this increases SA for exchange
  • on the other side of the membranes is the dialysis fluid
  • essential that people lose excess urea and mineral ions, and do not lose some substances like glucose and AAs
  • This is prevented by using dialysis fluid with the same composition of substances as blood plasma, eg [glucose] to ensure no net movement of glucose out the blood
  • the fluid contains no urea, creating steep conc grad for it to diffus out the blood into dialysis fluid
  • Dialysis fluid and blood flow in opposite directions for steep diffusion gradient
  • passive process, no active transport involved

  
• why are blood thinners used in dialysis?

  to prevent clotting
• Explain the process of a kidney transplant

  • Surgeon implants donor kidney into lower abdomen
  • Attaching it to blood supply (stub of renal artery) and bladder

  
• what are the advantages and disadvantages of dialysis?

  ADVANTAGES:

  • more readily available than donor organs- there whenever kidneys fail
  • enables patient to live relatively normal life as can be done at home

  DISADVANTAGES:

  • monitor diet carefully
  • need regular sessions on the machine
  • time-consuming
  • more expensive
  • can damage body
• what are the costs and benefits of a transplant?

  ADVANTAGES:

  • Cheaper than dialysis
  • Quality of life for patients is better if procedure is successful

  DISADVANTAGES:

  • Requires donor and finding a matching one can be difficult- as there's a risk of the immune system recognising the antigens on the transplanted kidney as foreign and attacking or rejecting it
  • Must be on immunosuppressants for life to prevent immune system rejecting the organ, which supresses immune system and leads to disease
  • transplanted organs don't work forever and may have to be replaced every 10 yrs
  • very few donors