SB7i- The kidneys

• What is kidney failure?

  Kidney failure is when the kidney stops working properly so excess substances build up in the body.
• What are the treatments for kidney failure?

  Dialysis and kidney transplant
• What is dialysis?

  Dialysis is like artifical kidneys that filters a patients blood for them, and must be carried out every 2-3 days in a hospital
• Dialysis

  1. Blood enters the machine from the patient.
  2. The patients blood is separated with the dialysis fluid through a partially permeable membrane. Only some substances can diffuse.
  3. Small molecules like water and ions will diffuse but bigger things like cells and proteins cannot
  4. The dialysis fluid contains the same concentration of water and other molecules as healthy blood, but no urea.
  5. The urea diffuses out of the blood into the fluid
  6. The cleaned blood will go back into the patient
• If the patient has too much of something in the blood

  These substances will diffuse past through the partially permeable membrane because there will be a concentration gradient of substances travelling to areas of high concentrations to areas of low concentrations. This will cause these substances to go into the dialysis fluid, bringing the patients level back to normal.
• Why dialysis fluid needs to be constantly replaced

  • After a while, substances travelling from the blood to dialysis fluid will reach equilibrium
  • Therefore nothing would diffuse
  • To prevent this, the dialysis fluid is constantly replaced to maintain the concentration gradient
  • Fluid is replaced through the bottom, and leaves through the top
• Problems with dialysis

  1. Treatment is time consuming (patients need to be hooked up to the machine for 3-4 hours)
  2. Unpleasant experience as it can cause blood clots and infections
  3. Expensive to run (people would also have to do it continually for the rest of their life)
• Main differences between dialysis and a healthy nephron

  A healthy nephron works all the time, so urea is removed continually.

  Dialysis uses a machine while the person is in a hospital therefore cannot do much.
• Kidney transplant

  A surgical procedure where living people can donate a kidney, or someone who has recently died can donate a kidney
• Kidney transplant (card 1)

  1. A healthy donor kidney is connected to the blood circulation
  2. Problem= risk of rejection
  3. The antigens on the transplanted kidney cells are different from the antigens on cells in the patients body
  4. The antibodies in the patients immune system attack the transplanted kidney and reject it
• The kidney (card 2)

  5. The antigens on the transplanted kidney and the patients tissues must be as similar as possible

  The patient must be treated for life with immunosuppressants to reduce the effects of the immune system.

  6. This means the patient may get more infections than normal
• Main consequences of kidney failure

  1. Waste substances (like urea) build up in the bloodstream
  2. Unable to regulate water and ion levels
• What is cheaper overall, dialysis or kidney transplant?

  Kidney transplant, however there is not enough organs therefore many people have to rely on dialysis
• What are the kidneys 3 main roles?

  1. Remove waste products (eg . urea)
  2. Regulate the levels of ions
  3. Regulate the amount of water in the blood
• Deamination

  Urea is made in the process of deamination.

  1. If the body has more amino acids than it needs, it can convert them to lipids or carbohydrates. These can be stored as a future energy source.
  2. This process is called deamination and takes place in the liver
  3. The downside of this process is that it produces the waste product urea, which needs to be excreted by the kidney
• How can we lose ions?

  • sweat
  • the kidney
• How can we lose water?

  • Sweat
  • urine
  • By the lungs when we breathe out
• Each kidney contains one million tiny units called nephrons. These nephrons make urine.
• The kidney (card 1- ultrafiltration)


  1. Blood passes through the kidneys in the capillaries, starting in the glomerulus
  2. The kidney tubules absorb anything small like water, glucose, amino acids and urea
  3. Except large things like proteins and cells
  4. This process is called ultrafiltration
• The kidney (card 2- selective reabsorption)

  1. As everything makes its way through the kidney tubules, the kidney reabsorbs everything we want to keep back into the bloodstream by active transport
  2. We reabsorb all the glucose, some water and no urea
  3. Reabsorption of water that the body needs from the tubule back into the blood is osmoregulation and is done by ADH
  4. This process is called selective reabsorption
• Name parts of the kidney

  Glomerulus, Bowman’s capsule, Loop of Henle, proximal convoluted tubule, distal convoluted tubule, collecting duct

  
• Collecting duct

  • The tubule holds the filtered fluid that becomes urine.
  • Any fluid that passes out of the collecting duct is classed as urine.
  • This passes down to the ureter into the bladder