The Kidneys

• Kidneys


  Really important in homeostasis
• Kidneys


  • Act as filters to clean the blood
  • Make urine by taking waste products and other unwanted substances out of the blood
  • Substances are filtered out of the blood as it passes through the kidneys
  • Useful substances like glucose, some ions and the right amount of water are then absorbed back into the blood
• Substances removed from the body in urine

  • Urea
  • Ions
  • Water
• Urea production


  1. Proteins (and amino acids) can't be stored, excess amino acids are converted into fats and carbohydrates in the liver

  2. Ammonia is produced as a waste product

  3. Ammonia is converted to urea in the liver

  4. Urea is transported to the kidneys and filtered out of the blood and excreted in urine
• Ions


  • Taken into the body in food, absorbed into the blood
  • If ion or water content is wrong, it can upset the balance and damage cells
  • Some ions are lost in sweat but this amount is not regulated, so the right balance must be maintained by the kidneys
• Water


  • The body has to constantly balance the water coming in against the water going out
  • We lose water from the skin in sweat and from the lungs when breathing out
  • The amount of water is balanced by the amount we consume and the amount removed by the kidneys in urine
• Anti-diuretic hormone (ADH)


  • Controls the concentration of urine
  • Released into the bloodstream by the pituitary gland
  • The brain monitors the water content of the blood and instructs the pituitary gland to release ADH accordingly
• Negative feedback control of water content

  1. If water content is too high, the brain detects this and the pituitary gland releases less ADH so less water is reabsorbed

  2. If water content is too low, the brain detects this and the pituitary gland releases more ADH so more water is reabsorbed
• If the kidneys don't work properly, waste substances build up in the blood and you lose your ability to control the levels of ions and water in your body, eventually resulting in death
• People with kidney failure can be kept alive by having dialysis treatment or a kidney transplant
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• Treatments for Kidney Failure

  Regular dialysis or a transplant
• Dialysis Machines Filter the Blood

  1. Dissolved substances in the blood are maintained at normal levels, and waste substances are removed

  2. Person's blood flows between partially permeable membranes, surrounded by dialysis fluid

  3. Membranes are permeable to ions and waste substances, but not big molecules like proteins

  4. Dialysis fluid has the same concentration of dissolved ions and glucose as healthy blood

  5. Useful dissolved ions and glucose won't be lost from the blood during dialysis

  6. Only waste substances (such as urea) and excess ions and water diffuse across the barrier

  7. Many patients have to have a dialysis session three times a week, each session takes 3-4 hours

  8. Dialysis may cause blood clots or infections

  9. Dialysis is not a pleasant experience and is expensive for the NHS to run

  10. Dialysis can buy a patient valuable time until a donor organ is found
• Kidney Transplants


  • The only cure for kidney failure
  • Healthy kidneys are usually transplanted from people who have died suddenly
  • The person who died has to be on the organ donor register or carry a donor card
  • Kidneys can also be transplanted from people who are still alive, but there is a small risk to the person donating the kidney
  • There is a risk that the donor kidney can be rejected by the patient's immune system
  • Transplants are cheaper (in the long run) than dialysis and they can put an end to the hours patients have to spend on dialysis, but there are long waiting lists for kidneys