kidneys

• Water can leave the human body in three ways: through the lungs when we exhale, through the skin when we sweat, and through the kidneys in urine
• Role of the kidney in maintaining the concentration of substances in the blood

  1. Filter out excess water, urea, and ions from the blood

  2. Reabsorb some of the filtered water and ions back into the blood

  3. Excrete excess water, urea, and ions as urine
• The body takes in water through food and drink, but has no control over water loss through the lungs and skin
• The body can control how much water is lost in urine
• Kidneys


  • Remove waste product urea from the blood
  • Adjust the levels of water and ions in the blood
• How the kidneys remove waste and adjust blood composition

  1. Blood passes through kidney capillaries

  2. Small molecules (urea, ions, water) are filtered out

  3. Glucose, some ions and water are reabsorbed back into blood

  4. Excess urea, ions and water are excreted as urine
• Concentration of glucose in blood


  Does not change after passing through kidneys
• Concentration of ions in blood

  Decreases after passing through kidneys
• Concentration of urea in blood


  Falls to virtually zero after passing through kidneys
• Deamination


  Process where the liver breaks down excess amino acids and produces ammonia
• Ammonia

  Toxic chemical produced from excess amino acids, converted to urea by the liver
• Urea can be safely excreted by the kidneys