Kidney

• Kidneys


  Main job is to filter the blood and remove waste products, regulate levels of ions and water
• Urea


  Main waste product, made in the liver during deamination
• Ions


  Obtained from diet, needed for various bodily functions, regulated by kidneys
• Water regulation


  Gained from food/drinks, lost through sweating, breathing, and urine, regulated by kidneys
• Too much water in body

  Water diffuses into cells by osmosis, causing them to swell and possibly burst
• Too little water in body


  Cells lose water and shrink
• Nephrons


  • Around 1 million in each kidney, responsible for filtration and selective reabsorption
• Filtration


  Kidney tubules absorb small substances like water, glucose, amino acids, urea
• Selective reabsorption


  Reabsorb useful substances, excrete waste
• Hypothalamus


  Detects water concentration in bloodstream
• Antidiuretic hormone (ADH)


  Released by pituitary gland when water levels are low, tells kidneys to reabsorb more water
• High water levels


  Hypothalamus stops releasing ADH, kidneys reabsorb less water, produce more urine
• Water regulation is an example of a negative feedback loop
• Kidneys

  Remove waste products like urea from the blood, regulate the levels of ions in the blood, and regulate the amount of water in the blood
• Blood flow through the kidneys

  1. Enters through renal arteries

  2. Passes through the kidneys

  3. Exits through renal veins
• Urine production

  1. Blood passes through the kidneys

  2. Kidneys produce urine

  3. Urine passes down the ureters

  4. Urine is stored in the bladder

  5. Urine is released through the urethra
• Nephron


  • Tubule carries the filtered fluid that becomes urine
  • Blood vessels
• Filtration

  1. Liquid part of the blood is forced from the glomerulus into the Bowman's capsule

  2. Only small substances like water, amino acids, urea, glucose, and ions are filtered through

  3. About 20% of the plasma in the blood is filtered
• Selective reabsorption

  1. Kidneys reabsorb useful substances like glucose and amino acids back into the blood vessels

  2. Kidneys reabsorb some water and ions

  3. Kidneys do not reabsorb urea
• Parts of the nephron

  • Glomerulus
  • Bowman's capsule
  • Proximal convoluted tubule
  • Loop of Henle
  • Distal convoluted tubule
  • Collecting duct
• Urine passes down the ureter to the bladder and can then be released as waste
• Kidney failure


  When somebody's kidneys suddenly stop working
• Kidney failure

  Waste substances build up in the bloodstream, unable to regulate water and ion levels
• Mild kidney disease can be treated with medication, but kidney failure requires dialysis or kidney transplant
• Dialysis

  1. Blood is connected to dialysis machine

  2. Blood passes through dialysis circuit

  3. Blood comes into contact with dialysis fluid separated by semi-permeable membrane

  4. Dialysis fluid is constantly replaced to maintain concentration gradient
• Dialysis

  • Filters patient's blood to remove waste, excess water and regulate ion levels
  • Dialysis fluid contains same concentrations as healthy blood except no urea
• Dialysis reaches equilibrium

  Nothing would diffuse anymore
• Problems with dialysis: time-consuming, unpleasant, expensive
• Kidney transplant

  Surgical procedure to transfer a healthy kidney from one person to a patient who needs it
• Transplants are better and cheaper than dialysis, but there are not enough available organs