kidneys

• 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
• Cells can lose or gain water through osmosis depending on water levels in the body
• Nephrons


  • Structures inside kidneys that filter blood and reabsorb useful substances
• Filtration


  Blood passes through kidney tubules, small substances are absorbed
• Selective reabsorption


  Useful substances like glucose are reabsorbed, waste like urea is not reabsorbed
• Hypothalamus


  Detects water concentration in blood, sends signal to pituitary gland
• Antidiuretic hormone (ADH)


  Released by pituitary gland, travels to kidneys and tells tubules to reabsorb more water
• Low water levels


  More ADH is released, more water is reabsorbed, less urine produced
• High water levels


  Less ADH is released, less water is reabsorbed, more urine produced
• 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 stored in the bladder

  5. Urine released through the urethra
• Nephron


  • Tiny structures in the kidney
  • Consists of a tubule and blood vessels
• Filtration in the nephron

  1. Blood enters the glomerulus

  2. Liquid part of blood filtered into Bowman's capsule

  3. Only small substances like water, amino acids, urea, glucose, and ions filtered

  4. About 20% of plasma filtered
• Selective reabsorption in the nephron


  1. Fluid passes along the tubules

  2. Kidneys reabsorb useful substances like glucose and amino acids

  3. Kidneys reabsorb some water and ions

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

  • Glomerulus
  • Bowman's capsule
  • Proximal convoluted tubule
  • Loop of Henle
  • Distal convoluted tubule
  • Collecting duct
• Fluid that passes out of the collecting duct is classed as urine
• 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 constantly replaced to maintain concentration gradient
• Dialysis


  • Filters patient's blood, removes unwanted substances like excess ions, amino acids, and urea
• Dialysis


  Restores patient's blood to normal levels
• Problems with dialysis


  • Time-consuming treatment, unpleasant experience, can cause complications, expensive
• Kidney transplant


  Surgical procedure to transfer a healthy kidney from one person to a patient in need
• Kidney transplant


  • Most donor kidneys from recently deceased people, living people can also donate
  • Risk of organ rejection
• Not enough available organs for everyone who needs a kidney transplant, many still rely on dialysis