the kidneys

• Kidneys


  Main job is to filter the blood and remove waste products
• 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/drink, lost through sweat and breathing, mainly regulated by kidneys
• Importance of water regulation
• Nephrons


  • Around 1 million in each kidney, contain tubules that absorb substances from blood (filtration), then selectively reabsorb what is needed (selective reabsorption)
• Urine formation


  1. Filtration

  2. Selective reabsorption

  3. Remaining substances form urine
• Hypothalamus


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


  Released by pituitary gland, travels to kidneys and tells tubules to reabsorb more water
• Blood flow through the kidneys

  1. Enters through renal arteries

  2. Passes through the kidneys

  3. Exits through renal veins
• Low water levels


  Hypothalamus releases more ADH, kidneys reabsorb more water, less urine produced
• High water levels


  Hypothalamus releases less ADH, kidneys reabsorb less water, more urine produced
• Urine production


  1. Blood filtered in glomerulus

  2. Filtered fluid passes into Bowman's capsule

  3. Fluid passes along tubules

  4. Selective reabsorption of useful substances

  5. Remaining fluid is urine

  6. Urine passes down ureters to bladder

  7. Urine is released through urethra
• Water regulation is an example of a negative feedback loop
• Nephron


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


  Liquid part of blood forced from glomerulus into Bowman's capsule
• Kidney failure


  When somebody's kidneys suddenly stop working
• Only small substances like water, amino acids, urea, glucose, and ions are filtered through to Bowman's capsule</b>
• About 20% of plasma in blood is filtered through to Bowman's capsule
• Kidney failure


  Waste substances build up in the bloodstream, unable to regulate water and ion levels
• Selective reabsorption


  1. Kidneys reabsorb useful substances like glucose and amino acids

  2. Kidneys reabsorb some water and ions

  3. Kidneys do not reabsorb urea
• Mild kidney disease can be treated with medication, but kidney failure requires dialysis or kidney transplant
• Dialysis


  Artificial kidneys that filter a patient's blood
• Parts of the nephron

  • Glomerulus
  • Bowman's capsule
  • Proximal convoluted tubule
  • Loop of Henle
  • Distal convoluted tubule
  • Collecting duct
• How dialysis works


  1. Patient's blood enters machine

  2. Blood comes into contact with dialysis fluid separated by permeable membrane

  3. Small molecules like water and ions can diffuse across membrane

  4. Larger things like cells and proteins cannot pass through

  5. Dialysis fluid constantly replaced to maintain concentration gradient and remove unwanted substances from blood

  6. Filtered blood returns to patient
• Fluid that passes out of the collecting duct is classified as urine
• Dialysis


  • Time consuming treatment, 3-4 days per week for 3-4 hours
  • Unpleasant experience, can cause problems like blood clots or infections
  • Very expensive to run, lifelong treatment
• 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, but living people can also donate
  • Small risk of complications from surgery
  • Main risk is organ rejection by patient's immune system
• Not enough available organs for everyone who needs a kidney transplant, so many still rely on dialysis