Controlling water content

• The concentration of urine is controlled by ADH (Anti-Diuretic Hormone)
• ADH is released by the pituitary gland
• ADH makes the kidney reabsord water
• Kidney

  Glomerulus

  • Small capillaries
  • Ultrafiltration - most of water, salt, glucose and urea filters in

  Bowman's capsule

  • All substances (water, salt, glucose and urea) diffuse into here

  PCT (Proximal Convoluted Tubule)

  • Glucose is selectively reabsorbed via active transport

  Descending loop of Henle

  • Water moves out via osmosis
  • Filtrate becomes more concentrated

  Ascending loop of Henle

  • Some salt is moved to capillaries
  • Filtrate becomes more dilute

  DCT (Distal Convoluted Tubule)

  • Any remaining useful substances are reabsorbed into the bloodstream (All glucose, some salt, water according to the level of ADH present)

  Collecting duct

  • All remaining substances form urine, which is collected in the collecting duct and stored in the bladder

  
• If your hydrated:

  • Less ADH from pituitary gland
  • Less permeable DCT
  • Less water reabsorbed into bloodstream
  • More water in the collecting duct
  • Less concentrated urine
• If your dehydrated

  • More ADH from pituitary gland
  • More permeable DCT
  • More water reabsorbed into bloodstream
  • Less water in the collecting duct
  • More concentrated urine