excretion (9)

• water reabsorbtion?

  - salts reabsorbed at loop of henle by diffusion and active transport

  • water follows via osmosis
  • also reabsorbed in collecting duct based on how much water is needed in body
• people with diabetes?

  high glucose levels, not all glucose filtered out is reabsorbed = cant anywhere else - collect in urine
• excretion?

  the removal of metabolic waste
• plants excrete through holes on leaf surface (stomata)
• plants excrete:

  in daylight = respire and photosynthesise - photosynthesis faster - excrete oxygen

  at night = respire only - excrete carbon dioxide
• skin excretes = water and mineral ions via sweat
• lungs excretes = carbon dioxide and water via breathing
• liver = produces urea by amino acids
• kidneys = excrete water, mineral ions and urea - filters blood
• urea = carried in plasma
• bladder stores urine
• urine created by kidneys in osmoregulation
• urine contains:

  water - urea - ions - some hormones
• kidneys: regulate water content of blood and excrete toxic waste products of metabolism
• waste substances removed by kidneys:

  uric acid, ammonia, creatine, urea, excess hormones - water - salt ions
• the nephron:

  a million tiny structures in each kidney

  starts in cortex of kidney, loop down to medulla and back to cortex

  drains innermost part of kidneys and urine collects there before it flows to ureter to bladder
• structure of nephron:

  glomerulus - bowmans capsule - proximal convoluted tubule - loop of henle - distal convoluted tubule - collecting duct
• ultrafiltration - in bowmans capsule and glomerulus
• blood in glomerulus = high pressure = forces substances out of blood to bowmans capsule - capillary narrows to create high pressure
• how does ultrafiltration happen?

  arterioles branch to each nephron off renal artery = form a knot of capillaries in the cup-shaped bowmans capsule - capillaries narrow further in = high pressure = forces out small molecules into bowmans capsule and form filtrate
• selective reabsorbtion: reabsorbed molecules:

  • water = loop of henle + collecting duct - osmosis
  • salts = loop of henle - diffusion
  • glucose = proximal convluted tubule - active transport
  • urea = not reabsorbed - created in collecting duct
• glucose reabsorption:

  • reabsorbed in proximal convoluted tubule by active transport
  • many mitochondria to provide energy for process
• role of ADH:

  • pituitary gland releases ADH
  • released when the water content of blood is too high - controls amount of water reabsorbed
• if water content in blood is too high = less ADH released = less water reabsorbed - dilute urine
• if water content of blood is too low = lots of ADH released = lots of water reabsorbed - concentrated urine