Kidneys

• the kidneys extrete waste and regulate blood water potential
• What is ultrafiltration?

  as blood passes through the capillaries in the cortex, substances are filtered out of the blood and into long tubules that surround the capillaries
• What is selective reabsorption?

  useful substances like glucose and some water are reabsorbed back into the blood
• Define nephron?

  long tubule along with the bundle of capillaries where blood is filtered (around a million nephrons in each kidney)
• How is blood filtred in the nephron?

  1. blood from renal artery enters smaller arterioles in the cortex
  2. each arteriole splits into glomerulus - a bundle of capillaries looped inside a hollow ball called bowmans capsule
  3. ultrafiltration occurs in the bowmans capsule
  4. blood into glomerulus= afferent arteriole so away= efferent
  5. efferent is smaller in diameter so glomerulus under high pressure
  6. HP forces liquid out of capillary into bowmans capsule
  7. liquid and small molecules pass through capillary wall, basement membrane an epithelium of bowmans capsule to enter tubules
  8. larger molecules e.g protein/rbc/wbc stay in blood
  9. ( substances that enter bowmans capsule are known as glomerular filtrate)
  10. the glomeluar filtrate passes along nephron and useful substances are reabsorbed
  11. filtrate flows through collecting duct enters bladder
• How are useful substances reabsorbed along the nephron tubules?

  1. selective reabsorption - glomerular filtrate flows along proxomal convoluted tubule (PCT) through loop of henle along distal convoluted tubule (DCT)
  2. useful substances leave tubules of nephron and entter capillary network thats wrapped around them
  3. epithelium of wall PCT has microvilli to provide large surface area for the reabsorption of useful materials from glomerular filtrate into the blood
  4. useful solutes e.g glucose are reabsorbed along PCT by A.T and F.D
  5. water enters the blood by osmosis as water potential of blood is lower than filtrate. water is reabsorbed from pct, loop of henle, dct and collecting duct
  6. urine remains and goes to bladder along ureter
• what is urine usually made up of?

  1. water and dissolved cells
  2. urea
  3. other substances e.g hormones and excess vitamins
• what does urine not usually contain?

  1. proteins and blood cells (too big to filter)
  2. glucose as actively reabsorbed back into blood