control of blood water potential

• where does osmoregulation occur

  the nephrons
• what is urine supposed to contain

  • water
  • dissolved salts
  • urea
  • small substances
• what is urine NOT meant to contain

  Glucose

  proteins

  blood cells
• why are proteins not found in urine

  too large to be filtered out of bloo
• why is glucose not found in urine

  filtered out but then reabsorbed during selective reabsorption at the proximal convuluted tubule
• what are the key five steps

  1. ultrafiltration
  2. selective reabsorption
  3. loop of henle
  4. water reabsorbed by blood
  5. water out of distal convuluted tubule and collecting duct
  6. collecting duct carries remaining liquid- urine- to the ureter
• describe ultrafiltration 


  afferent arteriole splits into smaller capillaries, known as glomerulus

  which increases hydrostatic pressure

  high hydrostatic pressure forces out water and small molecules such as glucose and mineral ions to form glomerulus filtrate

  they leave via gaps in the capillary endothelium cells and then pass through basement membrane and gaps between podocytes

  large proteins and blood cells remain in the blood and are carried away by the efferent arteriole
• where does the glomereulus filtrate pass too

  the proximal convuuted tubule
• what occurs at the proximal convoluted tubule

  selective reabsorption
• 85% of glomerulus filtrate is reabsorbed into the blood leaving urea and excess mineral ions behind
• what are some adaptations of the proximal convoluted tubule

  • microvilli- increase surface area for reabsorption
  • lots of mitochondria- energy for active transport
• describe selective reabsorption at the proximal convoluted tubule

  • sodium ions are actively transported out of the PCT CELL into the blood
  • this creates a concentration gradient for sodium ions to travel down their conc gradient from the lumen into the PCT cell
  • sodium ions diffuse down their conc gradient, through co-transport protein, which carries glucose with it
  • now high conc of glucose in the blood, glucose diffuse down conc gradient from the PCT epithelial cell into the blood down their conc gradient
• what is the function of the loop of henle

  • too maintain sodium ion gradient
• loop of henle describe how sodium gradient is maintained

  • ascending limb is thick and impermeable to water, and so sodium ions are actively transported out into the interstitial space
  • this lowers the water potential
  • causing water to move out of the descending limb by osmosis
  • at the bottom of the loop of henle some sodium ions diffuse out via diffusion as it is very dilute, high water potential at the bottom
• what is a result of a longer loop of henle

  more water reabsorbed as more active transport of sodium ions out
• what is required to coordinate a response

  hypothalamus, ADH, pituitary gland
• hypertonic blood


  blood has too little water potential
• hypotonic blood 


  blood has too high water potential
• what csn occur due too hypertonic blood

  water can leave cells by osmosis which can cause them too shrivel
• what can occur due too hypotonic blood

  water can enter cells by osmosis and cause them to burst- lysis
• why might blood water potential be too high

  drinking too much water or not enough salt in diet
• why might blood water potential be too low

  sweating

  not drinking enough water
• what does the hypothalamus contain

  osmoreceptors
• what is the role of the hypothalamus

  osmoreceptors detect changes in water potential
• what happens if water potential is too low

  water moves out of osmoreceptors- shrivel, stimulating hypothalamus to produce more ATP
• what happens if blood water potential is too high

  water moves into osmoreceptors, causing them too burst, and they therefore stimulates hypothalamus to produce less ADH
• Where is ADH secreted from

  posterior pituitary gland