Osmoregulation

• How is the water potential of the blood maintained

  Changing the concentration of urine
• What hormone controls the amount of water lost in the urine

  ADH
• Where is ADH produced and stored

  Produced in the hypothalamus and stored in the posterior pituitary gland
• What does ADH do

  Increase the permeability of the distal convoluted tubule
• What is a second messenger

  A molecule which receives signals and relays them
• How is ADH transported and where to

  In the bloodstream to the collecting duct
• How does ADH work

  the hormone binds to receptors on the cell surface membrane and triggers the formation of cAMP as a second messenger
• What does cAMP do

  It causes the vesicles in the Cells lining the collecting duct to fuse with the cell surface membrane on the side in contact with tissue fluid In medulla. The membrane of these vesicles contain aqua poring and where they are inserted into the the cell membrane they make it permeable to water
• What is an aquaporin


  a protein based water channel
• What does more ADH releases cause

  This means more water channels are inserted into the membrane of tubule cells, resulting in a small amount of concentrated urine
• What does less ADH relapse mean

  The levels of cAMP fall so the water channels are removed from the tubules so the collecting duct is impermeable to water so large amounts of dilute urine
• What are osmoreceptors 


  They are sensitive to the concentration of inorganic ions in the blood and linked to the relapse of ADH
• What happens when water is in short supply

  Concentration of inorganic ions rises and water potential becomes more negative. It is detected by osmoreceptors in the hypothalamus which send nerve impulses to posterior pituitary which releases ADH. This ADH is picked up by receptors in the collecting duct increasing permeability
• What happens when water is in excess

  The blood becomes dilute and water potential is less negative. It is detected by osmoreceptors so nerve impulses stop or reduced the relaxes of ADH, so very little re absorption takes place. Dilute urine produced