5.1.2 (d) Osmoregulation Flashcards
what is osmoregulation?
controlling of water potential in the blood within narrow boundaries
what hormone controls the amount of water in the urine?
ADH in a negative feedback system
where is ADH produced?
in the hypothalamus
where is ADH secreted?
into the POSTERIOR pituitary gland
where does ADH affect the permeability of?
the distal convoluted tubule
the collecting duct
what is ADH carried in to get to the kidney tubule cells?
the blood
outline ADH action
released from posterior pituitary gland
travels in the blood to tubule cells in the kidney
binds to receptors on the cell surface membrane
causes a cascade reaction to form cAMP which acts as a secondary messenger
cAMP stimulates vesicles containing aquaporins to fuse with the cells surface membrane
this increases the permeability
what does ADH do when it binds to the receptors on the cell surface membrane of kidney tubule cells?
triggers the formation of cAMP which acts as a secondary messenger
how does cAMP act as a secondary messenger?
causes vesicles containing aquaporins to fuse with the cell surface membrane of cells which line the DCT and collecting duct which increases it’s permeability to water
water moves out of the collecting duct/DCT into the medulla
what happens when more ADH is secreted?
more aquaporins are formed in the cell surface membrane
SO MORE PERMEABLE
what happens when less ADH is secreted?
aquaporins remove themselves from the cell surface membrane
SO LESS PERMEABLE
concentrated urine
more water reabsorbed back into blood
dilute urine
more water removed by excretion
ADH and urine conc relationship
more ADH =concentrated urine
less ADH = dilute urine
what detects changes in water potential in the blood?
osmoreceptors
where are osmoreceptors found?
in the hypothalamus
what happens to the conc of inorganic ions when water is in short supply?
it rises which causes the water potential to lower
this is detected by the osmoreceptors in hypothalamus and activates them
what do the osmoreceptors send when activated and to who?
they send nerve impulses to the posterior pituitary gland
what does the posterior pituitary do when there is water in short supply?
secrete more ADH
what happens to the walls of the collecting duct when water is in low supply?
the excess ADH secreted causes more aquaporins to fuse with the cell surface membrane which increases the permeability and allows more water to move back into the blood
urine more concentrated
what happens to the conc of inorganic ions when water is in excess?
decreases
osmoreceptors stimulate the posterior pituitary gland to stop secreting ADH
walls of PCT and CD become less permeable as aquaporins remove themselves
water is prevented from being reabsorbed into the blood
urine more dilute
