HK 3810 Package 2 Kidneys.docx

Na cl and k are moved out so osmolarity is lower

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Na+, Cl- and K+ are moved out, so osmolarity is lower Fluid is moved through the distal tubule and back through the collecting duct At low ADH late distal tubule and collecting duct is not permeable to H2O, so H2O is trapped as it is moving into the medullary space We end up with large volume of dilute urine Vasa recta is where stuff that we put into ISS gets reabsorbed, no special permeability characteristics
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HK 3810 Package 2 Kidneys o Blood enters the vasa recta o It is very concentrated on the outside, not so concentrated in the vasa recta, so Na+ will move down its concentration gradient o We are flowing vertically through so there is not enough time to equilibrate o At the bottom, the concentration of the blood is equal to the concentration in the medullary space o Blood goes back up through the concentration gradient, H2O will move into the vasa recta to dilute the highly concentrated blood o We leave a little more concentrated than we did because there was not enough time to equilibrate The loop makes the gradient and the loop can take it away Osmotic gradient in medulla – high ADH ; ADH acts on DT and CD principle cells increase H2O permeability (increase # of aquaporins) Water movement out of the thin ascending limb due to concentration gradient Since we are impermeable to H2O on the thin ascending limb and permeable to Na+, H2O will move down the gradient Symporters will take stuff out At the DT, we have a low concentration ADH added aquaporins on the distal tubule and collecting duct to increase H2O permeability, causing H2O to move out because it moves to dilute the concentrated outside Result is small volume of concentrated urine In vasa recta, blood comes in and flows vertically through concentration gradient, then flows horizontally at the bottom so very concentrated, then flow up through the gradient so by the time we leave we are more concentrated than the outside Actions of ADH in the kidney Makes DT and CD more permeable to H2O Vasoconstrictor of afferent > efferent o Decrease in PG decrease tubule Q increase equilibration time more time spent in thick ascending limb of loop of Henle increase Na+, K+, Cl- out into ISS (medullary space) concentrate medullary space increase drive to move H2O increase H2O reabsorption o Decrease Q through PTC (vasa recta) increase equilibration time remove less solute from ISS (medullary space) concentrate medullary space increase drive to move H2O increase H2O reabsorption ADH Released from posterior pituitary
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HK 3810 Package 2 Kidneys Stimulus are baroRc (sensors) Haemodynamic stimulus o Low and high pressure baroRc are plugged in indirectly here brain stem hypothalamus synapse onto ADH secreting cells o Tonic signals from baroRc inhibit ADH release: If decrease blood volume (decrease MAP) decrease AP frequency of sensors decrease inhibition increase ADH secretion o Insensitive to these changes
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