L27 - Kidneys: Regulation of Water and Salts

• Where is salt reabsorbed in the kidney?

  PCTAscending Loop of HenleCollecting Duct

  
• Where is water reabsorbed in kidney?

  Descending Loop of HenleCollecting Ducts

  
• Which hormone affects salt absorption in kidney?

  Aldosterone (steroid)
• Which hormones affects water reabsorption in kidney?

  Vasopressin / ADH (Anti-diuretic hormone)
• In PCT, which mechanisms move Na+ from tubules into tubule cells?

  Co-transport, (eg with glucose in)Counter-transport (with H+ out)

  
• In PCT, which mechanisms move Na+ from tubule cell into interstitial space?

  Na+/K+/ATPase pump

  
• Describe how salt (Na+) is reabsorbed in the PCT

  - Na+ moves from tubule into tubule cell via cotransport (w/glucose) and counter-transport (w/ H+ moving back into tubule)- Na+ moves from tubule cell to interstitial space via Na+/K+/ATPase pump(active transport)- K+ returns to interstitial space down ion channels to maintain [conc] gradient- high [K+] in cell, low [K+] in interstitial space

  
• What's the difference between transporters and ion channels?

  - Transporters only move one way, regardless of [conc]- Ion channels only move ions dependent on thei [conc] gradient

  
• In ascending Loop of Henle, through which mechanism is Na+ moved from tubule to tubule cell?How does K move back into tubule?

  NKCC: Na-K-Cl CotransporterK moves back into tubules down conc gradient via ion channels

  
• In ascending Loop of Henle, through which mechanism is Na+ moved from tubule cell to interstitial space?How does K+ return to interstitial space?

  Na+/K+/ATPase pump moves Na out and K into cellsK+ returns to interstitial space down conc gradient via ion channels

  
• Describe how salt (Na+) is reabsorbed in the descending loop of Henle

  - Na+ moved into tubule cell from tubule by Na/K/Cl Cotransporter (NKCC)- K+ moved back into tubule down [conc] gradient via ion channel- Na+ moved out from tubule cell to interstitial space by Na/K/ATPase pump.- K moved into cell against conc gradient, so returns to interstit. space down conc gradient via ion channels

  
• Describe how salt (Na+) is reabsorbed in the collecting ducts

  - Na+ moves from tubule intotubule cell down donc gradient via ion channels- Na+ moves into interstitial space via Na+/K+ ATPase pump. K+ moves back into tubule cell

  
• What type of receptor is an Aldosterone receptor?

  Nuclear Receptor

  
• Hormonal Control of salt reabsorption- which hormone? where does it act?- what does it do?

  - Aldosteroe acts at collecting duct stage (in tubule cells)- When aldosterone binds to its receptor, the receptor-agonist complex moves from cytoplasm into nucleus- In nucleus, complex binds to DNA, increasing production of ion channels and Na/KATPase to increase salt absorption

  
• What results from an increase in aldosterone?Fast or slow process?

  Increased aldosterone = increased production of ion channels/ Na/KATPase channels = MORE pumps = MORE reabsorptionSLOW bc aldosterone first must enter tubule cell nucleus, bind to receptor and DNA. Takes time for channels to be created.

  
• Which loop of Henle is permeable to water?

  Descending loop

  
• How is water reabsorbed in loop of Henle?How is nephron adapted for this?

  - Na+ reabsorbed in ascending loop- created hypertonic solution in interstitial space- causes water to diffuse out of descending loop- nephron highly vascularised: counter-current flow to that in loop of henle

  
• How does blood flow around loop of Henle aid water reabsorption?

  Counter-current flow:- filtered blood from glomerulus first encounters ascending loop, allowing salt reabsorption- blood now has high [Na+] conc when it meets descending loop, allowing rapid osmosis of water

  
• How is water reabsorbed in collecting ducts?

  Through aquaporinsFrom area of low to high water potential

  
• Hormonal Control of Water Reabsorption- which hormone?- which receptor type does it act on?- what does it do?

  - Vasopressin (ADH) enters interstit space from blood- acts on GPCRs on collecting duct tubule cells- binding initiates signalling cascade so MORE aquaporins are placed on csm (aquap. rich vesicles fuse with csm)MORE channels = MORE water reabsorption
• What results from an increase in vasopressin?Fast or slow process?

  MORE aquaporins = MORE reabsorptionFast - aquaporins already present so no lag time waiting for them to be made