L27 - kidney: regulation of water & salts
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where is salt reabsorbed?
• PCT • ascending loop of HENLE • collecting ducts • hormonal control
where is water reabsorbed?
• descending loop of henle • collecting ducts • hormonal control
where does filtration occur?
glomerulus + bowman’s capsule
how is salt reabsorbed in the PCT?
• Na+ moves from tubules into cells • via co transport with other molecuke • or via counter transport of H+ ions (Na+ in, H+ out) • Na+ moved from tubule cells to interstitial space and then blood via AT • Na+/K+ ATPase pump, requires ATP • K+ returns to interstitial fluid via ion channels down a conc gradient
how is salt reabsorbed in the ascending loop of henle?
• Na+ moved from tubules into cells through cotransport with K+ and Cl- • Na-K-Cl cotransporter (NKCC) • K+ moves back into tubule via ion channels down a conc gradient • Na+/K+ ATPase moves Na+ out to interstitial space and K+ into cells • K+ returns to interstitial fluid via ion channels down conc gradient
how is salt reabsorbed in collecting ducts?
• Na+ moves into cell and K+ moves out through ion channel down conc gradient • Na+/K+ ATPase moves Na+ out to interstitial space and K+ into cells
how salt is reabsorbed via hormonal control?
• aldosterone: steroid hormone • regulates Na+ reabsorption and blood pressure • acts in collecting duct tubule cells 4, increases expression of ion channels and Na+/K+ ATPase
how is water reabsorbed by the descending loop of henle?
• only descending loop is permeable to water • ascending loop reabsorbs salts and creates hypertonic solution in interstitial fluid around loop • causes water to diffuse out of descending loop
water reabsorption full process in loop of henle
• blood flow around LOH is counter to flow through LOH • filtered blood that is low in salt encounters the ascending loop • encouraging salt reabsorption • salt rich blood circulates around descending limb • water from descending loop moves into blood • maintains conc gradient
how is water reabsorbed by collecting ducts?
• collecting duct tubule cells contain water channels: aquaporins • interstitial space full of salt from Na+ reabsorption • allows free flow of water out of tubule through cell into interstitial space
how is water reabsorbed by hormonal control (collecting ducts)?
• vasopressin is a hormone that controls water reabsorption • acts on receptors on collecting duct cells • causes aquaporin rich vesicles inside cell to fuse with cell membrane • increases number of channels water can use to cross body