HK 3810 Package 2 Kidneys.docx

Thin ascending limb h2o impermeable na permeable

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Thin ascending limb – H2O impermeable, Na+ permeable Thick ascending limb – H2O impermeable, ability to manage H+ and bicarb (based on transporters present) o CA is present in these cells o K+/Cl-/Na+ symporter to move from the lumen of the tubule to inside of the cell, and then moved into ISS o Regulation Neural – direct SNS (NE) – increase Na+ reabsorption increase H2O reabsorption Hormonal ALDO – acts to increase # of symporters and Na+K+ ATPasees increase Na+ reabsorption Epi – increase reabsorption of Na+ increase H2O reabsorption Distal tubule and collecting duct Early distal tubule – H2O impermeable, Na+Cl- symport Late distal tubule and collecting duct (heads down to medullary space) – 2 separate cell types o Intercalated cells helps manage H+ excretion through ATPase on luminal side, it has CA to help with H+ and bicarb balance o Principle cells have regulation Neural – direct SNS (NE) – increase Na+ and H2O reabsorption Hormonal Epi Increase ADH-VP increase # of aquaporins on apical and basolateral membranes increase H2O permeability
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HK 3810 Package 2 Kidneys Decrease ADH-VP decrease # of aquaporins on apical and basolateral membranes decrease H2O permeability ALDO – increase Na+ reabsorption so H2O follows ANP and urodilantin – inhibits NA+ and H2O reabsorption o Urodilantin – local hormonal production through stimulation from increase in MAP and blood volume, which is then secreted by cells of the distal tubule and collecting duct Movement of out loop of Henle, distal tubule, collecting duct is dependent on: Osmotic gradient in medullary space Presence of ADH-VP – tubule very permeable to water, H2O goes from tube to ISS, but if no ADH then water that was in distal tubule stays in the tubule Presence of ANP Presence of AII-ALDO Osmotic gradient in medulla – low ADH Coming out of PT, the fluid in the tube has an osmolarity of 300mOsm, as it moves down the thin descending limb of loop of Henle, we move it through the concentration gradient Outside is getting more concentrated, thin descending limb is permeable to H2O and impermeable to Na+, so water will move from the lumen of the tubule and out to dilute the concentrated space as it goes down Because we are moving vertically through a gradient, we don’t always have enough time to equilibrate with the level we are at As the loop turns, it goes horizontally through and it spends at lot of time to equilibrate At the bottom of the loop of Henle, we will be at the same concentration as the outside As we head up through the thin ascending limb, we are very concentrated on the inside, we are permeable to Na+ but not to H2O, so sodium will move down its gradient By the time we reach the thick ascending limb, we are less concentrated than we were but not equilibrated with the external environment, but we have symporters that can take ions out and transport them
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