Phys3 K+ balance
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| Where does Medullary K+ recycling occur? | Long looped juxtaglomerular nephrons.
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| Steps of medullary K+ recycling | 1.K+ secreted into thin descending limb.
2.K+ is reabsorbed by both ascending limbs & deposits in the interstitium.
3.K+ is reabsorbed from medullary CDs and deposits in interstitium.
4.K+ becomes trapped in medullar interstitium.
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| What is the net movement of K+ in the loop of Henle? | REABSORPTION. ascending loops reabsorb more than descending loops secrete.
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| Where is interstitial K+ highest? | At the papilla.
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| Why is the high medullary [K+] created from K+ recycling important? | During high K+ intake, there is a lot of secretion into the tubule lumen (as high as 200mOsm). With a high interstitial [K+], there will be less passive diffusion out of the tubule lumen.
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| What type of reabsorption of K+ occurs in the PT? | paracellular.
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| How is K+ reabsorbed in the thick ascending limb? | Via NKCC (Na/2CL/K symporters) which are the target of loop diuretics.
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| How do principle cells effect [K+] | They secrete K+ through channels on the apical membrane into the tubule lumen.
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| How do loop diuretics affecting the PT, Loop of Henle, and DCT affect [K+] | 1.Inhibit K reabsorption.
2.Inc K secretion.
**INCREASE K+ EXCRETION.
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| Types of K+ channels on apical principal cell membrane and how they respond to [K+] | 2 types: ROMK & BK.
1.Low [K+]: ROMK sequestered, BK closed.
2.Normal [K+]: ROMK open, BK closed.
3.High [K+]: Both are OPEN.
**respond to K+ excretory rate.
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| When are principle BK channels on the apical membrane open? | Hyperkalemia.
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| What occurs on the apicl membrane of the CDs to affect [K+] | REASBSORPTION through H/K exchangers.
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| Factors causing Inc K+ secretion in distal nephron | 1.High K diet.
2.Non-Chloride anions in distal nephron.
3.High flow rate in distal nephron.
4.High Na delivery in distal nephron.
5.High plasma K.
**Hyperkalemia will trigger aldosterone.
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| Metabolic acidosis' affect on K+ | H+ wants to move out of the plasma and into the cell to restore pH. This causes K+ to move into plasma: HYPERKALEMIA.
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| Metabolic alkalosis' affect on K+ | H+ wants to move into the plasma to restore pH. Therefore K+ moves out into the cells causing: HYPOKALEMIA
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