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21 Cards in this Set
- Front
- Back
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What is internal K+ balance?
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shift of K+ between ICF and ECF
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What is external K+ balance?
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gain/loss of K+ from the body
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What body compartment has most of K+ in the body?
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ICF
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How must blood have shifted w/in the body to get hyperkalemia?
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shift of K+ from ICF to ECF (increase blood conc of K+)
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What things can cause a K+ shift INTO cells (hypokalemia)?
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1) insulin (puts K+ into cells as to not increase plasma K+ levels too much)
2) B-agonists 3) alkalosis (via H+/K+ exchange) |
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What things can cause a K+ shift OUT OF cells (hyperkalemia)?
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1) exercise - release K+ from muscle cells
2) lack of insulin (diabetes mellitus) 3) cell lysis (high K+ conc released) 4) B antagonists 5) hyperosmolarity (water flowing from ICF to ECF drags K+ with it) 6) acidosis (H+/K+ cotransporter - H+ enters cells and K+ leaves cells) |
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What is the major variable determining final urinary excretion of K+?
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rate of K+ secretion
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Name the % of K+ reabsorbed along the nephron by location.
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proximal tubule - 67% (like Na)
thick ascending limb - 20% (not as high as Na b/c some leaks out) early distal tubule - reabsorb K+ with low K+ diet only distal tubule and collecting duct - variable - K+ secretion |
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Why is controlling K+ so difficult?
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K+ ingestion is so variable from person to person and day to day
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What area of the nephron is responsible for "fine tuning" K+ excretion?
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distal tubule and collecting duct
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When is K+ reabsorbed in the late distal tubule and collecting ducts?
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via intercalated cells in only those with a very low K+ diet
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When is K+ secreted in the late distal tubule and collecting ducts?
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via the principal cells most of the time
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What factors does K+ secretion rate depend on?
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1) diet
2) aldosterone 3) acid-base balance 4) tubular flow rate |
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What is the method of K+ reabsorption in the intercalated cell?
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H+/K+ exchanger (H+ out/K+ in during hypokalemia only - low K+ diet)
* similar to that of the gastric parietal cells |
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What is the method of K+ secretion in the principal cell?
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passive K+ channel (down conc gradient) which is induced by aldosterone (Na+/K+ ATPase and informal H+/K+ exchanger on basolateral membrane keeps K+ high inside cell)
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What determines the magnitude of K+ secretion?
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the size of the electrochemical gradient
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How does diet alter K+ secretion?
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high K+ in diet increases K+ in principle cells, increases intracellular K+ concentration and increases driving force for K+ secretion
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How does aldosterone alter K+ secretion?
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induces synthesis of Na+ channels on the luminal membrane of principal cells, more Na+ inside cells, increases work of Na+/K+ transporter on basolateral side, increasing the K+ in cell, increasing secretion of K+; aldo also induces synthesis of the K+ channels in the luminal membrane
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How do acid/base changes alter K+ secretion?
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acidemia causes H+ to enter cells and K+ to be secreted via H+/K+ exchanger on luminal membrane
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How does flow rate through distal tubule and collecting duct change K+ secretion?
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increased flow rate (could be caused by diuretics) dilutes K+ luminal conc, increasing the conc gradient across the luminal membrane - K+ secretion is increased
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How do K+ sparing diuretics change K+ secretion?
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inhibit aldosterone's actions including K+ secretion
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