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21 Cards in this Set

  • Front
  • Back
What is internal K+ balance?
shift of K+ between ICF and ECF
What is external K+ balance?
gain/loss of K+ from the body
What body compartment has most of K+ in the body?
How must blood have shifted w/in the body to get hyperkalemia?
shift of K+ from ICF to ECF (increase blood conc of K+)
What things can cause a K+ shift INTO cells (hypokalemia)?
1) insulin (puts K+ into cells as to not increase plasma K+ levels too much)
2) B-agonists
3) alkalosis (via H+/K+ exchange)
What things can cause a K+ shift OUT OF cells (hyperkalemia)?
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)
What is the major variable determining final urinary excretion of K+?
rate of K+ secretion
Name the % of K+ reabsorbed along the nephron by location.
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
Why is controlling K+ so difficult?
K+ ingestion is so variable from person to person and day to day
What area of the nephron is responsible for "fine tuning" K+ excretion?
distal tubule and collecting duct
When is K+ reabsorbed in the late distal tubule and collecting ducts?
via intercalated cells in only those with a very low K+ diet
When is K+ secreted in the late distal tubule and collecting ducts?
via the principal cells most of the time
What factors does K+ secretion rate depend on?
1) diet
2) aldosterone
3) acid-base balance
4) tubular flow rate
What is the method of K+ reabsorption in the intercalated cell?
H+/K+ exchanger (H+ out/K+ in during hypokalemia only - low K+ diet)
* similar to that of the gastric parietal cells
What is the method of K+ secretion in the principal cell?
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)
What determines the magnitude of K+ secretion?
the size of the electrochemical gradient
How does diet alter K+ secretion?
high K+ in diet increases K+ in principle cells, increases intracellular K+ concentration and increases driving force for K+ secretion
How does aldosterone alter K+ secretion?
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
How do acid/base changes alter K+ secretion?
acidemia causes H+ to enter cells and K+ to be secreted via H+/K+ exchanger on luminal membrane
How does flow rate through distal tubule and collecting duct change K+ secretion?
increased flow rate (could be caused by diuretics) dilutes K+ luminal conc, increasing the conc gradient across the luminal membrane - K+ secretion is increased
How do K+ sparing diuretics change K+ secretion?
inhibit aldosterone's actions including K+ secretion