05.08 - K Balance (Showkat) - PP, No reading Flashcards
Daily intake and output of K
100 mEq/d in; 90-95 out kidney, 5-10 out GI
3 Factors Affecting K Secretion
(1) [K] across membrane - depends on serum [K]; (2) Electrical gradient deteremined by Na delivery to DT; (3) K permeability of luminal membrane determined by Aldosterone
3 Groups of Causes of Hyperkalemia
(1) Excessive K intake; (2) Dec Renal Excretion; (3) Internal Redistribution
How does vomitting affect K balance
Hypokalemia due to increased Aldosterone
K imbalance in Congenital Adrenal Hyperplasia
Hypokalemia
How is K reabsorbed in ThickALOH, and what else travels thru this route?
Paracellular Diffusion, also Na+, Ca2+, Mg+
5 Causes of Internal Redistribution of K leading to HyperK
Insulin Def., B2 blockade, Hypertonicity, Acidemia, Cell lysis
How does NG suction affect K balance
Hypokalemia due to increased Aldosterone
Three ways to move K outside body in Hyperkalemia Tx
Diuretics, Resins (cation exchange), Dialysis
What eliminates effect of DT flow rate on K secretion
Low K diet
Skeletal muscle clinical manifestations of Hypokalemia
Weakness, Rhabdomyolysis
Which has greater effect on K: Metabolic acidosis due to Organic Acids or Mineral Acids
Mineral Acids
K imbalance in Cushing’s
Hypokalemia
When are diuretics usually used for hypokalemia
K sparing in cases of chronic hypokalemia
K-related channels in ThickALOH
NaK2Cl on luminal border; K channel on luminal border; Na-K ATPase on basolateral border
What channel does Bartter’s affect?
Na-K-2Cl
What determines the number of K channels in luminal membrane of DT/CD
Aldosterone
What 3 factors promote K movement across cells
Plasma [K], Insulin, Epinephrine
Hypoaldosteronism will cause what K imbalance
Hyperkalemia (decreases secretion)
Metabolic Acidosis causes what change in K
H+ enters cell, K exits
Three ways to move K inside cells in Hyperkalemia tx
Insulin, Beta agonists, Bicarb
K imbalance in Renal Artery Stenosis
Hyper-reninemia - Hypokalemia
2 Actions of Aldosterone in Principal cells
(1) Adds ENaC (in) and ROMK (out) channels to luminal surface; (2) Stimulates Na-K pump -> Creates electronegativity -> Reabsorption of Na thru epithelial channel (ENaC)
Major site of K reabsorption
PT
Causes K movement into cells - Simtulates Na-H exchange - This activates Na-K ATPase
Insulin
Clincial manifestations of Hyperkalemia result primarily from
Depolarization of resting Vm in myocytes and neurons
What beta agonist is used for Hyperkalemia? How does it work?
Albuterol - Activates Na-K pump via beta 2 receptor
K imblanace in Renin-Secreting Tumor
Hypokalemia
Onset and duration of Kayexalate in Hyper K tx
2-3 hours, 4-6 hours
What K imbalance is caused by decreased plasma osmolality
Hypokalemia
How does increase in Plasma Osmolality change K balance
(1) Fluid shifts out cell and drags K with it; (2) Loss of water causes conc. gradient, K exits down gradient passively
How does insulin affect K movement
Causes movement into cells - Simtulates Na-H exchange - This activates Na-K ATPase
At what plasma [K] will you see sine wave morphology
12 mEq/L
K imbalance in Bartter’s, Gitelman’s
Hypokalemia
Rapid infusion of K can cause
Cardiac Arrhythmias
K imbalance in Conn’s Syndrome
Primary Hyper-Aldosteronism - Hypokalemia
What potentiates the affect of DT flow rate on K secretion
High vs Low K diet
What K imbalance is caused by renal failure
Hyperkalemia - Impaired secretion
EKG changes in Hyperkalemia
(1) Peaked T wave; (2) Wide QRS, Short QT, Long PR; (3) Further wide QRS, absent P wave; (4) Sine Wave
4 significant locations of intracellular K
Muscle, Liver, RBC, Bone
At what plasma [K] will you see peaked T wave
6 mEq/L
Renal clinical manifestations of Hypokalemia
Nephrogenic Diabetes Insipidus
Onset and duration of Furosemide in HyperK tx
5 min, 2 hours
How does Hyperaldosteronism affect K balance
Hypokalemia due to increased Aldosterone
Major site of K secretion
CD
How does rapid cellular proliferation affect K balance?
Rapid intake – Hypokalemia
Onset and duration of Ca2+ for HyperK tx
1-3 mins, 30-60 mins
2 classes of K-sparing diuretics used for Hypokalemia
(1) Aldosterone R Blockers; (2) ENaC inhibitors
Inhibiting this channel will inc. postive charge in lumen, prevent K secretion
ENaC
Onset and duration of Albuterol for HyperK tx
30 mins, 2-4 hours
How does too much Na reabsorption affect K secretion
Not enough Na enters ENaC on Principal cells, and there is a small electochemical gradient that is necessary to drive K secretion
At what plasma [K] will you see wide QRS, short QT, long PR?
8 mEq/L
Prolonged depolarization from Hyperkalemia decreases
Na permeability thru inactivation of V-gated Na channels - Reduction in membrane excitability
How does alpha receptor affect K movement
Inhibits Na-K ATPase, so prevents movement of K into cells
How do ENaC inhibitors tx Hypokalemia
Inhibiting this channel will inc. postive charge in lumen, prevent K secretion
How does High K diet affect amount of K secreted for given DT flow rate
Increases
How do Bartter’s and Gitelman’s affect K balance?
Hypokalemia due to increased distal Na delivery
4 Causes of Hypokalemia due to Internal Redistribution
Insulin excess, Catecholamine excess, Alkalemia, Cell proliferation
How do acid base disturbances affect K
Changes in extracellular pH produce reciprocal shifts in H+ and K+ across membrane
Smooth muscle manifestations of Hypokalemia
HTN, Ileus
Stimulates Na-K ATPase via B2 receptors - Move K intracellularly
Epinephrine
K imbalance in Prolonged Vomitting, NG suction
Hypokalemia
Which have greater effect on K: metabolic or respiratory acid base disturbances
Metabolic
Onset and duration of Insulin for HyperK tx
30 mins, 4-6 hours
How are diuretics used to tx Hypokalemia
K-sparing diuretics increase K reabsorption
K imblanace in Uretral diversion
Hypokalemia
Most common clinical cause of Hypokalemia
Exogenous glucocorticoid excess - Steroid Admin
K imbalance in Primary Hyper-Aldosteronism
Hypokalemia
What K imbalance is caused by increased plasma osmolality
Hyperkalemia
Alkalosis causes what change in K
H+ exits cell, K enters
EKG changes in Hypokalemia
(1) Flat T wave; (2) Prominent U wave; (3) Depressed ST segment
How does Epi affect K movement
Stimulates Na-K ATPase via B2 receptors - Move K intracellularly
How and why does distal tubular flow rate affect K secretion
Increase flow = Inc secretion Na delivery to DT
How do diuretics (Loop, Thiazide) affect K balance
Hypokalemia due to increased distal Na delivery
How is K usually given clinically
KCl, KPO4 - KCl tab or mixed with IV fluids
First-line tx of Hyperkalemia
Ca2+ (doesn’t lower K, just counters)
Amount of Intracellular K
3300 mEq
How does Beta receptor affect K movement
Stimulates Na-K ATPase, so moves K into cells
How does Na reabsorption affect K Secretion
If more Na is delivered distally, it enters thru ENaC channels in Principal Cells and creates electrochemical gradient favor K secretion
Why and How does beta blockade affect K balance
B2 receptors activate Na-K -> Without activation, K not taken up into cell -> Hyperkalemia
Hyperaldosteronism will cause what K imbalance
Hypokalemia (increases secretion)
4 causes of decreased renal K secretion
Kindey Failure, DT dysfxn, Dec DT flow, Hypoaldosteronism
If there is a deficiency in insulin, what channel is impaired and what ion is dysregulated?
Na-K pump is impaired, Elevated K in ECF
