L49 Flashcards
What transporter maintains the proper Na and K concentrations in cells?
2K in // 3 Na out transporter
What happens ↑[K] extracell?
Higher resting membrane potential - dangerous b/c shrinks gap between threshold = ↑automaticity
What happens with short term ↑extracell K?
Shift excess into cells w/o dramatically changing fxn
1ary storage = muscle
2ary = liver and blood
What substances enhance and inhibit the 2K/3Na transporter?
Enhance via ↑rate pump:
1. B ad agonists
2. Insulin
Inhibit = a-ad agonists
What is mechanism that maintains long-term K homeostasis?
Renal excretion of K
Explain the movement of K in the prox convoluted tubule?
> 50% K filtered in Bowman’s reabsorbed in PCT
What happen to K in the thick ascending loop?
Comes in via urine
Uptake via 2Cl/Na/K transporter
Regenerate K into urine to maintain charge
Also reabsorbed K from blood to ↑Na reabsorption via 2K/3Na ATPase transporter
What is the drug that targets the Na/2Cl/K transporter?
Loop diuretics
Which cell is responsible for K excretion in the collecting duct? Mechanism?
Principle cell
To reabsorb Na via ENAC, you must excrete K into negative urine lumen
[K enters this cell from the blood via 2K/3Na ATPase transporter]
What are the 3 factors that determine K excretion rate?
- Na+ getting absorbed = lumen negative voltage that pulls K out
- Faster flow rate, keeps urine [K] right outside low aka follow [ ] gradient
- Aldosterone = ↑rate ATPase + ↑ENAC + ↑K channels
2 populations that would have low dietary K and therefore are at risk for hypoK?
Alcoholics
Anorexic
2 main systems that can cause hypoK
Renal 1. Excess aldosterone 2. Diuretic use 3. Renal tubular acidosis 4. Chornic interstital nephritis 5. Mannitol or hyperglycemia = osmotic diuresis GI 1. NG tube suction 2. Diarrhea or vomiting
Which 3 diuretics are most likely to cause hypoK?
Furosemide
Hydrochlorothiazide
Why: force more Na to go downstream in nephron, ↑flow, ↑K excretion
Why is hypoK on diuretics limited?
↓intravasc volume = ↓flow
Stabalizes amt K excreted
What happens if you eat salty foods on a loop diuretic?
↑Na = more at distal nephron
You must save more Na there
You have to waste K
Which 2 drugs ↓K secretion but making the urine lumen less negative @ collecting duct?
Amiloride
SMX TMP
What drug ↑K secretion by ↑distal delivery of Na -> ↑flow?
Furosemide
What 3 drugs ↓K secretion by ↓effects of aldosterone?
ACE inhibitors
ARBs
Spironolactone
If pt is hypoK w/ U K
GI b/c kidney is holding onto K appropriately
If pt is hypoK w/ U K > 20, what is the source of the loss?
Renal - shouldn’t be losing K if hypoK!
EKG changes for hypoK
T wave flattens
Develop U wave right in front of T
Causes of pseudo-hyperK
Trauma when drawing blood
↑WBC or PLT (leukocytosis or thrombosis)
3 causes of hyperK
- Redistribution
- ↓excretion
- ↑input
Give the example of redistribution cause hyperK
Acidemia = excess H is buffered in cells, K moves out as consequence
Give the examples of ↓excretion causing hyperK - TESTQUESTION
Acute or chronic kidney disease K sparing diuretics **↓Aldosterone - Addison's - ↓renin -> ↓aldo = type 4 rental tubular acidosis**
Give the examples of ↑input causing hyperK
- Intravasc hemolysis - releasing intracell contents (Sickle, TTP, HUS)
- Rhabdo - pigment from these cells injures kidney, can’t properly secrete K
- K salt substitutes
- K penicillin
EKG changes with hyper K
EMERGENCY
- Peaked T waves
- Prolonged QRS
- Lose P wave
What do you give to treat hyperK to antagonize membrane effects?
Ca // hypertonic saline - ↓membrane effects
Aka increase threshold to re-est distance between elevated resting membrane potential
What do you give to treat hyperK via moving K back into cells?
Insulin (w/ glucose) - stim Na/K pump
B2 agonists - stim Na/K pump
NaHCO3 not shown to work in people
What do you give to remove excess K in hyperK?
Loop diuretics
K exchange resin - osmotically pulls K in gut
Dialysis
Why do subjects with chronic kidney disease tolerate higher K levels?
Better short term sequestration mechanism
High K diet in these pts is protective against K shifts
