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R8
Renal Regulation of Potassium Balance
21
Physiology
Professional
02/24/2013

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Term
What is the normal range of plasma K+?
Definition
3.3-5.1 meq/l
Term
What percentage of filtered K+ is normally reabsorbed?
Definition
85%
Term
What are the primary sites for K+ reabsorption?
Definition
Proximal tubule, thick ascending limb of Henle’s loop, and medullary collecting duct
Term
What are the primary sites for K+ secretion?
Definition
Late distal tubule and cortical collecting duct
Term
What protein transporter does Lasix/Furosemide affect?
Definition
It inhibits the NKCC transporter in the thick ascending loop of Henle
Term
Where is most of the potassium secreted in a high potassium diet?
Definition
distal convoluted tubule
Term
What are the two types of collecting duct cells? And which secretes and which reabsorbs potassium?
Definition
Principal cells – secrete K+
Intercalated cells – reabsorb K+
Term
What are ROMK channels?
Definition
Renal outer medullary potassium channels. They secrete potassium in normal diets.
Term
What are BK channels?
Definition
Big potassium channels. They are like a safety gauge – they are normally closed but they open during hyperkalemia and secrete potassium.
Term
What happens to BK and ROMK channels during hypokalemia?
Definition
BK channels close and ROMK channels are sequestered intracellularly
Term
What is the luminal potential as referenced to the blood?
Definition
-40 mV
*when potassium channels are open, K+ will leak into the urine because it is attracted to the negative charge
Term
How do arterial concentrations of K+ affect aldosterone release?
Definition
Hyperkalemia stimulates aldosterone release from adrenal cortex
Term
What protein channels does Amiloride affect?
Definition
It inhibits ENaC (epithelial sodium channels) which inhibits Na reabsorption in the late distal convoluted tubules and collecting ducts. This promotes loss of Na and water from the body
Term
Is Amiloride K+ wasting or K+ sparing?
Definition
K+ sparing
Term
How does Spironolactone/Aldactone work?
Definition
It is a competitive antagonist of the aldosterone receptor
Term
Is Spironolactone K+ wasting or K+ sparing?
Definition
K+ sparing
Term
What are the 6 factors that increase K+ secretion in the distal nephron?
Definition
1. high plasma potassium
2. aldosterone
3. high Na+ delivery to distal nephron
4. high flow rate in distal nephron
5. high potassium diet
6. nonchloride anions in distal nephron
Term
What is the mechanism of K+ wasting diuretics?
Definition
Block Na+ reabsorption
Increased Na+ in tubules stimulates Na/K ATPase downstream which increases Na+ reabsorption and K+ secretion
Term
How do K+ sparing diuretics work?
Definition
By inhibiting the Na/K ATPase pump or by decreasing the apical membrane permeability to Na+ inward diffusion
Term
What does enhanced secretion of K+ cause?
Definition
Hypokalemic metabolic alkalosis = an increase in H+ secretion which depletes the blood of protons
Term
Why is it counterintuitive to diagnose hypokalemic metabolic alkalosis from a urine sample?
Definition
The urine sample is acidic due to high content of protons
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