Regulation of Potassium Balance Flashcards
Potassium:
• where is it located?
• How is it eliminated?
Location:
• INTRACELLULAR Fluid
Elimination:
• Almost completely excreted through the Kidney
Given the storage location and elimination of K, what are 3 important ways its concentration could be increased in the extracellular Fluid or Blood?
- K can simply be released from ICF storage pool into ECF and blood
- Cell Damage can release large amounts of K from the ICF and blood
- Impairment of Renal Excretion can also raise levels
What does potassium balance refer to?
• External vs. Internal Balance.
K+ levels in the ECF
External:
• Intake throught the Diet and Excretion through GI tract and Kidney
Internal:
• Distribution between intracellular and Extracellular Compartments
In what parts of the kidney is most K reabsorbed in the kidney?
• most important areas for reabsorption?
• Area that becomes significant in Hypokalemia?
• PCT, TDLH, TALH, DCT, CCD (basically everywhere except the thin limbs)
2 most important areas of Absorption.
• Proximal Convoluted Tubules
• Thick Ascending LOH
Hypokalemia:
• K collected in the collecting duct becomes important
What Channels are important for potassium transport in the Thick Ascending Loop of Henle?
• describe the co-dependence.
APICAL SIDE:
NK2C channel:
• Electroneutral Channel that Brings K+ into the cell
ROMK:
• renal outer medullary potassium channel
NK2C is dependent on ROMK for recycling of some K+ into the TALH lumen
BASOLATERAL SIDE:
NKA:
• Imports K+ into the back side of the celll
Where does Furosemide act?
Furosemide:
• works by binding the Cl- channel on NK2C and preventing K+ and Na+ reabsorption
What Channels are important in Principal Cells found in the Cortical and Medullary Collecting tubules (ducts). How do they related to K+ Balance?
• How do they work together?
• hormonal Influence?
*ALDOSTERONE - major hormonal influence in the Collecting Tubules (ducts)
Increases expression of the 3 major pumps in the PRINCPAL cells:
Apical: Na+ channel and K+ channel
Basolateral: NKA
How it works:
Basolateral Side: NKA maintains gradient of Low intracellular Na+ and High intracellular K+
Apical:
• Na+ Channel (ENaC)- pumps Na+ INTO principal cells Down its gradient
- K+ Channel (ROMK)- pumps K+ into LUMEN from principal cells DOWN its gradient
- Cl- Channel pumps Cl- OUT to interstitium via PARACELLULAR pathway
Where does potassium absorption mostly occur?
• Excretion?
Absorption:
• Proximal Convoluted Tubule
Excretion:
• Cortical and Medullary Convoluted Tubules
What are 3 factors that affect K+ secretion in principal cells of the Collecting Tubule (duct)?
• What are these factors dependent on?
- Serum Potassium Concentration - affects concentration gradient of K across the basolateral membrane
- Electrochemical Gradient Across the Luminal Membrane - depends on Na+ concentration
- K Permeability of Luminal Membrane - controlled by aldosterone
What would be a consequence on Potassium reabsorption if Na+ was not properly reabsorbed in the Proximal Convoluted Tubule or Loop of Henle?
- More Na will be delivered to the Collecting Duct
- More Na+ will be Pumped into Principal cells through ENaC => therefore more K+ will be EXCRETED by ROMK
Overall effect = excessive K+ excretion
What affect does excess aldosterone have on K+ metabolism in kidney?
• where is this function seen?
Aldosterone - upregulates ENaC, ROMK, and NKA
• Excess aldosterone will lead to an overall INCREASED secretion of K+ so that Na+ can be reabsorbed down its concentration gradient
How does the body adjust K+ uptake and secretion in the collecting duct (tubule) to account for changes in Dietary K+ intake?
Ex. HIGH K+ diet:
- Increases K concentration gradient
- Increased Serum Aldosterone to increase K+ secretion
T or F: Collecting tubule dysfunction of whole kidney dysfunction can lead to HYPERkalemia.
True, this is because K+ is no longer excreted in the Collecting Tubule (duct)
What are 3 general factors that will lead to Decreased Renal Postassium Secretion?
• what is the effect on serum levels of potassium with impaired secretion?
- Renal Failure
- Decreased Distal Tubular Flow
- Hypoaldosteronism
Impaired secretion will lead to HYPERkalemia
What are two general causes of Increased Renal Potassium Secretion?
• overall effect on serum potassium?
- INCREASED Na+ DELIVERY to COLLECTING Tubule
- INCREASED Aldosterone
**HYPOkalemia will result from these processes
What are some cases in which the amount of Na+ delivered to the Collecting Tubule is increased?
Diuretic Use - LOOP diuretics and Thiazide Diruetics that don’t work on ENaC prevent Na+ reabsorption
• by the time the Na+ travels down the ENaC you will have a huge Na+ gradient and K+ will get rapidly shuttled to lumen via ROMK
- Bartter’s Syndrome
- Gitelman’s Syndrome
What are some cases in which aldosterone may be increased causing hypokalemia?
Secondary:
• Prolonged Vomitting
• Nasogastric Suction
Primary:
• Hyperaldosteronism
What pump is important in maintaining internal balance?
NKA - almost all factors that affect internal K balance work through the NKA pump
*note: K+ is constantly exiting through K+ Channels
What are 3 factors that are important in changing K+ concentration inside of Cells?
- Plasma K concentration
- Insulin
- Epinephrine
How does insulin work to Change K+ balance?
indirectly INCREASES intracellular K+
MOA:
• stimulates NaH exchanger which moves Na+ inside the cells which eases the gradient that NKA must work against
How does Epinephrine work to Change K+ balance?
Acts on Beta receptors to INCREASE intracellular K+
MOA:
• Stimulates NKA
What would a Beta Blocker do to Intracellular and Extracellular Potassium?
• albuterol?
Beta Blocker:
• Prevents E binding and thus reduces NKA stimulation leading to a REDUCTION in INTRACELLULAR K+
• While less K+ is influxing there is still a good amout EFFLUXING to ECF of the cell so BETA BLOCKER RAISE EXTRACELLULAR K+ concentration
Albuterol:
• Has essentially the same effect as epinephrine
What effect does low serum K+ have on K+ influx and efflux from cells?
Low Serum K+ will tend to PULL K+ OUT OF CELLs down its gradient
Other Factors that Affect Internal Potassium Balance
• Acid-Base Disturbance
• Plasma Tonicity
• Cell Lysis and Cell Proliferation
Other Factors that Affect Internal Potassium Balance
• Acid-Base Disturbance
• Plasma Tonicity
• Cell Lysis and Cell Proliferation
