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Flashcards in Regulation of Potassium Balance Deck (56)
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1

Potassium:
• where is it located?
• How is it eliminated?

Location:
• INTRACELLULAR Fluid

Elimination:
• Almost completely excreted through the Kidney

2

Given the storage location and elimination of K, what are 3 important ways its concentration could be increased in the extracellular Fluid or Blood?

1. K can simply be released from ICF storage pool into ECF and blood

2. Cell Damage can release large amounts of K from the ICF and blood

3. Impairment of Renal Excretion can also raise levels

3

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

4

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

5

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

6

Where does Furosemide act?

Furosemide:
• works by binding the Cl- channel on NK2C and preventing K+ and Na+ reabsorption

7

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

8

Where does potassium absorption mostly occur?
• Excretion?

Absorption:
• Proximal Convoluted Tubule

Excretion:
• Cortical and Medullary Convoluted Tubules

9

What are 3 factors that affect K+ secretion in principal cells of the Collecting Tubule (duct)?
• What are these factors dependent on?

1. Serum Potassium Concentration - affects concentration gradient of K across the basolateral membrane

2. Electrochemical Gradient Across the Luminal Membrane - depends on Na+ concentration

3. K Permeability of Luminal Membrane - controlled by aldosterone

10

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

11

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

12

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:

1. Increases K concentration gradient

2. Increased Serum Aldosterone to increase K+ secretion

13

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)

14

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?

1. Renal Failure
2. Decreased Distal Tubular Flow
3. Hypoaldosteronism

**Impaired secretion will lead to HYPERkalemia**

15

What are two general causes of Increased Renal Potassium Secretion?
• overall effect on serum potassium?

1. INCREASED Na+ DELIVERY to COLLECTING Tubule

2. INCREASED Aldosterone

**HYPOkalemia will result from these processes

16

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

17

What are some cases in which aldosterone may be increased causing hypokalemia?

Secondary:
• Prolonged Vomitting
• Nasogastric Suction

Primary:
• Hyperaldosteronism

18

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

19

What are 3 factors that are important in changing K+ concentration inside of Cells?

1. Plasma K concentration
2. Insulin
3. Epinephrine

20

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

21

How does Epinephrine work to Change K+ balance?

Acts on Beta receptors to INCREASE intracellular K+

MOA:
• Stimulates NKA

22

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

23

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

24

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

25

What affect do Acid Base disturbances have on K+ levels inside of cells?
• which are more disruptive of the H/K balance; metabolic or respiratory defects?

• K+ and H+ shift Reciprocally

ACIDOSIS:
• Metabolic Defects cause more of a disturbance than Respiratory Disturbances
• causes HYPERKALEMIA because H+ is flowing into cells and K+ then flows out

ALKALOSIS:
• leads to HYPOKALEMIA

26

Which will have more of a hyperkalemia associated with it:
• metabolic acidosis due to Mineral Acid or due to Organic Acid

Mineral Acids tend to have a greater effect on K+ levels

27

What is the effect of Hypertonicity on K+ levels in the ECF?

ECF = Hypertonic
Result is HYPERKALEMIA**** (more K+ in the ECF)

• H2O diffuses out of the cell as a result
• Some K+ comes with the H2O

Overall:
• Loss of Intracellular H2O increases intracellular K+ concentration

• Increases K+ gradient and some K+ diffuses through the potassium channel

28

What are some common causes of Hypertonicity?

• Diabetic Ketoacidosis or Diabetic Hyperosmolar state (caused by inc. Extracellular Glucose concentration)

29

What are some pathogenic causes of cell lysis and cellular proliferation that often cause disruption in K+ balance?

Cell Lysis => HYPERkalemia:
• Rhabdomyolysis
• Red Cell Lysis

Cell Proliferation => HYPOkalemia
• Cancer

30

When is a person considered to be Hyperkalemic?
• 3 general causes of hyperkalemia?

Serum Potassium greater than 5.5

3 causes:
1. Excessive Potassium Intake
2. Decreased Renal Excretion
3. Internal Redistribution