Potassium

Question 1

what is the average intracellular concentration of potassium?

Answer 1

150 mEq/L

Question 2

What is the normal concentration of potassium in the ECF?

Answer 2

4 mEq/L

range: 3.5 to 5

Question 3

What concentration of potassium in the ECF defines hyperkalemia?

Answer 3

> 5 mEq/L

Question 4

What concentration of potassium in the ECF defines hypokalemia?

Answer 4

< 3.5 mEq/L

Question 5

Which hormones promote the uptake of potassium by cells?

Answer 5

epinephrine and insulin - stimulate the ATPase pump

Question 6

What triggers insulin secretion by the pancreas and epinephrine secretion by the adrenal medulla?

Answer 6

. A rise in plasma [K+], subsequent to K+ absorption by the gastrointestinal tract

Question 7

In regards to diet, what is the most important hormone regulating potassium concentration?

Answer 7

insulin

Question 8

Why is rapid uptake by the cells important in preventing life threatening hyperkalemia following a meal?

Answer 8

If the K+ ingested during a normal meal ( 33 mEq) were to remain in the ECF compartment, plasma [K+] would increase by a potentially lethal 2.4 mEq/l. The rapid uptake of K+ into the cells prevents this rise in plasma [K+]. As the excretion of K+ by the kidneys after a meal is relatively slow (hours), the rapid uptake of K+ by the cells is essential to prevent life-threatening hyperkalemia

Question 9

What effect would low K have on the resting potential of a cell?

Answer 9

lower it, making it less excitable

Question 10

What effect would high K have on the resting potential of a cell?

Answer 10

increase it, making it more excitable

Question 11

What is true of K intake and excretion?

Answer 11

it is equal within a tenfold range

Question 12

How is most K excreted?

Answer 12

via the renal system

Question 13

What is the primary event that trigers urinary potassium excretion?

Answer 13

is K+ secretion from the blood into the tubular fluid by the cells of the distal tubule and collecting duct system.

Question 14

Potassium is freely filtered by the glomerulues, true or false. why?

Answer 14

true - not bound to protein

Question 15

When potassium intake is normal, what is true of potassium handling by the CCD?

Answer 15

it is secreting K

Question 16

What effect would a low potassium diet have on the distal tubule and collecting duct?

Answer 16

a low-potassium diet activates K+ reabsorption along the distal tubule and collecting duct so that the urinary excretion falls to 1% of the K+ filtered by the glomerulus

Question 17

Why is hypokalemia somewhat easier to develop due to dietary changes than hyponatremia?

Answer 17

the kidneys are not able to reduce K excretion by the same degree as it can na

Question 18

What are the main factors controlling the rate of K secretion by the distal renal tubule and collecting duct?

Answer 18

1. The activity of the Na+/K+ ATPase pump in the collecting tubule
2. The driving force (electrochemical gradient) for K+ movement across the apical membrane, which is influenced by urine flow rate
3. The ability of K+ to cross the apical membrane (potassium conductance) via a K+ channel called ROMK
4. The ability of the Na+ channels to function thereby, creating a favorable electrical gradient for potassium secretion.
5. Aldosterone which increases the activity of the Na+ K+ ATPase pump and opens the sodium channel.

Question 19

What are the 3 main physiologic regulators of potassium secretion?

Answer 19

plasma K, aldosterone, distal Na delivery

Question 20

What 3 factors can perturb K secretion?

Answer 20

1. aldosterone levels
2. flowof tubular fluid and distal sodium delivery
3. acid base balance

Question 21

What effect does alkalosis have on K secretion?

Answer 21

increase it

Question 22

what effect does acidosis have on K secretion?

Answer 22

decreases it

Question 23

what effect does chronic renal insufficiency have on potassium excretion?

Answer 23

The development of chronic renal insufficiency is associated with renal adaptation such that the quantity of potassium excreted per nephron is increased. This permits a normal absolute potassium excretion despite reduced GFR. Eventually, the mechanism for potassium adaptation is overwhelmed, and the absolute quantity of potassium excreted is less than potassium intake. Thus, hyperkalemia is expected whenever glomerular filtration fate (GFR) is markedly reduced (less than 10 mL/minute).

Question 24

What is the GFR at which hyperkalemia is expected ?

Answer 24

< 10 mL/min

Question 25

what are the most common causes of selective aldosterone deficiency?

Answer 25

diabetes and interstitial renal disease

Question 26

Which drugs are associated with acquired selective aldosterone deficiency leading to hyperkalemia?

Answer 26

NSAIDs and ACE I

• less common: chronic heparin therapy

Question 27

Patients with chronic obstructive nephorpathy frequently have what problem with potassium?

Answer 27

Inability to excrete potassium disproportionate to the degree of renal insufficiency can occur as part of a generalized defect in collecting tubule function, causing hyperkalemia. This syndrome has been best characterized in patients with chronic obstructive nephropathy in whom damage to the collecting duct cells interferes with both hydrogen ion and potassium secretion

Question 28

When is hypokalemia generally symptomatic?

Answer 28

< 2.5 mEq/L

Question 29

What are the two etiologies of hypokalemia?

Answer 29

depletional or non depletional, further divided into renal and extrarenal

Question 30

What causes extra reanl hypokalemia?

Answer 30

Hypokalemia in the setting of low total body potassium (i.e., depletional hypokalemia) may result from insufficient dietary potassium intake or a loss of potassium from the GI tract or kidneys.

Question 31

Does renal potassium loss occur with normal, high or low BP/

Answer 31

normal or high

Question 32

does renal potassium loss occur with low, normal, or high renin activity?

Answer 32

all three

Question 33

What is the most common cause of renal hypokalemia with normal BP?

Answer 33

One of the most common causes of renal potassium loss is diuretic use. Urinary potassium wasting and hypokalemia can occur with both proximal and distal renal tubular acidosis. Bartter’s syndrome is a rare disorder characterized by hypokalemia, hypochloremia, metabolic alkalosis, and hyperaldosteronism .

Question 34

What effect can proximal and distal renal tubular acidosis have on potassium handling?

Answer 34

causes urinary potassium wasting and hypokalemia

Question 35

What are common causes of renal hypokalemia associated with HTN?

Answer 35

Hypertension Causes of renal potassium loss with hypertension and low renin levels include states of primary aldosterone overproduction: aldosterone-producing adenoma, idiopathic hyperaldosteronism, and dexamethasone-suppressible hyperaldosteronism.

Question 36

What is pseudohyperaldosteronism? what effect does it have on potassium?

Answer 36

Two rare disorders (one caused by licorice ingestion, the other a rare genetic defect in Na+ transport referred to as Liddle’s syndrome) display the features of aldosterone excess, (hypokalemic metabolic alkalosis, and low renin hypertension) but aldosterone levels are vanishingly low.