04c: K regulation Flashcards
T/F: K is the most abundant cation in body.
True
Most, (X)%, of K is located in which body compartment? At which concentration?
X = 98
ICF;
150 mEq/L
Most K is found in which organ/structure?
Muscle
(X)% of K is in the ECF at (Y) concentration. Plasma K concentration is a (good/poor) indicator of total body K.
X = 2
Y = 3.5-5 mEq/L
Poor
T/F: In response to acute K load, kidney excretion plays key role in maintaining plasma K normal.
False - too slow of a process (hours)
In response to acute K load, (X) process plays key role in preventing life-threatening hyperkalemia. This process is controlled by (Y).
X = uptake of ingested K by cells
Y = hormones
After meal, most of K is taken up into cells via (X) (channel/transporter). List factors that activate (X) and star the most important one.
X = NaK pump
- Rise of plasma K
- Epi
- Insulin*
Subject treated with propranolol (beta adrenergic receptor blocker) will have (reduction/elevation) in plasma K after K load.
Elevation
Why is there a shift of K (into/out of) cells in acidosis?
Out of;
Increased H is buffered within cells, so as it moves in, K moves out
List two mechanisms proposed for loss of K from cells in acidosis.
- Release of protein-bound cellular K
2. Inhibition of NaK pump (due to low pH)
During exercise, there’s increased K movement (into/out of) cells. In which scenario can this be life-threatening?
Out;
Patient on beta-adr. receptor blocker
Increase in osmolality of ECF leads to K movement (into/out of) cells. Why? Give an example.
Out of
(i.e. hyperglycemia);
Cell shrinkage increases intracellular K conc and increases chem gradient for K efflux
To remain in K balance, individual must excrete about (X) K daily in urine. This excretion is regulated by which two factors?
X = 90 mEq
- Plasma K
- Aldosterone
T/F: K is freely filtered at glomerulus.
True
K is filtered at glomerulus at a rate of (X) per day. Most of K is reabsorbed at which tubular locations?
X = 600-900 mEq
PT (80%) and TAL (10%)
At PT, K reabsorption is primarily (passive/active) transport that’s secondary to (X).
Passive diffusion;
X = increased tubular K conc due to water reabsorption
T/F: Transcellular pathway is not involved in K reabsorption.
True
T/F: K reabsorption at PT is downhill.
False - although electrical potential favors K movement into cell, chemical gradient driving K out is much greater
Reabsorption of K at TAL involves mainly (X) transporter/channel at luminal membrane and (Y) transporter/channel at basolateral membrane.
X = NaKCl co-transporter Y = KCl transporter and K channels
T/F: PT, TAL, and distal tubules are capable of either reabsorption or secretion of K.
False - only distal tubules have dual capabilities
Changes in excretion rate of K is handled primarily by (PT/TAL/distal) segments.
Distal
List the cell types that influence K transport in distal nephron. Star the more numerous one, also responsible for (X) ion reabsorption.
X = Na
- Principal* (K secretion)
- Intercalated alpha-type (K reabsorption)
K reabsorption occurs mainly in (cortical/medullary) collecting duct/tubules. And secretion?
Reab: cortical;
Secretion: medullary
List the apical/basolateral transporters and channels involved in K secretion.
NaK pump (basolateral) followed by apical K channels secreting K into tubular lumen
T/F: There are K channels on both apical and basolateral membranes in collecting duct/tubules.
True
T/F: K preferentially diffuses across the basolateral membrane.
False - apical (K cahnenels have overall larger conductance on apical membrane)
At the cell level, list the three factors controlling K secretion from tubules.
- NaK pump activity
- Electrochemical gradient
- Apical membrane permeability to K
A K-H (transporter/pump) is present in (X) tubular cells and (cotransports/exchanges) H and K (into/out of) lumen.
Pump (ATPase);
X = alpha-intercalated
Exchanges; H into lumen, K into cell
In (high/low) ADH state, the medullary collecting duct is also able to passively reabsorb K.
High (high reabs of water favors K diffusion into tubular cell)
During K depletion (low K intake), you’d expect (reabsorption/secretion) of K to prevail in distal segments, thus (raising/lowering) K excretion values to about (X)% of filtered load.
Reabsorption;
Lowering;
X = 1%
With normal K intake, K excretion amounts to (X)% of filtration load per day.
X = 10-15
Hyperkalemia favors K (reabsorption/secretion) in distal segments by directly affecting (X) and (Y).
Secretion;
X = NaK pump (increases activity)
Y = K permeability (increased) of luminal membrane
T/F: Aldosterone secretion is stimulated by AII as well as low plasma K conc.
False - HIGH plasma K
The MAIN cellular effect of aldosterone is (X) in (Y) cells/segments of nephron.
X = Increase synthesis of transport proteins (NaK pumps, Na and K channels) Y = distal segments, principal cells
In general, aldosterone effect is to enhance (X) (reabsorption/secretion).
X = Na reabsorption and K secretion
A rise in the flow of tubular fluid would be expected to result from (diuresis/antidiuresis) and (expansion/contraction) of ECF.
Diuresis; expansion
You’d expect (increased/decreased) secretion of K from distal nephron during diuresis.
Increased (high tubular flow)
Severe vomiting/diarrhea results in (increase/decrease) of K secretion from distal tubule.
Decrease (low tubular flow)
High tubular flow rate (increases/decreases) K secretion mechanically through which proposed steps?
Increase;
- Deforms mechano-sensitive cilia of principal cell
- Prompts intracell release of Ca
- Opening of Ca-sensitive K channels
High tubular flow rate generally affects K secretion by which 3 mechanisms?
- Cilia
- Dilution of tubular K (chemical gradient favors secretion)
- Increased Na delivery/reabsorption
Diuretics (increase/decrease) K secretion by (increasing/decreasing) (X).
Increase;
Increasing;
X = tubular flow rate
Presence of ADH favors both K secretion via (X) and reabsorption by (Y).
X = enhancing Na reabsorption by principal cells Y = decreasing tubular flow (by increasing distal reabsorption of water)
Presence of AII favors both K secretion via (X) and reabsorption by (Y).
X = increasing aldosterone levels Y = decreasing tubular flow (by increasing proximal reabsorption of water)
Acidosis will (increase/decrease) K secretion.
Decrease
As transepithelial potential decreases (becomes more positive), K secretion (increases/decreases) in distal segments.
Decreases
