Regulation of K+ Balance Flashcards
What effect does epinephrine have on Serum [K+]?
Depends on whether it is activating alpha or beta adrenergic receptors
Alpha receptors - INCREASE serum [K+] by impairing cell uptake of K+ via Na-K-ATPase
Beta Receptors - DECREASE serum [K+] by enhancing cell uptake of K+ via Na-K-ATPase
What effect does insulin have on serum [K+]?
Insulin DECREASES serum [K+] by enhancing cell uptake of K+ via Na-K-ATPase
What effect does Aldosterone have on serum [K+]?
Aldosterone DECREASES serum [K+] by promoting K+ secretion into the Nephron tubule lumen
Also promotes K+ secretion into intestinal lumen and saliva
What effect does acidosis have on serum [K+]?
Acidosis means high serum [H+]
Principal cells have a K+/H+ Exchanger that moves H+ into the cell and moves K+ out of the cell, thus increasing Serum [K+] and reducing the driving force for K+ secretion
Additionally, acidosis inhibits Na-K-ATPase, which promotes an increase in ECF [K+]
What effect does alkalosis have on serum [K+]?
Alkalosis means serum [H+] is low
This causes movement of H+ into the serum while promoting K+ movement into the cells, increasing the driving force for K+ secretion.
“k is lo”
What effect does cell damage have on serum [K+]
Cell damage results in the emptying of cell contents into ECF, including the larger concentration of K+
Thus serum K+ increases
What effect does hyperosmolality have on cellular [K+}?
Hypersomolality (high salt concentration in ECF) causes movement of water from cell into interstitium (cell shrinks)
As cell shrinks, K+ concentration increases, and cell efflux of K+ increases
What effect does strenuous exercise have on K+ levels?
Strenuous exercise increases activation of alpha-adrenergic receptors (epinephrine). Therefore, inhibits Na-K-ATPase activity, resulting in cellular K+ efflux
How does K+ reabsorption occur in the Proximal Tubule?
Initially, in the early PCT, lots of Na+ is reabsorbed
This leaves a negative potential in the lumen that drives Cl- to be reabsorbed paracellularly
As Cl- leaves the lumen, the potential in the lumen becomes positive, resulting in Na+ and K+ being reabsorbed paracellularly
Explain how K+ recycling works and why it is important
K+ is secreted into the Cortical Collecting Duct
K+ is reabsorbed in the Medullary collecting duct where it it increases K+ concentration in the medullary interstitium.
K+ is secreted into the Late Proximal tubule and the Descending Thin Limb of the Loop of Henle
The Increase in medullary interstitium [K+] causes inactivation of the NKCC2 channels in the ascending Limb of the Loop of Henle.
Inactivation of NKCC2 causes accumulation of Na+ in the distal tubule
Accumulation of Na+ in Distal Tubule promotes Na+ reabsorption and K+ secretion
This is important for K+ excretion after dietary K+ loading
What do Principal Cells Reabsorb?
H2O and Na+
What do Principal Cells Secrete?
K+
What do Beta-Intercalated Cells Reabsorb?
H+ and Cl-
What do Beta Intercalated Cells Secrete?
K+ and HCO3-
What do Alpha Intercalated Cells Reabsorb?
K+ and HCO3-
What do Alpha Intercalated Cells Secrete?
H+ and Cl-
What channel(s) are found on the apical membrane of Principal Cells and what do they do?
ENaC (Epithelial Na+ Channel; allows Na+ movement into cell)
BK (Big K+ channel; allows K+ movement out into tubule lumen)
ROMK (Renal Outer Medullary K+ Channel; allows K+ movement out into the tubule lumen)
Aquaporin
What channel(s) are found on the Basolateral Membrane of the Principal Cells and what do they do?
Na-K-ATPase (move 3 Na+ out; move 2 K+ in; uses ATP)
What channel(s) are found on the apical membrane of of Beta-Interalated Cells and what do they do?
HCO3-/Cl Exchanger (Moves HCO3- out into tubule lumen; moves Cl- into the cell)
K+ Channel (allows K+ to move out into the tubule lumen)
What channel(s) are found on the basolateral membrane of the Beta-Intercalated cell and what do they do?
Na-K-ATPase (move 3 Na+ out; move 2 K+ in; use ATP)
H-K-ATPase (move H+ out into interstitium; move K+ into cell; use ATP)
H-ATPase (move H+ into the interstitium; use ATP)
Cl- Channel (move Cl- out into the intersititum
What channel(s) are found on the apical membrane of Alpha-Intercalated cells and what do they do?
H-ATPase (move H+ out into the tubule lumen; use ATP)
H-K-ATPase (move H+ out into the tubule lumen; move K+ into the cell)
Cl- Channel (move chlorine into the tubule lumen)
What channel(s) are found on the basolateral membrane of Alpha-Intercalated cells and what do they do?
HCO3-/Cl Exchanger (Move HCO3- out into the interstitium; move Cl- into the cell)
K+ Channel (Move K+ out into the interstitium)
What are the most important factors that stimulate K+ secretion?
Aldosterone
Increased ECF [K+]
Increased Tubular flow rate
What are the most important factors that stimulate K+ reabsorption?
K+ deficiency; Low dietary K+; hypokalemia
K+ loss through severe diarrhea
What five events would occur in response to a Buildup of extracellular [K+]?
- Activation of Na-K-ATPase on basolateral membrane
- Reduced back leakage of K+ from the ICF to renal interstiitum
- Aldosterone Secretion
- Increased Distal Tubular flow rate
- Synthesis and insertion of K+ channels on apical membrane
How does flow rate affect K+ secretion?
Flow rate inreases K+ secretion
What causes flow rate to increase?
High K+ or High Na+ intake
Explain the counterbalancing that occurs with K+ excretion after High Na+ intake
High sodium intake causes a decrease in aldosterone secretion, which inhibits K+ secretion
At the same time, Na+ intake causes an increase in GFR and Distal Tubule Flow rate, which increases K+ secretion.
What is Acute Alkalosis and what is its effect on K+?
Acute process that decreases H+ion concentration in the ECF
Promotes Na-K-ATPase activity Increases Intracellular [K+] Increases passive diffusion of K+ into the tubule lumen Increases K+ channels Increases K+ secretion End result: Hypokalemia (k is lo)
What is Acute Acidosis and what is its effect on K+?
Acute process that increases H+ ion concentration in the ECF
Inhibits Na-K-ATPase activity Decreases intracellular [K+] Decreases passive diffusion of K+ into the tubule lumen Decreases K+ channels Decreases K+ secretion End result: Hyperkalemia
How is acute acidosis different from chronic acidosis?
Acute Acidosis inhibits K+ secretion whereas Chronic Acidosis ultimately promotes K+ secretion
The reason this happens is because if acidosis initially blocks secretion of K+, this means that K+ accumulates causing Hyperkalemia.
Hyperkalemia triggers release of Aldosterone, which promotes K+ secretion.
What opposing factors in acidosis stabilize K+ seretion?
Acidosis blocks Na-K-ATPase activity, reducing intracellular [K+] (which inhibits Distal Secretion of K+)
Acidosis blocks Proximal reabsorption, which increases distal tubular flow (which promotes K+ secretion)
What opposing factors in volume expansion stabilize K+ secretion?
Volume expansion means Blood Pressure is increased, which decreases RAAS activation, and therefore decreased Aldosterone release (Decreases K+ secretion)
Volume expansion causes a decrease in proximal reabsorption which increases distal tubular flow (which promotes K+ secretion)
What opposing factors in High water intake (water diuresis) stabilize K+ secretion?
Water diuresis causes a decrease in ADH release from posterior pituitary gland. Decreased ADH results in a decrease in Blood Pressure, which will inhibit RAAS and Aldosterone activation (which decreases K+ secretion).
Water diuresis causes a decrease in ADH release, which reduces reabsorption of water (which increases distal flow; which promotes K+ secretion)
What opposite factors in Volume contraction stabilize K+ secretion?
Volume contraction stimulate Renin secretion, which activates Angiotensin II, which stimulates Aldosterone secretion (which promotes K+ secretion)
Volume Contraction means GFR will be decreased, which results in a decrease in Distal Tubular Flow (which decreases K+ secretion)
What effect do glucocorticoids have on K+ secretion?
Increase K+ secretion (via binding of mineralcorticoid receptor, increasing GFR, and fluid flow rate
How do the following factors affect K+ secretion: ADH Luminal Flow Rate Acidosis Akalosis Glucocorticoids Anion Delivery
ADH - Increases K+ secretion Luminal Flow Rate - Increases K+ secretion Acidosis - Decreases K+ secretion Alkalosis - Increases K+ secretion Glucocorticoids - Increases K+ secretion Anion Delivery - Increases K+ secretion
Which segment of the nephron is responsible for the greatest K+ reabsorption?
The proximal tubule
Control K+ excretion is highly regulated by K+ secretion in the late distal tubule and collecting duct, but very little K+ reabsorption occurs there.
Some K+ reabsorption occurs in the loop of Henle
