11_HST110 Potassium Regulation 2017 Flashcards
What percentage of K+ is intracellular? How is this maintained?
98%
Na+-K+-ATPase
What are the two major physiologic function of K+?
Cell metabolism (e.g. protein, glycogen synthesis)
Resting membrane potential across cell membranes
Ratio of the ICF and ECF [K+] is the major determinant of the (X)
X = resting membrane potential
Hypo- and hyperkalemia can alter conduction in skeletal and cardiac muscle Potentially fatal (X) and (Y)
X = muscle paralysis Y = cardiac arrhythmias
Low K+ (X) the resting membrane potential. High K+ does the opposite
(X) Decreases
This makes achieving the normal threshhold voltage more difficult
How is normal plasma [K+] maintained? 2 mechanisms?
Distribution of K+ between ICF and ECF
Renal excretion of K+
(X) is the key mediator for distribution of K+ between ICF/ECF
X = Na+-K+-ATPase
What are 3 physiological factors influence the distribution of K+ between ICF/ECF
Plasma [K+]
Catecholamines
Insulin
Catecholamines (Epinephrine): Can affect K+ distribution:
α-receptors = block cellular entry of (X)
β2-receptors = promote cellular entry of (X)
Uptake of K+ is mediated by activation of (Y)
Most occurs in skeletal muscle and liver
X = K+ Y = Na+-K+-ATPase
Insulin
Promotes entry of K+ into skeletal muscle and liver
Increases (X) activity
Plays a physiologic role in regulating plasma [K+] following ingestion of food
Can be used to treat (Y)
X = Na+-K+-ATPase Y = hyperkalemia
What other factors affect plasma[K+]?
Exercise
Acid-base balance
Plasma osmolality
Cell lysis
These factors SHIFT K+ between the ICF and ECF compartments
Exercise: Plasma [K+] rises with muscular exercise
Local increase in plasma [K+] has (X) effect and increases (Y)
X = vasodilatory Y = blood flow
Acid-Base Balance and [K+]
Metabolic acidosis increases plasma [K+]
Inhibits (X)
Metabolic alkalosis decreases plasma [K+]
Activates (X)
MAINTAIN ELECTRONEUTRALITY
Respiratory acidosis and alkalosis do not cause large changes in plasma [K+]
X = Na+-K+-ATPase
Describe the steps in the interaction between Plasma Osmolality and [K+]
Water shifts out of the cell, causing cell to shrink
- Intracellular [K+] rises, drives K+ out of cells
- Solvent drag
* [K+] increases 0.4-0.8 mEq/L per 10 mOsm/kg
Cell lysis releases cellular components, including K+
Name 3 conditions that can result in cell lysis
Severe trauma
Tumor lysis syndrome
Rhabdomyolysis
Renal K+ Excretion:
Kidneys maintain K+ balance by matching excretion with intake. Excrete (X) of ingested dietary K+
Some K+ is lost in sweat and feces, but amount is relatively constant and unregulated
Renal K+ excretion is regulated and primarily determined by K+ secretion in the (Y) and (Z)
X = 90-95% Y = distal tubule Z = collecting duct
Mechanisms of K+ Transport
(X) generates high intracellular [K+], provides driving force for (Y) K+ secretion
Principal cells secrete K+ via:
- (Z) channel
- (A) channel (flow sensitive)
- (B) symporter (KCC1)
α-intercalated cells:
- (A) channel
- Reabsorb K+ via (C)
X = Na+-K+-ATPase Y = apical Z = ROMK A = BK B = K+-Cl- C = H+-K+-ATPase
What are the 3 determinants of K+ secretion?
Electrochemical gradient across apical membrane
Permeability of apical membrane (ie, number of K+ channels)
Na+-K+-ATPase activity
What 3 factors influence K+ excretion?
Plasma [K+]
Aldosterone
Tubular flow rate
Regulation: Plasma [K+].
Plasma [K+] directly affects K+ secretion by (X) increasing the electrochemical gradient across apical membrane, (X) permeability of apical membrane, and (X) Na+-K+-ATPase activity
X = increasing
Regulation: Aldosterone.
Aldosterone directly affects K+ secretion by (X) increasing the electrochemical gradient across apical membrane, (X) permeability of apical membrane, and (X) Na+-K+-ATPase activity
X = increasing
Regulation: Tubular Flow Rate.
Increased tubular flow rate (X) K+ secretion
* e.g. Diuretics, volume expansion
Decreased tubular flow rate (Y) K+ secretion
*Volume depletion
Flow is sensed by primary cilia in (Z) cells, activates BK channels
X = increases Y = decreases Z = principal
