Exam 3 Lecture - Regulation of Potassium Flashcards
What is the main intracellular cation?
potassium
What is K important for inside of cells?
an important osmole, maintaining cell volume
Why is K important extracellularly?
to avoid the affects of hypokalemia and hyperkalemia
What is hypokalemia?
low levels of extracellular potassium
What is hyperkalemia?
high levels or extracellular potassium
Does the kidney regulate intracellular or extracellular potassium?
extracellular potassium
How does hypokalemia affect the generation of action potentials?
it makes generating them harder because it makes the resting membrane potential lower
How does hyperkalemia affect the generation of action potentials?
it makes generating action potentials easier, but Na levels inside of the cell are unable to reset, so the cell becomes less excitable
What are symptoms associated with hypokalemia?
muscle weakness, respiratory problems, cardiac arrhythmia, renal dysfuntion
What are symptoms associated with hyperkalemia?
muscle weakness and cardiac dysfunction
Is hypokalemia or hyperkalemia worse?
hyperkalemia
If enough K is not excreted, what will happen to the animal?
it will become hyperkalemic
If too much K is excreted, what will happen to the animal?
it will become hypokalemic
Where does the most K excretion occur?
in the kidney
What is the kidney’s short term response to an altered K concentration outside of the cell?
translocation: sends K out to the ECF it is too low, sends K into the cell if ECF is too high
What is translocation affected by?
insulin, catecholamines, acidosis/alkalosis
What is insulin given to correct?
hyperkalemia
How do catecholamines work?
they can move K in and out depending on whether they activate alpha or beta receptors
What is bicarb administered to correct?
hyperkalemia
How does insulin correct hyperkalemia?
it promotes movement of K into cells by stimulating NaKATPase
What receptors are associated with catecholamines?
alpha and beta
Do alpha receptors promote the movement of K into the cell or out of it?
out of it
Do beta receptors promote the movement of K into the cell or out of it?
into it by stimulating NaKATPase
What does acidosis promote in regards to potassium movement?
hyperkalemia - High H+ promotes movement of K out of the cells in order to maintain electroneutrality - but into the ECF
What does alkalosis promote in regards to potassium movement?
hypokalemia - Low H+ moves K into cells - but into the ECF
Under normal conditions what is the primary goal of the kidney in regards to K?
to retain it
What function must the kideny have in order to maintain homeostasis?
to secrete K
True or False: The proximal tubule can only secrete K.
False: the proximal tubule can only reabsorb K, it cannot secrete it
How is K reabsorbed in the proximal tubule?
paracellularly and transcellularly
Where can K be reabsorbed paracellularly in the proximal tubule?
only in the late proximal tubule
How is K reabsorbed in the proximal tubule transcellularly?
by the K Cl symporter in the basolateral membrane ‘ there are probably K channels in the luminal membrane too’
True or False: The distal tubule can only absorb K, and cannot secrete it
True
How is K reabsorbed in the distal tubule?
paracellularly and transcellularly
How is K reabsorbed transcellularly in the distal tubule?
via the NKCC1 transporter at the luminal membrane and K channels in the basolateral membrane
Is K reabsorbed or secreted in the collecting ducts?
both
Where is K secreted in the collecting ducts?
in the principle cells
How is K secreted in the collecting ducts?
- NaKATPase keeps intracellular K concentration high
- Na enters viathe amiloride-sensitive channels making the lumen negative
- K wants to move out of the cell and does so on the luminal side because it is more permeable to K (some does leave through the basolateral side
What part of the collecting ducts reabsorb K?
the alpha intercalated cells
How is K reabsorbed in the alpha intercalated cells?
- H leaves the cell via HATPase,
- H K ATPase brings K in at the luminal membrane
- K then leaves at the basolateral membrane into the extracellular fluid
What determines renal K excretion?
plasma K concentration, tubular flow rate, lumen electronegativity
What does increased plasma concentration of K lead to?
the translocation into the ICF increasing the K gradient in renal cells and pushing K into the lumen
also stimulates aldosterone
How does aldosterone affect K excretion?
it stimulates Na reabsorption which means K is being pushed out of the cells (Na channels and K channels are increased)
What does hyperaldosteronism lead to?
hypokalemia
What does hypoaldosteronism lead to?
hyperkalemia
How does decreased tubular flow rate affect K secretion?
it decreases it
How does increased tubular flow rate affect K secretion?
it increases it
How does increased lumen electronegativity affect K secretion?
it increases it
How does decreased lumen electronegativity affect K secretion?
it decreases it
How does Na intake affect renal handling of K?
increased dietary intake of Na leads to increase of tubular concentration therefore more Na reabsorption and more K secretion
How do loop, thiazide, and osmotic diuretics affect renal handling of K?
increase the flow rate and Na concentration in CD which increases K secretion and can cause hypokalemia
How do amiloride-like diuretics affect renal handling of K?
inhibit Na uptake in CD so inhibit K secretion; known as K sparing diuretics
