Regulation Of Potassium Flashcards
Distribution and balance of potassium
1) Intake 70 mmol /day via GI system
- 60 mmol is actually absorbed
2) ECF possesses 65 mmol at any given time, shuttling potassium to and from liver/muscles/bone/RBCs
- Muscles use the most/have the most potassium at any time!
3) kidneys reabsorb 800 mmol/day, filter 810 mmol/day and secrete 50 mmol/day
4) urine excretes roughly 60 mmol per day
Distribution and balance of sodium
1) Intake 120 mmol /day via GI system
- 110 mmol is actually absorbed
2) ECF possesses 2450 mmol at any given time, shuttling sodium to the ICF in all cells of the body.
- The ECF possess the most sodium at any time (other than kidneys when they are filtering)
3) kidneys reabsorb 25,400 mmol/day, filter 25,500 mmol/day
4) urine excretes roughly 100 mmol per day
How does the resting membrane potential change with potassium concentration?
High levels = lowers the threshold for action potential (makes the membrane potential more (+)
- easier to fire action potentials
- Nernst equation potential decreases
Low levels = increases the threshold for action potentials (makes the membrane potential more (-)
- harder to fire action potentials
- Nernst equation potential decreases
How do ECG’s change with respect to hypo and hyperkalemia?
Hypokalemia
- u waves become present
- T waves decrease in amplitude
Hyperkalemia
- T waves increase in amplitude (peak)
- PR interval prolongs
- V. Fib if bad enough
Normal balance of ECF and ICF potassium
ECF
- 4.2 mEq/L x 14L = 59mEq
ICF
- 140 mEq/L x 28L = 3920mEq
What happens in the body when you eat potassium in order to maintain normal potassium gradients?
the primary goal is to maintain ECF concentrations of potassium (dont change much)
1) the body net translocates K+ INTO cells (ICF) (typically kidneys)
- this is done via insulin and activation of K+/Na+-ATPase pumps in the CD
2) cumulative renal excretion of K+ occurs in order to get rid of excess potassium
Specific physiology steps to move potassium intracellularly
1) acute plasma K+ increase in blood is noted by the B-cells in the pancreas and both chromaffin (medulla) and glomerlousa (cortex) cells of the adrenal gland
2) these cells all activate to produce insulin, epinephrine and aldosterone respectively
3) epinephrine increases cAMP in muscle cells, insulin increases glucose reabsorption in muscle cells via activation of GLUT 4 and aldosterone activates mineralcorticoid receptors on muscle cells
4) everything in #3 works synergistically to increase sodium and potassium pump actions in muscle cells which casues them to uptake excess potassium
Factors that promote movement of potassium from ECF -> ICF
Hypokalemia
Insulin
Aldosterone
B2-adrenergic agonists via epinephrine/albuterol/etc
- these increase the activity of the Na+/K+/ATPase pumps which shifts K+ into cells
A-adrenergic antagonists
- these increase the activity of the Na+/K+/ATPase pumps which shifts K+ into cells
Alkalosis conditions
- body wants to throw H+ ions into the blood to correct, which causes K+ to move into cells
Factors that promote movement of potasssium from ICF -> ECF
Hyperkalemia
Insulin deficiency (diabetes mellitus) - Na/K+/ATPase pump doesnt work efficiently
Aldosterone deficiency (addisons disease)
B-adrenergic antagonists
- Na/K+/ATPase pump doesnt work efficiently
A-adrenergic agonists
- Na/K+/ATPase pump doesnt work efficiently
Acidosis conditions
- body wants to get H+ ions out of blood so it absorbs H+ ions intracellularly while excreting potassium
Cell lysis
Strenuous exercise
- depletion of ATP causes K+ channels to open and icnreases K+ potential to move out of the cell
Increased ECF osmolarity
causes hyperkalemia and acidemia
Why does potassium move out of the cell in conditions of high ECF total osmolarity?
Higher total ECF osmolarity pulls water out of the cells
This causes the potassium specific gradient to favor potassium movement out of the cell
(Too high concentration of K+ inside of cells = moves K+ ICF -> ECF)
the exact opposite happens in low osmolarity conditons of ECF
What is the relationship between kalemia levels and H+ ions (alkalosis/acidosis)
Hypokalemia always leads to alkalemia (and vise versa)
- potassium needs to move out of cells to balance hypokalemia which requires H+ ions to move into the cell in order for this to occur
Hyperkalemia always leads to acidemia (and vise versa)
- potassium needs to move into cells to balance hyperkalemia which requires H+ ions to move out of the cell in order for this to occur
the vise versa of each are seen as well, so these are direct relationships
Where does most potassium reabsorption occur along the nephron?
67% is seen in the PCT
20% is seen in thick ascending limb
Where does most sodium reabsorption occur along the nephron?
67% is in the PCT
25% is in the thick ascending limb
**tends to follow potassium reabsorption
How does K+ get reabsobed in the PCT and the TAL?
Two ways in the PCT
1) solvent drag (gets “dragged” with water through PCT)
2) paracellular diffusion
Two ways in the TAL
1) Na+/K+/Cl- cotransporters (primary)
2) paracellular diffusion
How does the principal and intercalated cells move potassium?
Principal cell
- moves potassium OUT of the cell via Na+/K+ co-exchanger (moves Na+ in and K+ out) And via K+/Cl- cotransporter out of the cell
- moves potassium IN the cell via the Na+/K+ ATPase pump
(A)-intercalated cell
- moves potassium IN the cell via H+/K+ cotransporter and via Na/K+ ATPase pumps
