Lect 14: Regulating Plasma K+ Flashcards
Extracellular K is tightly regulated in the plasma in a normal range of
3.5 - 5 mM but it is the outwardly directed K gradient. Na is low inside the cell and K is low outside of the cell
Why is K+ important?
that K+ gradient across the cell membrane is the major determinant of the potential or voltage difference across the cell membrane in both electrically excitable and unexcitable cells….certain tissues need these currents for the excitability (such a s cardiac tissue, neurons etc.
What organ maintains K+ balance?
the balance is maintained by the renal handing of K by the kidneys which increase or decrease K excretion to match increases and decreases in K+ consumption
the positive charge carried by the movement of the cation, K+ across the cell membrane may arise from passive, protein-mediated transport, or simple diffusion
The positive charge carried out of the cell by K current through membrane channels is the dominant ionic current determining the inside-negative cell membrane potential difference….for a certain K+ conc, the potential difference across the cell membrane (-60mV) is very close to the K+ equilibrium potential
Hyperkalemia - increased k+ conc in plasma (>5)
decreases the magnitude of the outwardly directed K+ conc gradient, decreasing the contribution of the gradient to the cell membrane potential–> less negative potential difference in both excitable and non-excitable cells
What happens to cells/organs as a result of hyperkalemia
when hyperkalemia occurs in excitable cells, electrical signaling is or impulse propagation is disturbed and may cause hyperexcitable muscle contraction, in heart–>uncontrolled muscle spasm–>cardiac arrest
Which type of acidosis can be cause by hyperkalemia?
metabolic acidosis because of the effective exchange of intracellular H+ for extracellular K+ across cell membranes, which adds acid (H+) to the plasma - more K+ want to go into the cell, so more H+ will come out.
Hypokalemia - decrease in plasma K+ so more K+ will want to flow out of the cell (outward gradient increased). What happens to the inside negative potential? difference?
it goes up because more K+ is leaving the cell
How would hypokalemia affect excitable organs?
it would weaken muscle contraction (muscle hypoexcitability) –> if this happens in the lungs, they won’t get adequately perfused and you would go into respiratory failure
Which kind of metabolic syndrome could hypokalemia?
METABOLIC ALKALOSIS - because as K+ is rushing out of the cell, H+ are rushing back into the cell and less is around int he blood so you drop H+ conc and you get alkalosis
External K+ balance
since K consumption is variable, the kidney must increase or decrease excrete of it accordingly…in order tot keep the plasma ECF constant
kidneys and feces…colon excretes 10% of ingested K+
Internal K+ balance
is regulated by the Na/K ATPase…keeps plasma K+ in balance….needs to be maintained because 1% shift in intracellular K+ would increase plasma [K+] by 50%
Increased uptake of K+ into cells is the first line of defense against hyperkalemia
plasma levels of K rises because of the food we eat and it could be from their release of diseased or injured cells. To compensate for this, the cell sequesters it inside. Upregulating Na/K ATPase synthesis.
–>insulin, epinephrine and aldosterone promote an increased cellular uptake of K+ and a shift from EC fluid into cells.
Why do diabetics have to watch their K intake
RBC do not have a nuclsus and therefore cannot upregulate synthesis of Na/K ATPase to protect it from hyperkalemia. So the dysregulation of insulin release and circulating levels of insulin in poorly conteolled diabetes mellitus may compromise the tolerance of diabetic patients to a K+ load and predispose them to hyperkalemia
Acidemia inhibits the Na/K ATPase and the Na/K/2Cl co-transporter causing loss of K+ from cells, resulting in hyperkalemia
acidosis - lots of H+ in blood will want to push H+ into cells and cause K+ to rush out of cells causing hyperkalemia.
alkalosis - not enough H+ in the blood so H+ rush out of the cell and K+ rushes in….causing hypokalemia