Physio 12

Question 1

hyperkalemia

Answer 1

plasma K concentration above 5 mM. decreases outwardly directed K gradient, depolarizing the resting membrane potential. muscle hyperexcitability leading to ventricular arrhythmias and fibrillations. leads to metabolic acidosis

Question 2

hypokalemia

Answer 2

plasma K concentration below 3.5 mM. increases outwardly directed K gradient, hyperpolarizing the membrane potential. Leads to hypoexcitability of the muscles, cardiac pace maker disturbances, and arrhythmias. can lead to metabolic alkalosis

Question 3

external K+ balance

Answer 3

gastro-intestinal K+ uptake into the body balanced by renal and fecal removal of K from the body. amount of K excreted every day must equal the amount consumed

Question 4

internal K+ balance

Answer 4

distribution of K+ between intracellular and extracellular fluids, due mostly to the Na/K ATPase pump. Most K+ is in muscle.

Question 5

what promotes uptake of K+ into the cells?

Answer 5

insulin, epinephrine, and aldosterone. these hormones induce synth of Na/K ATPase

Question 6

what happens during acidemia?

Answer 6

inhibition of Na/K ATPase and Na/K/2Cl cotransporter, causing loss of K+ from cells resulting in hyperkalemia

Question 7

what happens during alkalemia?

Answer 7

stimulation of the Na/K ATPase causing uptake of K+ into cells, resulting in hypokalemia

Question 8

renal handling of K+ equation

Answer 8

K excreted = (K filtered - K reabsorbed) + K secreted

Question 9

where is K+ reabsorbed

Answer 9

proximal tubule

Question 10

where is K+ secreted

Answer 10

distal nephron. some reabsorption happens here as well

Question 11

how does K+ reabsorption in the proximal tubule happen?

Answer 11

paracellular. occurs by solvent drag and by passive electrodiffusion

Question 12

how does K+ reabsorption happen in the thick ascending limb of the loop of Henle?

Answer 12

transcellular and paracellular. Transcellular uses Na-K-2Cl cotransporter and Na/K ATPase.

Paracellular is done using gradients

Question 13

how is K+ reabsorbed in the distal nephron?

Answer 13

transcellular. Done by alpha intercalated cells. Uses K/H ATPase, transports K in and H out. Deficit of intracellular H increases HCO3 inside cell, which is put into the interstitial space using a Cl/HCO3 exchanger. can lead to metabolic alkalosis if K+ reabsorption is maximal

Question 14

how is secretion of K+ performed?

Answer 14

transcellular. done by Principle cells in the distal nephron. Na/K ATPase on basolateral membrane gets K into cell, then it diffuses out passively into lumen

Question 15

tubular flow dependence of distal tubule K+ secretion

Answer 15

faster flow = more secretion. the high flow sweeps away the K+ quickly, keeping the concentration gradient high.

slower flow = less secretion. slower flow means the concentration gradient is lower, allowing for slower secretion

Question 16

regulation of K+ excretion at high dietary K+

Answer 16

increased secretion of K+ in the cortical distal nephron. DEcreased reabsorption of K+ in the cortical distal nephron

Question 17

aldosterone effects

Answer 17

increases K+ secretion. induces increased capacity for Na+ reabsorption and K+ secretion in the distal nephron. Induces synth of Na/K ATPase, Na and K channels, and mitochondrial enzymes. increased Na conductance depolarizes membrane increasing driving force for K to go out of the cell

Question 18

regulation of K+ excretion at low dietary K+

Answer 18

decreased secretion of K+ in the cortical distal nephron. increased reabsorption of K+ in the cortical distal nephron

Question 19

how does alkalosis affect distal nephron K+ secretion?

Answer 19

increases it. decreased plasma [H+] increases intracellular K+. increased intracellular K+ increases driving force and rate of K+ transport out of the cell, leading to hypokalemia (hypokalemic metabolic alkalosis)

Question 20

how does acidosis affect distal nephron K+ secretion

Answer 20

increased plasma [H+] induces decreased intracellular K+. thi decreases the driving force so less K+ goes out of the cell, leading to hyperkalemia (hyperkalemic metabolic acidosis)

Question 21

why is potassium so important?

Answer 21

K+ concentration gradient across the cell membrane is largely responsible for the potential or voltage difference across the cell membrane.