L21

Question 1

in a Low K diet what segments of the nephron will be reabsorbing K

Answer 1

all the segments of the nephron will be reabsorbing K

Question 2

in a normal to high K diet what is the nephron doing

Answer 2

A normal to high the upper parts of the nephron will still do reabsorption and the lower parts will do secretion

Question 3

What is the concentration of K+ in the ICF and the ECF?

Answer 3

• ICF - generally 150 mM

* ECF ~ 4 mM

Question 4

what is hyperkalemia

Answer 4

–ECF > 5 mM = hyperkalemia (High K+ blood)

Question 5

what is hypokalemia

Answer 5

–ECF < 3.5 mM = hypokalemia (Low K+ blood)

Question 6

Why is high K+ in the
ICF important?

there’s 5

Answer 6

• maintain cell volume
• regulation of pH
• controlling cell enzyme function

• controlling DNA and
protein synthesis

• controlling cell growth, cell cycling and cell proliferation

Question 7

Why is low K+ in the
ECF important?

theres 2

Answer 7

• maintain the steep K+
gradient across the
membrane to maintain the potential of cells

• Low K+ prevents problems with excitation and
contraction
– action potential
– muscle contraction
– cardiac rhythmicity

Question 8

what is a low extracellular K effect on the membrane potential

Answer 8

it makes the MP more -ive theefore the cell is less excitable

this would be the opposite if the ECF conc of K was high

Question 9

what is ataxia and what causes it

Answer 9

Ataxia leads to tremors and loss of fine motor control which is what happens when you have high K in extracellular fluid

Question 10

what is the intracellular effect of K on the volume of the cell

Answer 10

net loss of intracellular K = cell shrinks

gain of K = cell swells

Question 11

what is the intracellular effect of K on the pH of the cell

Answer 11

loss of K = cell acidosis

gain of K = alkalosis

Question 12

what is the P wave?

Answer 12

Atrial depolarisation

Question 13

what is the QRS wave?

Answer 13

Ventricular

depolarisation

Question 14

what is the T wave?

Answer 14

Ventricular

repolarisation

Question 15

repolarisation of a cardiac myocyte is dependent on how many K channels

Answer 15

6

Question 16

what is the effect of an ECF conc of K of 2.5mM (hypokalemia) on an ECG

Answer 16

low T wave

high U wave

low ST wave

the ecg looks very different therefore you have altered cardiac function

Question 17

what is the effect of an ECF conc of K of 10mM (hyperkalemia) on an ECG

Answer 17

initially
prolonged PR interval, depressed ST segment and high T wave

auricular standstill/intraventricular black

ventricular fibrillation = death

Question 18

Which of the following statements is TRUE?

A. A typical diet does not contain the proper amount of daily K+.

B. Low ICF K+ is very important for proper enzyme function.

C. K+ is the most abundant cation in the body.

D. K + is not invoved in the nerve action potential.

Answer 18

C is correct

Question 19

how do we get K into our bodies

then what happens

Answer 19

through our diet where it is absorbed through the intestine and absorbed into the blood

from her it goes into the ECF where it is either stored in the tissues via insulin, adrenaline or aldosterone (extra renal)

or excreted into the urine via ADH or aldosterone (and plasma conc)

Question 20

How does your body respond to changes in K+ to maintain K+ homeostasis?

external factors

Answer 20

• Extrarenal - to increase K+ uptake into cells (skeletal muscle, bone, liver, red blood cells)
– epinephrine
– insulin
– aldosterone
Occurs rapidly to prevent hyperkalemia (stops it by “hiding” the K away)

Question 21

How does your body respond to changes in K+ to maintain K+ homeostasis?

internal factors

Answer 21

• Intrarenal - regulation of reabsorption and
secretion of K+ along the nephron
Occurs over several hours

Question 22

what are the extrarenal effects of Epinephrine,Insulin, and

Aldosterone on uptake of K+

Answer 22

acute rise in plasma conc causes Epinephrine,Insulin, and Aldosterone to increase Na/K ATPase activity in some way

The mussle cells have an insulin and adrenaline receptor in the membrane and a aldosterone receptor intracellularly

adrenaline is produced in the chromaffin cells of the adrenal medulla.

When it binds to the receptor it increases intracellular cAMP which activates Na/K ATPase to get more K into the cell

insulin is produced by the b cells in the pancreas and when it binds to its receptors in acts on Na/K ATPase as well

Aldosterone also increases Na/K ATPase activity produced from zonular glomerulosa cells of the adrenal cortex

Question 23

how can we calculate the intrarenal effects of an increase in K

Answer 23

If we know the Glomerular Filtration Rate (GFR), we can calculate the daily filtered load of K+

GFR x [K+]plasma = Daily filtered load

eg
[K+]plasma = 4 mmol/L
180 L/day x 4 mmol/L = 720 mmoles/day
(filtered)

Question 24

how can you figure out the filtered load of an ion (eg K)

Answer 24

GFR x [K+]plasma = Daily filtered load

Question 25

the proximal tubule reabsorbs what % of the K+ filtered load

Answer 25

67%

this is where majority is absorbed

Question 26

in the PT is mainly reabsorbed through what mechanism

Answer 26

the paracellular pathway (because of the leaky absorptive epithelium and local environmental voltage)

Question 27

what causes K in the PT to be mostly reabsorbed through the paracellular pathway

Answer 27

local environmental voltage

Question 28

the thick ascending limb reabsorbs what % of the filtered load of K

Answer 28

20%

Question 29

how is K reabsorbed in the thick ascending limb

Answer 29

through NKCC2 (transcellular)

and paracellular pathways

Question 30

the cortical collecting duct contains 2 kinds of cells

these are the intercalated cells and the principal cells

what is their roles in terms of K

Answer 30

• Intercalated cells (~30% of the cells)
– K+ reabsorption (9% of K filtered load via K/H ATPase)

• Principal cells (~70% of the cells)
– Na+ reabsorption
– K+ secretion

Question 31

what transporters are located in an intercalated cell of the collecting duct

Answer 31

reabsorbs K in a low NA diet

These are tight absorbitive epithelial cells

Contain H ATPase
and K/H exchanger (also ATPase) in apical membrane

Basolateral = Cl bicarbonate exchanger and K/Cl channel and Na/K ATPase

Carbonic anhydrase and K/H exchanger is for pH regulation

Question 32

how do the principal cells and the late distal tubule secrete K

Answer 32

in a high K diet you get K+ secretion (luminal K+ channel ROMK) under the influence of aldosterone and the K+-Cl- cotransporter (electroneutral)

aldosterone increases the activity of these channels via increasing more ENaC into the apical membrane, this brings more Na into the cell increasing the activity of the Na/K ATPase which makes the inside of the cell more positive (more K inside the cell) which increases the driving force of K across the apical membrane

Question 33

If you have a low K+ diet, which statement is TRUE?

A. Your body would increase K+ secretion by the collecting duct cells.

B. Your body would reduce insulin release to reduce uptake of K+ into cells.

C. Your body would increase the release of epinephrine to increase uptake of K+ into cells.

D. Your body would decrease the amount of aldosterone

Answer 33

A. you wouldn’t increase secretion in a low K diet

C. decrease the release

D. aldosterone is not secreted actively in response to K it is so Na is reabsorbed and loss of K is just a byproduct maybe???

Question 34

what regulates K excretion/secretion

Answer 34

• high plasma K+ concentrations
• aldosterone
• flow rate of the filtrate

Question 35

how does an increase in K concentration in the plasma (hyperkalemia) increase K excretion

Answer 35

increase in plasma K is detected by the adrenal gland which causes aldosterone to be secreted which acts on the kidney to increase K secretion

Question 36

what is the effect of Aldosterone on K+ secretion by the

LDT and CD

Answer 36

there is an increase in activation and amount of the epithelial sodium channel (ENaC) which brings more Na into the cell increasing the Na driving force for the Na/K ATPase

an increase in the amount and activity of the Na+-K+-ATPase;
entry of K+ across basolateral membrane

entry of Na+ makes the cell potential more
positive enhancing the driving force for K+ exit
across the apical membrane (K+ secretion)

Question 37

what is the effect of flow of tubular fluid on K secretion

Answer 37

Low K+ diet = low flow rate = K+ secretion is low

• Normal or High K+ diet then K+ secretion is high when compared at a single flow rate

flow is about 5nL/min