Lecture 21

Question 1

What is the normal ICF conc of K+?

Answer 1

150mM

Question 2

What is the normal ECF conc of K+?

Answer 2

4mM

Question 3

What is the conc of K+ in the ECF to have hyperkalemia?

Answer 3

more than 5mM

Question 4

What is the conc of K+ in the ECF to have hypokalemia?

Answer 4

less than 3.5mM

Question 5

Why is high K+ in the ICF important?
• maintain __________ volume
• regulation of _______
• controlling _______ ______ function
• controlling __________ and _________ synthesis
• controlling cell ________, cell _________ and cell ___________

Answer 5

• maintain cell volume
• regulation of pH
• controlling cell enzyme function
• controlling DNA and protein synthesis
• controlling cell growth, cell cycling and cell proliferation

Question 6

Why is low K+ in the ECF important?
- maintain the steep ________ gradient across the membrane to maintain the _________ of cells
- Low K+ prevents problems with _______ and ________
– ________ potential
– muscle _______
– cardiac _________

Answer 6

• 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 7

A low ECF K+ concentration means what for the depolarisation?

Answer 7

A greater depolarisation is needed to bring the membrane potential to threshold

Question 8

A high K+ concentration means what for the depolarisation?

Answer 8

There is a greater rate of firing which results in slurred speech and ataxia

Question 9

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 involved in the nerve action potential.

Answer 9

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

Question 10

If the ECF K+ conc was as low as 2.5mM, what would the ECG look like?

Answer 10

It would have a low T wave, high U wave, low ST segment

Question 11

If the ECF K+ conc was as high as 10mM, what would the ECG look like?

Answer 11

There would be a lot of ventricular fibrillation and death

Question 12

Daily K+ intake = what?

What does this mean for the net?

Answer 12

daily intake = daily excreted so the net loss is zero

Question 13

If the K+ intake is greater than K+ excreted, is there a positive or negative K+ balance?

Answer 13

positive

Question 14

If the K+ intake is less than K+ excreted, is there a positive of negative K+ balance?

Answer 14

negative

Question 15

What are three hormones that get K+ into cells? What is the purpose of this?

Answer 15

• epinephrine
• insulin
• aldosterone
  this occurs rapidly to prevent hyperkalemia

Question 16

What is the purpose of extrarenal changes?

Answer 16

this is to increase K+ uptake into cells

Question 17

What are the extrarenal changes that occur? Is this a fast or slow process?

Answer 17

This is the release of hormones such as epinephrine, insulin and aldosterone which occurs rapidly

Question 18

What is the intrarenal changes that occur? Is this a fast or slow process?

Answer 18

This is the regulation of reabsorption and secretion of K+ along the nephron which occurs over several hours.

Question 19

What is the trigger for the release of epinephrine, insulin and aldosterone?

Answer 19

an acute increase in plasma K+ concentration

Question 20

Describe the process of epinephrine being released and what its effect is

Answer 20

This is released from the chromaffin cells from the adrenal medulla in response to an increase in the plasma K+ concentration. This binds to a receptor in the muscle cell membrane which activated cAMP which activates Na+/K+ ATPase which increases the amount of K+ getting into the cell.

Question 21

Describe the process of insulin being released and what its effect is

Answer 21

This is released from the β cells of the pancreas in response to an increase in the plasma K+ concentration. It binds to the insulin receptor on the muscle cells and increases the activity of Na+/K+ ATPase which increases the amount of K+ getting into the cell.

Question 22

Describe the process of aldosterone being released and what its effect is

Answer 22

This is released from the zona glomerulosa cells of the adrenal cortex in response to an increase in K+ plasma concentration. This binds to its intracellular receptor which increases the activity of Na+/K+ ATPase which increases the amount of K+ getting into the cell.

Question 23

What is the daily filtered load of K+ if the [K+]plasma is 4 mmol/L?

Answer 23

180 L/day x 4 mmol/L = 720 mmoles/day (filtered)

Question 24

The K+ filtered load depends on the what?

Answer 24

the K+ diet

Question 25

In which parts of the nephron is K+ reabsorbed and in which parts is it secreted?

Answer 25

it is reabsorbed in the proximal tubule, thick ascending loop, distal tubule and collecting duct

it is secreted by the distal tubule and collecting duct

Question 26

An individual with a low K+ diet will have how much of it excreted?

Answer 26

1% (and reabsorb 99%)

Question 27

In an individual with a low K+ diet, how much K+ is reabsorbed in each part of the nephron? Is there any part which secretes K+?

Answer 27

no part secreted because they have a low diet

PT reabsorbs 67%
ThickAL reabsorbs 20%
DT reabsorbs 3%
CD reabsorbs 9%
1% is excreted

Question 28

In an individual with a high or normal K+ diet, how much K+ is reabsorbed in each part of the nephron? Is there any part which secretes K+?

Answer 28

PT reabsorbs 67%
ThickAL reabsorbs 20%
DT secretes 10-50%
CD secretes 5-30%
15-80% is excreted

Question 29

How is K+ reabsorbed in the PT?

Answer 29

Leaky absorptive epithelium:
It depends on the local environment voltage. As things are transported across the apical membrane, a charge separation occurs between the early and late part of the lumen which drives K+ through the tight junctions in the paracellular pathway.

Question 30

How is K+ reabsorbed in the thick ascending loop of Henle?

Answer 30

The NKCC2 in the apical membrane brings K+ into the cell. There is also a change separation so K+ can move through paracellularly

Question 31

What are the two different cell types in the collecting duct? What percentage of cells do these make up and what is their purpose?

Answer 31

• intercalated cells (30% of the cells) for K+ reabsorption

- principle cells (70% of the cells) for K+ secreted and Na+ reabsorption

Question 32

Describe what happens in an intercalated cell in the collecting duct

Answer 32

This is for K+ reabsorption:
tight absorptive epithelium cells
This is done by the K+/H+ ATPase in the apical membrane. This can also maintain pH balance due to the movement of H+ across the membrane. H+ also leaves through V-ATPase.

Question 33

Describe what happens in the principle cells in the collecting duct

Answer 33

This is for K+ secretion:
tight absorptive epithelium
Under the influence of aldosterone to increase K+ secretion for a normal and high K+ diet.
Aldosterone increases ENaC activity so Na+ can come in which makes the cell more positive and this increase the K+ loss through ROMK in the apical membrane or KCC1

Question 34

What is the effect of aldosterone on K+ secretion by the LDT and CD?

Answer 34

increase activation and amount of the epithelial sodium channel (ENaC) so more Na+ enters the cell making it more positive

increases 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) through ROMK

Question 35

If there is a low K+ diet then there is a high or low flow rate and K+ secretion is high of low?

Answer 35

low flow rate

secretion in low

Question 36

If there is a normal or high K+ diet then K+ secretion high or low

Answer 36

high