Lecture 21 Flashcards
What is the normal ICF conc of K+?
150mM
What is the normal ECF conc of K+?
4mM
What is the conc of K+ in the ECF to have hyperkalemia?
more than 5mM
What is the conc of K+ in the ECF to have hypokalemia?
less than 3.5mM
Why is high K+ in the ICF important?
• maintain __________ volume
• regulation of _______
• controlling _______ ______ function
• controlling __________ and _________ synthesis
• controlling cell ________, cell _________ and cell ___________
- maintain cell volume
- regulation of pH
- controlling cell enzyme function
- controlling DNA and protein synthesis
- controlling cell growth, cell cycling and cell proliferation
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 _________
- 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
A low ECF K+ concentration means what for the depolarisation?
A greater depolarisation is needed to bring the membrane potential to threshold
A high K+ concentration means what for the depolarisation?
There is a greater rate of firing which results in slurred speech and ataxia
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.
C. K+ is the most abundant cation in the body.
If the ECF K+ conc was as low as 2.5mM, what would the ECG look like?
It would have a low T wave, high U wave, low ST segment
If the ECF K+ conc was as high as 10mM, what would the ECG look like?
There would be a lot of ventricular fibrillation and death
Daily K+ intake = what?
What does this mean for the net?
daily intake = daily excreted so the net loss is zero
If the K+ intake is greater than K+ excreted, is there a positive or negative K+ balance?
positive
If the K+ intake is less than K+ excreted, is there a positive of negative K+ balance?
negative
What are three hormones that get K+ into cells? What is the purpose of this?
- epinephrine
- insulin
- aldosterone
this occurs rapidly to prevent hyperkalemia
What is the purpose of extrarenal changes?
this is to increase K+ uptake into cells
What are the extrarenal changes that occur? Is this a fast or slow process?
This is the release of hormones such as epinephrine, insulin and aldosterone which occurs rapidly
What is the intrarenal changes that occur? Is this a fast or slow process?
This is the regulation of reabsorption and secretion of K+ along the nephron which occurs over several hours.
What is the trigger for the release of epinephrine, insulin and aldosterone?
an acute increase in plasma K+ concentration
Describe the process of epinephrine being released and what its effect is
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.
Describe the process of insulin being released and what its effect is
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.
Describe the process of aldosterone being released and what its effect is
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.
What is the daily filtered load of K+ if the [K+]plasma is 4 mmol/L?
180 L/day x 4 mmol/L = 720 mmoles/day (filtered)
The K+ filtered load depends on the what?
the K+ diet
In which parts of the nephron is K+ reabsorbed and in which parts is it secreted?
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
An individual with a low K+ diet will have how much of it excreted?
1% (and reabsorb 99%)
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+?
no part secreted because they have a low diet
PT reabsorbs 67% ThickAL reabsorbs 20% DT reabsorbs 3% CD reabsorbs 9% 1% is excreted
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+?
PT reabsorbs 67% ThickAL reabsorbs 20% DT secretes 10-50% CD secretes 5-30% 15-80% is excreted
How is K+ reabsorbed in the PT?
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.
How is K+ reabsorbed in the thick ascending loop of Henle?
The NKCC2 in the apical membrane brings K+ into the cell. There is also a change separation so K+ can move through paracellularly
What are the two different cell types in the collecting duct? What percentage of cells do these make up and what is their purpose?
- intercalated cells (30% of the cells) for K+ reabsorption
- principle cells (70% of the cells) for K+ secreted and Na+ reabsorption
Describe what happens in an intercalated cell in the collecting duct
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.
Describe what happens in the principle cells in the collecting duct
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
What is the effect of aldosterone on K+ secretion by the LDT and CD?
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
If there is a low K+ diet then there is a high or low flow rate and K+ secretion is high of low?
low flow rate
secretion in low
If there is a normal or high K+ diet then K+ secretion high or low
high
