Cell Homestasis Flashcards
What does the thick ascending limb of the loop of Henle do?
It reabsorbs sodium chloride in preference to water
This creates a transepithelial osmotic gradient which is responsible for the counter current multiplication later seen in the collecting duct
What is the sodium concentration typically outside of a cell?
145 mil mol
What does the NKCC in the loop of henle depend on?
It depends on the inward movement of sodium into the loop of henle
What happens if sodium levels inside of the cells at the loop of henle become too high?
Then sodium chloride absorption at the thick ascending limb decreases in the cell.
What happens if the transepithelial osmotic gradient is dissipated (abandoned)?
remember this is when water wasnt absorbed in the thick ascending limb of the loop of henle to make an osmotic gradient which would move water into the collecting duct. Instead sodium chloride was absorbed.
You would have an increase in levels of urine and increase sodium chloride moving into the urine. As the Na Cl wouldnt be absorbed at the ascending limb.
What is the normal voltage of sodium inside the cell, its nernst potential, the membrane potential of a excitable cell in general and how much sodium is usually found outside the cell
Sodium inside the cell = 15 mv
Nernst potential = +60mv
Vm = +70mv
Sodium outside of cell = 145 mv
Electrical gradient of sodium is largely into the cell.
What would be the effect of sodium voltage inside the cell increasing from 15 to 45mv? And what is the problem with this?
The nernst potential of the sodium becomes +30mv which keads to a decrease in electrical gradient
This would causes an issue with action potential
This leads to a slower conduction of the action potential.
Sodium potassium ATPase? What does it extrude? And is the NAKCC channel in the ascending limb of the loop of henle a pump?
3 sodium ions coupled to 1 hydrolysed ATP
No the NaKCC channel is not a pump. It doesnt need ATP
The specifics - how does the sodium potassium ATPase actually work? As in what happens with sodium, calcium and potassium
ATP binds to the pump (this forms ADP)
The pump is now phosphorylated
Sodium already bound to the pump, then dissociates from the pump.
In the next stage calcium enters and binds to the the cleft of the pump
Potassium then binds, exposing the cleft of the pump to the inside of the cell. This causes the pump to undergo a CONFORMATIONAL change. Potassium then enters the cell.
The turnover rate of the sodium potassium ATPase pump depends on?
ATP levels
What inhibits the sodium ATP pump?
It is inhibited by cardiac glycosides - ouabain and digoxin
They can stop the pump from dephosphorylating
What is the role of the ATPase?
Controls membrane potential
Net effect makes cell more negative inside
Allows potassium to accumulate in the cell so it can be used in the hyperpolarisation stage of an action potential = cell is more negative.
In the collecting duct. Amiloride sensitive channels are found on the apical membrane of the epithelial cells. Where is the sodium potassium pump found?
On the basolateral membrane
This allows sodium to be transported right across the cell from the lumen of the intestines right to the basolateral membrane and then into the blood.
Why is calcium regulation in cells important. And what in the general amount inside and outside of the cell?
There is usually 100nM inside the cells
In the extracellular is usually 1x10^6 nm
Calcium must be regulated in the cell because its an important second messenger. E.g. in pancreatic fusion cells
How do we keep calcium levels in the cell keep low and why do we use this method?
We use the sodium calcium exchanger and active calcium pumps to move calcium out
This is because gradients favour calcium entering the cell. Remember voltage gradients move from higher to lower voltages. And calcium outside the cell is at +120 mv so it wants to move into the cell where the voltage of calcium is lower.
