Osmolarity, Tonicity and Cell Preservation Flashcards
What is the most plentiful cation in the plasma?
Sodium ions.
What is the most plentiful cation in cells?
Potassium ions.
Are chloride ions found in higher concentrations inside or outside the cell?
Much higher outside the cell in the plasma.
How is the positive charge of potassium ions inside cells neutralised?
By a variety of anions such as proteins, nucleic acids and phosphorylated proteins.
What is the main intracellular anion?
Organic phosphate is the main intracellular anion and is a key intracellular metabolite with roles in ATP production and cell signaling.
Are proteins cations or anions?
Anions.
Proteins are found in relatively low concentrations but still have a measurable effect on the cell’s polarity. How is this possible?
They can have a highly negative charge (e.g. -17).
How does the pH of the plasma differ from the pH of cells?
Plasma is more neutral and more basic than cells at 7.4 compared to 7.1 of cells.
How does the osmolarity of plasma differ from cells? What is the significance of this?
It doesn’t, meaning there is not normally a significant osmotic effect (except for some regions of the kidneys where fluids are concentrated/diluted).
Osmosis moves water to an area with a higher or lower osmolarity?
Higher (think water moves towards salt, NaCl, which has an osmolarity of 2 mOsmoles, assuming 1mmol/L)
What is an osmole?
An osmole is the number of moles of solute that contribute to the osmotic pressure of a solution.
How do you calculate the number of mOsmoles?
1mmol/L of MgCl2 would be 3mOsmoles because 3 ions make up MgCl2.
2mmol/L of NaCl would be 4 mOsmoles because 2(2 ions) = 4.
Glucose has a mOsmole of 1 assuming a concentration of 1mmol/L
What is tonicity?
Tonicity is the strength of a solution as it affects the final cell volume.
What does tonicity depend on?
Tonicity depends on both cell membrane permeability and the solution composition.
Describe a hypertonic solution and its effect on a cell.
In hypertonic solutions, the osmolarity of the impermeant solutes outside the cell is greater than those inside the cell. The cell therefore shrinks (water moves out to reduce [solutes outside] and water moves towards areas of higher osmolarity).
Describe a hypotonic solution and its effect on a cell.
In hypotonic solutions, the osmolarity of the impermeant solutes outside the cell is the are less than those inside the cell. The cell, therefore, swells in the solution.
What is a negative consequence of differences in osmolarity between a cell and its enviroment?
Differences in the concentrations of permeant solutes can result in transient damages to cell volume. If the difference is very large, it can result in cell damage.
How are cell volumes maintained?
Ion pumps keep the osmolarity of the cell equal to its surroundings.
How are sodium and potassium concentrations maintained?
The Na+K+ ATPase pumps prevent the higher extracellular concentration of Na+ from entering the cell (and causing it to burst)) and vice versa with potassium.
How do we preserve tissues that have been cut off from oxygen?
Put in cold temperatures (about 4 degrees) to slow the ischaemic changes.
Perfuse the cell with UW (University of Wisconsin) solution to reduce hypothermic cell swelling and enhance preservation.
Why can putting a cell in cold temperatures cause further problems?
The Na+K+ ATPase pump stops functioning below 15 degrees, which is compounded by the lack of oxygen.
What are the three main factors that serve to reduce cell swelling in UW-infused tissues?
Lack of Na+ or Cl- (so no influx/efflux possible).
Presence of extracellular impermeant solutes.
Presence of a macromolecular colloid.
How can allopurinol and glutathione help preserve cells?
They act as antioxidants, preventing damage from ROS.
