Lecture 4: Osmolarity and Tonicity

Question 1

Osmotic pressure?

• what is it
• how to measure it?

Answer 1

-Associated with concentration of solutes within fluid (water moving from area of decreasing solutes concentration to increase concentration)

Van’t Hoff Equation:
Osmotic Pressure = (number of particles produced by a particle)(gas constant=0.082 Latm/mol-k)(Temp=Kelvin)(Concentration mol/L)

Effective osmotic Pressure:
-modified with reflection coefficient
Osmotic pressure (eff)= (# particles)(reflection coefficient)(Gas constant=0.082)(Temp)

Question 2

Hydrostatic Pressure

Answer 2

Effects of gravity on fluid across capillary endothelial cells (cv/renal)

Forces across membrane = 0 bc membranes cannot withstand large hydrostatic forces

Question 3

Osmolarity

Answer 3

Total concentration of all particles in a solution

• Iso-osmotic: equal osmotic pressure in and out of cell
• Hyperosmotic: Solution > Cell (>300 Mosm)
• Hypo-osmotic: Solution < Cell (<300 Mosm)

Question 4

Tonicity

Answer 4

Total concentration of non-penetrable solutes
Describes volume change of a cell at equilibrium

(Don’t include UGGS: Urea, glucose, glycerol)

• Iso-osmotic: Equal Non-penetrating Solute concentration on both sides of the membrane (Cell neither swells or shrinks)
• Hypertonic: Concentration higher on the inside (Causes cell to shrink)
• Hypotonic: Concentration is lower on the inside of the cell (Causes the cell to swell)