Cell Biology 7Cell Biology 7- transport 2- transport 2ndnd

Cell Biology 7Cell Biology 7- transport 2- transport 2ndnd

Sung Youn Lee, PhD. StudentSung Youn Lee, PhD. StudentVeterinary collage, Room 320Veterinary collage, Room 32002 450 3719, 016 293 605902 450 3719, 016 293 6059

leevet@paran.comleevet@paran.com

Cell membrane

Osmosis• Water can freely diffuse across membra

nes in the direction of lower to higher osmolarity.

Osmotic pressureVan’t Hoff’s law

• Osmotic pressure (∏) = iRTc

• i=number of ions (glucose 1, NaCl 2, MgCl2 3)• R=ideal gas constant (8.3145 J/mol K )• T=absolute temperature (K=C+273.16 )• C=molar concentration

Osmolarity

• Osmolarity=Φic=0.93x2x0.154 =0.286osm/L

Tonicity

• Isotonic fluid = 0.3osm/L• NaCl ; 0.15mole/L=(23+35.5)x0.15 =58.5x0.15=8.8g/L

≒ 0.9% NaCl• Glucose(C6H12O6)=(12x6+1x12+16x6)x0.3

=(72+12+96)=180x0.3=54g/L ≒ 0.5% dextrose

RBC behave as Almost perfectOsmometer.

Homeostasis• The major osmotic particle in extracellular flui

ds or plasma is Na+ ion.• Na+ is maintained at high concentrations in t

he extracellular fluid by Na/K-ATPase. • If Na/K-ATPase is inhibited by ouabain such t

hat it can no longer pump Na out into the extracelluar fluid, cells swell and then lyse.

Donnan effect and its relation to water flow

• These impermeable anion (protein & RNA) cause a redistribution of permeable anions in a manner predicted by Donnan and Gibbs.

• To maintain electroneutrality

Donnan effect• After these events, the concentration of protei

n-, Cl-, and K+ will be higher in compartment A, therefore, water will flow toward compartment A.

• For this same reason, the Donnan effect tends to cause water to flow into cells but is balanced by active outward pumping of ions by Na/K-ATPase.

Na+

Na+

Thank you for your attention ~Thank you for your attention ~