Diffusion Protein Mediated Diffusion integral membrane proteins transport proteins (transporters) –diffusion through hydrophilic channels –facilitated diffusion

Hydrophilic Channels Channels have specificity; they are (more or less) specific for certain ions, e.g., Na + channel, K + channel, Ca ++ channel, Cl - channel. Leak channels: Some are always open. Gated channels: usually closed, opened by a specific stimulus Fig. 3.8

Osmosis Water transport –diffusion across the phospholipid bilayer –diffusion through hydrophilic channels (aquaporins) Osmosis –diffusion of water across a semipermeable membrane Fig Water moves down its concentration gradient, from an area of higher water concentration to an area of lower water concentration. Therefore, the net movement of water is from an area of lower solute concentration to an area of higher solute concentration.

Fig units of measurement for osmotic pressure: mm Hg or osmolality osmolality = osmoles / (Kg solvent) for a dilute solution: osmolality  osmolarity = osmoles / (L solution) Osmolality is more accurate than osmolarity, because volume varies with temperature, but weight does not. But, you are more familiar with calculating molarities than molalities. Therefore, know how to calculate osmolarity. Osmosis No net movement because hydrostatic pressure = osmotic pressure

Osmolality/osmolarity is a measure of the number of particles in one liter of solution. [For the purposes of this course assume complete dissociation of any solutes.] –e.g.,1 mole of glucose  1 osmole of glucose –e.g., 1 mole of NaCl  2 osmoles NaCl (1 mole Na mole Cl - ) Osmolarity

Osmolarity is a colligative property. Therefore, osmolarity can be measured by freezing point depression or boiling point elevation. freezing point of plasma = °C therefore, osmolality = 290 mosmolal number to memorize: body osmolarity = 300 mosmolar

What is the osmolarity of “normal” saline? normal saline = 0.9% NaCl molecular weights: Na = 23, Cl = 35.5: NaCl = 58.5 g mole NaCl 0.9% NaCl = 0.9g NaCl x 1000 mL x 1 mole NaCl x 2 osmoles 100 mL sol’n 1 L sol’n 58.5g NaCl mole NaCl = osmoles NaCl x 1000 mosmoles NaCl 1 L sol’n1 osmole NaCl = 308 mosmoles NaCl L sol’n = 308 mosM

Behavior of Animal Cells in Solutions of Different Osmolarities same osmolarity as plasmaosmolarity lower than plasmaosmolarity higher than plasma assumptions: Solute is impermeant and is not metabolized. Fig. 3.16