Fluid Interactions

phospholipid bilayer

phospholipids

• hydrophilic head - charged, interact with water

• hydrophobic tail

cannot cross - charged molecules (Na+), polar molecules (glu) (not charged but uneven distribution of charge)

can cross - lipid soluble (aldosterone), small polar molecules (water)

simple diffusion

movement of particles between two regions from high to low

no energy required

rate of diffusion depends on size of gradient, permeability and temperature

• lipid soluble move through faster than H2O (polar)

• faster at higher temperatures

facilitated diffusion

movement of particles between two regions from high to low

facilitated by pores, channels, or transporters

molecules that cannot freely cross lipid bilayer

rate of diffusion depends on size of gradient, permeability, and temperature

electrochemical gradient

= concentration gradient + electric gradient

charged particles can move down electric gradients

rate of diffusion depends on size of gradient, permeability, and temperature

active transport

movement of particles between two regions, from low to high concentration or against electrochemical gradient

requires energy

secondary active transport

movement of particles between two regions, from low to high concentration or against electrochemical gradient

energy comes from active transport happening somewhere else in cell

symport via symporter - cotransport in same direction

antiport via antiporter - cotransport in opposite directions

osmosis

movement of water across a selectively permeable membrane from a dilute to a concentrated solution

effective osmole - membrane is not permeable to substrate, substrate will drive osmosis

ineffective osmole - membrane is permeable to substrate, substrate will not drive osmosis

water moves from low to high osmolarity

osmolarity

osmoles/L

concentration of potentially osmotically active molecules

high - concentrated

low - dilute

tonicity

concentration of effective osmoles in a fluid

concentration of solutes that drives osmosis

hypotonic

fluid with a lower effective osmolarity than another

hypertonic

fluid with a higher effective osmolarity than another

isotonic

fluid with the same effective osmolarity as another