PATHO: FLUX

Define flux

The rate of passive flow of substances down gradients

Four major types of flux

• Diffusion

• Bulk Flow

• Ion Movement

• Water Movement

Diffusion

• Def = movement of particles from high to low concentration

• Resistance = surface area; # of channels 

• Types = passive, facilitated, active transport 

Bulk Flow

• Def = movement of large volumes of fluid (and its constituents) moving together in one direction 

• Gradient = pressure difference

• Resistance = size of the plath or blockage in the path 

Ion Movement 

• Def = net movement of charged ions across an electrochemical gradient 

• Gradient = electrochemical (-electro = voltage, -chemical = concentration —> concentration and/or charge difference) 

• Resistance = # of channels

Water Movement

• Def = movement of water to maintain equilibrium

• Gradient = solute difference (-hypo, -iso, -hyper)

• Resistance = membrane permeability

Hyper, hypo, iso

• Hypertonic = higher solute outside; higher water inside (water moves out and cell shrinks)

• Hypotonic = higher solute inside; higher water outside (water moves in and cell swells)

• Isotonic = equal solute and water (no net movement and cell is normal)

Compare and contrast diffusion and bulk flow 

Diffusion 

• Concentration gradient

• Based on molecule concentration (random)

• Slow

• High selectivity

Bulk Flow

• Pressure gradient

• One-way (everything moves together; no selection)

• Fast (all molecules move in the same direction)

• No selectivity

Which factors affect flux?

• Gradient

• Resistance

Gradient

• Def = driving force for movement (a larger gradient increases flux)

• Technical def = a difference in the magnitude of the concentration, electrical potential, pressure, or temp between two points in a system

Resistance 

• Def = limits or slow down movement (a greater resistance decreases flux) 

• Technical def = something along the pathway that moderates the flow (opposition to flow in a system) 

Predict the effects of hypertonic and hypotonic environments on a cell

• Hypertonic = higher water concentration inside the cell —> osmotic flux outside of the cell —> cell shrinks (crenation)

• Hypotonic = higher water concentration outside the cell —> osmotic flux into the cell —> cell swells

Predict what will happen to the rate of movement of a substance (the flux) when you change the gradient or the resistance in a system

• Gradient = if the gradient increases, the flux also increases (there’s a direct relationship)

  • Larger gradient = greater driving force for movement

• Resistance = if the resistance increases, the flux will decrease (there’s an inverse relationship)

  • Greater resistance = harder for substances to flow