Lecture 2 - Osmosis, Tonicity, and Pressures

What is osmosis?

Flow of water across a semipermeable membrane due to differences in solute concentration (membrane blocks movement of solute)

concentration difference of solutes causes difference in _________ _____________, which will cause osmosis

osmotic pressure

true or false: osmosis is NOT simply diffusion of water; it occurs because of a pressure difference!

true

why will the water be pulled over?

the right side has more solute, thus greater osmotic pressure that will pull water over

- permeable to solvent, not permeable to solute (permeable to water (solvent), not solute)

how is osmotic pressure (pulling water) created?

created by a difference in solute concentration across a semipermeable membrane ~ impermeable to certain solutes

- measure of tendency of solution to pull in water (solvent) by osmosis

- also refers to the amount of hydrostatic pressure required to stop osmosis

what is hydrostatic pressure (pushing pressure)

pressure exerted by a stationary fluid at equilibrium which causes water/fluid to move or be pushed

why are osmotic and hydrostatic pressures very important in cells and blood exchange?

allows fluid exchange across capillaries

hydrostatic pressure = fluid pressure usually causes what?

water and some very small solutes to leave blood vessels, which is called dominant pressure

interstitial hydrostatic = exerted by fluids between cells in tissue

blood hydrostatic = exerted by fluid within blood vessels (high dominant)

osmotic

due to solutes

hydrostatic

due to fluid

true or false: hydrostatic pressure opposes osmotic pressure

true;

osmotic tends to pull

hydrostatic tends to push

osmotic pressure (aka colloidal osmotic or oncotic pressure if referring to tissues & cells):

High osmolarity (many solute particles) exerts ________ osmotic pressure to pull water into a space, such as a blood vessel

high;

pulling water in, blood pressure goes up

water leaving blood vessels = edema

true or false: pressures favor filtration out of capillaries and into tissues

true

true or false: osmolarity and osmolality are functionally the same

true

osmolar concentrations express what?

osmotic strength of solutions such as urine, plasma, NaCl

osmolarity is what?

concentration of osmotically active particles per liter of solution (osmotic/L or mOsm/L)

a 1 mol/L NaCl solution would have an osmolarity of what

2 mOsm/L

osmolality is what?

concentration of osmotically active particles expresses as osmoles/kg water

3 types of osmotic balance?

1. isosmotic

2. hyperosmotic

3. hypo-osmotic

isosmotic

solutions of equal solute concentrations

- same osmolarity/equal osmotic pressures

what happens to a normal cell placed in an isosmotic solution?

nothing!

hyperosmotic

refers to a solution with higher concentration of solute

- higher osmolarity compared to another solution

- solution exerts more pressure

what happens to a normal cell placed in a hyperosmotic solution?

- water moves from cell to the solution

- water follows the concentration gradient

- pulls it from the cell = shrivels up

hypo-osmotic

refers to a solution with lower concentration of solute

- lower osmolarity compared to another solution

- solution exerts less pressure

what happens to a normal cell placed in a hypo-osmotic solution?

- solution to the cell

- swells up

what is tonicity?

tissue tone: a measure of the effective osmotic pressure

tonicity = defined by the response of cells or tissue immersed in the solution

a solution is _________________ to cells/tissues if cells/tissues neither swell nor shrink when immersed in solution

- no osmotic pressure difference between cell interior and extracellular solution

isotonic

a solution is _______________ to cells/tissues if cells/tissues swell when immersed in solution

- more solutes inside cell (higher osmolarity) relative to extracellular environment, greater osmotic pressure inside cell

hypotonic

a solution is ________________ to cells/tissues if cells/tissues shrink when immersed in solution

- less solutes inside cell (lower osmolarity) relative to extracellular environment, greater osmotic pressure outside cell

hypertonic

oncotic pressure is also called what?

colloid osmotic pressure

what is oncotic pressure?

form of osmotic pressure specifically exerted by proteins, mostly ALBUMIN, within blood vessels

what does oncotic pressure tend to do?

tends to pull water into blood vessels

oncotic pressure opposes what?

interstitial colloidal osmotic pressure (tissue proteins that want to pull water out of vessels)

a decrease in blood oncotic pressure leads to what?

edema