Osmosis, Tonicity, and Pressures Flashcards
What is osmosis?
FLOW OF WATER across a semipermeable membrane DUE TO DIFFERENCES IN SOLUTE CONCENTRATION (membrane blocks movement of solute)
what do concentration difference in solutes cause?
causes difference in osmotic pressure, which will cause osmosis
most important point about osmosis?
osmosis is NOT simply diffusion of water; it occurs because of a pressure difference!
what is osmotic pressure (pulling pressure)?
- created by 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 act of hydrostatic pressure required to stop osmosis
what is hydrostatic pressure (pushing pressure)?
pressure exerted by stationary fluid at equilibrium- causes water/fluid to move or be pushed
- pressure exerted by a stationary fluid -> more pressure to move creates a driving force
why are osmotic and hydrostatic pressures very important in cells and blood vessels?
allow fluid exchange across capillaries
what is hydrostatic pressure?
- generally, this is the dominant pressure
- fluid pressure usually causing water and some very small solutes to leave blood vessels
what is interstitial hydrostatic?
exerted by fluids between cells in tissue
what is blood hydrostatic?
exerted by fluid within blood vessels and is usually HIGH
hydrostatic pressure opposes…
osmotic pressure
what is osmotic pressure? (aka colloidal osmotic or oncotic pressure if referring to tissues and cells)
high osmolarity (many solute particles, high osmolarity) exerts high osmotic pressure to pull water into a space, such as a blood vessel
what do pressures favor overall?
favor filtration out of capillaries and into tissues
what are osmolar concentrations?
express the osmotic strength of solutions such as urine, plasma, NaCl
what is osmolarity?
- concentration of osmotically active particles per liter of solution (ism/L or mOsm/L)
- a 1 mmol/L NaCl solution would have an osmolarity of 2 mOsm/L
what is osmolality?
- concentration of osmotically active particles expressed as osmoles/ kg WATER
- osmolality functionally same as osmolarity
what is isosmotic balance?
- solutions of equal solute concentrations, i.e., same osmolarity/equal osmotic pressures
what happens to a normal cell placed in an isosmotic solution?
nothing should happen
what is hyperosmotic balance?
- refers to solution with higher concentration of solute, i.e., 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- solution and cell shrivels
what is hypo-osmotic balance?
- refers to solution with lower concentration of solute, i.e., lower osmolarity compared to another solution
- solution exerts less pressure
what happens to a normal cell placed in a hypo-osmotic solution?
water moves into cell from solution, cell explodes
what is tissue tone?
a measure of the effective osmotic pressure
what is tonicity?
defined by the response of cells of tissues immersed in the solution
a solution is ISOTONIC to cells/tissues…
- if cells/tissues neither swell nor shrink when immersed in solution
- no osmotic pressure difference between cell interior and extracellular solution
a solution is HYPOTONIC 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
a solution is HYPERTONIC 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
what is oncotic pressure?
- aka colloid osmotic pressure
- form of osmotic pressure SPECIFICALLY EXERTED BY PROTEINS, mostly albumin, within blood vessels
- tends to pull water into blood vessels
- opposes interstitial colloidal osmotic pressure (tissue proteins that want to pull water out of vessels)
decrease in blood oncotic pressure=
edema
