Water as a solvent of "solid" solutes - the basics Flashcards
these solutes include…
and what do they all contribute too
ionic solutes - salts, acids, bases
colloids - high MW organic molecules
“substrate” organic molecules - amino acids, glucose, urea etc
All contribute to osmolarity of body fluids
all participate in physiological processes
what is colloid?
a general term for large particles (from 1-100 nm in diameter) maintained in a suspension
what do all colloidal solutes posess?
a surface charge
- include high molecular weight proteins, nucleic acids and carbohydrates
Do colloidal solutes have small or large hydration spheres?
very large hydration spheres with gegenions in the sphere
what is the most fundamental organic compounds in animals
colloidal solutes
what is osmosis?
the movement of water across a semi- or selectively permeable membrane, from an area of low solute concentration to high
what is a semi-permeable membrane?
permits passage of water, not solutes
what is a selectively permeable membrane
permits water and some solutes to pass through but not others
- most biological membranes are selectively permeable - plasma membrane, tissue layers, skin etc
Diffusion vs osmosis
Diffusion:
no selectively permeable membrane
solute particles move by diffusion
follow ficks equation
Osmosis:
selectively permeable membrane
water moves to area of high [solute]
movement of water greater than predicted from ficks equation
follows van’t hoff equation
colligative properties of solutions
what is
hypotonic
hypertonic
isotonic
swell
shrink
stay the same
is osmosis reversible?
yes it can be reversed
ie. when put into a piston device for direct measurement of osmotic pressure
- is the solution is placed under hydrostatic pressure that exactly opposed osmosis, by putting force back on the water creating energy, or stopping water movement
what is osmotic pressure?
mechanical pressure required to prevent movement of water across a semipermeable membrane
osmotic pressure can be predicted by the van’t hoff equation
what is that equation
Π = CRT
Π = osmotic pressure
C = osmolarity or concentration
R= universal gas constant 8.314 J/K/mol
T = absolute temperature
which equation is the van’t hoff related too?
RV=nRT
what does van’t hoff equation predict
all colligative properties, ficks does not since osmosis is not the diffusion of water
what is the cause of osmolarity
osmosis is faster than diffusion
- there must be the bulk flow of water driven by something other than kinetic motion
osmosis occurs at every membrane in the body when…
membrane is selectively permeable to at least one solute
- and there is a concentration gradient for the solute
membranes include all cellular membranes, any tubule in the body, and the skin
Nature of the capillary wall:
made of membranes - endothelial cells & basement membrane
- interstitial fluid comes from blood plasma via intercellular clefts
how permeable is the capillary wall
it is selectively permeable (especially through the pores between cells, the intercellular clefts)
- this means large proteins do not cross the membrane
- water, ions, small organic molecules do
what is C.O.P
this sets up a colloid osmotic pressure
- gradient across the capillary wall
what pressures acting at arterial side of capillary:
BP, neg IFP (negative interstitial fluid pressure), IF COP (interstitial fluid colloid osmotic pressure), P COP
Starling-Landis model
capillary fluid flow, where osmotic and mechanical fluid pressures interact
- is a net pressure forcing fluid out of capillary, and this fluid forms the interstitial fluid
- interstitial fluid hydrates cells helps deliver nutrients, carry away wastes etc.
The disrupting of Starling - Landis model may cause what
cause tissue swelling (edema)
The Second Law & Osmosis of Aqueous Solutions
-pure water is a very ordered substance due to extensive H-bonds
- creates a low entropy in pure water ( entropy = randomness thus less randomness)
- solutes in water decrease order
ie. increased entropy in solutions
