Crystalloid and Colloidand dialysis
Crystalloid and Colloid
•Different biomolecules and their building blockspresented in biological system can be broadly classifiedinto crystalloid (amicron) and colloid (submicron)depending on their particle size.
•Crystalloids: are substances with size <1 nm which canpass through semipermeable membrane, e.g.electrolyte, glucose, amino acid.
•Colloids: are substances with size 1-100 nm which can'tpass through semipermeable membrane, e.g. protein.90% of the organic matter of living tissue is colloid.
•Microns: solutes having size more than 100 nm andthey form unstable emulsion and suspension withwater.
Difference between crystalloid and colloid
Crystalloid (amicrons)
Colloid (submicrons)
Size <1 nm
1-100 nm
Not seen by ultramicroscope
Seen by ultramicroscope
Can pass through semipermeable membrane
Can’t pass through semipermeablemembrane
Form homogeneous solution with water(true solution)
Form heterogeneous colloidal solution withwater
Osmotically very active and exert highosmotic pressure in water
Osmotically less active and exert less osmoticpressure in water
dialyzable
Non dialyzable
Crystalline form
Amorphous form
Colloids:
•Colloidal system/phase is heterogeneous with twophases- 1) dispersed phase (internal phase)- whichconstitutes with colloidal particles, 2) dispersion medium(external phase)- which refers to the medium in whichcolloidal particles are suspended.
Types of colloids:
•Based on the affinity of dispersion medium withdispersed phase colloids are colloids are classified as – 1)lyophobic or hydrophobic colloid, 2) hydrophilic orlyophilic colloid.
•Lyophobic or hydrophobic: these are solvent hating andhave no affinity to water. These colloids don’t have anyattraction towards dispersion medium.
•Hydrophilic or lyophilic colloid: these are solvent lovingand have affinity to water and exist as emulsoid.
Hydrophilic colloid:
•They are easily solvated or hydrated where a shell ofwater molecule is formed around them. This providestability to colloid solution by preventing aggregation ofcolloid particles since the solvated particles repel eachother and that’s prevent the precipitation. So hydrophiliccolloids are called protective colloid.
State of colloidal system
•Sol: here dispersed phase (solute) is solid anddispersion medium (solvent) is liquid, e.g. plasma.
•Gel: here dispersed phase (solute) is liquid anddispersion medium (solvent) is solid, e.g. cytoplasm
Properties of colloids:
•Brownian movement: the continuous rapid andhaphazard movement of a colloidal particles due to theuninterrupted buffeting on colloid particles provided bysolvent molecules. It is seen under ultra microscope.
•Tyndall phenomenon: when a beam of light passedthrough colloidal solution and observed at right anglethe tract of light becomes visible as a white line due tothe dispersion of light rays by the colloid particles.
Cont...
•Electrical properties: they carry electrical charge eitherpositive and negative. The electrical charge may be dueto ionization of colloidal particles or adsorption of theions from the medium or both. The stability andprecipitation of colloids ids determined by the ioniccharge they carry. The separation of charged colloidscan be achieved by analytical technique.
•Osmotic pressure: colloidal particles are larger particlesin size, so their contribution to osmotic pressure is less.
•Surface tension: colloid particles have larger surfacearea per unit mass. So they show increasedphenomenon of adsorption and interfacial tension.
•Non dialyzable: the colloid particles , being largermolecule, can’t pass through semi permeablemembrane. This process is referred to as dialysis anduseful for separation of colloids.
•Donnan membrane equilibrium: the presence of nondiffusible colloidal particles (protein) in a biologicalsystem influence the concentration of some diffusibleion concentration across the membrane.
•Salting out: colloid particles can be allowed toprecipitate out by adding appropriate salts to thesolution.
Biological importance of colloids:
•Biological fluids as colloids: these include blood, milk andcerebrospinal fluid.
•Biological compounds as colloidal particles: the complexmolecules of life, the higher molecular weight protein,complex lipids and polysaccharides exits in colloidal state,
•Blood coagulation: when blood coagulation occurs the solis converted to gel.
•Fat digestion and absorption: the formation of emulsion,facilitated by the emulsifying agents bile salts, promotesfat digestion and adsorption in intestinal tract.
•Formation of urine: the filtration of urine is based on theprinciple of dialysis.
Suspension & Emulsion
•Suspension: it is a heterogenous system of a solute withwater where solute (dispersed phase) size is >100 nm, e.g.Antacid suspension.
•Emulsion: it is a liquid-liquid heterogenous systemproduced by dispersion of a liquid droplet to another liquidin which it is insiluble, here size of the dispersed phase(solte) is 100-1000nm.
•Emulsifier (emulsifying agent)- these are the substancewhich stabilize an emulsion. Dispersed droplets (solute) ofemulsion tends to coalesce due to surface tension.
Comparison of true solution, colloidal solutionand suspension
True solution
Colloidal solution
suspension
Solute size <1nm andhomogenous phase
1-100 & heterogenous (multiphase)
>100 nm and heterogenous(multi phase)
Solute exits as molecule orion
Solute exists as aggregates of100-1000 molecules
Solute exists as aggregates ofmillions of molecule
Solute never sediments outon standing
Solute never sediments outon standing
Solute sediments out onstanding
Exert high osmotic pressure
Exert very low osmoticpressure
Exert no osmotic pressure
Methods used to separate crystalloid & colloid
•Ultra filtration
•Ultra centrifugation
•Dialysis
•Electrophoresis
•Electro dialysis
•Isoelectric focusing
•Salting out
Dialysis
•It is one of the method used to separate colloids andcrystalloids from their mixture. The principle of dialysis isbased on the fact crystalloid substance in a solution canpass through semipermeable membrane while colloidparticles fail to cross.
•Dialyzing membrane act as a sieve retaining the largerparticles. Mixture of crystalloid and colloid is placedinside the tube or bag of dialyzer and then suspended ina vessel containing dialysis fluid. Dialysis fluid is preparedwithout the crystalloid substance which are to beseparated. The crystalloid particles from the mixture willdiffuse out to the dialysis to the dialysis fluid due toconcentration gradient.
cont....
•Colloid particles remain the same because they can'tcross the semipermeable membrane. Dialysis fluid ischanged either periodically or continuously as crystalloidparticles diffuse out from the interior of the dialyzer intothe surrounding dialysis fluid.
•Importance: 1) used artificial kidney for treatment ofrenal failure. In renal failure renal failure the crystalloiduremic toxins (urea, creatinine) accumulate in bloodsince kidney fail to excrete them. So dialysis removethese uremic toxins from blood
2) Treatment of hyperkalemia.
Filtration
•It is the process by which forced out through amembrane or other barrier because of a pressuredifference on the two sides of a membrane.
•At glomerular membrane of kidney that forms filtrateand urine
•Filtration at arterial end of capillary that allows exit offluid with nutrients out of blood vessel to reach the cell
