Crystalloid and Colloid and dialysis

Crystalloid and Colloid Different biomolecules and their building blocks presented in biological system can be broadly classified into crystalloid (amicron) and colloid (submicron) depending on their particle size. Crystalloids: are substances with size <1 nm which can pass through semipermeable membrane, e.g. electrolyte, glucose, amino acid. Colloids: are substances with size nm which can't pass through semipermeable membrane, e.g. protein. 90% of the organic matter of living tissue is colloid. Microns: solutes having size more than 100 nm and they form unstable emulsion and suspension with water.

Difference between crystalloid and colloid Crystalloid (amicrons)Colloid (submicrons) Size <1 nm1-100 nm Not seen by ultramicroscopeSeen by ultramicroscope Can pass through semipermeable membraneCan’t pass through semipermeable membrane Form homogeneous solution with water (true solution) Form heterogeneous colloidal solution with water Osmotically very active and exert high osmotic pressure in water Osmotically less active and exert less osmotic pressure in water dialyzableNon dialyzable Crystalline formAmorphous form

Colloids: Colloidal system/phase is heterogeneous with two phases- 1) dispersed phase (internal phase)- which constitutes with colloidal particles, 2) dispersion medium (external phase)- which refers to the medium in which colloidal particles are suspended.

Types of colloids: Based on the affinity of dispersion medium with dispersed phase colloids are colloids are classified as – 1) lyophobic or hydrophobic colloid, 2) hydrophilic or lyophilic colloid. Lyophobic or hydrophobic: these are solvent hating and have no affinity to water. These colloids don’t have any attraction towards dispersion medium. Hydrophilic or lyophilic colloid: these are solvent loving and have affinity to water and exist as emulsoid.

Hydrophilic colloid: They are easily solvated or hydrated where a shell of water molecule is formed around them. This provide stability to colloid solution by preventing aggregation of colloid particles since the solvated particles repel each other and that’s prevent the precipitation. So hydrophilic colloids are called protective colloid.

State of colloidal system Sol: here dispersed phase (solute) is solid and dispersion medium (solvent) is liquid, e.g. plasma. Gel: here dispersed phase (solute) is liquid and dispersion medium (solvent) is solid, e.g. cytoplasm

Properties of colloids: Brownian movement: the continuous rapid and haphazard movement of a colloidal particles due to the uninterrupted buffeting on colloid particles provided by solvent molecules. It is seen under ultra microscope.

Tyndall phenomenon: when a beam of light passed through colloidal solution and observed at right angle the tract of light becomes visible as a white line due to the dispersion of light rays by the colloid particles.

Cont... Electrical properties: they carry electrical charge either positive and negative. The electrical charge may be due to ionization of colloidal particles or adsorption of the ions from the medium or both. The stability and precipitation of colloids ids determined by the ionic charge they carry. The separation of charged colloids can be achieved by analytical technique. Osmotic pressure: colloidal particles are larger particles in size, so their contribution to osmotic pressure is less. Surface tension: colloid particles have larger surface area per unit mass. So they show increased phenomenon of adsorption and interfacial tension.

Non dialyzable: the colloid particles, being larger molecule, can’t pass through semi permeable membrane. This process is referred to as dialysis and useful for separation of colloids. Donnan membrane equilibrium: the presence of non diffusible colloidal particles (protein) in a biological system influence the concentration of some diffusible ion concentration across the membrane. Salting out: colloid particles can be allowed to precipitate out by adding appropriate salts to the solution.

Biological importance of colloids: Biological fluids as colloids: these include blood, milk and cerebrospinal fluid. Biological compounds as colloidal particles: the complex molecules of life, the higher molecular weight protein, complex lipids and polysaccharides exits in colloidal state, Blood coagulation: when blood coagulation occurs the sol is converted to gel. Fat digestion and absorption: the formation of emulsion, facilitated by the emulsifying agents bile salts, promotes fat digestion and adsorption in intestinal tract. Formation of urine: the filtration of urine is based on the principle of dialysis.

Suspension & Emulsion Suspension: it is a heterogenous system of a solute with water where solute (dispersed phase) size is >100 nm, e.g. Antacid suspension. Emulsion: it is a liquid-liquid heterogenous system produced by dispersion of a liquid droplet to another liquid in which it is insiluble, here size of the dispersed phase (solte) is nm. Emulsifier (emulsifying agent)- these are the substance which stabilize an emulsion. Dispersed droplets (solute) of emulsion tends to coalesce due to surface tension.

Comparison of true solution, colloidal solution and suspension True solutionColloidal solutionsuspension Solute size <1nm and homogenous phase & heterogenous (multi phase) >100 nm and heterogenous (multi phase) Solute exits as molecule or ion Solute exists as aggregates of molecules Solute exists as aggregates of millions of molecule Solute never sediments out on standing Solute sediments out on standing Exert high osmotic pressureExert very low osmotic pressure 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 and crystalloids from their mixture. The principle of dialysis is based on the fact crystalloid substance in a solution can pass through semipermeable membrane while colloid particles fail to cross. Dialyzing membrane act as a sieve retaining the larger particles. Mixture of crystalloid and colloid is placed inside the tube or bag of dialyzer and then suspended in a vessel containing dialysis fluid. Dialysis fluid is prepared without the crystalloid substance which are to be separated. The crystalloid particles from the mixture will diffuse out to the dialysis to the dialysis fluid due to concentration gradient.

cont.... Colloid particles remain the same because they can't cross the semipermeable membrane. Dialysis fluid is changed either periodically or continuously as crystalloid particles diffuse out from the interior of the dialyzer into the surrounding dialysis fluid. Importance: 1) used artificial kidney for treatment of renal failure. In renal failure renal failure the crystalloid uremic toxins (urea, creatinine) accumulate in blood since kidney fail to excrete them. So dialysis remove these uremic toxins from blood 2) Treatment of hyperkalemia.

Filtration It is the process by which forced out through a membrane or other barrier because of a pressure difference on the two sides of a membrane. At glomerular membrane of kidney that forms filtrate and urine Filtration at arterial end of capillary that allows exit of fluid with nutrients out of blood vessel to reach the cell