Colloids osmotic effect

When equilibrium is reached between the inside and outside of a membrane, the solution inside is under greater pressure— in principle the same situation as in an ordinary osmotic cell where no solute at all can pass through the membrane. This pressure difference is called the colloid osmotic pressure. Its magnitude depends on the molarity of the protein solution, and is generally rather low due to the high molecular weight. A serum albumin solution of 35 gm per liter (3.5%) is only 1/2000 M its osmotic pressure is 22.4/2000 atm or 122 mm of water. Nevertheless, colloid osmotic effects do play a role in physiology. 

Understanding the effects of colloid administration on circulating blood volume necessitates a review of those physiologic forces that determine fluid movement between capillaries and the interstitial space throughout the circulation (Fig. 10—5).4 Relative hydrostatic pressure between the capillary lumen and the interstitial space is one of the major determinants of net fluid flow into or out of the circulation. The other major determinant is the relative colloid osmotic pressure between the two spaces. Administration of exogenous colloids results in an increase in the intravascular colloid osmotic pressure. In the case of isosomotic colloids (5% albumin, 6% hetastarch, and dextran products), initial expansion of the intravascular space is essentially that of the volume of colloid administered. In the case of hyperoncotic solutions such as 25% albumin, fluid is pulled from the interstitial space into the vasculature... 

Human plasma has a colloid osmotic pressure of 3.6 kPa, of which 2.8 kPa is contributed by albumin. Volume-for-volume, 4.5% albumin is approximately four times more effective in expanding the plasma volume than crystalloid solutions, and the effect lasts 6-8 hours, compared to only 15-20 min with crystalloids. Although popular in the past as volume expanders, albumin solutions have fallen into disfavour. They are prepared from pooled human plasma, with all the inherent risks of pooled blood products. Albumin can cause adverse reactions, similar to other transfusion reactions, such as chills, urticaria, and vasodilatation. These may be caused by organic or inorganic substances formed during the processing... 

The main function of albumin in the plasma is to provide colloid osmotic pressure. It is of major importance in maintaining blood volume and in the exchange of fluid between blood and the tissues. Heavy proteinuria may involve the loss of >3.5 g of albumin per day and this, in turn, causes a reduction in plasma oncotic pressure. When plasma oncotic pressure is reduced, fluid is not completely reabsorbed from the tissues at the venous end of capillaries. The fluid is retained within the tissues, causing oedema. The effects of gravity on fluid accumulation in the body causes oedema to be more marked in the lower body than in the upper parts, so oedema is often noticed first around the ankles. 

Increased depletion attraction. The presence of nonadsorbing colloidal particles, such as biopolymers or surfactant micelles, in the continuous phase of an emulsion causes an increase in the attractive force between the droplets due to an osmotic effect associated with the exclusion of colloidal particles from a narrow region surrounding each droplet. This attractive force increases as the concentration of colloidal particles increases, until eventually, it may become large enough to overcome the repulsive interactions between the droplets and cause them to flocculate (68-72). This type of droplet aggregation is usually referred to as depletion flocculation (17, 18). 

Park GE, Hauch MA, Curlin F, Datta S, Bader AM. The effects of varying volumes of crystalloid administration before cesarean delivery on maternal hemodynamics and colloid osmotic pressure. Anesth Analg 1996 83(2) 299-303. 

Clinicopathologic effects of rapid infusion of 5% sodium bicarbonate in 5% dextrose in the horse. Journai of the American Veterinary Medicai Association 178 267-271 Runk D T, Madigan J E, Rahai C J et al 2000 Measurement of plasma colloid osmotic pressure in normal thoroughbred neonatal foals. Journal of Veterinary Internal Medicine 14 475-478... 

NF and RO pores are small and internal fouling by colloids is unlikely. The deposition of colloids on tight membranes may increase the boundary layer concentration, and give rise to an increased flux decline due to osmotic effects or cake resistance. 

Rejection and fouling anal3 sis in NF is more difficult than that of more open membranes such as MF and UF due to an increased interplay of colloids and natural organics with salt, which is retained to a greater extent. Osmotic effects become important. 

At critical fouling conditions ferric chloride successfully prevented fouling at any dosage. At the higher organic concentration the iron oxyhydroxide precipitates are neutralised and the osmotic effects observed are smaller. The impact on rejection of these less positively charged colloids is also reduced. 

Then follows a region, in which the opposite takes place. Both the conductivity and the osmotic effect decrease — the second decrease is more rapid — and from this Me Bain concludes that neutral colloidal particles have been formed. 

Hory also showed that the left-hand side in Equation 3.70 is proportional to the polymer segment-solvent interaction in dilute solutions. When this term is negative, the polymer likes the solvent. In colloids, the enthalpic contribution to the osmotic effects in its simplest form for a sphere becomes... 

Einarson and Berg (1993) have attempted to explain the data on flocculation kinetics of latex particles with a block copolymer adsorbed on them. The polymer was polyethylene oxide (PEO)/polypropylene oxide (PPO). PPO is water insoluble and forms the part that adsorbs on the latex PEO forms streaming tails into water. Some charge effects remain after the polymer adsorption. The total potential is DLVO plus elastic plus osmotic effects. After fitting the model to the experimental data, they were able to calculate the value of 6, which they called the adlayer thickness. Their data on the stability ratio of latex with and without the polymer and as a fimction of NaCl concentration are shown in Figure 3.23. Note that the polymer stabilizes the colloid by almost one order of magnimde in NaQ concentration. That is, polymers may be necessary to maintain stability in aqueous media containing substantial electrolyte. 

DONNAN EFFECT, DONNAN EQUILIBRIUM, COLLOIDAL OSMOTIC PRESSURE, AND MEMBRANE POTENTIAL... 

The existence of the Donnan effect, the colloid-osmotic pressure, and the membrane potential is not only important for biomedical and biotechnological applications. 

When the mole fraction of polymer in the medium approaches unity, that is in a polymer melt, osmotic effects are absent. Colloidal particles dispersed in a polymer melt may be stable because aggregation causes deformation with a decreased conformational entropy of the polymer molecules. 

The effective osmotic pressure of the blood across capillary walls. The greatest contribution to the colloid osmotic pressure comes from plasma proteins, which, unlike the plasma ions, cannot move through the capillary walls. The oncotic pressure balances the effect of capillary blood pressure which tends to force water into the interstitial spaces. 

---