Osmotic effects

The osmotic effect due to salt in soil-water environments is related to water availability. Water availability is determined by the soil-water potential, w, which is composed of the osmotic potential, 0, the matrix potential, m, and the gravitational potential, 

At any given matrix potential, m, under a constant gravitational potential, g, as salinity increases, w decreases. This is because osmotic potential, is directly related to total dissolved solids (TDS). The relationship between osmotic potential and TDS can be expressed by 

Another way to express the relationship is through the EC of a soil s solution. Since EC is directly related to salt content, the U.S. Salinity Laboratory Staff (1954) gave the following relationship relating EC to osmotic potential  

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Microreticular Resins. Microreticular resins, by contrast, are elastic gels that, in the dry state, avidly absorb water and other polar solvents in which they are immersed. While taking up solvent, the gel structure expands until the retractile stresses of the distended polymer network balance the osmotic effect. In nonpolar solvents, little or no swelling occurs and diffusion is impaired. 

Our strategy in proceeding, therefore, is to write separate expressions for the forces cited in items (1) and (2), and then set them equal to each other as required by item (3). Since we have discussed osmotic effects in Chap. 8 and elastic forces in Chap. 3, we shall invoke certain concepts and relationships from these chapters in this discussion. In this derivation we continue to omit numerical coefficients and some of the less pertinent parameters (although we retain Vj for the sake of Problem 5 at the end of the chapter), and focus attention on the relationship between a, M, and the interaction parameter x-... 

Sodium and potassium ions are actively absorbed from the intestine. As a consequence of the electrical potential caused by transport of these ions, an equivalent quantity of Cf is absorbed. The resulting osmotic effect causes absorption of water (56). 

A variety of methods have been devised to stabilize shales. The most successful method uses an oil or synthetic mud that avoids direct contact between the shale and the emulsified water. However, preventing direct contact does not prevent water uptake by the shale, because the organic phase forms a semipermeable membrane on the surface of the wellbore between the emulsified water in the mud and the water in the shale. Depending on the activity of the water, it can be drawn into the shale (activity lower in the shale) or into the mud (activity higher in the shale) (95—97). This osmotic effect is favorable when water is drawn out of the shale thus the aqueous phase of the oil or synthetic mud is maintained at a low water activity by a dding a salt, either sodium chloride or more commonly, calcium chloride. The salt concentration is carried somewhat above the concentration required to balance the water activity in the shale to ensure water movement into the mud. 

Armitage, W.J. Mazur, P. (1984). Toxic and osmotic effects of glycerol on human granulocytes. Am. J. Physiol. Cell Physiol. 247, (Cell Physiol. 16) C382-C389. 

Neutrophils represent an ideal system for studying osmotic effects on exocytosis. Stimulation of cytochalasin-B-treated neutrophils with the chemotactic peptide Jlf-formylmethionyl-leucyl-phenyl-alanine (FMLP) results in a rapid compound exocytosis up to 80% of lysosomal enzymes are released within 30 s (9-14). Secretion appears to be triggered by a rise in the level of cytosolic free calcium (15-18) promoted in part by entry of extracellular calcium through receptor-gated channels and in part by release of calcium that is sequestered or bound at some intracellular site (19-21). In this presentation, we augment our previously published data (22,23), which demonstrates that lysosomal enzyme release from neutrophils is inhibited under hyperosmotic conditions and that the rise in cytosolic calcium preceding secretion is inhibited as well. 

This application is designed to model the influence of various concentrations of a solute near one edge of the membrane, on the diffusion of water through the membrane. Specifically we are interested in determining whether the model reveals a difference in the flow of water out of one compartment relative to the other. It is well known that if a semipermeable membrane is impervious to a solute on one side of a membrane, a greater flow of water from the other side will occur. This is a model of the osmotic effect, the flow of water through the... 

Using cellular automata we have an opportunity to model the flow of water from each compartment into the membrane, when a solute is present on one side of the membrane. By design, the membrane in our model is composed of 31% empty cells. At iteration zero, in our dynamics, the membrane contains no water. After several iterations, there will be flows of water from the two compartments into the membrane. If we monitor the early stages of this process, we may detect a possible preference for water to flow from one of the compartments. Such a condition would model the early stages of the osmotic effect. 

The dynamics for each solute concentration study were run 10 times and averaged for each 10 iteration periods. Water molecules from the upper and lower compartments, within the membrane, are designated Wi and W2, respectively. It can be seen from these results that the presence of solutes in the lower compartment, W2, retards the flow of water into the membrane, relative to the flow from the upper compartment, Wi. In addition, this retardation of flow increases as the concentration of solute in W2 increases. We anticipate that these results are comparable to the situation at the earliest manifestation of the osmotic effect [5]. 

Fedors, J., Osmotic effects. 1. Water absorption by polymers,... 

The total mobile ion concentration (c++c ) inside the gel at equilibrium will inevitably exceed that in the external solution, c+ +c = vcj where v = v +v-. This must result in an osmotic pressure difference which tends to drive solvent into the gel from the less concentrated external solution. (We neglect for the moment the osmotic effects of polymer itself.) The osmotic pressure arising from the difference in mobile ion concentrations will be given approximately (see Appendix B), assuming the solutions to be dilute, by... 

Irretrievable loss of matrix-forming cations and anions can result in permanent damage to the cement surface. This is visible as milky or chalky patches or even raised blisters. For this reason it is customary to protect, temporarily, the freshly placed cement by varnish. Once hardened, attack by neutral solutions causes failure only when a cement has been poorly formulated and contains excessive amounts of soluble reaction products. In this case osmotic effects can cause blistering or even disintegration under the action of internal forces, as Figure 6.22 illustrates (Wilson Batchelor, 1967a). 

If osmotic effects are possible, several other effects would need to be considered in a geochemical-fate assessment, depending on whether the solute concentration is increased or decreased. If solute concentrations are increased, pressures associated with injection would increase beyond those predicted without osmotic effects. Also, the movement of ions to the injection zone from the aquifer with lower salinity (above the clay confining layer) would increase the salinity above those levels predicted by simple mixing of the reservoir fluid and the injected wastes. This action could affect the results of any geochemical modeling. 

Aldosterone acts on the distal tubule of the nephron to increase sodium reabsorption. The mechanism of action involves an increase in the number of sodium-permeable channels on the luminal surface of the distal tubule and an increase in the activity of the Na+-K+ ATPase pump on the basilar surface of the tubule. Sodium diffuses down its concentration gradient out of the lumen and into the tubular cells. The pump then actively removes the sodium from cells of the distal tubule and into the extracellular fluid so that it may diffuse into the surrounding capillaries and return to the circulation. Due to its osmotic effects, the retention of sodium is accompanied by the retention of water. In other words, wherever sodium goes, water follows. As a result, aldosterone is very important in regulation of blood volume and blood pressure. The retention of sodium and water expands the blood volume and, consequently, increases mean arterial pressure. 

Diuretics are a group of therapeutic agents designed to reduce the volume of body fluids. Their mechanism of action is at the level of the kidney and involves an increase in the excretion of Na+ and Cl ions and, consequently, an increase in urine production. As discussed in Chapter 2, sodium is the predominant extracellular cation and, due to its osmotic effects, a primary determinant of extracellular fluid volume. Therefore, if more sodium is excreted in the urine, then more water is also lost, thus reducing the volume of extracellular fluids including the plasma. 

Sodium is the major extracellular cation. Because of its osmotic effects, changes in sodium content in the body have an important influence on extracellular fluid volume, including plasma volume. For example, excess sodium leads to the retention of water and an increase in plasma volume. Increased plasma volume then causes an increase in blood pressure. Conversely, sodium deficit leads to water loss and decreased plasma volume. A decrease in plasma volume then causes a decrease in blood pressure. Therefore, homeostatic mechanisms involved in the regulation of plasma volume and blood pressure involve regulation of sodium content, or sodium balance, in the body. 

Lactulose is a disaccharide that causes an osmotic effect retained in the colon. It is generally not recommended as a first-line agent for the treatment of constipation because it is costly and not necessarily more effective than agents such as milk of magnesia. It may be justified as an alternative for acute constipation and has been found to be particularly useful in elderly patients. 

Because of thick intertwining protein fibers in the cell and in the area of the cell membrane, cell structure is rigid and remains so, but is altered by the osmotic effect of the penetrating water. The uptake of water entails a continual shifting of the cell... 

Osmotic effects are very important from a physiological standpoint. This is because biological membranes including the membrane of red blood cells behave like semipermeable membranes. Consequently, when red blood cells are immersed in a hypertonic solution (e.g., D5 A NS or D5NS), they shrink as water leaves the blood cells in an attempt to dilute and establish a concentration equilibrium across the blood cell membrane. Thus, when hypertonic solutions are administered into the blood stream, the fluid moves from interstitial and cellular space into the intravascular space. Conversely, when cells are placed in hypotonic environment (e.g., V2 NS), they swell because of the entry of fluid from the intravascular compartment, and may eventually undergo lysis. 

Metabolism via normal metabolic pathways or fast excretion without metabolism are desirable characteristics. Some intense sweeteners are excreted unchanged while others are metabolised. Bulk sweetener absorption is lower and slower than for carbohydrates and results in reduced caloric availability which is partly due to metabolites formed by intestinal bacteria. Such metabolites and osmotic effects of not fully absorbed bulk sweeteners can cause laxative effects. Generally, the calorific value of bulk sweeteners is lower than for carbohydrates. Intense and bulk sweeteners are, as far as they are metabolised, not dependent on insulin. They are therefore acceptable for diabetics as part of a suitable diet. 

Hunt JN, Pathak JD. The osmotic effects of some simple molecules and ions on gastric emptying. J Physiol 1960 154 254-269. 

Although these experiments showed growth was possible using casein hydrolysate, Rose also demonstrated that when the amino acid mixture was used rather than the intact protein, additional calories had to be provided as fat plus carbohydrate, if nitrogen balance was to be maintained. It was later shown that the carbohydrate was needed to protect the free amino acids from oxidation in the intestinal epithelium in the course of absorption. Further, amino acids are poorly tolerated by mouth, causing vomiting and/or diarrhea. After World War II attempts to feed very emaciated prisoners in concentration camps with protein hydrolysates were unsuccessful. It was then recognized that osmotic effects from the amino acids were responsible for the unpleasant consequences. 

The pressure that would be required to prevent the movement of water across a semipermeable membrane owing to the osmotic effect of large plasma proteins. (nc mmHg). 

The oxoacid is then metabolised in the usual way (see below). High activities of the oxidase are found in Uver and kidney where its function is to remove rapidly (i.e. detoxify) the D-amino acids. Failure to metabolise these amino acids could lead to their accumulation in cells with the danger of osmotic effects or interference in the metabolism of L-amino acids. 

Stimulation of aldosterone secretion from the adrenal cortex, which increases Na ion reabsorption in the tubules of the kidney. Via an osmotic effect, this increases water uptake from the glomerular filtrate, which increases... 

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