Osmotically active solute

A number of chapters in this volume (especially Chapters 5 and 6) provide a more thorough discussion of osmotic adjustment by intact plants and tissues in response to environmental stress and the role of osmotically active solutes in this response. The following section focuses on the role of organic osmotica in the response of plant cells to salt stress. Cultured plant cells offer the opportunity to evaluate the effect of both internally synthesised and externally administered organic osmotica. 

Moderate soil salt concentration. These are external concentrations at which substantial osmotic adjustment in the plant is required, and could not be achieved with NaCl without compartmentation between cytoplasm and vacuole. Damage may still be attributable to excessive internal concentrations, but simply minimising salt uptake is not a sufficient answer. The concentration of osmotically active solutes within the cells has to be... 

The answer is b. (Hardman, pp 695-697.) A significant increase in the amount of any osmotically active solute in voided urine is usually accompanied by an increase in urine volume Osmotic diuretics affect diuresis through this principle. The osmotic diuretics (such as mannitol) are nonelectrolytes that are freely filtered at the glomerulus, undergo limited re absorption by the renal tubules, retain water in the renal tubule, and promote an osmotic diuresis, generally without significant Na excretion. Ln addition, these diuretics resist alteration by metabolic processes. 

Osmotic diarrhoea. Occurs if osmotically active solutes are retained in the intestinal lumen water will not be absorbed and diarrhoea will result. Ingestion of poorly absorbed substrates, such as mannitol, sorbitol, Epson salts (MgS04) and some antacids (MgOHj), can occur in a number of malabsorption syndromes. For example, a failure to digest lactose (lactose intolerance) means that lactose remains in the intestinal lumen and osmotically holds water. 

Osmolality Where molality is the term used to express the concentration based on number of moles of a solute per mass of solvent, osmolality is the term used to express the number of moles of osmotically active solute particles per mass of solvent. The unit of osmolality is osmoles per kilograms. 

For other cases, the uptake or internal production of osmotically active solutes can control cell growth, including effects that involve the reversible cell extension caused by changes in internal hydrostatic pressure and are quantitatively described by the volumetric elastic modulus e (Eq. 1.17). For instance, when reversible or elastic changes in volume exist, then (1 )dPidt should be added to the right-hand side of Equation 2.33. Using Equation... 

The bile salt-independent pathway depends on osmotically active solutes such as glutathione and bicarbonate to generate water flow into the canaliculi. It has been shown that bile flow continues at zero bile salt excretion, i.e. a bile salt-independent process. 

Fluid compartments Osmotically active solutes. These are in fact the only clear exceptions I can think of to the principle that a dmg has to bind before acting. Applications include ... 

This non-SI expression is used to describe the number of moles of osmotically active solute particles per litre of solution (osmolL )- The need for such a term arises because some molecules dissociate to give more than one osmotically active particle in aqueous solution. 

This term describes the number of moles of osmotically active solute particles per unit mass of solvent (osmol kg ). For an ideal solute, the osmolality can be determined by multiplying the molality by n, the number of solute particles produced in solution (e.g. for NaCl, n = 2). However, for real solutes, a correction factor (the osmotic coefficient, (j>) is used ... 

Several properties vary in direct proportion to the effective number of osmotically active solute particles per unit mass of solvent and can be used to determine the osmolality of a solution. These colligative properties include freezing point, boiling point and vapour pressure. 

Whether an increase in vascular permeability results in mucosal edema depends on the balance between the amount of leakage into the mucosa and the rate of clearance from the mucosa, either through the lymphatics or across the epithelium into the airway lumen. The increase of vascular permeability produced by inflammatory stimuli can result in the bulk flow of plasma into the airway mucosa (Renkin, 1992). The amount of plasma leakage depends upon the number of gaps that form in the endothelium of the leaky vessels, the duration of the gaps and the intravascular pressure that drives the extravasation (Clough, 1991 Taylor and Ballard, 1992). The movement of plasma proteins and other osmotically active solutes into the mucosa can increase the interstitial oncotic pressure, which favors the net movement of fluid out of vessels and further increases the amount of leakage (Taylor and Ballard, 1992). 

The discussion to this point has considered the entry or exit of water. The movements of water depend critically on the concentration of osmotically active solutes. The next section will discuss the entry and exit of solutes into and out of cells. When osmotically active solutes change, cell water will change. An analogous set of rules may be stated for solutes. 

A. Mannitol is an osmotically active solute diuretic. Mannitol inhibits water reabsorption at the loop of Henie and the proximal tubule. The increase in urine output is usually accompanied by an increase in solute excretion. In addition, mannitol transiently increases serum osmolality and decreases cerebrospinal fluid pressure by creating an osmotic gradient between brain tissue and the vascular compartment. Water moves across this gradient into the blood vessels, lowering the cerebrospinal fluid pressure and decreasing intracranial pressure. 

DDS has been treated either by addition of osmotically active solute (glucose, glycerol, albumin, urea, fructose, NaQ, mannitol) to the dialysate, or by intravenous infusion of mannitol or glycerol. With the technique of pure ultrafiltration the patient is subjected to ultrafiltration without dialysis. The net result is loss of fluid without the patient undergoing dialysis. Ultrafiltration followed by dialysis does not appear to be associated with DDS (Ronco et al., 1998). Additionally, DDS can be prevented by decreasing the time on dialysis and inCTeasing the frequency of dialysis at the initiation of hemodialysis in patients. Mannitol infusion accompanying the initial... 

The sodium ion concentrations in body fluids are listed in Table 1 [2]. From a physiological viewpoint, Na provides the bulk of osmotically active solutes in plasma with its associated anions, thus affecting the distribution of the body water significantly. An excess translocation of Na into cells or a loss of it from the body results in a decrease of extracellular fluid volume, affecting circulation, renal function, and nervous system function. 

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