| diuretics, osmotic | Diuretics that are filtered at the glomerulus and reabsorbed in the renal tubule only to a limited extent. They thus increase the amount of osmotically active solute in the urine and a corresponding increase in urine volume. These compounds also increase the osmolality of plasma, thereby increasing the diffusion of water from the intraocular and cerebrospinal fluids; they can be used for reducing the pressure and volume of these fluids. (12 Dec 1998) |
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| iso-osmotic | <physiology> Having the same total osmotic pressure or osmolality as another fluid (ordinarily intracellular fluid); such a fluid is not isosmotic if it includes solutes that freely permeate cell membranes. Synonym: iso-osmotic. (05 Mar 2000) |
| osmotic | <chemistry> Pertaining to or of the nature of osmosis (= the passage of pure solvent from a solution of lesser to one of greater solute concentration when the two solutions are separated by a membrane which selectively prevents the passage of solute molecules, but is permeable to the solvent). (18 Nov 1997) |
| osmotic diuresis | Diuresis due to a high concentration of osmotically active substances in the renal tubules (e.g., urea, sodium sulfate), which limit the reabsorption of water. (05 Mar 2000) |
| osmotic diuretics | Drugs, such as mannitol, which by their osmotic effects retain water during urine formation and thus dilute electrolytes in the urine, making resorption less efficient; they promote the elimination of water and electrolytes in the urine. (05 Mar 2000) |
| osmotic fragility | The susceptibility, or lack of resistance, of erythrocytes to haemolysis when exposed to increasingly hypotonic saline solutions. (12 Dec 1998) |
| osmotic nephrosis | Swelling of renal tubular epithelium associated with glomerular filtration of sugars and dextrose; the swelling is due to formation of cytoplasmic vesicles by pinocytosis, and is reversible, probably with no dysfunction, when produced by glucose or mannitol. (05 Mar 2000) |
| osmotic pressure | See: osmosis. The pressure required to prevent osmotic flow across a semi permeable membrane separating two solutions of different solute concentration. Equal to the pressure that can be set up by osmotic flow in this system. (18 Nov 1997) |
| osmotic shock | Passage of solvent into a membrane bound structure due to osmosis, causing rupture of the membrane. A method of lysing cells or organelles. (18 Nov 1997) |
| effective osmotic pressure | That part of the total osmotic pressure of a solution that governs the tendency of its solvent to pass across a boundary, usually a semipermeable membrane; it is commonly represented by the product of the total osmotic pressure of the solution and the ratio (corrected for activities) of the number of dissolved particles that do not permeate the bounding membrane to the total number of particles in the solution; equivalent in meaning to tonicity; commonly expressed in equivalent units of osmolality rather than pressure per se. (05 Mar 2000) |
| activity | 1. The state of being active, the ability to produce some effect, the extent of some function or action. 2. <chemistry> A thermodynamic quantity that represents the effective concentration of a solute in a nonideal solution, if concentrations are replaced by activities, the equations for equilibrium constants, electrode potentials, osmotic pressure, boiling point elevation, freezing point depression and vapour pressures of volatile solutes are converted from approximations that hold only for dilute solutions to exact equations that hold for all concentrations. The activity is equal to the product of the concentration and the activity coefficient, a dimensionless number measuring deviation from nonideality. Symbol a. The potential or true thermodynamic activity of a substance, as opposed to its molar concentration. 3. <radiobiology> The number of nuclear transitions or disintegrations occurring in a given quantity of radioactive material per unit time. The SI unit of activity is s-1. The special name for the unit of activity is becquerel (Bq). The previously used special unit of activity, curie (Ci), is being replaced by the becquerel. 1 Bq = 2.7 x E-11 Ci. 1 Ci = 3.7 x E10 Bq. 4. Optical activity. (16 Dec 1997) |
| activity coefficient | <chemistry> The factor by which the value of a concentration of a solute must be multiplied to determine its true thermodynamic activity. (06 May 1997) |
| activity cycles | Bouts of physical irritability or movement alternating with periods of quiescence. It includes biochemical activity and hormonal activity which may be cellular. These cycles are shorter than 24 hours and include sleep-wakefulness cycles and the periodic activation of the digestive system. (12 Dec 1998) |
| activity, drug | A measure of the physiological response a drug produces in the body. A less active drug produces less response (and visa versa). (12 Dec 1998) |
| blocking activity | The repression or elimination of electrical activity in the brain by the arrival of a sensory stimulus. (05 Mar 2000) |