Isosmotic

Iso-polysaure,/. isopoly acid, -purpurinskure, /. isopurpuric acid. -saccharinsaure, /. isosaccharinic acid, isosmotisch, a. isosmotic. iso-therm, -thermisch, a. isothermal. Iso-therme, /. isotherm, -thlocyanat, -thio-cyanid, n. isothiocyanate, -thiocyansaure, f. isothiocyanic acid, -tonie, /. isotonicity. 

Intravenous solutions must be isosmotic (same osmotic pressure) with red blood cells. If red blood cells were to be exposed to an i.v. solution that was hypoosmotic (lower osmotic pressure), water would move into the cells causing them to swell and possibly lyse. If red blood cells were to be exposed to a hyperosmotic i.v. solution (higher osmotic pressure), water would move out of the cells causing them to dehydrate and shrink. Both of these conditions would damage the red blood cells and disrupt function. 

Patient discomfort is another important consideration. The stinging caused by a hypoosmotic or hyperosmotic i.v. solution is not experienced with one that is isosmotic. Intravenous injections are often prepared with 0.9% sodium chloride or 5% dextrose, both of which are approximately isosmotic with red blood cells. 

Referring or relating to or demonstrating equal tension. 2. Often referring to an equivalence of osmotic pressure (i.e., isosmotic). Thus, isotonic often refers to solutions having identical ionic strength. 

Buffer solutions that are isosmotic with respect to some standard, typically chosen such that suspended cells will neither shrink nor expand. Sodium chloride solutions (0.90% weight/volume or 0.155 M) at 37°C is often used to represent physiological conditions. These buffer systems are also important in studies of intact cells and membranal organelles likewise, many pharmaceutical formulations must be prepared as isotonic solutions. Most enzyme-catalyzed reactions are affected by ionic... 

Figure 3. Diagrammatic models and representative traces of absorbance changes that show the kinetics and inhibition by quercetin (Quer.) of (A) valinomycin-induced swelling of mung mitochondria suspended in isosmotic KCl (B) swelling of mung bean mitochondria suspended in isosmotic ammonium phosphate and (C) swelling of mung bean mitochondria suspended in isosmotic prollne.

A nephron, showing the major sites and percentage (in braces) of sodium absorption along with other features of solute transport. The filtered load = GFR (180 L/day) Xplasma Na+ (140 mEq/L) or 25,200 mEq/day. About 1% of this amount is excreted in voided urine. Sites where tubular fluid is isosmotic, hypertonic, or hypotonic relative to plasma are shown. POT, proximal convoluted tubule LH, loop of Henle DOT, distal convoluted tubule CCD, cortical collecting duct TAL, thick ascending loop. 

An important functional characteristic of the proximal tubule is that fluid reabsorption is isosmotic that is, proximal reabsorbed tubular fluid has the same osmotic concentration as plasma. Solute and water are transported in the same proportions as in the plasma because of the high water permeability of the proximal tubule. Thus, the total solute concentration of the fluid in the proximal convoluted tubule does not change as the fluid moves toward the descending loop of Henle. The corollary of this high water permeability is that unabsorbable or poorly permeable solutes in the luminal fluid retard fluid absorption by proximal tubules. This is an important consideration for understanding the actions of osmotic diuretics. 

In a dilute medium, synthesis of water results with production of ATP, whereas in a concentrated medium, synthesis of amino acid occurs. In both cases the process leads to the isosmotic regulation of intracellular fluid and therefore the maintenance of a constant cell volume.9... 

Thus, differences in permeability of solute can create curiously anomalous situations. In the case of the avian cestode, Tetrabothrius erostris, both sucrose at 0.192 m (d = 0.36 °C) and NaCl at 0.140 M (zl = 0.56 deg. C) appear to be isosmotic this result can be interpreted as showing that this species is less permeable to sucrose than to Na+ and Cl". 

Raymond, J.A. (1993). Glycerol and water balance in a near-isosmotic teleost, winter-acclimatized rainbow smelt. Can. J. Zool. 71 1849-1854. 

At least 11 different mammalian AQP have now been identified, of which seven (AQPl, -2, -3, -4, -6, -7, -8) are expressed in the Iddney. Many of these also have extra-renal expression sites (e.g, AQPl may be unportant in fluid removal across the peritoneal membrane). Two asparagine-prohne-alanine sequences in the molecule are thought to interact in the membrane to form a pathway for water translocation. AQPl is found in the proximal tubule and descending thin limb of the loop of Henle and constitutes almost 3% of total membrane protein in the kidney. It appears to be constitutively expressed and is present in both the apical and basolateral plasma membranes, representing the entry and exit ports for. water transport across the cell, respectively. Approximately 70% of water reabsorption occurs at this site, predominantly via a transcellular (i.e., AQPl) rather than a paracellular route. Water reabsorption in the proximal tubule passively follows sodium reabsorption, so that the fluid entering the loop of Henle is still almost isosmotic with plasma. 

NaHCOs, glucose amino acids water (isosmotic)... 

Hyponatremia has occurred in the settings of hypo-osmotic, hyperosmotic, and isosmotic plasma thus the measurement (or occasionally a calculation) of plasma osmolality is an important initial step in.the assessment of hyponatremia. Of these, the most common is hypoosmotic hyponatremia, since Na is the primary determinant of plasma osmolality. Figure 46-2 describes an algorithm for laboratory measurements and physical examination findings in the differential diagnosis of a plasma Na" <135 mmol/L. 

Depletional hyponatremia (excess loss of Na ) is almost always accompanied by a loss of ECF water, but to a lesser extent tlian the Na loss. Hypovolemia is apparent in the physical examination (orthostatic hypotension, tachycardia, decreased skin turgor). Loss of isosmotic or hypertonic fluid is the cause and this can occur through renal or extrarenal losses. If urine Na is low (generally <10 mmol/L), the loss is extrarenal (see Figure 46-2) because the kidneys are properly retaining filtered Na in response to increased aldosterone (stimulated by the hypovolemia and hyponatremia). Causes of extrarenal loss of Na" in excess of H2O include losses from the gastrointestinal tract or skin (see Figure 46-2). 

A.P. Quist, S.K. Rhee, H. Lin, R. Lai, Physiological role of gap-junctional hemichannels. Extracellular calcium-dependent isosmotic volume regulation, Cell Biol 48, 1063-1074 (2000). 

Biliary excretion of contrast medium is affected by the bile flow (688, 734, 745, 777, 778). Bile is isosmotic with plasma and is produced from the transport of water from the liver cell into the bile canaliculi (canalicular bile flow) and from the excretion and reabsorption of water and electrolytes in the bile ductules (ductular bile flow). Bile flow is increased by taurocholate and dehydrocholate their presence in the canaliculi creates an osmotic gradient that produces the flow of water and solute. There is a positive correlation between the canalicular bile flow stimulated by taurocholate and the amount of iopanoic acid excreted by the liver. Feeding the patient a fatty meal or taurocholate at the time that iopanoic acid is administered can improve the quality of cholecystograms(734). 

Response of Cell Volume to an Isosmotic Medium The Effect of Weak Acids and Bases on Cell Volume Ion Channels and their Effect on Cell Water The Sodium/Proton Exchanger... 

From the upper curve, cell volume did not change. The cell volume is 100 and remains constant in 0.3 osmolar sodium chloride medium. If no net change in cell watCT occurred, then the free energy of water inside the cell must equal the free energy of water in the medium. Expressed in osmolalities, the osmolality of the cells must be 0.3 osmolar. The other possibility is that the cell membrane is impermeable to water. However, the middle and the lower curves rule out that possibility because the cells lose water in an isosmotic media. 

Figure 2a. Swelling of lymphocytes and erythrocytes in salts of weak acids and bases. Ion channels were not functional. Lymphocytes with a buffering power of 25 mM/L/pH were suspended in isosmotic solutions of ammonium chloride or sodium propionate. Erythrocytes with a buffering power of 100 mMA-/pH were suspended in similar solutions.

Let us use a set of figures to illustrate the concepts that we just discussed. Figure 2a illustrates the relative increase in cell water that lymphocytes or erythrocytes would undergo if they were put into isosmotic solutions of sodium propionate or ammonium chloride at pH 7.4. The starting cell pH was 7.05. The buffering power was set at 25 mM/L/change in pH for lymphocytes or 100 mM/L/change in pH for erythrocytes. In this illustration, we will prevent any other solute movements except the entry of the weak acid or weak base. We will open other ion channels a little later in the discussion. 

Figure 2b. Accumulation of ammonium ion (square) or propionate ion (diamond) by lymphocytes or erythrocytes suspended in isosmotic solutions of ammonium chloride or sodium propionate.

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