Solution isosmotic

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.

A more quantifafive measure of urine concentration ability is the clearance of free wafer (Cnp), derived in furn from fhe osmolal clearance, (UV/P) osmol. The laffer in effect represents the volume that would be required to excrete total urinary solute in isosmotic solution, that is, at a concentration of 300 mOsm. If filtrate were excreted as such, the osmolal clearance would equal the GFR. If the urine is more dilute than the filtrate, the dilution may be visualized as that volume of filtrated from which solute was removed without reabsorption of wafer this volume is defined as the free water clearance (Cnp), or free wafer excretion, and is given below, where V stands as usual for the urine volume excreted per unit time ... 

Isosmotic solution Hyperosmotic solution Hyposmotic solution... 

FIGURE 12.18 Red Blood Cells and Osmosis (a) In an isosmotic solution, red blood cells have the normal shape shown here. In a hyperosmotic solution (b), they lose water and shrivel. In a hyposmotic solution (c), they swell up and may burst as water flows into the cell. 

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... 

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. 

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". 

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). 

As promised, let us now remove the constraints on the permeability of the membrane to other solutes. For clarity, however, let us do so in a stepwise fashion. Figures 3a-d show the effect on erythrocytes when the cells are placed in isosmotic ammonium chloride or sodium propionate and chloride anion is allowed to exchange for bicarbonate anion. The erythrocyte membrane has an intrinsic protein called Band 3 (after its position in gel electrophoresis) which permits the rapid exchange of chloride anion for bicarbonate anion. In the presence of physiological concentrations of medium bicarbonate (24 mM/L) the half-time for exchange is... 

Let us now put what we have learned about ion channels into a physiological context. Let us discuss how the cells use ion channels to regulate their cell volume. To do so, let us challenge the cells by putting them into a hypoosmotic medium. The cell of choice for our example will be the lymphocyte. When lymphocytes are placed into 0.6 isosmotic sodium chloride, i.e., only 0.6 the cell s osmolality, they swell immediately as water enters the cells and dilutes the cell solutes until their concentration is also 0.6 isosmotic. This response of the cells occurs in seconds because the membrane of the lymphocyte is very permeable to water. However, during the next few minutes, the cells lose water and cell volume returns toward normal. 

In microdialysis, when the perfusion solution is pumped through the fiber capillary, there is ideally no change in volume of the perfusate and no fluid removed from the tissue. This requires a negligible pressure gradient across the membrane. The perfusate must be isosmotic with the tissue. If either the membrane capillary or the outlet capillary is very long, the back pressure at the membrane can become sufficient for it to leak. This can be minimized by using low flow rates and membranes that have relatively low molecular weight cutoffs. 

If two solutions contain the same number of particles they may be said to be iso-osmotic, or simply isosmotic, with respect to each other. If one solution exhibits a greater osmolarity than another solution it is hyperosmotic with respect to the less concentrated solution. If one solution has a lower osmolarity than another solution then it is hypo-osmotic or hyposmotic, with respect to the more concentrated solution. Iso-, hyper- and hypo-osmolarity should always be stated with respect to another solution. 

Intravenous solutions—those that are administered directly into a patient s veins— must have osmotic pressures equal to those of body fluids. These solutions are called isosmotic (or isotonic). When a patient is given an IV in a hospital, the majority of the fluid is usually an isosmotic saline solution—a solution containing 0.9 g NaCl per 100 mL of solution. In medicine and in other health-related fields, solution concentrations are often reported in units that indicate the mass of the solute per given volume of solution. Also common is percent mass to volume— which is the mass of the solute in grams divided by the volume of the solution in milliUters times 100%. In these units, the concentration of an isotonic saline solution is 0.9% mass/volume. 

Fig. 1, Method of production of large quantities of nonnucleate fragments of unfertilized eggs of sea urchins and other animals by centrifugation on layers of sucrose-seawater solutions of increasing density. For many species of echino-deims the following mixtures of isosmotic (1.1 M) sucrose and seawater are suitable for each of the four layers starting from the bottom 3 1, 3 2 2 2, and 0 1. The eggs are introduced with the 2 2 layer centrifugation is at 12,000g for 10-15 minutes. From Tyler and Tyler (1966b). ...

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