Protein osmotic pressure

Figure 12.1 illustrates the main structure of a nephron [1], The measurements to be reported in this chapter were performed on rats. A rat kidney contains approximately 30000 nephrons as compared to the one million nephrons in a human kidney. The process of urine formation starts with the filtration of plasma in the glomerulus, a system of 20-40 capillary loops. The presence of a relatively high hydrostatic pressure in this system allows water, salts and small molecules to pass out through the capillary wall and into the proximal tubule. Blood cells and proteins are retained, and the filtration process saturates when the protein osmotic pressure balances the hydrostatic pressure difference between the blood and the filtrate in the tubule. For superficial nephrons, the proximal tubule is visible in the surface of the kidney and easily accessible for pressure measurements by means of a thin glass pipette. 

Keywords Polyelectrolytes, globular proteins, osmotic pressure, Poissson-Boltzman theory,... 

Analytic expressions for the protein osmotic pressure were needed to test the applicability of uniform wall flux theory. Vilker s data (3) at pH 7.4 were used for BSA, interpolated over our range of interest and converted to our concentration units (g/1 of olutlon) by using a protein partial specific volume of... 

The hydrostatic pressure in an arteriole is the force that "pushes" fluid out of the capillary and into the interstitial spaces. The plasma protein osmotic pressure, plus the tissue pressure, is the force that "pulls" water from interstitial spaces into the venular side of the capillary. Thus, if the hydrostatic pressure is greater than the osmotic pressure, fluid will leave the circulation if it is less, fluid will enter the circulation. 

In this section we briefly consider the osmotic pressure of polymers which carry an electric charge in solution. These include synthetic polymers with ionizable functional groups such as -NH2 and -COOH, as well as biopolymers such as proteins and nucleic acids. In this discussion we shall restrict our consideration... 

Ultrafiltration. Membranes are used that are capable of selectively passing large molecules (>500 daltons). Pressures of 0.1—1.4 MPa (<200 psi) are exerted over the solution to overcome the osmotic pressure, while providing an adequate dow through the membrane for use. Ultrafiltration (qv) has been particulady successhil for the separation of whey from cheese. It separates protein from lactose and mineral salts, protein being the concentrate. Ultrafiltration is also used to obtain a protein-rich concentrate of skimmed milk from which cheese is made. The whey protein obtained by ultrafiltration is 50—80% protein which can be spray dried. 

Van den Berg, G.B. Hanemajer, J.H. and Smolders, C.A., "Ultrafiltration of Protein Solutions the Role of Protein Association in Rejection and Osmotic Pressure," Journal of Membrane Science, 31 (1987) 307-320. 

A biochemist isolates a new protein and determines its molar mass by osmotic pressure measurements. A 50.0-mL solution is prepared by dissolving 225 mg of the protein in water. The solution has an osmotic pressure of 4.18 mm Hg at 25°C. What is the molar mass of the new protein ... 

Plasma protein fractions include human plasma protein fraction 5% and normal serum albumin 5% (Albuminar-5, Buminate 5%) and 25% (Albuminar-25, Buminate 25%). Plasma protein fraction 5% is an IV solution containing 5% human plasma proteins. Serum albumin is obtained from donated whole blood and is a protein found in plasma The albumin fraction of human blood acts to maintain plasma colloid osmotic pressure and as a carrier of intermediate metabolites in the transport and exchange of tissue products. It is critical in regulating the volume of circulating blood. When blood is lost from shock, such as in hemorrhage, there is a reduced plasma volume. When blood volume is reduced, albumin quickly restores the volume in most situations. 

A sample consisting of 155 mg of a purified protein is dissolved in 10.0 mL of ethanol. This solution is placed in a device for measuring osmotic pressure and rises to a final height of 32.5 cm above the level of pure ethanol. The experiment is performed at 1.00 atm and 298 K. The density of ethanol at 298 K is 0.79 g-cm "3. What is the molar mass of the protein Assume that the density of the solution is the same as that of pure ethanol. See Exercise 8.95. 

In arterioles, the hydrostatic pressure is about 37 mm Hg, with an interstitial (tissue) pressure of 1 mm Hg opposing it. The osmotic pressure (oncotic pressure) exerted by the plasma proteins is approximately 25 mm Hg. Thus, a net outward force of about 11 mm Hg drives fluid out into the interstitial spaces. In venules, the hydrostatic pressure is about 17 mm Hg, with the oncotic and interstitial pressures as described above thus, a net force of about 9 mm Hg attracts water back into the circulation. The above pressures are often referred to as the Starling forces. If the concentration of plasma proteins is markedly diminished (eg, due to severe protein malnutrition), fluid is not attracted back into the intravascular compartment and accumulates in the extravascular tissue spaces, a condition known as edema. Edema has many causes protein deficiency is one of them. 

Mature human albumin consists of one polypeptide chain of 585 amino acids and contains 17 disulfide bonds. By the use of proteases, albumin can be subdivided into three domains, which have different functions. Albumin has an ellipsoidal shape, which means that it does not increase the viscosity of the plasma as much as an elongated molecule such as fibrinogen does. Because of its relatively low molecular mass (about 69 kDa) and high concentration, albumin is thought to be responsible for 75-80% of the osmotic pressure of human plasma. Electrophoretic smdies have shown that the plasma of certain humans lacks albumin. These subjects are said to exhibit analbuminemia. One cause of this condition is a mutation that affects spUcing. Subjects with analbuminemia show only moderate edema, despite the fact that albumin is the major determinant of plasma osmotic pressure. It is thought that the amounts of the other plasma proteins increase and compensate for the lack of albumin. 

Albumin, which is not glycosylated, is the major protein and is the principal determinant of intravascular osmotic pressure it also binds many Hgands, such as drugs and bilirubin. 

C12-0018. When 7.50 mg of a protein is dissolved in water to give 10.00 mL of solution, the osmotic pressure is found to be 1.66 torr at 21°C. Determine the molar mass of the protein. 

Equation (20-80) requires a mass transfer coefficient k to calculate Cu, and a relation between protein concentration and osmotic pressure. Pure water flux obtained from a plot of flux versus pressure is used to calculate membrane resistance (t ically small). The LMH/psi slope is referred to as the NWP (normal water permeability). The membrane plus fouling resistances are determined after removing the reversible polarization layer through a buffer flush. To illustrate the components of the osmotic flux model. Fig. 20-63 shows flux versus TMP curves corresponding to just the membrane in buffer (Rfouimg = 0, = 0),... 

A semi-permeable membrane, which is unequally permeable to different components and thus may show a potential difference across the membrane. In case (1), a diffusion potential occurs only if there is a difference in mobility between cation and anion. In case (2), we have to deal with the biologically important Donnan equilibrium e.g., a cell membrane may be permeable to small inorganic ions but impermeable to ions derived from high-molecular-weight proteins, so that across the membrane an osmotic pressure occurs in addition to a Donnan potential. The values concerned can be approximately calculated from the equations derived by Donnan35. In case (3), an intermediate situation, there is a combined effect of diffusion and the Donnan potential, so that its calculation becomes uncertain. 

Plasma colloid osmotic pressure is generated by proteins in the plasma that cannot cross the capillary wall. These proteins exert an osmotic force, pulling fluid into the capillary. In fact, the plasma colloid osmotic pressure, which is about 28 mmHg, is the only force holding fluid within the capillaries. Interstitial fluid colloid osmotic pressure is generated by the small amount of plasma proteins that leaks into the interstitial space. Because these proteins... 

Figure 15.7 Starling principle a summary of forces determining the bulk flow of fluid across the wall of a capillary. Hydrostatic forces include capillary pressure (Pc) and interstitial fluid pressure (PJ. Capillary pressure pushes fluid out of the capillary. Interstitial fluid pressure is negative and acts as a suction pulling fluid out of the capillary. Osmotic forces include plasma colloid osmotic pressure (np) and interstitial fluid colloid osmotic pressure (n,). These forces are caused by proteins that pull fluid toward them. The sum of these four forces results in net filtration of fluid at the arteriolar end of the capillary (where Pc is high) and net reabsorption of fluid at the venular end of the capillary (where Pc is low).

Increased capillary permeability may allow plasma proteins to leak into the interstitial spaces of a tissue. The presence of excess protein in these spaces causes an increase in interstitial fluid colloid osmotic pressure and pulls more fluid out of the capillaries. Mediators of inflammation such as histamine and bradykinin, which are active following tissue injury and during allergic reactions, increase capillary permeability and cause swelling. 

A decrease in the concentration of plasma proteins causes a decrease in the plasma colloid osmotic pressure. As a result, filtration is increased, reabsorption is decreased, and fluid accumulates in the tissue. Most plasma proteins are made in the liver therefore, a decrease in protein synthesis due to liver failure is an important cause of this condition. Malnutrition may also impair protein synthesis. Finally, kidney disease leading to proteinuria (protein loss in the urine) decreases the concentration of plasma proteins. 

Albumin is the most abundant (about 55%) of the plasma proteins. An important function of albumin is to bind with various molecules in the blood and serve as a carrier protein, transporting these substances throughout the circulation. Substances that bind with albumin include hormones amino acids fatty acids bile salts and vitamins. Albumin also serves as an osmotic regulator. Because capillary walls are impermeable to plasma proteins, these molecules exert a powerful osmotic force on water in the blood. In fact, the plasma colloid osmotic pressure exerted by plasma proteins is the only force that retains water within the vascular compartment and therefore maintains blood volume (see Chapter 15). Albumin is synthesized in the liver. 

Plasma colloid osmotic pressure nGC) is generated by the plasma proteins. These proteins exert an osmotic force on the fluid, which opposes filtration... 

Fraenkel-Conrat H, Mecham DK. The reaction of formaldehyde with proteins demonstration of intermolecular cross-linking by means of osmotic pressure measurements. J. Biol. Chem. 1949 177 477-486. 

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