Blood-tissue solute exchange

Part II of this book represents the bulk of the material on the analysis and modeling of biochemical systems. Concepts covered include biochemical reaction kinetics and kinetics of enzyme-mediated reactions simulation and analysis of biochemical systems including non-equilibrium open systems, metabolic networks, and phosphorylation cascades transport processes including membrane transport and electrophysiological systems. Part III covers the specialized topics of spatially distributed transport modeling and blood-tissue solute exchange, constraint-based analysis of large-scale biochemical networks, protein-protein interactions, and stochastic systems. 

One-dimensional advection will be used in Chapter 8 as a component in models of cellular biochemical systems that are coupled to blood-tissue solute exchange. 

A better solution can be achieved by adding one or more additional data sets. For example, if counts over an extremity are included in the model fit, it will be possible to determine the shape of the disappearance curve from the slow-exchange compartment, since the extremity contains only blood and slow-exchange tissues such as skin, muscle... 

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. 

Bulk flow plays only a minor role in the exchange of specific solutes between blood and tissue cells. A far more important function of bulk flow is to regulate distribution of extracellular fluid between the vascular compartment (plasma) and the interstitial space. Maintenance of an appropriate circulating volume of blood is an important factor in the maintenance of blood pressure. For example, dehydration and hemorrhage will cause a decrease in blood pressure leading to a decrease in capillary hydrostatic pressure. As a result, net filtration decreases and net reabsorption increases, causing movement, or bulk flow, of extracellular fluid from interstitial space into the vascular compartment. This fluid shift expands the plasma volume and compensates for the fall in blood pressure. 

General Concepts. The capillary endothelium is the major site of exchange for nutrients, hormones, and proteins between blood and tissues. When the solute is a macromolecule, transport occurs through pores in the endothelium. Capillaries in the general circulation are highly permeable to water and glucose, and nearly impermeable to proteins larger than albumin (Table 5.8). Capillary permeability is qualitatively different from cell... 

Riviere and Williams (1992) suggested that when the exchanging capillary volume was increased from 1 to 2 ml and all other model parameters were kept constant, higher solute absorption rates resulted (Figure 13.6). Hence, they snggested that it was possible that increases in percutaneons absorption could be mistakenly attribnted to an increased dermal blood flow when the effect was caused by an increase in the volume of tissue actually perfused. 

Blood-brain barrier the barrier that must be crossed when water and solutes are exchanged between blood and extracellular fluid of the central nervous system. Many substances, when injected intravenously, become distributed throughout the various tissues and organs of the body, except for the central nervous system, e. g. acidic dyes, bile acids, tetanus toxin, sodium ferricyanide, trypan blue. 

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