Plasma substitutes, essential

Other important examples are blood and blood products, which are collected and processed in sterile containers, and plasma substitutes, for example dextrans and degraded gelatin. Dextrans, glucose polymers consisting essentially of (1 - 6) a-links, are produced as a result of the biochemical activities of certain bacteria of the genus Leuconostoc, e.g. L. mesenteroides (see Chapter 25). 

To eliminate the threat of shock, replenishment of the circulation is essential. With moderate loss of blood, administration of a plasma volume expander may be sufficient Blood plasma consists basically of water, electrolytes, and plasma proteins. However, a plasma substitute need not contain plasma proteins. These can be suitably replaced with macromolecules ( colloids ) that like plasma proteins, (1) do not readily leave the circulation and are poorly filtrable in the renal glomerulus and (2) bind water along with its solutes due to their colloid osmotic properties. In this manner, they will maintain circulatory filling pressure for many hours. On the other hand, volume substitution is only transiently needed and therefore complete elimination of these colloids from the body is clearly desirable. 

In EFA deficiency, oleic acid can be dehydrogenated to yield polyunsaturated fatty acids (PUFAs) that are nonessential and do not substitute for the essential fatty acids. One suchPUFA is 5,8,11-eicosatrienoic acid, which occurs in significant amounts in heart, liver, adipose tissue, and erythrocytes of animals fed diets deficient in EFAs but decreases after supplementation with linoleic or linolenic acids. Its appearance in tissues and plasma has been used in the assessment of EFA deficiency. 

Linoleic acid normally is converted to arachidonic acid (a tetraene fatty acid). If linoleic acid is unavailable, oleic acid will be substituted, which results in production of eicosatrienoic acid (atriene fatty acid) as the metabolic end product. Therefore essential fatty acid deficiency can be detected on the basis of decreased tetraene production and increased triene production. Normally, the ratio of trienes to tetraenes is less than 0.4 when this ratio becomes greater than 0.4, the diagnosis of essential fatty acid deficiency is established. Analysis of plasma fatty acids, however, is expensive and not widely available. 

Witte et al. [79] found that the corrosion rates of AZ91D and LAE442 measured in vivo were orders of magnitude lower than those measured in substitute ocean water prepared according to ASTM-Dl 141-98 [80]. Subsequently, in vitro testing has been carried out in a variety of solutions including (i) Hank s solution, (ii) simulated body fluid (SBF), (iii) artificial plasma (AP), (iv) phosphate buffered saline (PBS) and (v) minimum essential medium (MEM, Invitrogen). 

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