Physiological factors defined

Well-defined physiological factors pH value Concentration of salts Surfactants Enzymes... 

Less well-defined physiological factors Agitation... 

Previously, in vitro recovery was the most commonly used method for estimating ECF concentrations of a substance (Benveniste, 1989 Stable et al., 1991). To determine in vitro recovery, the probe is immersed in a known concentration of the analyte, preferably at brain temperature, and perfused with a medium free of the analyte. Percent recovery (or relative recovery) is defined as the ratio between two measures (a) the concentration of the analyte that is recovered from the probe and (b) the known concentration. In vitro calibration is limited and no longer considered appropriate, because it fails to factor in physiological factors, such as extracellular tortuosity and neurochemical reuptake, which iirfluence in vivo but not in vitro recovery (Benveniste, 1989 Benveniste and Huttemeier, 1990 Bungay et al., 1990 Hsiao et al., 1990 Morrison et al., 1991 Parsons et al., 1991b Parsons and Justice, 1992 Stable, 2000). 

Various different sets of criteria are used to interpret the quality of a food product. The term "acceptability" is a practical approach when comparing it to the "quality limit". Below this limit a product is then rejected. The acceptance limit is mainly defined by economic and physiological factors, whereas the quality of a product is basically defined by its fundamental characteristics. For food products such as fruits and vegetables, properties such as color, firmness, and taste will change over time. Shelf life is calculated as the time before the product qualities drop below the acceptance limit under standardized storage conditions (Tijskens, 2000 Rico et al., 2007). 

Although various criteria are used in interpreting the quality and acceptance of a food product, the acceptance limit is still mainly defined by economic and physiological factors (Rico et alv 2007). Research has been intensified, shifting the focus on the implications of decontamination on pathogen behavior, in association with the overall microbial ecology of food products (Samelis et al., 2002). 

Physiologic factors affecting tubular secretion are renal plasma flow, plasma binding, and intrinsic clearance. Renal extraction ratio is defined as the ratio of renal clearance and renal plasma flow. The extraction ratio of a drug can be classified as restrictive or... 

Some of the observed patterns of accumulation of PAHs from laboratory and field studies may be explained by the rates of uptake and elimination. These rates can be affected by several environmental and physiological factors hence, care must be taken to define the conditions under which bioaccumulation is observed. A laboratory investigation that compared accumulation of PAHs in oysters Crassostrea virginica) and clams Mercen-aria mercenaria) from field-contaminated sediments found that the oyster accumulated about three times as much PAH as the clam (Bender et al. 1988). For most individual PAHs, the ratios between oyster and clam tissue concentrations were between 1 and 5. The authors found no species differences in uptake clearance k and concluded that the differences in equilibrium BCF values resulted from the higher elimination rate k in the clam for most PAHs, which would lead to lower body burdens for a given... 

In human exercise physiology, fatigue is often defined as an inability of a muscle or a group of muscles to sustain the required or expected force (Edwards, 1981). This definition is very applicable for the study of factors limiting dynamic or isometric exercise in intact organisms at varying intensities. 

The solubility of the drug is affected by several physiological and physicochemical factors [26], Drug properties are defined not only by the chemical structure but also by the solid material, and a drug can potentially exist in many different solid state forms which may differ in solubility. Amorphous materials tend to show much higher aqueous solubility than crystalline forms of the same compound and different crystal modifications of the same compound may also have different solubility (e.g., [25]). 

The main input parameter used to define the highest possible drug concentration in the intestine and to calculate the dissolution rate in the GI tract is the solubility of the dmg in the GI fluids. As described earlier (Sect. 21.2) there are several, both physiological and physicochemical, factors that can affect the solubility in the GI tract and it is therefore important to consider the relevance of the solubility data generated in the early drug discovery phase. A common approach is to use in silico models to predict the solubility of drugs (e.g., [5]). The advantage of this approach is that only the chemical... 

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