Physiology, defined

These models have relatively few parameters, and the parameters have a limited physiological or anatomical meaning. For example, a compartmental volume relates the quantity of the drug to its concentration in a compartment, and does not refer to an anatomically- or physiologically-defined area of the body. 

Flocculins and especially Flo 11 are responsible for morphogenic phenomena such as pseudohyphal growth and biofilm formation in yeast. Biofilm formation is an adhesive phenomenon akin to flocculation. The majority of bacteria exist in highly organized natural biofilm populations rather than in free floating cultures. Within the biofilm, bacteria display coordinated behavior. They form structures, release toxins or emit light. They, sometimes, differentiate to form physiologically defined... 

Burton H, Fabri M. 1995. Ipsilateral intracortical connections of physiologically defined cutaneous representations in areas 3b and 1 of macaque monkeys Projections in the vicinity of the central sulcus. J Comp Neurol 355 508-538. 

A more complete account of the physiologically defined minicolumns can be found in the review by Mountcastle (1997) and in his book on cerebral cortex (Mountcastle, 1998). The sizes of the physiologically defined minicolumns are derived from experiments such as those of Favorov and Whitsel (1988), and Favorov and Diamond (1990), who showed that when electrode penetrations of the somatic sensory cortex of the cat are made slightly off vertical, and the skin stimulated, there is a abrupt shift in receptive field properties of the cortical neurons about midway through the depth of the cortex. Such shifts occur with lateral movements of the recording electrode every 40-50 xm, which indicates that the electrode is moving from one minicolumn to the next one. 

Another example of an experiment showing the sizes of the physiologically defined minicolumns is the nerve regeneration study carried out by Kaas et al. (1981). These experimenters made an initial electrode penetration of the somatic sensory hand area in a monkey s neocortex in a direction more or less parallel to the surface of the cortex and showed that over a considerable distance the same modality type is observed. They then sectioned the median nerve and allowed time for the nerve to regenerate and re-innervate of the skin. The recording experiment was then... 

Andersen R Asanuma, C, Essick, G, Siegel, RM (1990) Corticocortical connections of anatomically and physiologically defined subdivisions within the inferior parietal lobule. J. Comp. Neurol, 296, 65-113. 

It should be stressed that these compartments do not correspond to physiologically defined spaces (e.g. the liver is not a compartment). 

The aroma of fmit, the taste of candy, and the texture of bread are examples of flavor perception. In each case, physical and chemical stmctures ia these foods stimulate receptors ia the nose and mouth. Impulses from these receptors are then processed iato perceptions of flavor by the brain. Attention, emotion, memory, cognition, and other brain functions combine with these perceptions to cause behavior, eg, a sense of pleasure, a memory, an idea, a fantasy, a purchase. These are psychological processes and as such have all the complexities of the human mind. Flavor characterization attempts to define what causes flavor and to determine if human response to flavor can be predicted. The ways ia which simple flavor active substances, flavorants, produce perceptions are described both ia terms of the physiology, ie, transduction, and psychophysics, ie, dose-response relationships, of flavor (1,2). Progress has been made ia understanding how perceptions of simple flavorants are processed iato hedonic behavior, ie, degree of liking, or concept formation, eg, crispy or umami (savory) (3,4). However, it is unclear how complex mixtures of flavorants are perceived or what behavior they cause. Flavor characterization involves the chemical measurement of iadividual flavorants and the use of sensory tests to determine their impact on behavior. 

Dmg distribution into tissue reservoirs depends on the physicochemical properties of the dmg. Tissue reservoirs include fat, bone, and the principal body organs. Access of dmgs to these reservoirs depends on partition coefficient, charge or degree of ionization at physiological pH, and extent of protein binding. Thus, lipophilic molecules accumulate in fat reservoirs and this accumulation can alter considerably both the duration and the concentration—response curves of dmg action. Some dmgs may accumulate selectively in defined tissues, for example, the tetracycline antibiotics in bone (see Antibiotics,tetracyclines). 

The biological response to chemical insult may take numerous forms, depending on the physicochemical properties of the material and the conditions of exposure. Listed below are some of the more significant and frequendy encountered types of injury or toxic response they may be defined in terms of tissue pathology, altered or aberrant biochemical processes, or extreme physiological responses. 

The clinical performance of a hemodialy2er is usually described in terms of clearance, a term having its roots in renal physiology, which is defined as the rate of solute removal divided by the inlet flow concentration as shown in equation 7, where Cl is clearance in ml,/min and all other terms are as defined previously except that, in deference to convention, flow rates are now expressed in minutes rather than seconds and feed side (/) is now synonymous with blood flow on the luminal side. 

A model can be defined as a set of relationships between the variables of interest in the system being investigated. A set of relationships may be in the form of equations the variables depend on the use to which the model is applied. Therefore, mathematical equations based on mass and energy balances, transport phenomena, essential metabolic pathway, and physiology of the culture are employed to describe the reaction processes taking place in a bioreactor. These equations form a model that enables reactor outputs to be related to geometrical aspects and operating conditions of the system. 

Operational model, devised and published by James Black and Paul Leff (Proc. R. Soc. Lond. Biol. 220,141-162, 1983), this model uses experimental observation to describe the production of a physiological response by an agonist in general terms. It defines affinity and the ability of a drug to induce a response as a value of x, which is a term describing the system (receptor density and efficiency of the cell to convert an activated receptor stimulus into a response) and the agonist (efficacy). It has provided a major advance in the description of functional effects of drugs see Chapter 3.6 for further discussion. 

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