Biochemical responses, balance

Physiological, pharmacological, and biochemical responses do not usually lead to a tissue lesion, although there may be organ failure as a result. They may result from interactions of chemicals with receptors or specific enzymes leading to anoxia, inhibition of cellular respiration, respiratory failure, changes in pH, temperature, blood pressure or electrolyte balance, for example. 

The perception of flavor is a fine balance between the sensory input of both desirable and undesirable flavors. It involves a complex series of biochemical and physiological reactions that occur at the cellular and subcellular level (see Chapters 1-3). Final sensory perception or response to the food is regulated by the action and interaction of flavor compounds and their products on two neur networks, the olfactory and gustatory systems or the smell and taste systems, respectively (Figure 1). The major food flavor components involved in the initiation and transduction of the flavor response are the food s lipids, carbohydrates, and proteins, as well as their reaction products. Since proteins and peptides of meat constitute the major chemical components of muscle foods, they will be the major focus of discussion in this chapter. 

Vitamin D-binding protein and its associated vitamin are lost in nephrotic urine. Biochemical abnormalities in nephrotic patients (children and adults) include hypocalcemia, both total (protein-bound) and ionized hypocalciuria, reduced intestinal calcium absorption and negative calcium balance reduced plasma 25-hydroxycholecalciferol and 24,25-dihydroxycholecalciferol and, surprisingly, also 1,25-dihydroxycholecalciferol and blunted response to parathormon (PTH) administration and increased PTH levels. Clinically, both osteomalacia and hyperparathyroidism have been described in nephrotic patients, more commonly in children than in adults, but bone biopsies are commonly normal, and clinically significant bone disease is very rare in nephrotic subjects. There is, however, evidence that patients with renal failure accompanied by nephrotic range proteinuria may be particularly prone to develop renal osteodystrophy. 

It is clear from these studies that external mechanical loading not only affects the cellular response through changes in genetic expression by cells, but it also sets into motion a cascade of events that balances cellular biochemical and biomechanical responses with changes in the environmental... 

Metabolic fluxes are responsible for maintaining the homeostatic state of the cell. This condition may be translated into the assumption that the metabolic network functions in or near a non-equilibrium steady state (NESS). That is, all of the concentrations are treated as constant in time. Under this assumption, the biochemical fluxes are balanced to maintain constant concentrations of all internal metabolic species. If the stoichiometry of a system made up of M species and N fluxes is known, then the stoichiometric numbers can be systematically tabulated in a... 

Minerals dissolved in the body fluids are responsible for nerve impulses and the contraction of muscles, as well as for water- and acid-base balance. They play an important role in maintaining the respiration, heart rate, and blood pressure in normal limits. Deficiency of minerals in the diet may lead to severe, chronic clinical signs of diseases, frequently reversible after their supplementation in the diet, or following the total parenteral nutrition. Their influence on biochemical reactions in living systems also makes it possible to use them intentionally in many food processes. 

Saxena and Pathak (3) made systematic studies of BPH-rice plant interactions, particularly behavioral and physiological responses involved in BPH establishment on rice plants. They found that resistant plants were as suitable as susceptible plants in eliciting some responses. The interaction of all the responses determined the overall susceptibility or resistance to the pest. Saxena and Pathak (3) Saxena and Puma (30), and Saxena and Okech (31) also determined the biochemical basis of suitability of rice varieties to BPH. They found that allelochemics and nutritive balance of rice varieties were important in eliciting optimal or suboptimal responses, thereby affecting BPH ability to establish on rice plants. The steam distillate extracts of resistant varieties and of the barnyard grass were repellent and, when applied topically, caused high mortalities even at low doses. In contrast, extracts of susceptible varieties possessed moderate to high attractance and were relatively nontoxic to the insect. Recently, Obata et al. (32) isolated and identified constituents of BPH attractant in the Japanese rice cultivar Nihonbare . 

Thus, low levels of such neurotransmitters as serotonin, dopamine, and norepinephrine are the biochemical basis of anxiety and depression, whether the levels of these chemicals are naturally low, as for Jennifer, or have fallen in response to a series of crises, as for Dave. That s why a psychiatrist s first task is often to determine which chemicals are out of balance. 

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