Homeostatic mechanisms situation

Homeostatic mechanisms also allow animals to control their intracellular pH very strictly. In humans for example, blood pH (usually taken as a reliable but indirect measure of cellular pH) is 7.4 0.04. At 37 °C cytosolic pH is actually slightly lower at about 7.0 but different compartments within the eukaryotic cells may have quite different pH, for example, lysosomes have an internal pH of about 5 the inside of a mitochondrion is more alkaline than the outside whilst the inside of a phagosome in a white blood cell is more acidic than its surrounding cytosol, both situations arising due to proton pumping across a membrane. 

The reversal of the pH gradient at tumor cells has been known for quite some time. While, in normal tissue, the extracellular medium is slightly basic, the opposite situation is observed in tumor tissues [104]. The intracellular pH, on the other hand, is almost the same for both kinds of cells due to homeostatic mechanisms. Therefore triggering MRI contrast agents by pH variation seems like a promising method for highlighting tumors. Several pH sensitive MRI contrast agents have already been developed. 

SYMPATHOMIMETICS-EPINEPHRINE ANTIDIABETIC DRUGS May t antidiabetic therapy requirement Epinephrine causes the release of glucose from the liver and is an important defence/homeostatic mechanism. Hyperglycaemia may occur due to an antagonistic effect Larger doses of antidiabetic therapy may be needed during the period of epinephrine use, which is usually in the short term or in emergency situations... 

The extrapolation of animal toxicology data and combination with human exposure data aiay be used to estimate risk for those situations where exposure is likely. Methods for integrating these data as well as the assumptions for extrapolation from the animal studies are dependent upon the safety data. Risk assessment includes consideration of the type of toxicity involved and its potency, species comparisons, time considerations, dose response, kinetics of homeostatic mechanisms, and mechanisms of toxicity. When the essential components for extrapolations are well understood, more precise estimates can be made. In the absence of such understanding, more conservative approaches are appropriate. 

The interactions between rates and efficiencies are complex, involving homeostatic mechanisms that influence an insect s behavior, physiology, growth and reproduction. These interactions are influenced by starvation, induction of preference, nutrients, allelochemics and various environmental (climatic) factors. Classification of a chemical as a repellent, deterrent, feeding suppressant, toxin or digestibility-reducer may be situation-dependent, dose-dependent, and involve chemicals, behavioral and physiological feedback systems (Blau et al., 1978 Duffey, 1977,1980 Reese, 1979 Grabstein and Scriber, 1981). 

The autonomic nervous system through homeostatic mechanisms adjusts airway size to meet the body s demands. An imbalance of these mechanisms may increase the work of breathing throughout an asthmatic attack. During relaxed situations when there is a decreased demand for airflow, parasympathetic stimulation promotes broncho-constriction leading to increased air-... 

So far it has been implied that adaptation of homeostatic mechanisms within the limits of overload may be without risk in the short term, but the situation may be different when one considers chronic stress over a lifespan. Thus it has been claimed that overstimulation of pancreatic secretion of insulin by excessive consumption of sugar can lead to exhaustion of the homeostatic process, i.e. while adaptation can be sustained in the short term, ultimately the control breaks down and diabetes results. Hence the acute toxicity of sucrose is low and probably results from dehydration, whereas a completely different mechanism may apply to the chronic toxicity. Acute and short-term tests cannot give a complete picture of the consequences of metabolic overload, and chronic toxicity tests will continue to be required in the foreseeable future—and not merely to assess carcinogenic hazard. 

In general, the eicosanoids derived from AA have potent prothrombotic and proinflammatory activity. In contrast, the eicosanoids derived from EPA have reduced biological activity and are less prothrombotic and proinflammatory. Eicosanoid production is generally tightly controlled through homeostatic mechanisms. However, eicosanoid production can be significantly altered in situations in which endothelial dysfunction, atherosclerosis and plaque rupture, or various thrombotic or inflammatory conditions are present. 

Regarding the adrenal steroids, the behavioral activation of hormonal secretion in stress is part of a mechanism for restoring homeostatic balance. For example, an encounter with a predator may require rapid evasive action, in which neural activity and rapidly mobilized hormones such as epinephrine play a role. Adrenal steroid secretion is slower, reaching a peak minutes after the stressful event, and therefore is not expected to play a role in coping with the immediate situation. If the evasive action is successful and... 

These studies show that it is possible to predict the time course of drug effects in vivo in situations in which complex homeostatic control mechanisms are operative. As such, they form the basis for the development of an entirely new class of pharmacokinetic-dynamic models. These models are important for the development of new drugs and the application of such drugs in clinical practice. For example, on the basis of this kind of model, it becomes possible to predict whether withdrawal symptoms will occur on cessation of (chronic) drug... 

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