Human body metabolism

Oxidation-reduction reactions are among the most important in chemistry, biochemistry, and industry. Combustion of coal, natural gas, and gasoline for heat and power are redox reactions, as are the recovery of metals such as iron and aluminum from their oxide ores and the production of chemicals such as sulfuric acid from sulfur, air, and water. The human body metabolizes sugars through redox reactions to obtain energy the reaction products are liquid water and gaseous carbon dioxide. 

In 1970, Danish scholar Fanger summed up the two widely used evaluating indicators of heat comfort which are PMV (Predicted Mean Vote) and PPD (Predicted Percentage of Dissatisfied) (Bo S S et al. 2011). These two indicators combine six factors which are air temperature, average radiant temperature, air velocity, air humidity, human body metabolism and heat-resistance of clothes, so they are the most comprehensive evaluating indicators of heat environment until now and have been compiled into international standard ISO7730. 

Because the human body metabolizes inorganic arsenic by reductive methyla-tion, all the reaction products have to be analyzed. Body fluids such as urine have a high chloride content therefore, interferences are observed due to the... 

Cobalamin (vitamin B12) a water-soluble B vitamin, normally involved in the human body metabolism, affecting DNA synthesis and regulation, fatty acid synthesis and energy production. Supplied by animal food, its defieiency leads to macrocytic anaemia, decreased bone marrow cell production, neurological problems, as well as metabolic issues (methylmalonyl-CoA acidosis, hyperhomocysteinemia). 

Sorbitol (C6H14O6,182.17g/mol) is a sugar alcohol (polyol) and water soluble. Its International Union of Pme and Applied Chemistry name is (2S,3R,4R,5R)-Hexane-l,2,3,4,5,6-hexol, and it is also known as glucitol. It is sweet in taste and the human body metabolizes it slowly. It is naturally foxmd in many fruits, eg, berries (except grapes), cherries, plums, pears, and apples (Budavari et al., 1996 Wrolstad and Shallenberger, 1981). Sorbitol is nontoxic, nonirritant, stable, and chemically inert. It is a noncariogenic chemical, and it is resistant to metabolism by oral bacteria, prevents the formation of dental caries, and is less vulnerable to mold growth. 

Nitronaphthalene is metabolized to the carcinogenic 2-naphthylarnine in the human body (39). Respirators, protective clothing, proper engineering controls, and medical monitoring programs for workers involved in making by-product 2-nitronaphthalene should be used. 

Biosynthesis of Protein. The dynamic equilibrium of body protein was confirmed by animal experiments using A/-labeled amino acids in 1939 (104). The human body is maintained by a continuous equilibrium between the biosynthesis of proteins and their degradative metabolism where the nitrogen lost as urea (about 85% of total excreted nitrogen) and other nitrogen compounds is about 12 g/d under ordinary conditions. The details of protein biosynthesis in living cells have been described (2,6) (see also Proteins). 

Carbon dioxide production The quantity of carbon dioxide exhaled from the human body, depends on the metabolic rate. 

Suppose we know the reaction enthalpy for one temperature but require it for another temperature. For instance, the temperature of the human body is about 37°C, but the data in Appendix 2A are for 25°C. Does an increase of 12°C make much difference to the reaction enthalpy of a metabolic process ... 

The human body generates a steady flow of acidic by-products during its normal metabolic processes. Foremost among these is carbon dioxide, which is a major product of the reactions the body uses to produce energy (see Section 14-). An average person produces from 10 to 20 mol (440 to 880 g) of CO2 every day. Blood carries CO2 from the cells to the lungs to be exhaled. In aqueous solution, dissolved CO2 is in equilibrium with carbonic acid H2 O + CO2 H2 CO3... 

PBPK models have also been used to explain the rate of excretion of inhaled trichloroethylene and its major metabolites (Bogen 1988 Fisher et al. 1989, 1990, 1991 Ikeda et al. 1972 Ramsey and Anderson 1984 Sato et al. 1977). One model was based on the results of trichloroethylene inhalation studies using volunteers who inhaled 100 ppm trichloroethylene for 4 horns (Sato et al. 1977). The model used first-order kinetics to describe the major metabolic pathways for trichloroethylene in vessel-rich tissues (brain, liver, kidney), low perfused muscle tissue, and poorly perfused fat tissue and assumed that the compartments were at equilibrium. A value of 104 L/hour for whole-body metabolic clearance of trichloroethylene was predicted. Another PBPK model was developed to fit human metabolism data to urinary metabolites measured in chronically exposed workers (Bogen 1988). This model assumed that pulmonary uptake is continuous, so that the alveolar concentration is in equilibrium with that in the blood and all tissue compartments, and was an expansion of a model developed to predict the behavior of styrene (another volatile organic compound) in four tissue groups (Ramsey and Andersen 1984). 

In the Unites States, the daily intake of 3-carotene is around 2 mg/day Several epidemiological studies have reported that consumption of carotenoid-rich foods is associated with reduced risks of certain chronic diseases such as cancers, cardiovascular disease, and age-related macular degeneration. These preventive effects of carotenoids may be related to their major function as vitamin A precursors and/or their actions as antioxidants, modulators of the immune response, and inducers of gap-junction communications. Not all carotenoids exert similar protective effects against specific diseases. By reason of the potential use of carotenoids as natural food colorants and/or for their health-promoting effects, research has focused on better understanding how they are absorbed by and metabolized in the human body. 

Like other xenobiotics, cannabinoids also undergo extensive metabolism in the human body to increase their hydrophihc properties for a facihtated ehmination. The metaboHsm of A9-THC has been very well investigated. More than 100 metabolites of A9-THC are known [99] and a good overview of the most important human metaboHtes is given in [100]. MetaboHsm takes place mainly in hepatic microsomes, but also in intestines, brain. 

Active transport is of basic importance for life processes. For example, it consumes 30-40 per cent of the metabolic energy in the human body. The nervous system, which constitutes only 2 per cent of the weight of the organism, utilizes 20 per cent of the total amount of oxygen consumed in respiration to produce energy for active transport. 

Determine stability and/or absorption of drugs and follow their metabolism in human body... 

An interesting example of the above difference is l-DOPA 4, which is used in the treatment of Parkinson s disease. The active drug is the achiral compound dopamine formed from 4 via in vivo decarboxylation. As dopamine cannot cross the blood-brain barrier to reach the required site of action, the prodrug 4 is administered. Enzyme-catalyzed in vivo decarboxylation releases the drug in its active form (dopamine). The enzyme l-DOPA decarboxylase, however, discriminates the stereoisomers of DOPA specifically and only decarboxylates the L-enantiomer of 4. It is therefore essential to administer DOPA in its pure L-form. Otherwise, the accumulation of d-DOPA, which cannot be metabolized by enzymes in the human body, may be dangerous. Currently l-DOPA is prepared on an industrial scale via asymmetric catalytic hydrogenation. 

When evaluating the safety of chemicals in humans, it is very important to know the fate of chemicals in the human body and the amounts of exposure in daily activity. This section reviews the metabolic reactions of pyrethroids in humans, and the biomonitoring of pyrethroid metabolites in human urine for the exposure assessment. Mathematical modeling is a useful tool to predict the fate of chemicals in humans. This section also deals with the recent advance of mathematical modeling of pyrethroids to predict the pharmacokinetics of pyrethroids. 

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