Absorption and Assimilation

The absorption, bioavailability, and retention of radionuclides in mammals are modified by the age, sex, species, and diet of the organism season of collection the chemical form of the radionuclide in tissue and blood residence time in the digestive tract preferential accumulation by selected organs and tissues and many other variables. 

Many radionuclides preferentially accumulate in certain organs or tissues, but the critical organ is different for different radionuclides liver for Mn, erythrocytes and spleen for 

Alkali metals (K, Rb, Cs) behave similarly and sometimes one is accumulated preferentially when another is deficient a similar case is made for Sr and Ca. The most important alkali metal isotope is Cs because of its long physical half-life (30 years) and its abundance as a fission product in fallout from nuclear weapons and in the inventory of a nuclear reactor or a fuel-reprocessing plant. Cesium behaves much like potassium. It is rapidly absorbed into the bloodstream and distributes throughout the active tissues of the body, especially muscle. The P and y radiation from the decay of Cs and its daughter, result in 

Beacause Ra and °Sr are metabolic analogs of calcium, they are deposited in the skeleton both isotopes are associated with bone cancers. In pregnant rats, the total amount of Ra transferred from the dam to the 

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These results indicate it may be possible to improve the efficiency of absorption and assimilation by altering the process of regulation. However the mechanisms governing regulation are poorly understood. It is not known whether the regulation is linked to the concentration of NH4+ or NOs" itself or to the concentrations of products of N assimilation downstream from NH4+ or NOs", such as particular amino acids. Nor is it known what the targets of the resulting feedback mechanisms are. 

These results suggest various possibilities for increasing the efficiency of N absorption and assimilation. The fact that the NH4+ and NO3 transport systems... 

An obligatory component, which results from the energy cost of digestion, absorption and assimilation of the food. 

Of nutrient chelates in the human diet, oxalates and phytules arc Ihe most common. Oxalic acid, found principally in spinach, rhubarb leaves, beet leaves, some fruits, and mushrooms, is u primary chelator of calcium. Oxalate present in pineapple, kiwifmil, and possibly in other foods, occurs as calcium oxalale. CaCiOj. This compound is in the form of needle-like crystals, known as raphidcs. which can produce painful sensations in the mouth when eaten raw. The effects of oxalic acid in the diet may he twofold. First, it forms strong chelates with dietary calcium, rendering the culcium unavailable for absorption and assimilation. Secondly, absorbed oxalic acid causes assimilated Ca to be precipitated as insoluble salts that accumulate in the renal glomeruli and contribute to the formation of renal calculi. 

The routes for entry of essential oils into the body are by absorption from vaporizers, baths and skin massage. Oral administration and ingestion of essential oils are the most potent and effective methods, while rectal and vaginal routes can be harmful if the mucous membranes are damaged. This is summarized in Fig. 8.2, which also shows their absorption and assimilation and their loss from the body by elimination or excretion. 

There are instances in which, despite an apparently adequate intake of trace elements, either in the diet alone or from the combination of diet plus supplementation, the clinical symptoms persist. This may be due to a flaw or deficiency in the underlying, highly complicated biochemistry of trace element absorption and assimilation such a deficiency may be because there is an inadequate presence of some essential co-factors. 

Gage, S. H., and P. A. Fish Fat digestion, absorption and assimilation in man and animals as determined by the dark-field microscope and a fat soluble dye. Amer. J. Anat. 34,1 (1924). Gitlin, D., and D. Cornwell Plasma lipoprotein metabolism in normal individuals and nephrotic children. J. din. Invest. 35, 706 (1956). 

Figure 11 The different steps of nitrogen metabolism in the extraradical hyphae, ccto-mycorrhizal roots, and roots of the host plant. I, absorption 2, assimilation 3. storage 4. translocation A, extramatrical hyphae B. ectomycorrhizal sheath C, Hartig net D, root cortical cells AA amino. acids.

Responses to activation of the parasympathetic system. Parasympathetic nerves regulate processes connected with energy assimilation (food intake, digestion, absorption) and storage. These processes operate when the body is at rest, allowing a decreased tidal volume (increased bronchomotor tone) and decreased cardiac activity. Secretion of saliva and intestinal fluids promotes the digestion of foodstuffs transport of intestinal contents is speeded up because of enhanced peristaltic activity and lowered tone of sphincteric muscles. To empty the urinary bladder (micturition), wall tension is increased by detrusor activation with a concurrent relaxation of sphincter tonus. 

Because these patients may be exquisitely sensitive to the effects of medication, the general principle is always to start with the lowest dose and increase medication only if necessary and very slowly. The route of administration may also be problematic, because some patients have very poor absorption, and thus medications may not be adequately assimilated. Parenteral administration is also often complicated by decreased muscle mass, thrombocytopenia, and difficulty in finding veins. 

Absorption The assimilation of a solute, gas, or liquid into the interior of a solid material, an absorbent. Absorption may include the migration of solutes into internal pores or the migration or exchange of atoms within the crystalline structure of a mineral. Some researchers use the generic term sorption to refer to a natural or artificial process where both absorption and adsorption may be involved or if absorption and adsorption cannot be distinguished (compare with adsorption and sorption). 

Nutri tion.—That branch of Physiology which includes the absorption, distribution and assimilation of food stufis. 

The general principles of metal uptake by biota from soil systems are treated in chapters 7 to 10 of the book. The same rules govern radionuclide uptake by biological systems. Uptake and assimilation depend on the chemical and biological properties of the element. The rate-limiting step for the uptake of many radionuclides, those strongly immobilized by soil constituents, is the movement to the interface between the soil solution and the biological membrane. If absorption is more rapid than the movement of the solute to the interface, uptake becomes diffusion limited. The adsorption properties of the soil are therefore determinant. 

Exposure pathways for adult amphibians include soils (dermal contact, liquid water uptake), water (dermal contact with surface water), air (cutaneous and lung absorption), and diet (adults are carnivores). All routes of exposure are affected by various physical, chemical, and other factors. Dietary exposure in adults, for example, is related to season of year, activity rates, food availability, consumption rate, and assimilation rates. Knowledge of these modifiers is necessary for adequate risk assessment of mercury as a possible factor in declining amphibian populations worldwide. 

Thus, in considering two important sources of n-3 fatty acids, namely, MO and SBO, although n-3 fatty acids, especially DHA, are located primarily in the sn-2 position in MO, they are mainly in the sn-1 and sn-3 positions of SBO (Table 2) (6). These differences undoubtedly have a definite influence on their assimilation, absorption, and health benefits as well as reactions in which they are involved. 

Osmond,C.B. CO2 assimilation and dissimilation in the light and dark in CAM plants. In CO2 metabolism and plant productivity. Burris,R.H., Black, C.C. (eds.), pp. 217-233. Baltimore, London, Tokyo University Park Press 1976 Osmond, C.B. Ion absorption and carbon metabolism in cells of higher plants. In Transport in plants II, Part A. Enzyclopedia of plant physiology. New Series, Vol. II. Luttge,U., Pitman,MG. (eds.), pp.347-366. Berlin, Heidelberg, New York Springer 1976b Osmond,C.B. Crassulacean Acid Metabolism A curiosity in context. Ann. Rev. Plant Physiol. 29,379-414(1978)... 

Therefore, it could be concluded that, both selenite (SeOs- ) and selenate (Se04" ) are the major forms that are toxic to nonaccumulators because they are readily absorbed and assimilated by plants. Increased Se levels in plants suppress their concentrations of N, P, and S, as well as several amino acids, thus high Se concentrations inhibit the absorption of metals, mainly Mn, Zn, Cu, and Cd. These relationships are dependent on the ratio between the elanents. The application of N, P, and S is known to help in detoxifying Se, which may be a result either of depressing the Se uptake by roots or of establishing a beneficial ratio of Se to these elements. 

The points of Figure 26 were calculated from Equation (25) using a= 12 A and assimilating the potentiometric results to the free fraction y. Oosawa s treatment best fits the experimental data for 2>1. The ion-selectivity [20] (Figure 25) or the ultrasonic absorption [21] increases with the number of counterions whilst the effective ionisation approaches the y2 1 limit. 

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