Tissues macroscopic

It is truly possible to imagine the characteristics of an ideal radiopharmaceutical only in the context of a specific disease and organ system to which it might be appHed. Apart from the physical factors related to the radioisotope used, the only general characteristic that is important in defining the efficacy of these materials is the macroscopic distribution in the body, or biodistribution. This time-dependent distribution at the organ level is a function of many parameters which may be divided into four categories factors related to deUvery of the radiopharmaceutical to a particular tissue factors related to the extraction of the compound from circulation factors related to retention of the compound by that tissue and factors deterrnined by clearance. The factors in the last set are rarely independent of the others. 

Although the pH-partition hypothesis and the absorption potential concept are useful indicators of oral drug absorption, physiologically based quantitative approaches need to be developed to estimate the fraction of dose absorbed in humans. We can reasonably assume that a direct measure of tissue permeability, either in situ or in vitro, will be more likely to yield successful predictions of drug absorption. Amidon et al. [30] developed a simplified film model to correlate the extent of absorption with membrane permeability. Sinko et al. [31] extended this approach by including the effect of solubility and proposed a macroscopic mass balance approach. That approach was then further extended to include facili-... 

From the atomic to the macroscopic level chirality is a characteristic feature of biological systems and plays an important role in the interplay of structure and function. Originating from small chiral precursors complex macromolecules such as proteins or DNA have developed during evolution. On a supramolecular level chirality is expressed in molecular organization, e.g. in the secondary and tertiary structure of proteins, in membranes, cells or tissues. On a macroscopic level, it appears in the chirality of our hands or in the asymmetric arrangement of our organs, or in the helicity of snail shells. Nature usually displays a preference for one sense of chirality over the other. This leads to specific interactions called chiral recognition. 

At a macroscopic biological level, the damage to tissue is related to the concentration of photosensitizer and dioxygen in the tissues being irradiated, and to the light flux the key mechanistic questions here are—in which compartment does the photosensitizer accumulate,... 

For high-speed FLIM applications, including real-time imaging of biological tissue using endoscopes or macroscopes, as well as for imaging live cell dynamics and microfluidic systems, we have... 

Bone is an extremely dense connective tissue that, in various shapes, constitutes the skeleton. Although it is one of the hardest structures in the body, bone maintains a degree of elasticity owing to its structure and composition. It possesses a hierarchical structure and, as most of the tissues, is nanostructured in fact, it is a nanoscaled composite of collagen (organic extracellular matrix) and hydroxycarbonate apatite, (HCA, bone mineral). This nanostructure is in intimate contact with the bone cells (several microns in size), which result (at the macroscopic level) in the bone tissue. Figure 12.2 shows the bone hierarchical ordering from the bone to the crystalline structure of HCA. 

Albers, P.H., D.E. Green, and C.J. Sanderson. 1996. Diagnostic criteria for selenium toxicosis in aquatic birds dietary exposure, tissue concentrations, and macroscopic effects. Jour. Wildl. Dis. 32 468-485 Correction. Jour. Wildl. Dis. 32 725-726. 

Young In any calculation you allow for a number of variables in terms of trying to model the system of action potential propagation. We know that action potentials have to travel within a fasciculus, which is a macroscopic 1—2 mm connective tissue grouping of bundles. Those do not follow a very tortuous route, at the most they wind once or twice over 30 cm, but not much larger than that. The best simulation that s been done using action potential alone used around nine parameters and was totally unrealistic. I probably didn t point it out but the dashed line that overlayed my clinical contraction was where I actually assumed a 350 /tm size bundle. I assumed an intracellular Ca2+ wave and cell activity for 20 s, and I was able to fit it except for the foot at the end (Young 1997). 

Ad. 4. Alteration of anatomical features. Finally, several studies have attempted to manipulate the macroscopic features of muscle/meat tissue in order to verify or disprove the intra-/extra-cellular model. Efforts have been made to disrupt cell membranes by glycerination and DMSO treatment in order to make assessment of the potential role of membranes possible.30,40,41 All these studies showed unaltered relaxation behaviour upon membrane disintegration, which suggests that intact cell membranes in themselves are not necessary for a non-mono-exponential relaxation. Irrelevance of membranes... 

Postmortem Procedures. Rabbits are euthanized by lethal dose of a barbiturate soon after the last vaginal irritation scores are collected. The vagina is opened by longitudinal section and examined for evidence of mucosal damage such as erosion, localized hemorrhage, and so on. No other tissues are examined. No tissues are collected. After the macroscopic description of the vagina is recorded, the animal is discarded. 

However, an intrinsic physiological requirement for the cornea is the maintenance of its transparency, ensuring proper vision. This clarity as well as maintenance of the corneal shape (surface smoothness and total thickness) is critical to refraction. The unique transparency of corneal tissues is strongly dependent on their avascularity and a functionally intact endothelium, which are crucial for the maintenance of both stromal clarity and thickness by regulating corneal hydration. Macroscopically, the cornea is a transparent and avascular tissue... 

The intention to study transport processes at pulmonary epithelia, however, raised two particular problems (i) the apical side of these epithelia is typically in contact with air rather than with a liquid and (ii) in order to maximize the surface area, the lungs have a complex treelike structure, ending in millions of tiny alveolar bubbles. The total surface area of the human alveolar epithelium is almost half of that of the intestines (100-120 m2), with its macroscopic appearance resembling a sponge, and it is virtually impossible to use such a tissue for transport experiments in a diffusion-chamber setup. 

At termination, full macroscopic examination and microscopic examination of limited tissues (usually heart, lungs, liver, kidneys, spleen and any tissues related to route of administration tissues) are performed. Blood levels of the drug are not usually determined, as often an assay is still to be developed. Systemic exposure can be approximated, however, using a scaling model (see Section 3.8.3.S). 

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