Site of Entry

It is logical to suspect that insecticides would penetrate the thinner, less complex regions of the cuticle more rapidly than the thicker parts. Evidence shows that thin-cuticle areas 

There is another theory, also supported by experimental evidence, that a contact insecticide spreads laterally within the integument and then reaches the site of toxic action via the integument of the tracheal system (Gerolt, 1969). This mode of entry, also known as lateral transport, does not involve the hemolymph as carrier. 

Some of the evidence obtained by Gerolt (1970) is presented in Table 6.2, which compares the toxicity of four insecticides applied externally and internally to the housefly. It can be seen that in each case the insecticides were more toxic when applied to the body surface than when deposited internally as crystals or liquids (by inserting small squares of filter paper treated with insecticide). However, Gerolt s conclusion has been contradicted by the results of other workers, and more direct experiments are required to resolve this controversy. To date the evidence for lateral transport is not conclusive. For the time being, it seems that there is no compelling reason to reject the concept that insecticides after having entered the insect are distributed throughout the body by hemolymph. 

Source From Gerolt, P., Pestic. Sci., 1,209,1970. With Permission. 

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As a rule, drugs reach their target organs via the blood Therefore, they must first enter the blood, usually the venous Umb of the circulation. There are several possible sites of entry. 

TABLE 14-4 by Site of Entry Glucogenic Amino Acids, Grouped... 

FIGURE 21-4 Acyl carrier protein (ACP). The prosthetic group is 4 -phosphopantetheine, which is covalently attached to the hydroxyl group of a Ser residue in ACP. Phosphopantetheine contains the B vitamin pantothenic acid, also found in the coenzyme A molecule. Its —SH group is the site of entry of malonyl groups during fatty acid synthesis. 

Figure 6.3 illustrates the absorption of a toxic substance through the skin and its entry into the circulatory system, where it may be distributed through the body. Often the skin suffers little or no harm at the site of entry of systemic poisons, which may act with devastating effects on receptors far from the location of absorption. 

The pulmonary system is the site of entry for numerous toxicants. Examples of toxic substances inhaled by human lungs include fly ash and ozone from polluted atmospheres, vapors of volatile chemicals used in the workplace, tobacco smoke, radioactive radon gas, and vapors from paints, varnishes, and synthetic materials used for building construction. 

In a majority of instances, particularly with pesticides, combinations of chemicals (e.g., organic solvents, mineral oils) are mixed to enhance the chemical toxicity. Consequently, the toxicity profile is altered. Lipophilicity modulates the absorption rate of the chemical from the site of entry into the system (lung, skin, mucous membrane). Thus, the fat-solubility pattern of a test chemical helps for easy cell membrane transport to reach the active site of intracellular enzymes and trigger possible toxic effects. The toxicity profile of active ingredients of pesticides and those of formulated products of pesticides differ widely. 

Figure 2.3(B). Sites of entry of amino acids into the Krebs cycle these are requisite steps for the complete catabolism of amino acids and proteins. (Modified from Hochachka, 1994.)...

Using the linear assay range from each assay studied, calculate a rate of 02 consumption in units of microliters of 02 consumed per minute. Explain your results for each tube in all four series in terms of our current knowledge of electron transport (see Fig. 14-4). Estimate a Km for succinate from the data of Series I, tubes 1 through 3. (If you do not remember how to do this, see Experiment 7.) Which tubes represent controls for other tubes Are the sites of entry of the various electron donors and the modes of action of the inhibitors depicted in Figure 14-4 consistent with... 

The nasopharynx and the oropharynx are posterior to the nose and mouth, respectively, and join to form the pharynx. The pharyngeal cavities are lined by a mucociliary epithelium coated with mucus. Humans and rodents handle inspired air in the upper respiratory tract differently. In rodents, the nose is the only site of entry into the respiratory system for inhaled materials. For this reason, rodents are referred to as obligate nose breathers. Humans breathe in air either through the mouth or the nose. Therefore, the mouth is also an important site of entry for inhaled materials in humans. Large particles (>5 pm) inhaled orally tend to impact the wall of the pharynx. 

Fig. 5. Copper homeostasis in Enterococcus hirae. Under copper-limiting conditions, copper is pumped into the cell by CopA. The CopZ copper chaperone picks up copper at this site of entry. Under physiological copper conditions, Zn(II)CopY binds to the promoter and represses transcription of the cop operon. Under conditions of copper excess, Cu-CopZ donates Cu(I) to CopY, which leads to the replacement of the Zn(II), loss of DNA-binding affinity, and ultimately synthesis of the operon products. Excess copper is secreted by the CopB efflux pump. The substrate for this pump may be a copper-glutathione (GSH) complex, rather than Cu-CopZ.

The open spaces within the fiber represent sites of entry for the liquids, and thus accessibility of the fiber to the liquid [276]. Figure 5.40 shows this layering at higher magnification, revealing the fibrils that compose the layers of the secondary wall. 

The substance moves from the site of entry to other areas of the body. 

The puriflcation of the y-secretase complex (59) has allowed the first glimpse into its structure. Electron microscopy and single particle analysis reveals that the complex has a globular structure that at low resolution (10-15 A) appears rather amorphous (66). [Another structure, elucidated in a similar manner but of poorer resolution ( 45 A), also has been reported (67).] Nevertheless, two important features can be gleaned. The first is a rather large interior cavity of 20 A diameter that is presumably where the active site resides, a characteristic reminiscent of the proteasome. The second is the presence of two small openings that may be the site of entry for water. Other structural features have been revealed by cysteine mutagenesis with... 

A somewhat different note has been sounded from the Committee on Occupational Medical Practice of the American College of Occupational and Environmental Medicine. The committee pointed out that risks to laboratory workers resulting from spontaneous infection are presumably similar to those involved in vaccination. The positive aspect of immunization is that it renders possible control over the time and initial site of entry of the virus. In the Committee s opinion, it is important for scientists and technicians to understand the US Public Health Service recommendations and to have the opportunity to receive Vaccinia immunization. They should also understand the possible drawbacks and have the opportunity to refuse vaccination (17). These different recommendations in the USA are also reflected in different national recommendations in other countries. 

Absorption is the process by which a chemical crosses the various membrane barriers of the body before it enters the bloodstream. The main sites of entry are the gastrointestinal tract, the lungs, and the skin. In drug therapy, other convenient, but more rarely used, portals of entry are the intravenous, subcutaneous, and intramuscular routes. 

Chronic exposure to PAHs can produce a variety of effects. Exposure to the eyes can result in irritation and photosensitivity. Dermal exposure can result in erythema, burns, and coal tar warts (precancerous lesions enhanced by ultraviolet light exposure). Inhalation exposure may cause irritation to the respiratory tract accompanied by cough and bronchitis. Oral exposure may produce a thickening and/or whitening of the oral mucous membranes. In addition to the local effects at the site of entry, systemic toxicity may occur, which could result in hepatic or renal effects. Some PAH compounds have been noted to cause hematological effects (anemia, leukopenia, and pancytopenia) in animals and suppression of selective components of the immune system. 

Rhabdoviruses Rabies virus Bullet-shaped particles, 75-180 nm, enveloped, helical capsids The virus has a very wide host range, infecting all mammals so far tested dogs, cats and cattle are particularly susceptible. The incubation period of rabies is extremely varied, ranging from 6 days up to 1 year. The virus remains localized at the wound site of entry for a while before passing along nerve fibres to central nervous system, where it invariably produces a fatal encephalitis... 

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