Modes of Intake and Absorption
Metals and their compounds are usually ingested or inhaled. Industrial accidents (slivers, cuts, and abrasions) cause subcutaneous exposure in man. The route of intake and the dosage determine the intensity and duration of the harmful effects (the dosage-time curve) of a toxicant. Oral administration provides processing of the toxicant by digestive enzymes, microbic cells, host intestinal cells, and often hepatic cells before the material is transported to other tissues (Fig. 2–1). Inhalation results in the direct transfer of soluble metal compounds from the pulmonary tissues to the blood; it can also provide a circuitous route for the transport of the toxicant to the tissues. Cilia of epithelial cells can carry insoluble metal particulates or compounds from the lungs into the gastrointestinal tract via the pharynx. Macrophages can transfer the metal directly to regional lymph nodes, blood, and other tissues or to the gastrointestinal tract. Dermal administration usually provides prolonged absorption of small quantities of material, especially lipid-soluble compounds, over an extended period. Intravenous (including intraarterial) administration distributes the dose to tissues within seconds, and—other than absorption to plasma proteins, cell walls, or other membranes—there is little systemic processing of the material. Metabolic processing is generally less important for minerals than for organic toxicants.
KeywordsHair Follicle Goblet Cell Alimentary Tract Mucosal Cell Metal Compound
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