Gastrointestinal tract absorption through

Exposure of mancozeb to humans can occur via absorption through the gastrointestinal tract, absorption through the skin or lungs. Human exposure to mancozeb, similar to maneb, has been calculated for... 

It is possible that in this case, although chlorhexidine was poorly absorbed from the gastrointestinal tract, absorption occurred through the pulmonary alveoh. 

Data from animal experiments indicate that methyl acrylate is readily absorbed from the respiratory and gastrointestinal tracts. Absorption of methyl acrylate through the skin occurs less readily and may be limited by evaporation of methyl acrylate if the applied dose is unoccluded. 

The major routes of manganese absorption in animals and humans are via the gastrointestinal and respiratory tracts. Absorption through the skin is thought to be minimal for inorganic manganese compounds, but may be important for organomanganese compounds (WHO 1981). 

Compounds in animal diets can exert their effects in the gastrointestinal tract or after absorption through the gut epithelial tissue into the bloodstream, or both. On some occasions the administered compounds may be applied topically (Table 1). 

Chemicals have to pass through either the skin or mucous membranes lining the respiratory airways and gastrointestinal tract to enter the circulation and reach their site of action. This process is called absorption. Different mechanisms of entry into the body also greatly affect the absorption of a compound. Passive diffusion is the most important transfer mechanism. According to Pick s law, diffusion velocity v depends on the diffusion constant (D), the surface area of the membrane (A), concentration difference across the membrane (Ac), and thickness of the membrane (L)... 

Delivery of peptides and proteins via the gastrointestinal tract has not been successful because of poor penetration through the intestinal epithelium and high levels of proteolytic activity in the gastrointestinal tract. Liposomal encapsulation of proteins and peptides will not improve the efficiency and capacity of this absorption pathway considerably (e.g., Ryman et al., 1982 Machy and Leserman, 1987 Weiner and Chia-Ming Chiang, 1988). These difficulties in delivery via the oral route caused the parenteral route to remain the preferred route for the administration of therapeutic peptides... 

Other than the different approaches mentioned above, commercial packages such as GastroPlus (Simulations Plus, Lancaster, CA) [19] and IDEA (LionBioscience, Inc. Cambridge, MA) [19] are available to predict oral absorption and other pharmacokinetic properties. They are both based on the advanced compartmental absorption and transit (CAT) model [20], which incorporates the effects of drug moving through the gastrointestinal tract and its absorption into each compartment at the same time (see also Chapter 22). 

Distribution. Once inside the body, trichloroethylene is easily absorbed into and distributed through the circulatory system. The amount that is not absorbed initially on inhalation is expired unchanged (see Section 2.3.1.1). Absorption from the gastrointestinal tract often leads to a first pass through the liver, where toxic metabolites can form (see Section 2.3.3). Trichloroethylene and its metabolites may form adducts with blood proteins, and the metabolite glyoxylate may become incorporated into amino acids (Stevens et al. 1992), thus facilitating their distribution. The ability of these compounds to traverse membranes accounts for then-generalized systemic effects. 

The final mechanism of action of PTH involves the activation of vitamin D3 through the stimulation of la-hydroxylase in the kidney. In the gastrointestinal tract, vitamin D3 is essential for the absorption of calcium. Enhanced absorption of calcium from dietary sources serves to further increase the concentration of calcium in the blood. Many foods, in particular, dairy products, which are rich in calcium, are fortified with vitamin D. The release of PTH from the parathyroid glands is regulated by plasma calcium levels through negative feedback. A decrease in the level of calcium in the blood stimulates the secretion of PTH and an increase in the calcium level in the blood inhibits it. 

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