Gastrointestinal system osmotics

Drug delivery systems of once-daily products (Concerta, Metadate CD, Ritalin LA, Adderall XR) provide 8 to 12 hours of symptom control. Concerta uses an oral osmotic (OROS) controlled-release delivery system, while other preparations use combinations of immediate-release or extended-release beads containing drug. Concerta is a nondeformable tablet and it should not be given to children with gastrointestinal narrowing due to the risk of obstruction. Older wax-matrix sustained-release products (e.g., Ritalin SR)... 

In contrast to calcium or iron, there exists in blood no remarkable protein-based transport system for Cl". That anion is dissolved within the plants or animals fluid volumes and contributes to the osmotic condition. At first view, any movement of Cl includes transport of water, and vice versa. That is visible in the relationship between Cl and water in the gastrointestinal tract (Meyer 1996). However, living cells require suitable osmotic conditions both outside and inside, and so a system which drives ions through membranes is needed. The capacity of such a system is impressively established in fish. Marine fish live in a hyperosmotic environment which withdraws water from the animal this exosmosis is counteracted by a high oral water intake (Evans 1998, Pelis etal. 2001). Cl uptake by the mucosa cells occurs in relation to the osmotic gradient, and chloride extrusion... 

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