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Topic starter 07/12/2021 5:07 pm
Hi) The main mechanisms of drug absorption in the body. What determines the absorption of drugs?
07/12/2021 7:06 pm
Hi, in fact it depends on many factors: the presence of carrier proteins, certain enzymes, pH of the medium, electrolytes, the properties of the xenobiotics themselves
07/12/2021 7:08 pm
Hi) The main mechanisms of drug absorption in the body. What determines the absorption of drugs?
There are 4 main mechanisms of absorption: diffusion, filtration, active transport, pinocytosis. Passive diffusion occurs through the cell membrane. Absorption occurs until the concentration of the drug substance on both sides of the biomembrane is equal. Lipophilic substances (for example, barbiturates, benzodiazepines, metoprolol, etc.) are absorbed in a similar way, and the higher their lipophilicity, the more active their penetration through the cell membrane. Passive diffusion of substances occurs without energy consumption along the concentration gradient. Facilitated diffusion is the transport of drugs across biological membranes with the participation of specific carrier molecules. In this case, the drug is also transferred along the concentration gradient, but the transfer rate is much higher. For example, cyanocobalamin is absorbed in this way. In the implementation of its diffusion, a specific protein is involved - gastromucoprotein (internal Castle factor), which is formed in the stomach. If the production of this compound is impaired, then the absorption of cyanocobalamin decreases and, as a result, pernicious anemia develops. Filtration is carried out through the pores of the cell membranes. This mechanism of passive absorption occurs without energy consumption and is carried out along a concentration gradient. It is characteristic of hydrophilic substances (for example, atenolol, lisinopril, etc.), as well as ionized compounds. Active transport is carried out with the participation of specific transport systems of cell membranes. In contrast to passive diffusion and filtration, active transport is an energy-consuming process and can be carried out against a concentration gradient. In this case, several substances can compete for the same transport mechanism. The methods of active transport are highly specific, since they were formed during the long evolution of the organism to meet its physiological needs. It is these mechanisms that are basic for the delivery of nutrients into cells and the excretion of metabolic products. Pinocytosis (corpuscular absorption or pension absorption) is also a type of absorption with the expenditure of energy, the implementation of which is possible against the concentration gradient. In this case, the drug substance is captured and the cell membrane is invaginated with the formation of a vacuole, which is directed to the opposite side of the cell, where exocytosis occurs with the release of the drug compound.
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