Many large molecules and particles can not Extracellular fluid enter cells via ● passive or active Membrane mechanisms。 However, some may enter, as yet, by a process known as Cytoplasm endocytosis(内吞)
◼ Many large molecules and particles can not enter cells via passive or active mechanisms. However, some may enter, as yet, by a process known as endocytosis(内吞)
In phagocytosis(吞噬) cell eating),arge particles suspended in the extracellular fluid are engulfed and either transported into cells or are destroyed within the cell. This is a very important process for lung phagocytes and certain liver and spleen cells. Pinocytosis(胞饮)( cell drinking)isa similar process but involves the engulfing of liquids or very small particles that are in suspension within the extracellular fluid
◼ In phagocytosis (吞噬) (cell eating), large particles suspended in the extracellular fluid are engulfed and either transported into cells or are destroyed within the cell. This is a very important process for lung phagocytes and certain liver and spleen cells. ◼ Pinocytosis (胞饮) (cell drinking) is a similar process but involves the engulfing of liquids or very small particles that are in suspension within the extracellular fluid
II. Dissolution and drug absorption a The process by which a drug particle dissolves is termed dissolution a The dissolution of a substance may be described by the modified Noyes-Whitney equation dc/dt=kS(cs-c+ in which dc/dt is the rate of dissolution k is the dissolution rate constant S is the surface area of the dissolving solid Cs is the saturation concentration of drug in the diffusion laver Ct is the concentration of the drug in the dissolution medium at time t
II. Dissolution and drug absorption ◼ The process by which a drug particle dissolves is termed dissolution. ◼ The dissolution of a substance may be described by the modified Noyes-Whitney equation: dc/dt=kS(cs -ct ) in which dc/dt is the rate of dissolution k is the dissolution rate constant S is the surface area of the dissolving solid, Cs is the saturation concentration of drug in the diffusion layer Ct is the concentration of the drug in the dissolution medium at time t
The equation reveals that the dissolution rate of a drug may be increased by increasing the surface area of the drug increasing the solubility of the drug in the diffusion layer. factors embodied in the dissolution rate constant k, including the intensity of agitation of the solvent, the diffusion coefficient of the dissolving drug
The equation reveals that the dissolution rate of a drug may be increased by - increasing the surface area of the drug, - increasing the solubility of the drug in the diffusion layer, - factors embodied in the dissolution rate constant, k, including the intensity of agitation of the solvent, - the diffusion coefficient of the dissolving drug
1)Surface area a When a drug particle is reduced to a larger number of smaller particles, the total surface area created is increased a For drug substances that are poorly or slowly soluble, this generally results in an increase in the rate of dissolution a Micronized powders consist of drug particles reduced in size to about 5 microns and smaller
1) Surface area ◼ When a drug particle is reduced to a larger number of smaller particles, the total surface area created is increased. ◼ For drug substances that are poorly or slowly soluble, this generally results in an increase in the rate of dissolution. ◼ Micronized powders consist of drug particles reduced in size to about 5 microns and smaller