圈上生一 Pathways of drug absorption 国生 Pathways of drug absorption 国Passive diffusion Along the concentration gradient 主动转运 No specific carrier proteins involved ·No energy usage 饱和点 Absorption type of most drugs 破动扩散 药张以一 皮 Pathways of drug absorption 国一 Anatomical structure of GIT ©Passive diffusion ·Fick's first law of diffusion菲克第一扩散定律 (do） (Cx-C dt g =DAwRa/g△Xe SALIVARY GLANDS- -PHARYNX (dQ/dt)the rate of the quantity Q entering the bloodstream D the diffusion coefficient of the drug through the membrane ESOPHAGUS A the surface area of the absorbing membrane available for drug diffusion R the partition coefficient of the drug between the membrane and aqueous LIVER GALLBLADDER STOMACH gut fluids (c-c)the concentrate gradient across the membrane LARGE SMALL INTESTINE AX the thickness of the membrane ®(dQdt)。b=KC. Pathways of drug absorption 国秋生 Stomach Active transport The primary functions of stomach are storage, Works against a concentration mixing,and reducing all components to a slurry gradient with the aid of gastric secretions;and then Requires a specific carrier protein emptying these contents in a controlled manner and cnergy Carrior loads Abaorption type of glucose,amino 0us8ca into the upper small intestine. acids.k'Na and some vitamins The surface tension of gastric fluid is low. The pH of gastric fluid is 1~3.5 and then 22 Shanghai Jiao Tong University Passive diffusion • Along the concentration gradient • No specific carrier proteins involved • No energy usage • Absorption type of most drugs Pathways of drug absorption Shanghai Jiao Tong University Passive diffusion • Fick’s first law of diffusion 菲克第一扩散定律 (dQ/dt) g→b the rate of the quantity Q entering the bloodstream Dm the diffusion coefficient of the drug through the membrane Am the surface area of the absorbing membrane available for drug diffusion Rm/aq the partition coefficient of the drug between the membrane and aqueous gut fluids (cg-cb) the concentrate gradient across the membrane ∆Xm the thickness of the membrane (dQ/dt) g→b =KCg Pathways of drug absorption Shanghai Jiao Tong University Pathways of drug absorption Active transport • Works against a concentration gradient • Requires a specific carrier protein and energy • Absorption type of glucose, amino acids, k+,Na+ and some vitamins Shanghai Jiao Tong University Pathways of drug absorption Shanghai Jiao Tong University Anatomical structure of GIT Shanghai Jiao Tong University Stomach The primary functions of stomach are storage, mixing, and reducing all components to a slurry with the aid of gastric secretions; and then emptying these contents in a controlled manner into the upper small intestine. The surface tension of gastric fluid is low. The pH of gastric fluid is 1~3.5