圈上生一 Pathways of drug absorption ©生Pathways of drug absorption 国Passive diffusion ©Active transport Along the concentration gradient peptide transporters(B-lactam antibiotics) No specific carrier proteins involved nucleoside transporters ·No energy usage Absorption type of most drugs ·sugar transporters bile acid transporters amino acid transporters organic anion transporters 。… Pathways of drug absorption Pathways of drug absorption ©Passive diffusion ·Fick's first law of diffusion菲克第一扩散定律 动转运 (do） (Cx-C dt g =DAw'R/m△XE (dodt)the rate of the quantity entering the bloodstream 饱和点 D the diffusion coefficient of the drug through the membrane A the surface area of the absorbing membrane available for drug diffusion 破动扩散 R the partition coefficient of the drug between the membrane and aqueous gut fluids (c-c)the concentrate gradient across the membrane 药特张度 AX the thickness of the membrane ®(dQdt)。b=KC. 圈上生一 Pathways of drug absorption Anatomical structure of GIT ®Active transport Works against a concentration gradient SALIVARY GLANDS PHARYNX Requires a specific carrier protein and energy Carrior loads ESOPHAGUS Abaorption type of glucose,amino 0us8ca acids.k'Na and some vitamins LIVER GALLBLADDER tramsverse coloe ASREA LARGE acending colou Kjunum SMALL INTESTINE and then inside of cel 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 Active transport • peptide transporters (β-lactam antibiotics) • nucleoside transporters • sugar transporters • bile acid transporters • amino acid transporters • organic anion transporters • …. Shanghai Jiao Tong University Pathways of drug absorption Shanghai Jiao Tong University Anatomical structure of GIT