This document discusses methods for studying drug uptake, including in vitro, in situ, in vivo, and in silico methods. In vitro methods involve studying drug transport through membranes outside of living organisms using techniques like diffusion cells and cell cultures. In situ methods like the everted sac technique and intestinal loop technique involve isolated intestinal segments with intact blood supply. In vivo methods directly measure drug concentrations in blood or urine over time or assess pharmacological response. In silico methods like the PAMPA model use computer simulations to predict absorption. The document provides details on techniques like Caco-2 cell cultures, everted sac modifications, and pharmacokinetic modeling approaches.