Pharmacokinetics
Vd is a hypothetical volume of fluid that will contain the total amount of drug administered to the body. One inside thebody, the drug can move around either by diffusion (soaking through a membrane due to a lower concentration), or by transport in the blood. The body should be considered as being multicompartmental, where drugs can be distributed into plasma (blood) - 8% , interstitial fluid (a liquid that surrounds tissues) - 24%,  intracelullar fluid (which surrounds cells) - 65% and also fat.