This is a real flow-limited PBPK (physiologically-based pharmacokinetic) model. Blood is pumped through four tissue compartments at their real fraction of cardiac output; each tissue is assumed to equilibrate instantly with the blood leaving it, scaled by its drug/tissue partition coefficient Kp:
dA_blood/dt = Σᵢ Qᵢ·(Cᵢ/Kpᵢ − C_blood)
dAᵢ/dt = Qᵢ·(C_blood − Cᵢ/Kpᵢ) − CLᵢ·(Cᵢ/Kpᵢ)
Cᵢ = Aᵢ / Vᵢ (tissue concentration)
CL_liver = hepatic slider × 0.9 L/min
CL_kidney = renal slider × 0.6 L/min
Blood flow is split the way it really is in an adult (cardiac output ≈ 5 L/min): liver 1.35 L/min, kidney 1.1 L/min, fat 0.25 L/min, everything else (muscle, skin, etc.) 2.3 L/min. Lipophilicity raises every Kp — especially fat's, which is why lipophilic drugs (chloroquine-like) accumulate in adipose tissue for a slow, delayed release, while hydrophilic drugs stay confined to blood and lean tissue.
- Hepatic clearance only removes drug while it's inside the liver compartment (CYP450 metabolism) — raise it and the liver empties itself faster instead of returning drug to blood.
- Renal clearance does the same from the kidney compartment (glomerular filtration + secretion).
- The flowing particles are drug molecules riding the blood between the central pool and each organ; their brightness tracks the local concentration, so a saturated fat compartment glows long after blood has cleared.
This is the same organ-by-organ approach used in real PBPK software (e.g. Simcyp, GastroPlus) to predict tissue exposure before a drug ever reaches a clinical trial.