  We present a dynamical model of lipoprotein metabolism derived by combining a
cascading process in the blood stream and cellular level regulatory dynamics.
We analyse the existence and stability of equilibria and show that this
low-dimensional, nonlinear model exhibits bistability between a low and a high
cholesterol state. A sensitivity analysis indicates that the intracellular
concentration of cholesterol is robust to parametric variations while the
plasma cholesterol can vary widely. We show how the dynamical response to
time-dependent inputs can be used to diagnose the state of the system. We also
establish the connection between parameters in the system and medical and
genetic conditions.
