Insulin pumps treat patients with type I diabetes by releasing insulin
continuously into the fat in the patient's stomach or thigh. We will develop a
model for the transport of insulin from the site where it is released by the
pump, by treating the fat as a compartment in a single-compartment model.
Let's suppose that the pump releases insulin at a constant rate, \(r(r\) is the
amount added in one unit of time).
(a) Explain why, if insulin is not transported from the site of release, the
amount of insulin at the site of release, \(a(t)\), will obey a differential
equation:
$$
\frac{d a}{d t}=r
$$
(b) From the fat, the insulin enters the patient's bloodstream. Suppose that a
fraction \(p\) of the insulin present in the patient's fat enters the blood in
unit time. Explain why:
$$
\frac{d a}{d t}=r-p a
$$
(c) Find the equilibrium from the differential equation in part
(b) and determine whether this equilibrium is stable or unstable.