Blood glucose regulation is a textbook negative-feedback control system: a narrow setpoint, two antagonistic actuators, a sensor with a measurable lag, and a failure mode that modern medicine now patches with an actual external controller. A tour of the insulin-glucagon loop, what HbA1c and continuous glucose monitors really measure, how insulin resistance degrades the actuator, and how PID and model predictive control ended up running inside an insulin pump.
Glucose
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Glucose and Insulin: The Body's Control Loop