Enhancing the Natural Biological Control in the Thyroid Hormone Homeostasis As a First-Order Control System

This study explores the natural control system that exists within the pituitary gland. More specifically, this study investigates the regulation of the thyroid stimulating hormone (TSH), released by the anterior pituitary, with regards to the thyroid releasing hormone (TRH), which is released by the hypothalamus. Using appropriate assumptions on the behavior of the hormones, along with relevant boundary conditions, we modeled an output of TSH using constant TRH input over the course of a six-hour period. Other relevant hormones such as thyroxine (T4), triiodothyronine (T3), and their relevant intermediaries were also modeled as a means to complete the natural feedback found physiologically. Due to our boundary conditions, we do not consider the consumption or final function of these hormones since they leave the pituitary gland, our control system; instead, we consider a constant TRH since it is produced by the hypothalamus. Finally, we explore the results of reducing the TRH input while observing the TSH response. We append a short loop controller feedback that uses the TSH output to regulate a TRH input to remedy the reduction of TRH. The open-loop transfer function derived presented three poles at the clearance exponents for T4, TSH, and central T3, with a phase margin of 74.1°, characterizing a stable but slow system that can be improved with a simple proportional control.