If you are familiar with the Star Wars franchise, you know there is a light side and a dark side of the force. These sides represent either the selfless or the selfish and essentially act to hold the galaxy together. If you consider our galactic friends and their adventures for a second, you may be able to see there is a large parallel between the galaxy and the human body. After all, the goal for all Jedi is to keep the force within balance, or in the context of the human body and for our purposes, within homeostasis.
So then, what happens when the body is no longer in homeostasis? If you go back to our simplified analogy, you’ll find it suggests some aspect within the body has pulled a Darth Vader and gone to the dark side which can predictably have devastating consequences. This Star Wars analogy is also a stellar example for the pathogenesis of cancer as a cancerous cell is in essence simply a Darth Vader cell, but we will dive further into cancer a couple weeks from now (so stay tuned).
The thyroid gland is situated at the base of the neck and plays an important role in metabolism and development within the human body.1 The thyroid is glandular in nature meaning it secretes hormones and can therefore be categorized under dysfunctions of the endocrine system. Specifically, we can identify the type of thyroid dysfunction or disease by looking a little closer at where exactly regulation goes haywire. Regulation of the thyroid occurs through the hypothalamic-pituitary-thyroid (HPT) axis.1 It is important to understand the HPT axis encompasses the hypothalamus, anterior pituitary and thyroid gland which also stores the hormones T3 (triiodothyronine) and T4 (thyroxine).1 An appropriate feedback loop for the HPT axis is illustrated below:
As annotated in the figure, the hypothalamus releases thyrotropin-releasing hormone (TRH) allowing for positive feedback to the pituitary gland. The pituitary gland then produces thyroid-stimulating hormone (TSH) allowing for positive feedback to the thyroid gland. Lastly, the thyroid gland produces T3 and T4 allowing for negative feedback on hypothalamus and pituitary gland to decrease levels of TRH + TSH so homeostasis and balance is upheld within the body.
In the context of a thyroid gland, an appropriate regulation of homeostasis like the example above would be referred to as euthyroid, meaning everything is working as it should be and the force is in balance. When the force is unbalanced, we see cases of hypothyroidism and hyperthyroidism where your glands officially go to the dark side. The good thing about thyroid dysfunction is these processes are entirely predictable if you understand what goes wrong in what part of the loop.
I hope our little galactic journey through primary thyroid disorders has been informative and helpful. Notice how in both cases of primary hyperthyroidism and primary hypothyroidism, the negative feedback loop is still trying to work, it just does not matter because there is an autoimmune issue with the gland itself. Although the negative feedback loop is still there, the process fails due to either the destruction or dysfunction of the gland itself.
- DiPiro JT, Talbert RL, Yee GC, et al, eds. Pharmacotherapy: A Pathophysiologic Approach. 11th ed. McGraw-Hill; 2020.