Final answer:
The primary mechanism regulating hormone levels in a first-order feedback loop is the negative feedback loop, which maintains hormone levels within a narrow range to ensure homeostasis. Positive feedback loops, which amplify hormone production, are less common in the human body.
Step-by-step explanation:
The mechanisms regulating hormone levels in a first-order feedback loop are primarily the negative feedback loop and, to a lesser extent, the positive feedback loop. In a negative feedback loop, the production and release of hormones are controlled such that when a hormone level rises, it inhibits further hormone release, effectively maintaining the hormone concentration within a narrow, optimal range. For example, the release of thyroid hormones by the thyroid gland prompts the hypothalamus and anterior pituitary to inhibit further signaling to the thyroid gland as hormone levels rise. Conversely, a positive feedback loop amplifies a response and the release of a hormone leads to an even greater release. However, this is much less common as it may lead to runaway processes rather than homeostasis.
Positive feedback mechanisms are less common because they can lead to states far removed from equilibrium, which can be dangerous in a biological context. Negative feedback is more conducive to maintaining homeostasis. One such example of negative feedback regulation is with glucocorticoid hormones; increased glucocorticoid levels in the blood signal the hypothalamus and pituitary to reduce their stimulation of the adrenal glands, preventing excess hormone production.