NCCAOM Biomedicine Board Practice Exam 2025 - Free Biomedicine Practice Questions and Study Guide

The correct response is based on the regulatory mechanism of thyroid hormones in relation to thyroid-stimulating hormone (TSH) secretion. T3 (triiodothyronine) and T4 (thyroxine) hormones are produced by the thyroid gland and play a critical role in regulating metabolism, development, and overall homeostasis in the body.

When the levels of T3 and T4 in the bloodstream rise, they exert a negative feedback effect on the anterior pituitary gland and the hypothalamus. This means that high levels of these thyroid hormones signal the anterior pituitary to decrease the secretion of TSH. Simultaneously, the hypothalamus reduces the release of thyrotropin-releasing hormone (TRH), which is responsible for stimulating TSH production.

This feedback mechanism helps maintain hormonal balance; it prevents the overproduction of TSH, which, if unchecked, could lead to excessive stimulation of the thyroid gland and potentially hyperthyroidism. Therefore, the interaction between T3, T4, and TSH exemplifies a classic negative feedback loop that governs hormonal regulation in the endocrine system.