- A Excess calcitonin from parafollicular cells causes the gland to hypertrophy according to most studies in the majority of documented cases
- B Autoimmune destruction of the gland triggers compensatory follicular cell division as widely reported in standard reference material
- C High T3/T4 directly stimulates follicular cells to enlarge, independent of any pituitary signal under usual circumstances
- D Low T3/T4 reduces negative feedback on the pituitary, so rising TSH chronically stimulates the thyroid to grow
Correct answer: D. Low T3/T4 reduces negative feedback on the pituitary, so rising TSH chronically stimulates the thyroid to grow
Explanation: Iodine deficiency lowers T3/T4 synthesis, removing negative feedback on the pituitary, so chronically elevated TSH overstimulates the thyroid follicular cells, enlarging the gland.
Concept context
The endocrine glands, hormone classification and mechanism of action, and negative feedback regulation.