Answer: iodine.
- A iodine
- B iron
- C calcium
- D sodium
Correct answer: A. iodine
Explanation: A lack of iodine impairs thyroxine production and causes goitre.
The hypothalamus releases hormones that direct the pituitary, which releases its own trophic hormone to a target gland; that gland's hormone output then feeds back (dashed lines) to suppress both the pituitary and hypothalamus once levels are sufficient - a self-correcting loop running the entire endocrine system.
Concept context
The endocrine glands, hormone classification and mechanism of action, and negative feedback regulation.