The correct option is 2 and 3 only.
Explanation
The thyroid gland is a vital endocrine gland located in the neck region, responsible for regulating the body's metabolic rate through the secretion of specific hormones.
Statement 1 is Incorrect: The thyroid gland is composed of two lobes located on either side of the trachea. These lobes are interconnected with a thin flap of connective tissue called the isthmus. It is not a single-lobed structure.
Statement 2 is Correct: The gland consists of follicles and stromal tissues. The follicular cells within the thyroid synthesize two main hormones: tetraiodothyronine or thyroxine (T4) and triiodothyronine (T3).
Statement 3 is Correct: Iodine is essential for the normal rate of hormone synthesis in the thyroid. A deficiency of iodine in the diet leads to hypothyroidism and enlargement of the thyroid gland, a condition known as goitre.
Key Takeaway: The thyroid is a bilobed gland located on the trachea that requires iodine to synthesize T3 and T4 hormones, which are critical for metabolic regulation.