Question

Which of the following statements concerning thyroid function are correct?

• A. T3 and T4 stimulate the secretion of TSH by the anterior pituitary
• B. People who have an underactive thyroid gland have a low BMR
• C. Most of the iodine in the body is present in the thyroid gland
• D. Thyroid hormones are essential for the early development and maturation of the central nervous system

Answer 1

Answer: (B), (C), (D)

Thyroid hormones are essential for the early development and maturation of the central nervous system

The thyroid gland secretes thyroxine and smaller amounts of triiodothyronine (T3), which stimulate oxidative respiration in most cells in the body and, in doing so, help set the body’s basal metabolic rate (BMR). Thyroid hormones stimulate metabolism and when thyroid hormone levels are low, BMR is reduced. High levels of thyroid hormones will increase BMR and elevate the heart rate. The thyroid gland avidly takes up iodine and incorporates it into thyroglobulin. In children, these thyroid hormones also promote growth and stimulate maturation of the central nervous system. Children with underactive thyroid glands are therefore stunted in their growth and suffer severe mental retardation, a condition called cretinism. Thyroid hormones inhibit the secretion of TSH by negative feedback. The hypothalamus secretes
TRH, which stimulates the anterior pituitary to secrete TSH. The TSH then stimulates the thyroid to secrete thyroxine, which exerts negative feedback control of the hypothalamus and anterior pituitary.