Which of the following elements is required for the synthesis of thyroid hormone?

Correct Answer: B

Rationale: The correct answer is B: iodine. Iodine is an essential element required for the synthesis of thyroid hormone. Thyroid hormones such as thyroxine (T4) and triiodothyronine (T3) contain iodine atoms. Without sufficient iodine, the thyroid gland cannot produce these hormones, leading to thyroid disorders like hypothyroidism or goiter. Copper (A), sulfur (C), and zinc (D) are not directly involved in the synthesis of thyroid hormone. Copper is important for enzyme function, sulfur is present in amino acids, and zinc is involved in various cellular processes but not specifically in thyroid hormone synthesis.

Correct Answer: C

Rationale: The middle thyroid vein drains into the internal jugular vein due to its anatomical location in the neck. The internal jugular vein receives blood from the brain, face, and neck, making it a suitable drainage site for the thyroid gland. The other options (A, B, D) are incorrect because the brachiocephalic vein drains the upper body, the external jugular vein drains the scalp and face, and the subclavian vein drains the upper extremities, none of which are anatomically linked to the thyroid gland.

Correct Answer: c

Rationale: The correct answer is D: Parathyroid. The parathyroid gland secretes parathyroid hormone (PTH) when blood calcium levels are elevated. PTH acts to increase calcium reabsorption in the kidneys, release calcium from bones, and enhance calcium absorption in the intestines, ultimately lowering blood calcium levels back to normal. A: The hypothalamus plays a role in regulating body temperature, thirst, hunger, and circadian rhythms, but not in calcium homeostasis. B: The pituitary gland secretes various hormones, but none specifically involved in regulating blood calcium levels. C: The thyroid gland secretes thyroid hormones that regulate metabolism and growth, not calcium levels.

Correct Answer: D

Rationale: The correct answer is D because glucocorticoids have multiple functions including converting amino acids into glucose (A), burning protein and fat for energy production (B), and enabling other hormones to perform normally (C). Glucocorticoids regulate metabolism, immune response, and help the body cope with stress. Therefore, all of the choices are applicable in describing the functions of glucocorticoids.

Correct Answer: A

Rationale: Step-by-step rationale for why choice A is correct: 1. Enlargement of the thyroid gland is known as a goiter. 2. A goiter can result from various conditions like iodine deficiency or thyroid disorders. 3. It is a common sign of thyroid dysfunction. 4. Goiter may or may not cause symptoms depending on the underlying cause. 5. Therefore, choice A is the correct answer. Summary: - Choice B (Addisonian crisis) is incorrect as it is associated with adrenal insufficiency, not thyroid enlargement. - Choice C (cushingoid appearance) is incorrect as it is related to excess cortisol production, not thyroid enlargement. - Choice D (hypocalcemic tetany) is incorrect as it is due to low calcium levels, not thyroid enlargement.