Iodination of thyroid hormones is mediated by __________.

Correct Answer: D

Rationale: The correct answer is D: peroxidase enzymes. Peroxidase enzymes are responsible for catalyzing the iodination process of thyroid hormones in the thyroid gland. They facilitate the incorporation of iodine atoms into tyrosine residues within thyroglobulin to form thyroid hormones T3 and T4. Lysosomes (choice A) are involved in cellular waste disposal, not iodination. The Golgi apparatus (choice B) is responsible for processing and packaging proteins, not iodination. Colloid endocytosis (choice C) is the process of internalizing colloid-containing vesicles in thyroid follicular cells, but it is not directly involved in iodination.

Correct Answer: a

Rationale: The correct answer is A: Calcitonin-parathyroid hormone. 1. Calcitonin lowers blood calcium levels by inhibiting bone breakdown, while parathyroid hormone raises blood calcium levels by stimulating bone breakdown. 2. This hormone pair directly opposes each other in regulating blood calcium levels. 3. Choices B, C, and D do not involve hormones with antagonistic effects on the same physiological process.

Correct Answer: C

Rationale: Step-by-step rationale for why choice C is correct: 1. The adrenal medulla is part of the adrenal glands. 2. It secretes adrenaline and noradrenaline during the fight-or-flight response. 3. These hormones increase heart rate, blood flow to muscles, and provide energy for emergencies. 4. This physiological response helps the body deal with stressful situations. 5. Choices A, B, and D are incorrect because the adrenal medulla is not primarily controlled by ACTH, does not secrete steroids, and does not secrete iodine-containing hormones.

Correct Answer: B

Rationale: The correct answer is B: Graves' disease. Graves' disease is an autoimmune disorder that leads to overproduction of thyroid hormones, causing hyperthyroidism. This is characterized by symptoms such as weight loss, increased heart rate, and anxiety. Cushing syndrome (A) is caused by excess cortisol, not thyroid hormones. Addison's disease (C) is a condition where the adrenal glands do not produce enough hormones. ADH hypersecretion (D) refers to excessive production of antidiuretic hormone, not thyroid hormones. Therefore, the correct answer is Graves' disease due to its direct association with hyperthyroidism.

Correct Answer: D

Rationale: Step-by-step rationale: 1. TSH stands for Thyroid Stimulating Hormone. 2. TSH is secreted by the anterior pituitary gland. 3. It stimulates the thyroid gland to produce thyroid hormones, not calcitonin. 4. It is not secreted by the neurohypophysis or stimulate the hypothalamus to secrete TRH. Therefore, choice D is correct as it accurately describes the function and origin of TSH.