Iodine is:

Correct Answer: C

Rationale: The correct answer is C because iodine is essential for the synthesis of thyroid hormones such as thyroxine (T4) and triiodothyronine (T3) in the thyroid gland. These hormones play a crucial role in regulating metabolism and growth. Choice A is incorrect because the adenohypophysis produces TSH, not iodine. Choice B is incorrect because calcitonin is produced by the parafollicular cells of the thyroid gland and does not require iodine for its synthesis. Choice D is incorrect because PTH (parathyroid hormone) is produced by the parathyroid glands and does not require iodine for its synthesis.

Correct Answer: D

Rationale: The correct answer is D: follicle-stimulating hormone (FSH). FSH is produced by the pituitary gland and plays a crucial role in both male and female reproductive systems. In males, FSH stimulates the testes to produce sperm. In females, FSH stimulates the development of ovarian follicles, which contain eggs. This hormone is essential for the process of ovulation and the menstrual cycle. A: Growth hormone is not directly involved in the reproductive system but rather promotes overall growth and development. B: Luteinizing hormone (LH) is responsible for ovulation and the production of testosterone in males. It does not directly stimulate sperm production or follicle development. C: Prolactin is primarily involved in milk production and has no direct role in sperm production or follicle development.

Correct Answer: D

Rationale: The correct answer is D because the ovaries and testes are the only endocrine glands that are dormant during childhood and activate at puberty to produce sex hormones. The ovaries produce estrogen and progesterone in females, while the testes produce testosterone in males. This activation is essential for the development of secondary sexual characteristics and reproductive functions. Pancreas (choice A), adrenal glands (choice B), and thyroid gland (choice C) are all active during childhood and do not specifically activate at puberty. The pancreas regulates blood sugar levels, the adrenal glands produce hormones like cortisol, and the thyroid gland regulates metabolism. Hence, choices A, B, and C are incorrect in the context of endocrine glands that lay dormant during childhood to activate at puberty.

Correct Answer: C

Rationale: The correct answer is C: pancreas. The pancreas is classified as both an endocrine gland, producing hormones like insulin and glucagon, and an exocrine gland, secreting digestive enzymes into the small intestine. This dual functionality makes it unique among the other options. The hypothalamus (A) is primarily an endocrine gland involved in hormone regulation, while the thymus gland (B) is solely an endocrine gland responsible for T-cell maturation. The pituitary gland (D) is also an endocrine gland that regulates various bodily functions but does not have exocrine functions like the pancreas.

Correct Answer: D

Rationale: The correct answer is D: Sweat. Sweat glands are not considered ductless glands as they secrete sweat through ducts onto the skin surface. Adrenal, Pituitary, and Thyroid glands are all ductless endocrine glands that secrete hormones directly into the bloodstream. Adrenal glands produce hormones like cortisol and adrenaline, Pituitary gland secretes hormones that regulate various bodily functions, and Thyroid gland produces hormones that control metabolism. Therefore, sweat gland is the only option that does not fit the criteria of a ductless gland, making it the correct answer.