Which hormone acts through a cytoplasmic receptor:

Correct Answer: A

Rationale: Calcitriol, the active form of vitamin D, acts through a cytoplasmic receptor. First, calcitriol enters the cell and binds to its cytoplasmic receptor. Then, the hormone-receptor complex translocates to the nucleus, where it regulates gene expression. This mechanism is characteristic of hormones that act through cytoplasmic receptors. Prolactin and vasopressin, on the other hand, act through cell surface receptors, triggering signaling cascades without entering the cell. Therefore, the correct answer is A (Calcitriol), as it follows the characteristic pathway of a hormone acting through a cytoplasmic receptor.

Correct Answer: C

Rationale: Hyperprolactinemia causes an increase in prolactin levels, which can lead to amenorrhea due to inhibition of gonadotropin-releasing hormone, gynecomastia due to decreased testosterone levels, and depressed fertility due to disrupted ovulation. Multiple ovulation is not typically a direct consequence of hyperprolactinemia, as it primarily affects the menstrual cycle and fertility. Therefore, the correct answer is C.

Correct Answer: B

Rationale: The correct answer is B: Cryptorchism in a boy less than 7 years old. Gonadotropins are not indicated in cryptorchism as it is a condition where one or both testes fail to descend into the scrotum. Gonadotropins are used to treat conditions like hypogonadotrophic hypogonadism, amenorrhoea, infertility, and polycystic ovaries by stimulating the production of sex hormones. For the other choices: A) Hypogonadotrophic hypogonadism in males - correct, as gonadotropins can help stimulate testosterone production. C) Amenorrhoea and infertility in women - correct, as gonadotropins can help induce ovulation. D) Polycystic ovaries - correct, as gonadotropins can help regulate hormone levels and promote ovulation.

Correct Answer: D

Rationale: The correct answer is D: Serum TSH level. Serum TSH level is the most reliable guide for adjusting thyroxine dose in hypothyroidism because it directly reflects the body's feedback mechanism to regulate thyroid hormone levels. Elevated TSH indicates the body is trying to stimulate the thyroid gland to produce more hormone, suggesting the need for an increase in thyroxine dose. Conversely, low TSH levels indicate potential over-replacement, necessitating a reduction in thyroxine dose. Pulse rate (A) and body weight (B) can be influenced by various factors and are not specific indicators of thyroid hormone levels. Serum thyroxine level (C) can be affected by the timing of the last medication dose and does not provide feedback on the body's overall thyroid status like TSH does.

Correct Answer: C

Rationale: Step-by-step rationale for correct answer (C): 1. Radioactive iodine destroys overactive thyroid tissue, reducing hormone production. 2. Unlike anti-thyroid medications (A and B), radioactive iodine does not directly inhibit thyroid function. 3. Sodium thiocyanate (D) inhibits iodine uptake by the thyroid, potentially leading to goiter. Summary of incorrect choices: A. Propyl thiouracil and B. Carbimazole are anti-thyroid medications that can cause goiter in overdose. D. Sodium thiocyanate can lead to goiter by interfering with iodine uptake.