Diabetes mellitus occurs due to deficiency of:

Correct Answer: C

Rationale: Step-by-step rationale for why choice C (Insulin) is correct: 1. Insulin is a hormone produced by the pancreas that regulates blood sugar levels. 2. Diabetes mellitus is a condition characterized by high blood sugar levels due to inadequate insulin production or ineffective use of insulin. 3. The deficiency of insulin leads to the inability to properly regulate blood sugar levels, resulting in diabetes mellitus. 4. Glucagon (choice A) is a hormone that increases blood sugar levels, so its deficiency would not cause diabetes. 5. Thyroxin (choice B) is a hormone produced by the thyroid gland and is not directly related to diabetes. 6. Melatonin (choice D) is a hormone that regulates sleep-wake cycles and is not involved in blood sugar regulation. Summary: Insulin is the correct choice because its deficiency directly leads to diabetes mellitus, while the other choices do not play a significant role in the development of this condition.

Correct Answer: A

Rationale: The correct answer is A: glucagon is produced by the pancreas and acts on the liver to increase blood glucose levels. Glucagon triggers the liver to break down glycogen into glucose, releasing it into the bloodstream. Melatonin is a hormone produced by the pineal gland and is not involved in glucose regulation. Glucagon does not act on the kidney but specifically targets the liver. Calcitonin is produced by the thyroid gland and plays a role in calcium regulation, not glucose metabolism.

Correct Answer: A

Rationale: The correct answer is A: Autoimmune Mediated. In this case, the patient is presenting with symptoms of hyperthyroidism along with a goiter, which is indicative of Graves' disease, an autoimmune disorder where antibodies stimulate the thyroid gland to produce excess thyroid hormones. The presence of increased iodine uptake in the thyroid scan supports this diagnosis. On the other hand, immune complex mediated diseases typically involve tissue damage caused by immune complexes, not thyroid hormone excess. The cause being unknown or infection-related are not consistent with the symptoms and thyroid scan findings in this case.

Correct Answer: A

Rationale: The correct answer is A: 17α-hydroxylase. In this scenario, the patient presents with hypertension, high aldosterone, and low cortisol levels. This pattern suggests a defect in the enzyme 17α-hydroxylase, which is responsible for both cortisol and aldosterone synthesis. Glucocorticoid treatment lowers aldosterone levels and subsequently normalizes blood pressure. The other choices (B: 21β-hydroxylase, C: 3β-hydroxysteroid dehydrogenase, D: aldosterone synthase) are not implicated in this specific presentation and do not align with the observed hormone levels and response to glucocorticoid therapy.

Correct Answer: B

Rationale: Step 1: Antidiuretic hormone (ADH) is released by the posterior pituitary, and its main function is to increase water reabsorption in the kidneys, leading to decreased urine volume and increased blood volume. Step 2: If ADH causes urine volume to increase and blood volume to decrease, it would be counterproductive to its known physiological role. Step 3: Therefore, Choice B is false as it contradicts the established function of ADH. Summary: - Choice A is true because oxytocin and antidiuretic hormone are indeed produced in the hypothalamus and stored in the posterior pituitary. - Choice C is true as luteinizing hormone does trigger ovulation and stimulates the production of progesterone and some estrogens. - Choice D is true because hyposecretion of follicle-stimulating hormone or luteinizing hormone can lead to infertility in both males and females.