Endocrinology Practice Questions

Correct Answer: C

Rationale: Step-by-step rationale: 1. Tertiary hyperparathyroidism occurs due to prolonged secondary hyperparathyroidism in response to chronic renal failure. 2. In chronic renal failure, impaired kidney function leads to reduced activation of vitamin D and impaired calcium regulation. 3. Persistent hypocalcemia triggers the parathyroid glands to overproduce parathyroid hormone, leading to tertiary hyperparathyroidism. 4. Rickets (choice A) is associated with vitamin D deficiency, pseudohypoparathyroidism (choice B) is a genetic disorder, and malabsorption syndrome (choice D) affects nutrient absorption, but they are not commonly linked to tertiary hyperparathyroidism.

Correct Answer: B

Rationale: The correct answer is B: Inhibition of the function of thyroid peroxidase. Propylthiouracil inhibits thyroid peroxidase, an enzyme essential for thyroid hormone synthesis. By blocking this enzyme, propylthiouracil reduces the production of thyroid hormones, helping to manage hyperthyroidism in Graves' disease. Explanation: 1. Propylthiouracil directly inhibits thyroid peroxidase, unlike other antithyroid medications that target different mechanisms. 2. Inhibition of thyroid peroxidase leads to decreased synthesis of thyroid hormones, effectively controlling hyperthyroidism. 3. Other choices are incorrect because propylthiouracil does not primarily affect the production of thyroid-stimulating immunoglobulins (choice A), peripheral conversion of T4 to T3 (choice C), or iodine organification (choice D) in the treatment of Graves' disease. In summary, the inhibition of thyroid peroxidase by

Correct Answer: C

Rationale: The correct answer is C: Purple skin striae. This is the most common sign of Cushing's syndrome due to the excessive production of cortisol leading to thinning of the skin and formation of purple stretch marks. Hirsutism (A) is excessive hair growth, not specific to Cushing's. Obesity (B) can be a symptom, but it is not the most common. Skin hyperpigmentation (D) is seen in Addison's disease, not Cushing's.

Correct Answer: C

Rationale: Leydig cells are found in the testes and are responsible for producing testosterone, a crucial male sex hormone. This hormone is essential for the development of male reproductive organs, secondary sexual characteristics, and sperm production. Oestrogen is primarily produced by the ovaries in females. Androgen binding globulin is a protein that binds to testosterone in the bloodstream but is not produced by Leydig cells. Semen is produced by the accessory glands in the male reproductive system, not by Leydig cells. Therefore, the correct answer is C: Testosterone.

Correct Answer: D

Rationale: Step 1: Toxic thyroid adenoma is characterized by a benign tumor in the thyroid gland. Step 2: This tumor produces excessive amounts of thyroid hormones, particularly T3 and T4. Step 3: The tumor arises from the follicular cells of the thyroid gland. Step 4: Choice D accurately describes a toxic thyroid adenoma as a benign tumor producing excessive thyroid hormones from follicular cells. Summary: Choice A is incorrect because it describes autoimmune thyroid disease, not a toxic adenoma. Choice B is incorrect as it describes a malignant tumor, not a benign one. Choice C is incorrect as it describes thyroiditis, not a toxic adenoma.