Which of the following statements correctly describes the pathophysiology of Cushing's disease?

Correct Answer: A

Rationale: Rationale: A: Correct. Cushing's disease is caused by a pituitary adenoma secreting excess ACTH, stimulating adrenal cortex to produce excess cortisol. B: Incorrect. Cushing's disease does not result from excess cortisol secretion by the pituitary adenoma. C: Incorrect. Cushing's disease is not caused by an adrenal adenoma secreting excess ACTH. D: Incorrect. Cushing's disease is not caused by an adrenal adenoma secreting excess cortisol. Summary: The correct answer is A because it accurately describes the pathophysiology of Cushing's disease, where a pituitary adenoma secretes excess ACTH leading to increased cortisol production. Choices B, C, and D are incorrect as they misinterpret the primary source of hormone overproduction in Cushing's disease.

Correct Answer: C

Rationale: Erythropoietin is primarily secreted from the kidney, specifically by the Juxtaglomerular cells in the kidney's cortex. These cells are responsible for sensing oxygen levels and regulating erythropoietin production accordingly. Mesenchymal tumors, cerebellar haemangioblastoma, and lymphoma are not associated with erythropoietin secretion, making them incorrect choices. Mesenchymal tumors originate from connective tissues, cerebellar haemangioblastoma is a type of brain tumor, and lymphoma is a cancer of the lymphatic system. Only the Juxtaglomerular cells in the kidney have the physiological role of secreting erythropoietin in response to hypoxia.

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: Stress. Stress triggers the release of growth hormone through the activation of the hypothalamic-pituitary-adrenal axis. When the body is under stress, the hypothalamus signals the pituitary gland to release growth hormone. This hormone then stimulates growth and cell reproduction. Glucocorticoids (A) and somatostatin (B) actually inhibit the release of growth hormone. Obesity (D) can lead to decreased growth hormone release due to disrupted hormonal regulation. In summary, stress is the correct answer as it directly stimulates the release of growth hormone, while the other choices inhibit or have a negative impact on growth hormone release.

Correct Answer: C

Rationale: Diabetes insipidus is a condition where the kidneys are unable to conserve water, leading to the excretion of large volumes of dilute urine. This is due to either a lack of antidiuretic hormone (ADH) production (central DI) or the kidneys' insensitivity to ADH (nephrogenic DI). Choice A is incorrect as the urine is dilute, not concentrated. Choice B is incorrect as diabetes insipidus results in large, not small, urine volumes. Choice D is incorrect as the urine is dilute, not concentrated. Therefore, choice C accurately describes diabetes insipidus.

Correct Answer: A

Rationale: Step-by-step rationale for why answer A is correct: 1. Oxytocin is synthesized in the hypothalamus and released into the bloodstream. 2. In the plasma, oxytocin binds to neurophysin, a carrier protein. 3. This binding helps stabilize oxytocin and regulate its release and distribution. 4. Therefore, choice A is correct as oxytocin is bound to neurophysin in plasma. Summary: - Choice B is incorrect as oxytocin stimulates milk ejection, not inhibits milk production. - Choice C is incorrect as oxytocin promotes myometrial contraction during labor. - Choice D is incorrect as oxytocin can enhance sperm motility, not inhibit it.

Correct Answer: C

Rationale: Elevated glucose levels in obese individuals are often due to insulin resistance. Insulin resistance occurs when the body's cells do not respond effectively to insulin, leading to decreased glucose uptake. This results in elevated blood glucose levels. Diabetic acidosis (choice A) is a complication of uncontrolled diabetes characterized by high blood ketone levels, not directly related to obesity. Glucose intolerance (choice B) refers to the body's inability to regulate blood glucose levels efficiently but is not specific to obesity. Insulin deficiency (choice D) is characteristic of type 1 diabetes, where the body does not produce enough insulin, which is distinct from insulin resistance seen in obesity.

Correct Answer: C

Rationale: The correct answer is C: Glucose-6-phosphatase deficiency. This enzyme is essential for gluconeogenesis and glycogenolysis, so its deficiency leads to fasting hypoglycemia. Galactosaemia (A) can cause hypoglycemia due to impaired galactose metabolism. Insulinoma (B) results in excess insulin production causing hypoglycemia. Systemic carnitine deficiency (D) can lead to hypoglycemia by impairing fatty acid oxidation, but it does not directly cause fasting hypoglycemia as seen in Glucose-6-phosphatase deficiency.

Correct Answer: A

Rationale: The correct answer is A: Cirrhosis. In cirrhosis, there is a decrease in the binding proteins for T4, leading to decreased total T4 levels in the plasma. Pregnancy, euthyroid sick syndrome, and familial excess thyroid binding globulin are all conditions associated with increased total T4 levels due to various physiological changes. In pregnancy, there is an increase in thyroid hormone production to support fetal development. Euthyroid sick syndrome is a condition where there is a decrease in binding proteins, leading to an increase in free T4 levels but normal total T4 levels. Familial excess thyroid binding globulin causes an increase in total T4 levels due to excessive binding proteins.