A girl presents with delayed puberty, absent secondary sexual characteristics, and primary amenorrhea. She also appears to be hypertensive and hypokalemia. Which of the following enzymes is increased if there is virilization of a person?

Correct Answer: A

Rationale: The correct answer is A: 11b-Hydroxylase. In cases of virilization, increased androgen production occurs. 11b-Hydroxylase is involved in the synthesis of cortisol and aldosterone. When there is a deficiency in this enzyme, excess androgens are diverted towards the production of testosterone, leading to virilization. In contrast, choices B (17a-Hydroxylase) and C (21b-Hydroxylase) deficiencies result in decreased androgen production. Choice D, Pyruvate Kinase, is not related to steroid hormone synthesis. Therefore, the correct enzyme in this scenario is 11b-Hydroxylase.

Correct Answer: A

Rationale: Step 1: Steroids are lipid-soluble molecules, allowing them to easily diffuse through the plasma membrane of target cells. Step 2: Once inside the cell, steroids can enter the nucleus to bind to specific receptors and regulate gene expression. Step 3: Steroids do not catalyze cyclic AMP; this function is typically associated with non-steroid hormones like adrenaline. Step 4: Therefore, the correct answer is A because steroids do not catalyze cyclic AMP, unlike other hormones.

Correct Answer: B

Rationale: The correct answer is B because the bloodstream can carry hormones throughout the body simultaneously, reaching various target cells and organs. This enables a single endocrine hormone to produce responses in multiple parts of the body. In contrast, nerve cells can only target a limited number of cells through direct connections. Choice A is incorrect because endocrine hormones can also target multiple responses, not just one. Choice C is incorrect as the endocrine system and nervous system can interact. Choice D is incorrect as endocrine hormones can have broad effects on multiple target cells.

Correct Answer: D

Rationale: In Graves disease, there is an overproduction of thyroid hormones due to autoimmune stimulation. Thyroid-stimulating hormone (TSH) is decreased because the excessive thyroid hormones suppress its production through negative feedback. A and B are incorrect because both T3 and T4 levels are elevated in Graves disease. C is incorrect as DIT is a precursor to thyroid hormones and its levels may not necessarily be decreased in Graves disease.

Correct Answer: C

Rationale: The correct answer is C: down-regulation. Prolonged exposure to high hormone concentrations can lead to down-regulation, where cells decrease their responsiveness to the hormone by reducing the number of hormone receptors. This is a regulatory mechanism to prevent overstimulation. A: Diabetes mellitus is a chronic condition characterized by high blood sugar levels, usually caused by insulin deficiency or insulin resistance, not directly related to prolonged exposure to high hormone concentrations. B: Cellular inhibition is a broad term that may refer to various cellular processes being inhibited, but it is not a specific phenomenon resulting from prolonged exposure to high hormone concentrations. D: Metabolism of protein kinases is a cellular process involved in signal transduction, but it is not a direct consequence of prolonged exposure to high hormone concentrations.