Being lipid soluble, steroids can do all the following EXCEPT:

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: 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.

Correct Answer: B

Rationale: The correct answer is B because the parathyroid glands target the bone and activate osteoclasts to release calcium into the bloodstream. This process helps maintain adequate blood calcium levels. By activating osteoclasts, calcium is released from the bone into the blood, ensuring a balance of calcium levels. A: Blocking the action of growth hormone is unrelated to the function of parathyroid glands in maintaining blood calcium levels. C: Antagonizing the synthesis of calcitonin is not the primary mechanism through which parathyroid glands regulate blood calcium levels. D: Slowing the activity of tissues that require calcium for activity would not help maintain adequate blood calcium levels as it does not address the direct release of calcium from bone by activating osteoclasts.

Correct Answer: A

Rationale: The correct answer is A: TH (Thyroid Hormone). TH is the only amine hormone that acts like a steroid because it is derived from an amino acid but functions similarly to steroid hormones by entering target cells and binding to intracellular receptors to regulate gene expression. ACTH, GH, and ADH are peptide hormones that do not act like steroids. ACTH stimulates the adrenal glands to produce cortisol, GH stimulates growth, and ADH regulates water balance in the body.