The following cytotoxic drugs may be associated with profound and prolonged myelosuppression:

Correct Answer: B

Rationale: Melphalan (B) is associated with profound and prolonged myelosuppression, an alkylating agent causing dose-limiting neutropenia and thrombocytopenia, common in multiple myeloma treatment. Chlorambucil (A) causes milder, reversible suppression. BCNU (C), or carmustine, also causes severe, delayed myelosuppression, notable in brain tumors. Bleomycin (D) primarily causes pulmonary toxicity, not myelosuppression. Vincristine (original E) affects nerves, not marrow. Melphalan's DNA cross-linking halts cell division, effective in hematologic malignancies, but its marrow toxicity requires growth factor support or dose delays, balancing efficacy with infection risk.

Correct Answer: D

Rationale: Protonation (D) is the correct answer, as it describes the process where a weak acid gains a proton (H⁺) in a low pH environment, becoming un-ionized, less water-soluble, and more lipid-soluble. This enhances membrane permeation, as seen with aspirin in the stomach (pH ~2). Distribution (A) is movement into tissues, not a solubility change. Elimination (B) is excretion, unrelated to solubility shifts. First-pass effect (C) is hepatic metabolism post-absorption, not a physical process. Permeation (original E) is movement across membranes, not the solubility change itself. Protonation leverages the Henderson-Hasselbalch equation, where a weak acid's pKa (e.g., aspirin 3.5) relative to pH dictates ionization, impacting absorption and distribution in acidic compartments like the stomach.

Correct Answer: C

Rationale: Steroid hormone action involves diffusion into the cytoplasm and binding to an intracellular receptor (C), as lipophilic steroids (e.g., cortisol) cross membranes, bind nuclear receptors, and regulate gene expression. Option A describes tyrosine kinase receptors (e.g., insulin). Option B fits G-protein-coupled receptors (e.g., epinephrine). Option D involves JAK-STAT pathways (e.g., cytokines), not steroids. Option E (original) about ion channels applies to neurotransmitters. This genomic mechanism, slow but sustained, contrasts with rapid membrane receptor signaling, altering protein synthesis for effects like anti-inflammation, critical in endocrinology and pharmacology.

Correct Answer: A

Rationale: Bronchial smooth muscle (A) is not a nicotinic site; it's primarily muscarinic, responding to acetylcholine via G-protein-coupled receptors for bronchoconstriction. Nicotinic sites, ligand-gated ion channels, include adrenal medullary cells (B) for catecholamine release, parasympathetic (C) and sympathetic (original E) ganglia for autonomic transmission, and skeletal muscle (D) for contraction. Nicotinic receptors' rapid ionotropic action contrasts with muscarinic metabotropic effects, critical in pharmacology (e.g., nicotine mimics ACh at these sites). This distinction guides cholinergic drug targeting, like neuromuscular blockers (skeletal) vs. bronchodilators (smooth muscle).

Correct Answer: D

Rationale: The pH value is the negative log of the hydrogen ion (H⁺) concentration (D), defined as pH = -log[H⁺], measuring acidity (e.g., pH 7 = 10⁻⁷ M H⁺). Option A (log[OH⁻]) and B (-log[OH⁻]) relate to pOH, not pH. Option C (log[H⁺]) omits the negative, yielding incorrect values. Option E (original) about ratios is unrelated. This logarithmic scale, rooted in the water dissociation constant (pH + pOH = 14), quantifies acidity impacting drug ionization (e.g., weak acids in stomach), a cornerstone of pharmaceutical chemistry.