Which of the following is not a steroid hormone?

Correct Answer: C

Rationale: Adrenaline (epinephrine), from the adrenal medulla, is a catecholamine derived from tyrosine, not cholesterol, acting rapidly via cell membrane receptors. Estrogen, cortisone, and testosterone, from gonads or adrenal cortex, are steroid hormones, cholesterol-based, penetrating cells to alter gene expression. Adrenaline's amino acid origin and fast, non-genomic action contrast with steroids' lipid-derived, slower nuclear effects, distinguishing it in endocrine classification, vital for understanding hormone mechanisms.

Correct Answer: A

Rationale: Epinephrine, from the adrenal medulla, mimics sympathetic activation, raising heart rate, dilating pupils, and mobilizing glucose, akin to fight-or-flight. Cortisol, a glucocorticoid, manages chronic stress and metabolism, not acute sympathetic effects. Androgens (e.g., testosterone) drive sex traits, not sympathetic. Aldosterone regulates electrolytes, not mimicking neural responses. Epinephrine's rapid, catecholamine-driven action distinguishes it, critical for acute stress, unlike slower or unrelated hormones.

Correct Answer: C

Rationale: Negative feedback, like cortisol inhibiting ACTH, works by reducing hypothalamic releasing factor (e.g., CRH) secretion, decreasing pituitary output. Stimulating releasing factors increases pituitary hormones, opposite to feedback. Inhibiting an inhibiting factor (e.g., dopamine for prolactin) raises secretion, not shuts it off. 'All' overcomplicates only releasing factor inhibition fits most (e.g., TSH, ACTH). This mechanism distinguishes it, key to endocrine regulation, unlike stimulatory or mixed effects.

Correct Answer: C

Rationale: Negative feedback in the endocrine system adjusts hormone levels inversely: low T₃ and T₄ (thyroid hormones) signal the pituitary to increase TSH, stimulating thyroid output to restore levels. High T₃/T₄ would decrease TSH, not increase, opposing feedback's corrective nature. Low T₃/T₄ decreasing TSH would worsen deficiency, defying regulation. No effect ignores feedback entirely TSH rises to compensate. This inverse response exemplifies negative feedback, distinguishing it, essential for homeostasis, unlike positive or null reactions.

Correct Answer: B

Rationale: Intracellular hormone receptors, typically in the nucleus or cytoplasm, bind steroid or thyroid hormones, which cross membranes due to lipid solubility. Thyroid hormone (T3/T4) uses such receptors to regulate metabolism. Melatonin, growth hormone, and insulin act via membrane receptors, not intracellular ones. Pesticide binding could mimic or block thyroid hormone, disrupting metabolic balance, distinguishing it as the likely target, critical for endocrine disruption studies.