Harr Clinical Chemistry Practice Test 2026 – Complete Exam Prep

Catecholamines, which include epinephrine, norepinephrine, and dopamine, are important neurotransmitters and hormones that are produced primarily in the adrenal medulla. The correct statement indicates that plasma levels of catecholamines exhibit both diurnal variations, which is the fluctuation in levels throughout a 24-hour cycle, and pulsed variations, which are more acute fluctuations related to physiological responses such as stress or activity.

These variations are influenced by factors such as circadian rhythms and stress responses, making it important to understand how catecholamine levels can change in various conditions. Measuring these levels is crucial in clinical settings, especially for diagnosing conditions like pheochromocytoma, where catecholamine production is abnormally elevated.

The other options do not accurately describe catecholamines. The derivation of catecholamines is from the amino acid tyrosine, not tryptophan. They are not produced in the zona glomerulosa; that area of the adrenal cortex produces mineralocorticoids such as aldosterone. Lastly, while catecholamines can be excreted in urine, they are primarily found as their metabolites (like metanephrines and normetanephrines) rather than as free catecholamines