Biogenic amines — Small charged molecules commonly act as what type of chemical signals?

Introduction:
Biogenic amines such as epinephrine, norepinephrine, dopamine, serotonin, and histamine mediate fast signaling in physiology. This question asks in which contexts these small, often positively charged molecules function.

Given Data / Assumptions:

• Biogenic amines are derived from amino acids.
• They are typically stored in vesicles and released upon stimulation.
• They can act locally at synapses or systemically via the bloodstream.

Concept / Approach:
Many biogenic amines act as neurotransmitters in the nervous system and as hormones when secreted into circulation. For example, epinephrine is a hormone from the adrenal medulla, while dopamine and serotonin are classic neurotransmitters in synaptic signaling.

Step-by-Step Solution:

Verification / Alternative check:
Clinical pharmacology uses the same ligand class for neural and endocrine effects (e.g., beta blockers targeting adrenergic receptors affect both cardiac responses and certain neural pathways), confirming dual roles.

Why Other Options Are Wrong:

• Hormones only or neurotransmitters only: too narrow.
• None of these: incorrect.
• Structural membrane lipids: biogenic amines are not lipids.

Common Pitfalls:
Assuming a molecule has a fixed identity. The role depends on site of release and route of delivery.

Final Answer:
both (a) and (b).