Receptor superfamilies
What it means
Four targets by speed: 1. Ligand-gated ion channels (ms) — nicotinic ACh, GABA-A, NMDA. 2. G-protein-coupled receptors (seconds) — β-adrenergic, muscarinic, opioid, dopamine, most drug targets. 3. Kinase-linked / enzyme-linked (minutes) — insulin, growth factors. 4. Nuclear receptors (hours) — glucocorticoids, thyroid hormone, sex steroids, vitamin D (gene transcription).
Worked example
Steroids act on nuclear receptors → effects (and side effects) develop over hours via altered transcription, not instantly.
In the exam
A hormone produces its effects only after several hours because it binds an intracellular receptor that alters gene transcription.
What settles it
Nuclear receptors = slow (hours, transcriptional); ligand-gated ion channels = millisecond responses.
Classically confused with
Bioavailability & first-pass
Source: Rang & Dale; StatPearls