Pharmacodynamics, Receptors and Signalling
Receptor families, agonism and antagonism, affinity, efficacy, dose–response, adaptation, intracellular signalling and time course.
How to prepare for MRCPsych Paper A
Build mechanisms first, connect them to development and assessment, then practise distinguishing one best answer within SBA and extended-matching formats.
Core concepts
Concept 1
Pharmacodynamics links drug concentration to receptor binding, intrinsic efficacy, dose–response, therapeutic effect and harm.
Exam cue: Distinguish affinity, efficacy and potency before comparing drugs or explaining antagonism.
Concept 2
Receptor regulation and intracellular signalling explain why biological and clinical effects can outlast plasma exposure or emerge after delay.
Exam cue: Use the full dose–response relation, including maximum effect and safety, rather than one dose point.
Risk pitfalls and guardrails
Calling a high-affinity ligand a strong agonist without considering intrinsic efficacy.
Guardrail: Do not select an option because it is merely associated or familiar; choose the one that answers the exact lead-in.
Assuming the most potent drug necessarily has the greatest maximum effect or clinical value.
Guardrail: Do not select an option because it is merely associated or familiar; choose the one that answers the exact lead-in.
Memory anchors
What is affinity?
The tendency of a ligand to bind to a receptor.
What is intrinsic efficacy?
The capacity of a bound ligand to activate the receptor system and produce a response.
How does a competitive antagonist affect an agonist curve?
It usually shifts the curve to the right without reducing the achievable maximum when enough agonist can overcome the blockade.
How do potency and efficacy differ?
Potency concerns the dose or concentration needed for an effect; efficacy concerns the maximum effect achievable.
What is receptor desensitisation?
Reduced receptor-system response after sustained or repeated stimulation through receptor or downstream adaptation.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
Pharmacodynamics is best summarised as what?
Affinity describes which property of a ligand?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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