Receptors in our Body

 

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📘 Comparative Table of Major Receptor Types (Rang & Dale + KD Tripathi)

(High-yield for Pharmacology Exams)

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1. Cholinergic Receptors

Receptor	Type	Location	Mechanism of Action	Physiological Role	Deficiency / Excess Disorders
M1 (Muscarinic)	GPCR (Gq)	CNS (cortex, hippocampus), Gastric parietal cells	↑IP3, ↑DAG — excitatory	Cognitive function, Gastric acid secretion	↓ → Cognitive decline, memory loss; ↑ → Peptic ulcers
M2	GPCR (Gi)	Heart (SA & AV nodes), presynaptic neurons	↓cAMP, K+ channel opening → inhibitory	↓HR, ↓conduction	↓ → Tachycardia; ↑ → Bradycardia, AV block
M3	GPCR (Gq)	Smooth muscles, glands, eye	↑IP3/DAG → contraction & secretion	Bronchoconstriction, miosis, gland secretion	↓ → Constipation, dry eyes; ↑ → Asthma, hypersecretion
Nn (Nicotinic neuronal)	Ligand-gated ion channel (Na+, K+)	Autonomic ganglia, CNS	Fast depolarization	Ganglionic transmission	Block → Hypotension, paralysis
Nm (Nicotinic muscle)	Ion channel	NMJ skeletal muscle	Depolarization → contraction	Voluntary muscle contraction	Block → Paralysis (e.g., curare)

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2. Adrenergic Receptors

Receptor	Location	Mechanism	Actions	Deficiency / Excess
α1	Vascular smooth muscle, iris, bladder	Gq → ↑IP3/DAG	Vasoconstriction, mydriasis	↓ → Hypotension; ↑ → Hypertension
α2	Presynaptic nerve terminals	Gi → ↓cAMP	↓NE release	↓ → Sympathetic overactivity; ↑ → Sedation
β1	Heart, kidney	Gs → ↑cAMP	↑HR, ↑contractility, ↑renin	↓ → Heart failure; ↑ → Tachycardia
β2	Lungs, uterus, skeletal muscles	Gs	Bronchodilation, vasodilation	↓ → Asthma symptoms; ↑ → Tremors
β3	Adipose tissue	Gs	Lipolysis	↓ → Obesity; ↑ → Weight loss

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3. Dopamine Receptors

Receptor	Location	Mechanism	Actions	Deficiency / Excess
D1	Renal vessels, CNS	Gs ↑cAMP	Vasodilation, cognition	↓ → Cognitive impairment
D2	CNS (basal ganglia), pituitary	Gi ↓cAMP	Motor control, ↓prolactin	↓ → Parkinson’s, ↑prolactin; ↑ → Psychosis
D3/D4	Limbic system	Gi	Emotion, mood	Abnormality → Schizophrenia
D5	Limbic, hypothalamus	Gs	Neuronal excitation	–

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4. Serotonin (5-HT) Receptors

Receptor	Location	MOA	Role	Disorders
5-HT1A/B/D	CNS	Gi ↓cAMP	Mood, migraine	↓ → Depression; ↑ → Serotonin syndrome
5-HT2A/C	CNS, platelets	Gq	Behavior, vasoconstriction	↑ → Hallucinations (LSD action)
5-HT3	Area postrema, GI	Ion channel (Na/K)	Vomiting reflex	↑ → Nausea/vomiting
5-HT4	GI tract	Gs ↑cAMP	↑GI motility	↓ → Constipation

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5. Histamine Receptors

Receptor	Location	MOA	Actions	Disorders
H1	Smooth muscle, endothelium, CNS	Gq	Allergy, vasodilation	↑ → Allergic rhinitis
H2	Gastric parietal cells	Gs	↑Acid secretion	↑ → Peptic ulcers
H3	Presynaptic neurons	Gi	↓Histamine release	Abnormality → Sleep disorders
H4	Bone marrow, immune cells	Gi	Chemotaxis	↑ → Chronic inflammation

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6. GABA Receptors

Receptor	Location	MOA	Role	Disorders
GABA-A	CNS	Cl⁻ ion channel	Fast inhibitory neurotransmission	↓ → Anxiety, seizures; ↑ → Sedation
GABA-B	CNS	Gi → ↓cAMP	Slow inhibitory	↓ → Spasticity

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7. Glutamate Receptors (Excitatory)

Receptor	Type	Role	Disorders
NMDA	Ca²⁺/Na⁺ ion channel	Learning, memory	↑ → Excitotoxicity, stroke
AMPA	Ion channel	Fast excitation	–
Kainate	Ion channel	Neuronal excitation	–
mGluR1-8	GPCR	Modulates synaptic transmission	Abnormality → Schizophrenia

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8. Opioid Receptors

Receptor	Location	MOA	Role	Disorders
Mu (μ)	CNS, GI	Gi	Analgesia, euphoria	Overstim → Dependence
Kappa (κ)	Spinal cord	Gi	Analgesia	↑ → Dysphoria
Delta (δ)	CNS	Gi	Mood modulation	–

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9. Purinergic Receptors (Adenosine, ATP)

Receptor	Location	MOA	Role
A1 (Adenosine)	Heart, CNS	Gi ↓cAMP	↓HR, sedation
A2A	Coronary vessels	Gs ↑cAMP	Vasodilation
P2X	Peripheral nerves	Ion channel	Pain
P2Y	Platelets	Gq/Gi	Aggregation

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