Purines
Adenosine |
Formed from the breakdown of ATP. Acts via adenosine receptors (A1, A2A, A2B, A3). Functions: Vasodilation (especially coronary arteries) Sedative and sleep-promoting effects in the brain. Inhibits neurotransmitter release. Anti-inflammatory and immunosuppressive effects |
ADP (Adenosine Diphosphate) |
Plays a critical role in platelet aggregation. Released during tissue injury → binds P2Y12 receptors on platelets → promotes clot formation. |
ATP (Adenosine Triphosphate) |
Beyond being the "energy currency," extracellular ATP: Acts via P2 receptors (P2X and P2Y). Mediates pain, inflammation, and immune responses. Can trigger cell death pathways or survival signalling. |
Cannabinoids (Endocannabinoids)
Anandamide and 2-AG are naturally occurring ligands. Bind to CB1 (central nervous system) and CB2 (immune cells) receptors. |
Roles: |
Modulate pain, appetite, mood, memory. Regulate immune responses. Provide neuroprotection |
Cannabinoids (Endocannabinoids)
Anandamide and 2-AG are naturally occurring ligands. Bind to CB1 (central nervous system) and CB2 (immune cells) receptors. |
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Roles: |
Modulate pain, appetite, mood, memory. Regulate immune responses. Provide neuroprotection |
Cannabinoids (Endocannabinoids)
Anandamide and 2-AG are naturally occurring ligands. Bind to CB1 (central nervous system) and CB2 (immune cells) receptors. |
Cannabinoids (Endocannabinoids)
Anandamide and 2-AG are naturally occurring ligands. Bind to CB1 (central nervous system) and CB2 (immune cells) receptors. |
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Histamine
Histamine |
Stored in mast cells, basophils, and enterochromaffin-like cells in the stomach. Released in response to allergens, injury, or inflammation.Receptors: H1, H2, H3, H4 |
H1 |
Inflammation, allergy (vasodilation, bronchoconstriction, itching) |
H2 |
Gastric acid secretion in the stomach |
H3 |
Neurotransmission in the brain (auto-inhibition) |
H4 |
Chemotaxis in immune cells |
Serotonin (5-HT)
Location: |
Derived from tryptophan, found in the CNS, GI tract, and platelets. |
Roles |
Mood regulation (CNS). GI motility. Platelet aggregation and vasoconstriction. Sleep, appetite, thermoregulation. |
Receptors |
Multiple (5-HT1 to 5-HT7), all involved in diverse functions like anxiety, pain, nausea, and cardiovascular tone. |
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Eicosanoids
These are derived from arachidonic acid and include: |
Prostaglandins, Thromboxanes, Leukotrienes |
Key Enzymes |
COX (Cyclooxygenase) → Prostaglandins & Thromboxanes. LOX (Lipoxygenase) → Leukotrienes. |
Roles |
Inflammation and immunity.Fever, pain.Bronchoconstriction (asthma).Platelet function (e.g., TXA2 promotes clotting, PGI2 inhibits).Gastric protection and renal blood flow regulation. |
Bradykinin
A nonapeptide released during tissue injury or inflammation. Very potent vasodilator and pain mediator.Increases vascular permeability and causes edema. Also causes bronchoconstriction and stimulates prostaglandin and nitric oxide release. |
Neuropeptides
These are small protein-like molecules used by neurons to communicate. |
Substance P |
Pain transmission, vasodilation |
Neuropeptide Y (NPY) |
Appetite stimulation, vasoconstriction |
Calcitonin gene-related peptide (CGRP) |
Potent vasodilator, involved in migraines |
Endorphins/Enkephalins |
Pain inhibition (natural opioids) |
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Interferons
A type of cytokine (usually classified separately but functionally similar to autacoids). |
Produced in response to viral infections and other immune triggers |
Type I (IFN-α, IFN-β) |
Antiviral |
Type II (IFN-γ) |
Activates macrophages and promotes antigen presentation |
Nitric Oxide (NO)
A gaseous signaling molecule, synthesized by nitric oxide synthases (NOS). |
NO diffuses across cell membranes and activates guanylyl cyclase, increasing cGMP. |
Functions: |
Vasodilation (endothelium-derived relaxing factor). Neurotransmission (e.g., in memory and learning). Antimicrobial and antitumor effects (in macrophages). |
Cytokines
Small proteins involved in cell signaling, especially in the immune system. Produced by various cells (T-cells, macrophages, endothelial cells). |
Interleukins (IL-1, IL-6) |
Inflammation, fever |
TNF-α (Tumor Necrosis Factor) |
Inflammation, apoptosis |
IL-10 |
Anti-inflammatory |
Cytokines can act locally (autocrine/paracrine) or systemically. |
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