adrenergic receptor
(noun)
Any of several sites in the surface membranes of cells innervated by adrenergic neurons.
Examples of adrenergic receptor in the following topics:
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Adrenergic Neurons and Receptors
- Adrenergic receptors are molecules that bind catecholamines.
- There are two main groups of adrenergic receptors, α and β, with several subtypes. α receptors have the subtypes α1 (a Gq coupled receptor) and α2 (a Gi coupled receptor).
- Adrenaline or noradrenaline are receptor ligands to α1, α2, or β-adrenergic receptors (the pathway is shown in the following diagram).
- α1-adrenergic receptors are members of the G protein-coupled receptor superfamily.
- This schematic shows the mechanism of adrenergic receptors.
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Local Regulation of Blood Flow
- Generally, norepinephrine and epinephrine (hormones secreted by sympathetic nerves and the adrenal gland medulla) are vasoconstrictive, acting on alpha-1-adrenergic receptors.
- However, the arterioles of skeletal muscle, cardiac muscle, and the pulmonary circulation vasodilate in response to these hormones acting on beta-adrenergic receptors.
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Agonists, Antagonists, and Drugs
- Acetylcholine receptor agonists and antagonists can have a direct effect on the receptors or exert their effects indirectly.
- Muscarinic receptor antagonists bind to muscarinic receptors, thereby preventing ACh from binding to and activating the receptor.
- Beta blockers (sometimes written as β-blockers) or beta-adrenergic blocking agents, beta-adrenergic antagonists, beta-adrenoreceptor antagonists, or beta antagonists, are a class of drugs used for various indications.
- As beta-adrenergic receptor antagonists, they diminish the effects of epinephrine (adrenaline) and other stress hormones.
- Beta blockers block the action of endogenous catecholamines—epinephrine (adrenaline) and norepinephrine (noradrenaline) in particular—on β-adrenergic receptors, part of the sympathetic nervous system that mediates the fight-or-flight response.
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Postganglionic Neurons
- In the sympathetic division, most are adrenergic, meaning they use norepinephrine as their neurotransmitter.
- In response to this stimulus, postganglionic neurons—with two important exceptions—release norepinephrine, which activates adrenergic receptors on the peripheral target tissues.
- The activation of target tissue receptors causes the effects associated with the sympathetic system.
- The ACh acts on two types of receptors, the muscarinic and nicotinic cholinergic receptors.
- The postganglionic nerve then releases ACh to stimulate the muscarinic receptors of the target organ.
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Heart Circulation
- This mechanism is due to beta-adrenergic receptors in the coronary arteries and helps enable the increased cardiac output associated with fight-or-flight responses.
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Classification of Receptors by Stimulus
- Sensory receptors can be classified by the type of stimulus that generates a response in the receptor.
- Sensory receptors perform countless functions in our bodies.
- Cutaneous receptors are sensory receptors found in the dermis or epidermis.
- Encapsulated receptors consist of the remaining types of cutaneous receptors.
- A tonic receptor is a sensory receptor that adapts slowly to a stimulus, while a phasic receptor is a sensory receptor that adapts rapidly to a stimulus.
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Ionotropic and Metabotropic Receptors
- Although both ionotropic and metabotropic receptors are activated by neurotransmitters, ionotropic receptors are channel-linked while metabotropic receptors initiate a cascade of molecules via G-proteins.
- Two types of membrane-bound receptors are activated with the binding of neurotransmitters: ligand-gated ion channels (LGICs) inotropic receptors and metabotropic G- protein coupled receptors.
- Examples of metabotropic receptors include glutamate receptors, muscarinic acetylcholine receptors, GABAB receptors, most serotonin receptors, and receptors for norepinephrine, epinephrine, histamine, dopamine, neuropeptides, and endocannabinoids.
- Since opening channels by metabotropic receptors involves activating a number of molecules in the intracellular mechanism, these receptors take longer to open than the inotropic receptors.
- While ionotropic channels have an effect only in the immediate region of the receptor, the effects of metabotropic receptors can be more widespread throughout the cell.
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Blocking of Hormone Receptors
- A receptor antagonist does not provoke a biological response upon receptor binding, but limits or dampens agonist-mediated responses.
- A receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a receptor, but blocks or dampens agonist-mediated responses.
- Binding to the active site on the receptor regulates receptor activation directly.
- The current accepted definition of receptor antagonist is based on the receptor occupancy model.
- Irreversible antagonists covalently bind to the receptor target and, in general, cannot be removed; inactivating the receptor for the duration of the antagonist effects is determined by the rate of receptor turnover, the rate of synthesis of new receptors.
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Classification of Receptors by Location
- Some sensory receptors can be classified by the physical location of the receptor.
- Sensory receptors code four aspects of a stimulus:
- Receptors are sensitive to discrete stimuli and are often classified by both the systemic function and the location of the receptor.
- Sensory receptors are found throughout our bodies, and sensory receptors that share a common location often share a common function.
- For example, sensory receptors in the retina are almost entirely photoreceptors.
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Target Cell Specificity
- Hormones target a limited number of cells (based on the presence of a specific receptor) as they circulate in the bloodstream.
- This androgen insensitivity occurs when the receptors on the target cells are unable to accept the hormone due to an impairment in receptor shape.
- Target cells are capable of responding to hormones because they display receptors to which the circulating hormone can bind.
- Finally, hormone–receptor affinity can be altered by the expression of associated inhibitory or co-activating factors.
- In some instances, alterations of receptor structure due to a genetic mutation can lead to a reduction in hormone–receptor affinity, as in the case of androgen insensitivity.