Examples of receptors in the following topics:
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- 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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- 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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- 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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- 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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- There are two types of receptors: internal receptors and cell-surface receptors.
- Internal receptors can directly influence gene expression without having to pass the signal on to other receptors or messengers.
- There are three general categories of cell-surface receptors: ion channel-linked receptors, G-protein-linked receptors, and enzyme-linked receptors.
- Enzyme-linked receptors are cell-surface receptors with intracellular domains that are associated with an enzyme.
- An example of this type of enzyme-linked receptor is the tyrosine kinase receptor.
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- 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.
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- Hormones can alter cell activity by binding with a receptor.
- Receptors that can directly influence gene expression are termed nuclear receptors.
- Type I nuclear receptors are located in the cytosol.
- Type II receptors are retained in the nucleus.
- Most hormone receptors are G protein-coupled receptors.
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- 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).
- β-receptors have the subtypes β1, β2, and β3.
- 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.
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- Ligand binding to cell-surface receptors activates the receptor's intracellular components setting off a signaling pathway or cascade.
- Cell-surface receptors, also known as transmembrane receptors, are membrane-anchored (integral) proteins that bind to external ligand molecules.
- There are three general categories of cell-surface receptors: ion channel-linked receptors, G-protein-linked receptors, and enzyme-linked receptors.
- All G-protein-linked receptors have seven transmembrane domains, but each receptor has its own specific extracellular domain and G-protein-binding site.
- Enzyme-linked receptors are cell-surface receptors with intracellular domains that are associated with an enzyme.
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- Lipid-insoluble hormones bind to receptors on the outer surface of the plasma membrane, via plasma membrane hormone receptors.
- When a hormone binds to its membrane receptor, a G protein that is associated with the receptor is activated.
- G proteins are proteins separate from receptors that are found in the cell membrane.
- When a hormone is not bound to the receptor, the G protein is inactive and is bound to guanosine diphosphate, or GDP.
- Describe the events that occur when a hormone binds to a plasma hormone receptor