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receptor

 [re-sep´tor]
1. a molecule on the cell surface (cell-surface or membrane receptor) or within a cell, usually in its nucleus (nuclear receptor) that recognizes and binds with specific molecules, producing some effect in the cell; e.g., the cell-surface receptors of immunocompetent cells that recognize antigens, complement components, or lymphokines; or those of neurons and target organs that recognize neurotransmitters or hormones.
2. a sensory nerve ending that responds to various stimuli.
General sense receptors. (From Applegate, 2000.)
α-r's (α-adrenergic r's) alpha-adrenergic receptors.
adrenergic r's receptors for epinephrine or norepinephrine, such as those on effector organs innervated by postganglionic adrenergic fibers of the sympathetic nervous system. There are two types, alpha-adrenergic receptors and beta-adrenergic receptors.
alpha r's (alpha-adrenergic r's) adrenergic receptors found in cardiac muscle and vascular smooth muscle; they are stimulated by norepinephrine and blocked by agents such as phenoxybenzamine. They are subdivided into two types: α1, found in smooth muscle, heart, and liver, with effects including vasoconstriction, intestinal relaxation, uterine contraction and pupillary dilation, and α2, found in platelets, vascular smooth muscle, nerve termini, and pancreatic islets, with effects including platelet aggregation, vasoconstriction, and inhibition of norepinephrine release and of insulin secretion. Called also α-receptors and α-adrenergic receptors.
β-r's (β-adrenergic r's) beta-adrenergic receptors.
B cell antigen r's monomeric IgM, IgD, and (on memory cells only) IgG that is attached to the cell membrane of B lymphocytes (B cells); in conjunction with helper T cells, it triggers B cell activation on contact with antigen.
beta r's (beta-adrenergic r's) adrenergic receptors that are stimulated by epinephrine and blocked by agents such as propranolol. They are subdivided into two basic types: β1-receptors are found in the myocardium and cause lipolysis and cardiac stimulation, and β2-receptors are found in smooth and skeletal muscle and liver and cause bronchodilation and vasodilation. A third type, β3, is atypical; it is more sensitive to norepinephrine than to epinephrine, relatively resistant to propranolol blockade, and may be involved in lipolysis regulation in adipose tissue. Called also β-receptors and β-adrenergic receptors.
cell-surface receptor membrane receptor.
cholinergic r's membrane receptors on cells of effector organs, innervated by cholinergic nerve fibers and responsive to the acetylcholine secreted by these fibers. There are two types, muscarinic receptors and nicotinic receptors.
complement receptor a membrane receptor that can bind activated complement components. For example, component C3b binds to complement receptors of neutrophils, B lymphocytes, and macrophages.
estrogen receptor a cellular regulatory protein that binds estrogenic hormones, found particularly in estrogen-sensitive tissues such as the uterus and breast. Cytoplasmic levels are measured in surgically removed breast carcinomas; high levels indicate that a positive response to endocrine therapy is likely.
Fc r's specific membrane receptors for antigen-antibody complexes or aggregated immunoglobulins that bind a site in the Fc portion of the immunoglobulin molecule and may exhibit specificity for particular immunoglobulin classes. Fc receptors are found on B cells, K cells, macrophages, neutrophils, and eosinophils, and, during some developmental stages, on T cells.
histamine r's receptors for histamine. H1-receptors mediate contraction of smooth muscles and dilation of capillaries, causing effects such as bronchoconstriction and contraction of the intestine; they are blocked by antihistamines such as pyrilamine or chlorpheniramine. H2-receptors mediate acceleration of the heart rate and produce gastric acid secretion; they are blocked by agents such as cimetidine.
IgE r's membrane receptors for IgE, found on mast cells and basophils.
insulin r's a type of membrane receptors specific for insulin, found on target cells.
LDL r's (low-density lipoprotein r's) specific receptors for low-density lipoproteins found in coated pits on the surface of mammalian cells. The coated pits are internalized forming coated vesicles from which the receptors are recycled back to the plasma membrane while particles of low-density lipoprotein are transferred to lysosomes where they are degraded, releasing free cholesterol, phospholipids, and amino acids. Genetic defects in LDL receptors are responsible for familial hypercholesterolemia.
membrane receptor a receptor located on or in the membrane of a cell. Called also cell-surface receptor.
muscarinic r's cholinergic receptors on autonomic effector cells (and also on some autonomic ganglion cells and in some central neurons) that are stimulated by muscarine and parasympathomimetic drugs and blocked by atropine.
nicotinic r's cholinergic receptors of autonomic ganglion cells and motor end-plates of skeletal muscle that are stimulated by low doses of nicotine and blockaded by high doses of nicotine or by tubocurarine.
olfactory receptor a specialized sensory nerve-ending sensitive to stimulation giving rise to the sensation of odors; called also osmoreceptor.
Structure of the olfactory receptors. (From Applegate, 2000.)
opiate r's (opioid r's) receptors that combine with particular opiates to create analgesia and certain other effects. Several different ones have been identified and assigned Greek letters; the μ receptor gives superior analgesia, and the κ receptor is associated with a low degree of physical dependency.
pain r's free nerve endings that are receptors for pain.
stretch receptor a sense organ in a muscle or tendon that responds to elongation.
T cell r's the characteristic marker of T lymphocytes (T cells) that recognize specific foreign antigens as well as self MHC antigens; both must be seen simultaneously to trigger T cell activation (see also lymphocyte activation). The receptor is not a complete immunoglobulin molecule but may contain heavy and light chain variable regions.

re·cep·tor

(rē-sep'tŏr, tōr),
1. A structural protein molecule on the cell surface or within the cytoplasm that binds to a specific factor, such as a drug, hormone, antigen, or neurotransmitter.
2. Any one of the various sensory nerve endings in the skin, deep tissues, viscera, and special sense organs.
[L. receiver, fr. recipio, to receive]

receptor

/re·cep·tor/ (-ter)
1. a molecule on the surface or within a cell that recognizes and binds with specific molecules, producing a specific effect in the cell; e.g., the cell-surface receptors for antigens or cytoplasmic receptors for steroid hormones.
2. a sensory nerve ending that responds to various stimuli.

α-adrenergic receptors  adrenergic receptors that respond to norepinephrine and to such blocking agents as phenoxybenzamine. They are subdivided into two types: α1, found in smooth muscle, heart, and liver, with effects including vasoconstriction, intestinal relaxation, uterine contraction and pupillary dilation, and α2, found in platelets, vascular smooth muscle, nerve termini, and pancreatic islets, with effects including platelet aggregation, vasoconstriction, and inhibition of norepinephrine release and of insulin secretion.
adrenergic receptors  receptors for epinephrine or norepinephrine, such as those on effector organs innervated by postganglionic adrenergic fibers of the sympathetic nervous system. Classified as α and β.
alpha-adrenergic receptors  α.
β-adrenergic receptors , beta-adrenergic receptors adrenergic receptors that respond particularly to epinephrine and to such blocking agents as propranolol. They are subdivided into two basic types: β1, in myocardium and causing lipolysis and cardiac stimulation, and β2, in smooth and skeletal muscle and liver and causing bronchodilation and vasodilation. The atypical type β3 may be involved in lipolysis regulation in adipose tissue.
cholinergic receptors  cell-surface receptor molecules that bind the neurotransmitter acetylcholine and mediate its action on postjunctional cells.
complement receptors  cell-surface receptors for products of complement reactions, playing roles including recognition of pathogens, phagocytosis, adhesion, and clearance of immune complexes. The best characterized are C1–C4, which bind C3 fragments already bound to a surface.
cutaneous receptor  any of the various types of sense organs found in the dermis or epidermis, usually a mechanoreceptor, thermoreceptor, or nociceptor.
cytokine receptors  membrane-spanning proteins that bind cytokines via extracellular domains, acting to convert an extracellular signal to an intracellular one.
H1 receptors , H2 receptors see histamine.
joint receptor  any of several mechanoreceptors that occur in joint capsules and respond to deep pressure and to other stimuli such as stress or change in position.
muscarinic receptors  cholinergic receptors that are stimulated by the alkaloid muscarine and blocked by atropine; they are found on automatic effector cells and on central neurons in the thalamus and cerebral cortex.
muscle receptor  a mechanoreceptor found in a muscle or tendon.
nicotinic receptors  cholinergic receptors that are stimulated initially and blocked at high doses by the alkaloid nicotine and blocked by tubocurarine; they are found on automatic ganglion cells, on striated muscle cells, and on spinal central neurons.
nonadapting receptor  a mechanoreceptor, such as a nociceptor, that responds to stimulation with a continual steady discharge and little or no accommodation over time.
olfactory receptor  a chemoreceptor in the nasal epithelium that is sensitive to stimulation, giving rise to the sensation of odors.
opiate receptor , opioid receptor any of a number of receptors for opiates and opioids, grouped into at least seven types on the basis of their substrates and physiological effects.
orphan receptor  a protein identified as a putative receptor on the basis of its structure but without identification of possible ligands or evidence of function.
pain receptor  nociceptor.
rapidly adapting receptor  a mechanoreceptor that responds quickly to stimulation but that rapidly accommodates and stops firing if the stimulus remains constant.
sensory receptor  receptor (2).
slowly adapting receptor  a mechanoreceptor that responds slowly to stimulation and continues firing as long as the stimulus continues.
stretch receptor  a sense organ in a muscle or tendon that responds to elongation.
tactile receptor  a mechanoreceptor for the sense of touch.
thermal receptor  thermoreceptor.

receptor

(rĭ-sĕp′tər)
n.
1. Physiology A specialized cell or group of nerve endings that responds to sensory stimuli.
2. Biochemistry A molecular structure or site on the surface or interior of a cell that binds with substances such as hormones, antigens, or neurotransmitters or is activated by events such as a change in the concentration of an ion.

receptor

[risep′tər]
Etymology: L, recipere, to receive
1 a chemical structure, usually of protein or carbohydrate, on the surface of a cell that combines with an antigen to produce a discrete immunological component.
2 a sensory nerve ending that responds to various kinds of stimulation.
3 a specific cellular protein that must first bind a hormone before cellular response can be elicited. The protein may be in the cytoplasm or in the cell membrane and has a special affinity for toxins and amboceptors.

re·cep·tor

(rĕ-sep'tŏr)
1. A structural protein molecule on the cell surface or within the cytoplasm that binds to a specific factor, such as a drug, hormone, antigen, or neurotransmitter.
2. Any one of the various sensory nerve endings in the skin, deep tissues, viscera, and special sense organs.
[L. receiver, fr. recipio, to receive]

receptor

1. Any structure on or penetrating a plasma cell membrane or other membrane, capable of binding a specific external substance, such as a HORMONE, CYTOKINE, STEROID or NEUROTRANSMITTER, and, as a result, effecting a response within the cell. Plasma membrane receptors commonly respond by releasing a ‘second messenger’ within the cell.
2. A sensory nerve ending capable of receiving stimuli of various kinds and responding by the production of nerve impulses. The receptor has gradually come to be recognized as one of the fundamentally important entities in physiology, pathology, pharmacology and medical science generally.

receptor

any cell or organ of an animal capable of detecting a stimulus, i.e. a change in the external or internal environment, and which subsequently brings about a response in the behaviour of the animal. A receptor, for example the eye, receives and transforms stimuli into sensory nerve impulses. Receptors vary in complexity from the end of a sensory neurone to a sense cell and complex organs such as the eye. They may occur externally (EXTEROCEPTOR) or internally (ENTEROCEPTOR) or be positioned to receive body movement (PROPRIOCEPTOR). They also may be classified according to the type of stimulus received, e.g. PHOTORECEPTOR, THERMORECEPTOR, CHEMORECEPTOR,MECHANORECEPTOR, electro-receptor. See also REFLEX ARC. In microorganisms specific cell surface components act as receptors, for example for the adsorption of PHAGES (in phage infection) or for the attachment of SEX PILI (in bacterial CONJUGATION).

Receptor

A molecular structure in a cell or on the surface of a cell that allows binding of a specific substance that causes a specific physiologic response.

receptor

(1) in the nervous system, the distal ending of an afferent nerve, or specialist structure served by such a nerve, which signals the incidence of a mechanical, chemical, thermal or other stimulus (termed sensory receptor if the signal can reach consciousness); (2) in the context of cell signalling, a molecular structure on the surface of a cell (membrane receptor) or in its nucleus, to which hormonal or other signalling molecules or drugs must bind to initiate their effect. See also proprioceptor.

receptor

terminal structure at a sensory nerve; appears to react preferentially to specific stimuli (e.g. Meissner corpuscles) Table 1
Table 1: Sensory evaluation of the lower limb
ModalityType of sensory nerve fibreMeans of evaluation
Light touchMerkel's discs and Meissner's corpuscles of A-beta nerve fibresAwareness of the contact of cotton wool applied to the skin surface
Pinprick painFree, fine nerve endings of A-delta and C fibresAwareness of the weight of the tip of a sterile hypodermic needle on a 2-mL syringe, filled with water, on the skin
Or awareness of the pressure exerted by the metal end of a Neurotip
Or awareness of the pressure applied to the skin by an algometer
Blunt/sharpNeurotip (plastic end) + Neurotip (metal end)
TemperatureFree, fine nerve endings of C nerve fibresAwareness of the contact of cold or heat (e.g. tubes of hot or cold water)
VibrationPacinian corpuscles at the termini of A-beta nerve fibresAwareness of vibration when the instrument is placed against a bony prominence, using:
1. a 128-Hz (middle C) tuning fork (which is appreciated as present or absent)
2. a Rykel-Seiffer 128-Hz tuning fork (the tips of which are weighted and indicate the degree of perceived vibration, in arbitrary units, so that the level of sensory awareness can be recorded; normal sensation = >4)
3. Neuraethesiometer; normal sensation = appreciation of > 23V vibratory stimulus
ProprioceptionThe examiner moves a joint and the patient identifies the direction of movement
Protective painFree, fine nerve endings of A-delta and C fibres10G monofilament (also known as the 5.07 Semmes-Weinstein monofilament)
The normal patient will be able to detect the contact of the tip of the nylon monofilament across the majority of the plantar surface
Ankle jerkGolgi organs in tendons and muscle stretch receptors of A-beta nerve fibresAnkle jerk test, where sudden stretch of the muscle unit, from the contact of the tendon hammer at the tendo Achilles approximately 5cm proximal to its insertion at the calcaneum, excites afferent nerve endings which link within the spinal cord to efferent nerves that pass to the gastrocnemius muscle and cause a brief muscle contraction or twitch

Patients may be unaware of their loss of some or all distal sensation; sensory loss may present as degrees of numbness, paraesthesia or hyperalgesia. The patient should lie relaxed on a couch throughout the assessment, and not watch the tests, in order to avoid visual prompts. Sensory evaluation should be carried out in a systematic manner, with all areas of the foot and all sensory modalities assessed. The distribution of altered sensation (e.g. dermatomal loss; distal loss) is noted on an appropriate form retained within the patient's case notes. Where possible the same clinician should carry out any repeat tests, and repeat tests, e.g. every 6-12 months should be made at the same time of day as the original assessment, due to the diurnal variation in sensory awareness.

photoreceptor 

A receptor capable of reacting when stimulated by light, such as the rods and cones of the retina. See cone cell; rod cell.

re·cep·tor

(rĕ-sep'tŏr)
1. A structural protein molecule on cell surface or within cytoplasm that binds to a specific factor.
2. Any sensory nerve endings in the skin or elsewhere.

receptor(s) (rēsep´tur),

n a site or location within a cell or its membrane that combines with a haptophore group of a toxin, drug, enzyme, hormone, or other substance and that may elicit a specific or general response; a sensory nerve terminal that responds to stimuli of various kinds.
receptor, sensory,
n receptor system built on the theory that receptor organs are specialized and respond to the law of specific nerve energies; i.e., each type of end-organ, no matter what stimulus is applied, will respond (if it responds) with only a single appropriate type of sensation. Common experience shows this to be true; e.g., when a person receives a blow to the eye, light is experienced as a consequence of the blow. Another factor is that the impulse will travel in only one direction, from the receptor organ back to the central nervous system. The receptor system is thus the summation in the brain of all the sensory stimuli that come from the special senses, general senses, mucous membrane, skin, and deeper tissues and is the basis for instruction sent to the musculoskeletal system for action, as in the masticatory phenomenon.
receptors, adrenergic,
n alpha and beta “units” associated with sympathetic neuroeffectors that react with sympathomimetic drugs to elicit the response of the effector cells.
receptors, beta,
n sites on some cell membranes in the sympathetic nervous system that either activate or block the normal functions of the cell by binding with epinephrine (adrenaline). Cells with beta receptors normally control physiologic responses such as heart rate.

receptor

1. a molecule on the surface or within a cell that recognizes and binds with specific molecules, producing some effect in the cell, e.g. the cell-surface receptors of immunocompetent cells that recognize antigens, complement components or lymphokines, or those of neurons and target organs that recognize neurotransmitters or hormones; see also opioid receptors.
2. a sensory nerve ending that responds to various stimuli, e.g. arterial stretch, baroreceptors, cold, Golgi tendon organs, joint, muscle and tendon, olfactory, retinal, taste and warmth.

receptor activation
the cell of a sensory receptor responds to a specific energy change in its environment and initiates a corresponding sensory input.
adrenergic r's
receptors for epinephrine or norepinephrine, such as those on effector organs innervated by postganglionic adrenergic fibers of the sympathetic nervous system. Classified as α-adrenergic receptors, which are stimulated by norepinephrine, and β-adrenergic receptors, which are stimulated by epinephrine. See also adrenergic receptors.
autonomic r's
includes adrenergic and muscarinic receptors.
cholinergic r's
receptor sites on effector organs innervated by cholinergic nerve fibers and which respond to the acetylcholine secreted by these fibers. There are two types: muscarinic receptors and nicotinic receptors.
complement receptor
a cell-surface receptor capable of binding activated complement components. For example, component C3b is bound to neutrophils, B lymphocytes and macrophages.
dopamine r's
there are dopamine-inhibitory and dopamine-excitatory receptors.
drug receptor
a component of tissue with which a drug reacts. Classified according to the type of drugs that react with them.
Fc receptor
bind immunoglobulins via Fc part of the molecule.
histamine r's
receptors for histamine, classified as H1-receptors, which produce bronchoconstriction and contraction of the gut and are blocked by antihistamines, such as mepyramine or chlorpheniramine, and H2-receptors, which produce gastric acid secretion and are blocked by H2-receptor blockers, such as cimetidine.
muscarinic receptor
see muscarinic receptors.
nicotinic receptor
see nicotinic receptors.
peripheral receptor
sensory receptors including cutaneous warm and cold, dermoreceptors touch and pain plus receptors in the mucosae.
sensory receptor
an endorgan at the end of an afferent neuron which is capable of stimulation by a specific change, physical or chemical, in the internal or external environment of the patient.
toll-like r's
a family of transmembrane proteins that differentially recognize pathogen-associated molecular patterns through an extra cellular domain and initiate inflammatory signaling pathways through an intracellular domain; they play a central role in the innate immune response to pathogens.
receptor tyrosine kinases
a large class of cell-surface receptors with tyrosine-specific protein kinase activity.
References in periodicals archive ?
A human complement receptor 1 polymorphism that reduces Plasmodium falciparum resetting confers protection against severe malaria.
Complement receptor 1: CR1 (CD35, C3b/C4b receptor) is a polymorphic membrane bound glycoprotein, differentially expressed on erythrocytes, eosinophils, monocytes, B-lymphocytes, T-lymphocytes, dendritic cells and kidney podocytes (11).
The complement C3dg moiety could also serve as a ligand, facilitating the binding of the whole complex to complement receptor 2 (30).

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