Definition

A membrane receptor is a protein which is located on the membrane that surrounds each cell of the body, specifically this membrane is known as plasma membrane. The role of membrane receptors is to receive a message. See a plasma membrane.

Classification

Sympathetic or adrenergic receptors are specific receptors of the adrenergic hormone also known as Catecholamines. It’s the noradrenaline and adrenaline. Specialists distinguish two varieties of adrenergic receptor. More specifically it is molecular structure located at the level of the termination of the sympathetic nets and which have the capacity to respond to the mediators adrenergic calculated sympathicomimetic amines introducing a very characteristic response. Specialists in neurology-biology is Ahlquist, in 1948, allowing to distinguish receptors alpha sensitive to the action of noradrenaline and responsible for most of the excitatory effects of sympathetic stimulation i.e. vasoconstriction, tachycardia contraction of the uterus and the spleen. It highlighted only an inhibitory effect on the bowel. Beta receptors, they are susceptible to other stimulation (by isoprenaline) and sympathetic stimulation causes an inhibitory effect resulting in vasodilation (opening of the calibre of the vessels) device, the relaxation of bronchial muscles, relaxation of the muscles of the digestive tract, uterus and bladder. Beta receptors nevertheless have an effect on the heart excitatory. All of these two types of receptors are sensitive to the action of adrenaline. (1) adrenergic alpha receptors are present on the muscle cells of the heart and arteries. Stimulation of the receptor causes an increase in the rate and force of contraction of the heart. The intensity of the tone of the vessels called vasoconstriction is also accentuated. (C) ECI in the end leads to the increase in blood pressure. Substances which possess such capacity are noradrenaline and adrenaline, phentolamine. (2) Beta Adrenergic receptors to be three types: Beta 1, Beta 2 and Beta Adrenergic 3. Beta Adrenergic receptors are mainly present at the level of the cells of the heart and vessels. Their stimulation results in a relaxation of the tone of the vessels which facilitates the work of the heart. Drugs containing Mimetic 1 beta are part of this variety of beta receptor. Beta receptor 2 are essentially present on muscle cells and the bronchi as well as on the cells of the uterus. Their stimulation results in a release. These properties is used by drug Mimetic Beta2. 3 Beta receptors are present on the surface i.e. adipocytes fat cells and the cells of the intestines. Leu r. stimulation essentially causes a Thermogenesis, i.e. the production of heat. Cholinergic receptors are molecular structures formed by proteins present in certain (effector) cell in the nervous system. Cholinergic receptors that are sensitive to the action of acetylcholine are on the membrane of the neuron. It is necessary to distinguish two varieties of Cholinergic receptor on the effects of their excitement: the Cholinergic receptor Nicotinic and muscarinic cholinergic receptors. (1) Nicotinic cholinergic receptors respond to the action of acetylcholine Nicotinic effects. The Nicotinic effect is an action (pharmacodynamics) which is obtained at the level of the neuromuscular junction (located at the level of muscle synapse) but also at the level of the ganglion relays of the autonomic nervous system (nervous system, automatic sort). Its action is close to that of nicotine. In small quantities the nicotine causes excitation of ganglionic synapses. These are first of all the synapses of the parasympathetic nervous system and sympathetic nervous system and adrenal Medulla gland synapses which are excited. This causes tachycardia (increased heart rate) a rise in blood pressure, acceleration of respiration by Nicotinic depressant effect and paralysis of synapses ganglion this results in Mydriasis (increase of the calibre of the pupils) and an acceleration of peristalsis. More high-dose nicotine leads to a paralysis of the synapses of the lymph nodes is called the ganglioplégique action to depressant effect. (2) The muscarinic cholinergic receptors respond to the action of acetylcholine by muscarinic effects or muscariniens. The muscarinic effects are obtained by the action of muscarine which is an alkaloid (plant material) present in various poisonous mushrooms. The muscarinien effect a result slow heart rate, lowers blood pressure, dilate arterioles, to contract the intestines and the bronchi and increase the secretions of the body. This effect is obtained by the excitation of muscarinic receptor which is comparable to that of the postganglionic stimulations that parasympathetic nervous system. The serotonin receptors are molecular structures which are located in certain organs and that have the capacity to respond to serotonin. They are also called 5-hydroxytryptamine (5-HT). It is necessary to distinguish between three types of serotonin receptors. (1) S1 type which when it stimulates lowered blood pressure. A substance: the urapidil is used in this sense. (2) The type S2, when he is inhibited causing a vasodilatory action. Ketanserin has these properties. L ‘ inhibition of type S2 serotonin receptors results in an antidepressant effect. (3) Type S3, when he was inhibited decreases vomiting. This property is used to treat some patients who have undergone a cancer chemotherapy (ondansetron, gralisétron). Opiate receptors are structures found on the surface of certain cells. Through these opiate receptors, morphine and its derivatives have an action on the cells on which they wish to act. The Organization has on the other hand the ability to manufacture equivalents known as endorphins. Opiate receptors have specific sites. These receptors binding of molecules is reversible and may be inhibited by antagonistic substances. For example the naloxone which is a day drug a role of inhibition. There are different types of opiate receptors. (1) Mu receptors are present on the nerve cells whose specialty is the transmission of pain. For stimulation of the mu receptors there analgesia i.e. a reduction or abolition of pain. The excitement of these same receptors leads to depression of the respiratory centres and a contraction of the pupils known as miosis. On the other hand these mu receptors, when they are stimulated have a psychological effect. Thus the patient has an indifference or on the contrary a euphoria. Finally the mu receptors are closely related phenomena in dependence. The term arm refers to the State of a usual person, subject to a substance any more often a drug which may not happen. This type of receptor is stimulated by morphine and its derivatives (morphine: whose action is equivalent to that of morphine) and by endorphins like beta endorphin among others. The endorphin is a substance (more specifically a peptide: protein consisting of a number of amino acids) which forms naturally in the brain. It consists of many amino acids that is found mainly in the hypothalamus and which has an analgesic action (reducing or eliminating pain). Specialists in neuro-Endocrinology view endorphins and enkephalins as of endogenous morphines (which the training is done within the body). (2) The epsilon receptor have a distribution and a function nearby mu receptors. This variety of receptors is specifically stimulated by the dymorphine which is a variety of endorphin. (3) The beta receptors are located in the limbic system of the brain. The limbic system is made up of structures whose onset dates back at the evolution of the vertebrates. It was sort of one of the oldest parts of the brain. On the outskirts of the limbic system is the cortex with different appointments which the cortex transition. The limbic system is the set of structures located on the inner side of each hemisphere including the hippocampus, the fornix, pads body, septal nuclei, the amygdala and the diagonal strip of Broca. It structures that have in common a distant origin after the evolution of the human species. Following the development of the system indicates appeared more precisely called neocortex cerebral cortex which is somewhat the most recent brain. The limbic system is involved in Physiology specifically in neurophysiology (medical specialty of Neurobiology) emotions and memory essentially. The limbic system receives information from different sensory reception systems. Part of messages is processed by the limbic system which on the other hand establishes connections with the thalamus and hypothalamus and other midbrain (upper part of the brainstem). All of these connections allows the development of Behavioral responses. The thalamus is an important (in volume and function) located in the deep part of the brain, specifically nerve centre of any of the third ventricle. The thalamus has functions multiple especially to collect information from the nerve pathways of sensitivity (pain, touch, the position in space etc.). Then, the thalamus sends data to the cerebral cortex and ascending parietal air specifically. The thalamus plays an important role with regard to the balance and the orientation of the body in space, in association with the cerebellum. Some areas of the cortex in particular ascending frontal area receive the data from the thalamus, thus allowing the body to be in balance in space. (D) ‘ on the other hand the thalamus establishes connections with the limbic system which we have to speak in particular with regard to emotion and memory. Stimulation of beta receptors, therefore located in the system States, resulted in the appearance of psychoaffectifs and psychomotor phenomena such as hallucinations or a lesser agitation. There is a type of encephalitis called limbic encephalitis which is a neurological disease characterized by disorders of memory which are the result of inflammation of certain brain cells. This type of neurological diseases is generally observed in small-cell lung cancer and lymphoma. (4) The delta receptors are particularly sensitive to the endorphins but this time of enkephalin type. The serotonin receptors are molecular structures which are located in different organs and that have the capacity to respond to serotonin or 5-hydroxytryptamine (5-HT on bracket.) I l is necessary to distinguish three varieties of serotonin receptors. The type is a stimulation to treat high blood pressure through a substance: the urapidil, the type is that, when he is inhibited causing a vasodilation (ketanserin) & ys histamine receptor or receptor H, are present (molecular) structures that has inside cer­taines effector cells with the capacity to react to histamine. There are different types of histamine receptors. (1) The H2 of Ash and Schild receptors whose stimulation results in the fall of blood pressure, the dilata­tion of the capillaries and contraction of smooth muscles of the gut and bronchial tubes. (2) H2 receptor in relation to gastric acid secretion and the excitement causes a rise in heart rate (tachycardia), inhibition of contractions of the uterus. Some drugs are likely to block the action of histamine receptor, it is the anti­histaminiques and antiallergic for the first type of receptors. In regards the second type of receptors, cimetidine, ranitidine and other antisecretory are prescribed for peptic ulcers. (3) The settled H3 receptors, discovered en1983. It’s receptors located in the brain, for specialists of type presynaptic and who have been implicated in the development of an auto-inhibition of histamine release. Dopamine receptors have the capacity to respond to dopamine. They sit in nerve synapses essentially at the level of the vessels of the kidney, intestines and brain. There are three types of dopamine D1, D2 and D3 receptors. The dopamine system consists of a set of neurons which, within the central nervous system and peripheral nervous system have the capacity to release dopamine. It is also sensitive to dopamine neurons. Dopamine is also called dihydroxyphénéthylamine. It’s amino acids that constitute the dépens of dopa immediately prior to the formation of noradrenaline. The synthesis of this chemical mediator is done inside of some neurons of the central nervous system and peripheral nervous system. From other Catecholamines dopamine has vasodilatory effects at the level of certain organs such as the intestine, kidney, and coronary. The disappearance of dopamine is related to Parkinson’s disease. Angiotensin II receptors are membrane receptors that are located in the heart, kidney, vascular smooth muscle, adrenal cortical glands, nervous system and liver. There are two varieties of angiotensin receptors but it seems that only 1 type receptor have intense physiological activity. Some substances (called non-peptide antagonists of type 1) whose leader is losartan are used in therapy to combat high blood pressure. Leu r action and block the Renin-angiotensin system in a specific way to angiotensin converting enzyme inhibitors. LDL receptors have been shown by Goldstein and Brown in August 1973. It is membrane receptor of hydrazinolysis nature (combining a sugar and a protein) with the ability to set the LDL. It is a lipoprotein called lipoprotein, protidolipidique, lipidoprotidique, proteolipid or lipidoprotéinique cénapse or also complex. This mixed nature lipido-protein molecule is a form of these fats in the blood. The LDL receptors not only attach the LDL but transports them within the cell. Liver and specifically dense LDL receptors. The decrease in the rate of cholesterol in the blood is directly related to the multiplication of the LDL receptor. The number of LDL receptors is important more endogenous cholesterol is low. The pharmaceutical industry has developed enzyme inhibitor type medications which have the ability to cause this multiplication of receptors LDL. They thus treating hypercholesterolemia (excess cholesterol in the blood) of a family nature. More specifically a substance called clathrin (from the latin clatare: close with bars, English coated pits) is a protein lining the inside of some membranes called membrane areas invaginated, plays a role in Endocytosis of LDL receptor-related. Endocytosis is the mode of penetration used by the cell more precisely by its membrane, to introduce the particle to ingest it. This is achieved by wrapping the substance to ingest .poumon soluble Transferrin receptor are fragments of the membrane Transferrin receptor (blood protein, also called sidérophiline, which combines with the iron and the transports to the organs). It is a protein which is located on the surface of all cells except erythrocytes (red blood cells). The increase in the amount of soluble Transferrin receptor indicates functional iron deficiency. Determination of soluble Transferrin receptor is useful when there is a decrease in the rate of ferritin serum (the fluid part of blood), but this decline is particularly difficult to understand.

Physiology

Membrane receptor possess the ability to both recognize and set a specific substance from outside of the cell. This substance has the property to lay an information or a signal. The best-known reception mode of the general public is membrane receipt of the hormone. Neurotransmitters also called neuromediators and other growth factors are also made of proteins causing chemical changes within the cell through the membrane thereof and which results in a specific response. As a specific to a given message receiver arrives at the level of the membrane of the cell or cell in General, this always leads to the same type of response regardless of the cell. The foregoing does not prevent a cell to have several messages at a time-sensitive receptors. Each hormone or each Ombudsman (neurotransmitter in particular) is called receptor ligand. The insulin receptor. To better understand the mechanism of membrane receptors consider the regulation of the rate of glucose (sugar) in the blood. In an individual not diabetes (excess of sugar in the blood), with other words which membrane receptor function properly to sugar in the blood, an increase in the rate of glucose in the blood (high blood sugar) triggers the secretion of insulin is the hormone for controlling sugar in the blood. This hormone is secreted by the pancreas. The mechanism is as follows. Insulin binds to membrane receptors that are specific to this hormone and only to this hormone, but at the level of the muscle cells, liver and fat tissue. Because of the binding of insulin on some receptor of the cell membrane component bodies just to talk, there is an absorption i.e. penetration of glucose from the blood and then, a storage of glucose. It is necessary to distinguish the insulin receptor with low affinity and high capacity of high-affinity receptors and low capacity. The number of these receptors and their activity is in direct relation to the levels of insulin in the blood (plasma insulin levels). A drug (studied by Jean Sternn) and containing metformin, is likely to make them more effective. B cell receptors. Another example of a membrane receptor is possessed by certain white blood cells, particularly lymphocytes B. The moment where a foreign suspense penetrates the body, this foreign substance (called Antigen) comes in contact with a specific receptor situated on the membrane of the white blood cell (lymphocyte B.) This phenomenon raises the manufacture (synthesis) in large quantities of antibody that corresponds to the Antigen from getting inside the body. This process results in turn release within the Organization of other antibodies after a type immune cascade reaction. These receptors are also called recognition receptors. This is of particular structures that are located on the surface of some cells more surely lymphocytes B (bursodépendants) and perhaps of T (thymodépendants). It’s immunoglobulins (antibodies) that are secreted by the cell and which are part of the cell membrane. For this reason they are called membrane or surface immunoglobulins. These cells have the ability to recognize and capture, through these antibodies, Antigen (foreign substance) that they will be able to immobilize or destroy. Some drugs have the ability to modify the action of membrane receptors. They are therefore used as stimulators of receptors of substance. They are called agonists substances. This is the case for example of drugs containing molecules of type alpha stimulating, cholinergic, bêtastimulant, opiate etc. Are drugs that inhibit receptor, called antagonists. This is the case of β-blockers (that allow to lower blood pressure for example) of the alpha-blocker, anticholinergics, anti serotonin, antihistamines (used in allergy for example) etc. When affinity is strong but the ligand triggers little biological effect, talking about binding setting an antagonist. Indeed, in this case the ligand occupies the receiver which is more accessible to its normal stimulus. The affinity is strong and therefore the effect resulting from this fixation is intense, the mechanism defined in this case an agonist substance. The affinity is high but that the intensity of the message remains lower than that normally triggers the ligand physiologically, this is called interaction effect agonist-antagonist.