Neurotransmitters specific paracrine signaling cells

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Neurotransmitters: specific paracrine signaling; cells that are next to each other but the secretory cell is going to be a neuron (nerve cell) that releases the message o Hormones “Endocrine Signaling” Hormones enter the blood stream Usually for long distance signaling; has to enter the blood stream to get there Insulin = produced by the pancreas but acts on about every cell in the body that receives this hormone; has to enter the blood stream
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20 Paracrines, neurotransmitters and hormones are ligands that bind to receptors; if there is no receptor, it is not a target cell For a cell, how does it know what it wants it to do? Either have one receptor or it doesn’t Hydrophilic messenger: likes water and makes it way into the blood stream and is just fine Hydrophobic messenger: doesn’t like water and therefore cannot be in blood; has to have a carrier protein; less than 1% of these are floating in the blood o Receptor proteins A target cell receives a signal because it has receptor proteins specific to it on the plasma membrane or inside the cell Nonpolar signal molecules such as steroid hormones can penetrate the plasma membrane and interact with receptors inside the cell Hydrophilic ligand: Hydrophobic ligand: Specificity : each type of receptor only binds one type of ligand/molecule Will only bind to specific receptor Affinity : strength of binding between a ligand and its receptor Receptor activation depends on Concentration of ligand Expression level of ligand Affinity o receptor for ligand Relationship between ligand concentration and receptor activation If all the receptors are bound, you can continue to add ligand but there won’t be any receptors to be bond to You will reach the maximum How can number of receptors change? Receptor synthesis <> receptor turnover (degradation) o Upregulation: increase in receptor synthesis; can have an increase in gene expression o Downregulation: decrease in receptor synthesis; getting rid of the ones already have “Normal” conditions = depend on how much ligand it receives o For certain situations, if there are more than it should be, the receptors can up the number of binding sites for more ligand (Upregulation) o If there isn’t much ligand present, can remove some of the receptors in the membrane because they are not needed (downregulation) - Drug Interaction o Every addictive drug available today takes advantage of pre-existing receptors in the human body Indigenous ligand = our body produces it Most addictive drug on the planet is nicotine and it is completely legal o Binding of the drug to these receptors often activates a network of dopaminergic cells in the mesolimbic region of the brain that are involved in emotional reward Not enough dopamine = Parkinson’s disease, Attention Deficit Disorder Too much dopamine = schizophrenia o Drug Addiction
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21 Opiates : painkillers such codeine, morphine, oxycodone, oxycontin, heroin, etc.
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